computer vs. refrigerator
Tom Grayson
The Computers in this world are very susceptible to voltage spikes and other
disturbances to the supply voltage such as harmonics etc, However Spikes are
the worst. The power supply , being the thing actually connected to the
power is the thing that usually dies ( if you are lucky ) when you get
spikes on the system.
What happens to a refrigerator motor however is a different story all
together, If the System voltage drops too low, The motor will draw more
current to give the same power ( The refrigeration compressor knows nothing
about voltage, it just requires a given amount of power to run the
compressor at a given speed ), You know the old Power = volts * Amps thing,
well it applies equally to DC and AC , just a few other components in the
calculation.
So If you get a " Brown Out" for any sustained period of time the increased
current draw in the motor will cause excessive heating which will eventually
Fail the insulation system. It might survive a couple of these or it might
die the first time, One of the Mysteries :o)
So Power quality does effect both things, just different problems in the
power do different things to each.
Tom
"AC/DCdude17" <Je...@prontoREMOVETHISmail.com> wrote in message
news:3CE656B5...@prontoREMOVETHISmail.com...
> X-No-Archive: Yes
>
> "protect sensitive loads such as computer equipments" kind of
> statements are everywhere. How much truth is there in such
> statement? From surge protectors to low harmonic distortion misc.
> electrical items. Next to resisitve loads, in theory, computers are the
> least sensitive load to power quality and the worst power polluter. It
> simply rectifies input voltage to the peak value and process the
> resulting DC power into computer logic voltages. On the other hand,
> something like refrigerator uses a relatively large induction motor and
> induction motor depends on clean sinewave for efficient operation. That
> said, which is more sensitive to power quality: the average computer or
> the average refrigerator?
>
Pctchrisgibson
>
>The Computers in this world are very susceptible to voltage spikes and other
>disturbances to the supply voltage such as harmonics etc, However Spikes are
>the worst. The power supply , being the thing actually connected to the
>power is the thing that usually dies ( if you are lucky ) when you get
>spikes on the system.
>
>What happens to a refrigerator motor however is a different story all
>together, If the System voltage drops too low, The motor will draw more
>current to give the same power ( The refrigeration compressor knows nothing
>about voltage, it just requires a given amount of power to run the
>compressor at a given speed ), You know the old Power = volts * Amps thing,
>well it applies equally to DC and AC , just a few other components in the
>calculation.
>
>So If you get a " Brown Out" for any sustained period of time the increased
>current draw in the motor will cause excessive heating which will eventually
>Fail the insulation system. It might survive a couple of these or it might
>die the first time, One of the Mysteries :o)
>
>So Power quality does effect both things, just different problems in the
>power do different things to each.
>
>Tom
>
Hmmmmmmm
I have to completely disagree here but I really don't want to start an
argument.
If you swap the terms "refridgerator" with "computer power supplies" I think
you will be much, much closer to the truth. :)
Computer power supplies are one of the most tolerant pieces of equipment
around. Happily running on just about anything from DC through to 1KHz with
just about anywaveform and any amount of distortion (within reason). They are
usually auto voltage adjusting happily accepting from 80 to 260 volts. Spikes
usually cause no problem as they are protected against them by design and also
as a by product of the filtering. Computer power supplies are, on the other
hand (except the latest spec units with power factor correction and adequate
filtering), one of the worst polluters of the mains supply. A lower voltage
into a computer power supply will result in increased current draw as it is a
constant power device.
A fridge compressor motor on the other hand is just the opposite. It is *not* a
constant power device. A lower input voltage will result in a lower current
draw and lower power. Down to the point at which the motor stalls. Distortion
on the incoming AC will produce overheating. Voltage spikes are unlikey to
cause any problems whatsoever unless they are long in duration, which, by
definition, means they are no longer "spikes"
Chris
w_tom
is very much correct. For example, a computer by design must
withstand 2000 volts common mode transients. Look at that
number. Yes, thousands. A computer must not only work just
fine, but must even startup when at 100% load even when the
120 VAC is at 90. That is voltage so low that incandescent
lamps would be at less than 50% intensity.
Those requirements are what any properly designed power
supply must do. However, to sell power supplies to MBA
mentalities for less than $100, then many of those functions
required in a power supply are forgotten. A computer power
supply should be one of the most robust appliances in the
house. But then too many clone builders cut costs without any
idea of why their clone machine cost less than a brand name
machine.
If refrigerators created so much spikes and harmonics, then
dimmer switches would be replaced daily before there was even
an IBM PC. Those who claim electrical threats from
refrigerators or other household appliances do so only from
theory - have not been tempered by experiences in reality. If
any appliance can damage a computer, then that appliance must
be removed immediately as a threat to human safety. The human
easily knows that appliance is defective because he is
replacing GFCI, dimmer switches, IR proximity detectors,
electronic timer switches, on-off lamps, and microwave ovens
daily.
Pctchrisgibson has accurately defanged another urban myth
about spikes, brownouts, computers, and household appliances.
Tom Grayson
*not* a
> constant power device. A lower input voltage will result in a lower
current
> draw and lower power
Can you please tell me which university you studied Electrical Engineering
at ?
Pctchrisgibson
>at ?
>
I'll give you benifit of the doubt and assume you are asking a serious question
in which case I will answer University of Manchester Institute of Science and
Technology. UK.
If it was an attempt at sarcasm I will reply by saying you clearly have so
little knowledge that you're not worth discussin the matter with. Anyone who
think an electric motor exhibits negative resistance characteristics has a
serious issue with his basic electrical theory.
Chris
Paul Miller
If the System voltage drops too low, The motor will draw more
> current to give the same power ( The refrigeration compressor knows
nothing
> about voltage, it just requires a given amount of power to run the
> compressor at a given speed ), You know the old Power = volts * Amps
thing,
> well it applies equally to DC and AC , just a few other components in the
> calculation.
what? An motor will take less current when given less voltage. Its basic
Ohms law.
Paul Miller.
Pctchrisgibson
>Ohms law.
>
You won't convince him :)
Chris
indago
what? An motor will take less current when given less voltage. Its basic
Ohms law.
>If the System voltage drops too low, The motor will draw more
> current to give the same power ( The refrigeration compressor knows
>nothing about voltage, it just requires a given amount of power to run the
> compressor at a given speed )
---------------------------------------------------------------
He seems to be saying that as the motor gets less and less voltage to
operate, the load of the compressor drags the motor into locked rotor
condition, and, therefore, more current, to the point of destruction.
Pctchrisgibson
>operate, the load of the compressor drags the motor into locked rotor
>condition, and, therefore, more current, to the point of destruction.
>
I think that he thinks a motor will draw more current as the voltage drops in
order to keep the power the same. The reason I say that, is because that is
what he said ! He thinks a motor is a constant power device, ie it exhibits a
negative resistance at the input. Then he had the nerve to ask me where I
studied electrical engineering.
I have no objection to people being wrong or making mistakes. We are all human,
we all do it. But when someone does so, then has the nerve to be rude about it
and say something such as "where did you study electrical engineering" it does
nothing other than show his own ignorance and arrogance.
Chris
indago
I have no objection to people being wrong or making mistakes. We are all
human, we all do it. But when someone does so, then has the nerve to be rude
about it and say something such as "where did you study electrical
engineering" it does nothing other than show his own ignorance and
arrogance.
-------------------------------------------------------------------
Yes, I can agree with that...
Bob Penoyer
wrote:
I think you should be a little easy on Tom. He's an example of "a
little knowledge is a dangerous thing." I'm confident that he has had
a little explosure to electricity/electronics, however nothing deep.
He feels good about what he knows and is confident that he has enough
understanding to conceive of answers to questions that are outside his
range of knowledge. He also feels that it's not possible for people to
truly understand--in detail!--those things about which he can only
guess. I think his challenge to you came from this context.
As a result, he was probably a little surprised to find that you
really do have an engineering education. (In fact, with the education
you list, you probably have as much or more education as any of his
instructors.) And, he probably has no idea what "negative resistance"
means.
Pctchrisgibson
>I think you should be a little easy on Tom. He's an example of "a
>little knowledge is a dangerous thing." I'm confident that he has had
>a little explosure to electricity/electronics, however nothing deep.
>He feels good about what he knows and is confident that he has enough
>understanding to conceive of answers to questions that are outside his
>range of knowledge. He also feels that it's not possible for people to
>truly understand--in detail!--those things about which he can only
>guess. I think his challenge to you came from this context.
>
>As a result, he was probably a little surprised to find that you
>really do have an engineering education. (In fact, with the education
>you list, you probably have as much or more education as any of his
>instructors.) And, he probably has no idea what "negative resistance"
>means.
>
Well I did try to be gentle with:-
"Hmmmmmmm
I have to completely disagree here but I really don't want to start an
argument.
If you swap the terms "refridgerator" with "computer power supplies" I think
you will be much, much closer to the truth. :)"
Contaned in my second post where I attempted to, politely, correct him.
It was met with:-
"Can you please tell me which university you studied Electrical Engineering
at ?"
Which seems, to me at least, rather an odd way to reply. Ah well.
Chris
Tom MacIntyre
(Pctchrisgibson) wrote:
>> "protect sensitive loads such as computer equipments" kind of
>>statements are everywhere. How much truth is there in such
>>statement? From surge protectors to low harmonic distortion misc.
>>electrical items. Next to resisitve loads, in theory, computers are the
>>least sensitive load to power quality and the worst power polluter. It
>>simply rectifies input voltage to the peak value and process the
>>resulting DC power into computer logic voltages. On the other hand,
>>something like refrigerator uses a relatively large induction motor and
>>induction motor depends on clean sinewave for efficient operation. That
>>said, which is more sensitive to power quality: the average computer or
>>the average refrigerator?
>>
>
>I am involved in back up power systems. Not UPS systems for PCs but just
>general back up power. Inverters, battery chargers, wind power, etc.
>
>Here's how I describe the situation to clients when asked this very same
>question....
>
>Computers ? No, they'll run on any old shit you throw at them. AC or DC, any
>old frequency, spikes, dropouts, anything you like (within reason). They are
>the most insensitive, uncaring items you will find in a house.
>
>Chris
>
>I'm sure you can work out the reference to xollob in the email address is an
>anti spammer and not an insult !
The same is true of most devices with a switching power supply, isn't
it?
Tom
Pctchrisgibson
>it?
>
Yes. it's the switchng power supply that does it.
Chris
w_tom
subject of this thread, is correct. Tom Grayson rather
humorously noted one flaw. As voltage drops, the power in a
motor does drop (curves vary for different motors). But
current typically increases. To reduce load, utilities may
drop voltage by as much as 3% or 5%. They don't lower more
because the current increase in motors may already be damaging
customer motors. Yes, power output may drop as a motor sees
less voltage. But the current, typically, increases - just
not enough to maintain or increase motor output.
Returning to the original point. Some UPSes in battery
backup mode output so much 'dirtier' power (high THD at many
harmonic frequencies) that small motors may be damaged. IOW
power that can damage a small motor will not hurt any
computer. Refrigerators can be more susceptible to damage
from AC mains than computers. The bottom line conclusion,
correctly posted, is that computers are more resilient than
refrigerators.
Tom MacIntyre
wrote:
I thought so. I work in electronics repair, and we use a metered
isolation variac. I usually try to see how low I can get the voltage
before regulation is a problem, and some switching supplies are
amazing. I had one TV one day that stayed stable at 30 volts, 1/4 of
the line voltage. Of course, I don't let them run long like that.
Tom
Pctchrisgibson
>motor does drop (curves vary for different motors). But
>current typically increases.
>
Noooooooo, at a fixed voltage the current drawn is proportonal to the work
done. If you lower the voltage the motor will do less work ! It will draw less
current.
Chris
Pctchrisgibson
>isolation variac. I usually try to see how low I can get the voltage
>before regulation is a problem, and some switching supplies are
>amazing. I had one TV one day that stayed stable at 30 volts, 1/4 of
>the line voltage. Of course, I don't let them run long like that.
>
Yeah some SMPS don't have undervoltage lock out. If they don't, at low input
voltage they can destroy themsleves as a result of the increased current draw.
Undervoltage lock out really is a must for this reason amongst many others.
Chris
Tom MacIntyre
ground" <TutAm...@theheartofthecheopspyramid.hol> wrote:
>On Sat, 25 May 2002 20:59:45 GMT, tom__ma...@hotmail.com (Tom
>MacIntyre) Gave us:
>
>>
>>I thought so. I work in electronics repair, and we use a metered
>>isolation variac. I usually try to see how low I can get the voltage
>>before regulation is a problem, and some switching supplies are
>>amazing. I had one TV one day that stayed stable at 30 volts, 1/4 of
>>the line voltage. Of course, I don't let them run long like that.
>>
>>Tom
>
>
> You also have to remember to hook up a load which loads the supply
>to it's rated load regulation point. Then, I would wager that you
>don't get many that can sustain proper output much below 85 volts for
>a 120 nominal rating.
>
> You gotta remember that load. Hell, any supply can push into
>nothing.
I am referring to a running TV with an SMPS. Turned on, that's the
load.
Tom
w_tom
various motors (series, shunt, AC induction, synchronous, etc)
in engineering class were in error. Lab work was to build the
equations for each motor by changing voltage so that current
increased with a voltage drop. Eventually, power drops so
that the shaft freezes and current maximizes. But while
approaching this condition, current increases to the motor as
voltage drops causes increased heating in the windings - and
potential failure. Power to the shaft decreases but power
dissipated in motor windings increases - an undesirable
condition if you don't want to replace the motor.
w_tom
it will continue to power its outputs, regardless of line
voltage. Specs for 120 VAC supplies have long (probably
longer than a majority of lurkers have existed) demanded that
power supplies provide full load at 90 VAC. ATX specs demand
that every ATX supply can even power up, while at 100% load
when AC mains are at 90 VAC.
I have immediate respect for Tom MacIntyre. He does what
too many posters fail to do. He experiments. I perform same
brownout experiments, but never got a 120 VAC power supply to
operate below 50 VAC. Most switching power supplies cut off
at about 85 volts.
This being fundamental. Any power supply damaged by a
brownout is defective - probably by design. The power supply
must either work or cutoff, without damage, at every line
voltage from specification maximum right down to zero volts.
After all, what happens to a power supply when switched off?
It operates at those brownout voltages until electrolytic
capacitors finally discharge. A power supply damaged by a
brownout could also be damaged by power cutoff.
"Tut AmongUs @ the hole in the ground" wrote:
>
> On Sat, 25 May 2002 20:59:45 GMT, tom__ma...@hotmail.com (Tom
> MacIntyre) Gave us:
>
> >
> >I thought so. I work in electronics repair, and we use a metered
> >isolation variac. I usually try to see how low I can get the voltage
> >before regulation is a problem, and some switching supplies are
> >amazing. I had one TV one day that stayed stable at 30 volts, 1/4 of
> >the line voltage. Of course, I don't let them run long like that.
> >
> >Tom
>
Robert Richter
This much I will give you: If the compressor has a run capacitor, the
leg it is connected to will see less current as the voltage drops.
It is possible to get a degree in electrical engineering and not know
anything about motors. EASA publishes a nice little handbook dealing
with motors, but refrigeration compressors are not in this book; they
are, however, an induction motor, and unless you are operating in the
iron saturation region of a motor, decreasing voltage will cause a
current increase. Most induction motors will go about 2-3% above
rated voltage and still decrease in current; after this, iron
saturation occurs and current draw starts to increase.
Keep in mind that current is a result of back EMF and motor
resistance; motors do, indeed have a negative resistance
characteristic. The motor wants to spin at synchronous speed
regardless of the voltage. With a lower voltage, the slip is higher
and the back EMF is lower relative to the line voltage, hence the
current increases. Fortunately, most modern fridges have a
self-resetting overload that protects the fridge against a brown-out.
It isn't just when the motor stalls that this increase in current
occurs.
Tom Grayson
interposing postings.
First up let me tell you that , no I am not a back yard electronics guy, I
work in heavy industry where getting computers to run in noisy environments
is our everyday concern. I also work with DC and Ac motors from 5 hp right
through to 10,000 HP ( induction, Wound Rotor and Synchronoius ).
I really hate to denigrate anyone but anybody who tries to equate the
operation of AC Motors to a simple Ohms law is clearly not in touch with
motors at all.
I wasn't going to go into depth but clearly some people here need to be
educated.
The power drawn by a motor in an uncontrolled situation ( No Variable speed
drive ) is simply the function ot the load it is driving. You put no load on
it and it draws only excitation current. You put a low load on it and it
draws some current. If you put rated load on the motor it will draw rated
current, If you overload it , it will draw whatever current it needs to try
to drive against the load at the relatively constant speed. For this reason
we put overload devices on motors. ( They all have them, Even Refrigerator
motors) to prevent the things catching fire if the load exceeds the motors
rating for any length of time.
now Our humble refrigerator requires a given amount of torque to drive the
compressor at any given speed. Assuming that the line frequency remains
constant , the motor will run at relatively constant speed, Thus, in the
mechanical Realm, from the equation, Power = torque * Speed, The load on
the motor is constant. SO now we have a motor driving a constant load, at a
realtively constant speed ( Slip comes into it of course, but it is not all
that significant at the moment ), The load WILL be constant therefore the
motor will still be trying to deliver this power. If the voltage is lower,
The current WILL go up. This is not just theory, Like one of the postings
here mentioned, This is based on actual experience, Measiring real motors in
real situations.
similarly, In a heavy industrial world, PC's configured as workstations have
many power supply failures, I Do agree with Chris that the switch mode power
supplies are fairly robust and in a normal domestic situation will last for
many years, however in most industrial environments the power supply is
normally the first thing to go. Again These comments are based on actual
experience, Not looking at specifications sheets and listening to
manufacturers Sales pitches.
You may be right in saying I was hasty to condem Chris and his comments
however I also learned at university that it is always wise to be cautions
before passing judgement in an area that is not your area of expertise and
in this situation, Motors is clearly not Chris' area of expertise. He did
not hesitate to start telling me I was wrong. I am not wrong and any
Electrical Engineer that is involved in motors ( or electrician that has
replaced burned out motors ) in heavy industry will also tell you the same
thing .
Tom Grayson
Tom Grayson
I suggest you go check your university textbooks before you continue to make
an even bigger fool of yourself then you already have.
Tom
"Bob Penoyer" <rpen...@NOSPAMieee.org> wrote in message
news:cekveuoi8u63rnocs...@4ax.com...
Tom Grayson
intervening years have mostly been spent working with motors and Motor
controls.
It is obvious that you can graduate from The university of Manchester with
an Electrical Engineering degree and still not know very much about electric
motors.
I suggest you go back and check your old text books before continuing with
your " Less Voltage thus Less current" Ohms Law type thinking.
Tom Grayson
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
news:20020525050519...@mb-fq.aol.com...
Pctchrisgibson
>That said, my motor doesn't seem to have inversely proportional
>relationship between its voltage and current. This is my result from
>actual experiment.
>
>when V running is 121V, I running is 9.03A
>
>when Vrunning is 106V, Irunning is 7.5A
>
And that is what you *will* find if you actually try the experiment.
Chris
Tom Grayson
the same experiment using a motor connected to a constant torque load such
as , a pump or compressor,
Then your experiment will be a representation of what really is going on.
Tom Grayson
"AC/DCdude17" <Je...@prontoREMOVETHISmail.com> wrote in message
news:3CF09FD8...@prontoREMOVETHISmail.com...
> X-No-Archive: Yes
>
> w_tom wrote:
>
> >
> >
> > I have immediate respect for Tom MacIntyre. He does what
> > too many posters fail to do. He experiments.
>
Pctchrisgibson
>the same experiment using a motor connected to a constant torque load such
>as , a pump or compressor,
>Then your experiment will be a representation of what really is going on.
>
>Tom Grayson
>
Ahh..... sort of. I can see where you're coming from. Surely a constant torque
load would keep the current roughly the same at lower voltages ? A "constant
load" load would produce an increase in current as the voltage was lowered. In
that case the "constant load" load would be the mechanism with the negative
resistance characterisitc (albeit a mechanical one) which would be reflected
back to the electrical side. However, a fridge compressor is not such a load.
Chris
Tom Grayson
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
news:20020526050835...@mb-fj.aol.com...
Pctchrisgibson
>load.
>>
Tom Grayson wrote:
>
>why wouldn't it be ?
>
No idea ! :)
I just now it isn't from measurements I have made.
You can in actual fact run a fridge from a lower voltage. The compressor runs
slower and it draws less current. Some misguided companies used to sell a
gadgtet that chopped part of the waveform out reducing the RMS voltage in an
attempt to reduce the fridge power consumption. I'm sure you'll see the mistake
in that logic :)
Chris
Robert Richter
indeed get reduced current with reduced voltage up to a point. Reduce
voltage below the value that gives minimum current and current will
start to increase. The reactive current needed to sustain rotor
fields drops with a decrease in voltage and this drop may be more than
the increase in active current needed to get close to the same power
with reduced voltage.
Tom MacIntyre
ground" <TutAm...@theheartofthecheopspyramid.hol> wrote:
>On Sat, 25 May 2002 21:40:29 GMT, tom__ma...@hotmail.com (Tom
>MacIntyre) Gave us:
>
>
>>I am referring to a running TV with an SMPS. Turned on, that's the
>>load.
>>
>>Tom
>
>
> I am referring to monitoring what voltages are put out, and what
>ripple is carried with them, and whether or not it is still inside its
>spec. Regardless of whether or not the TV is still "up".
I am referring to watching the screen, and monitoring the B+, so as to
see what the differences are. I am curious about these things. I don't
consider a TV power supply as working properly when the picture is
shrunken up and vibrating. Normally these supplies don't stay stable
below 70 volts AC, but this one supply was good to 30 volts, with full
horizontal and vertical deflection, and full B+.
Ripple will show up on the screen anyway. I am not trying to say that
my eye replaces test equipment, I am trying to say that it verifies
and enhances what the test equipment tells me.
Tom
Tom MacIntyre
<tgra...@bigpond.net.au> wrote:
>Queensland University of technology Here, 1979 graduation and the
>intervening years have mostly been spent working with motors and Motor
>controls.
>
>It is obvious that you can graduate from The university of Manchester with
>an Electrical Engineering degree and still not know very much about electric
>motors.
>I suggest you go back and check your old text books before continuing with
>your " Less Voltage thus Less current" Ohms Law type thinking.
>
>Tom Grayson
>
BTW...College of Cape Breton, Electronics Engineering Technology,
Class of '82... :-)
Tom
Tom Grayson
fail to see how they can happily run at a slower speed with the reduced
voltage unless they have a high resistance rotor, ( like a wound rotor
motor) I know they are hematically sealed so I would imagine getting heat
out of them would be a problem. Also having this type of rotor would make
the efficiency very low, Kind of wastefull in todays energy conscious world.
So many Refrigerators, So Little energy :o)
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
news:20020526065120...@mb-fe.aol.com...
Tom MacIntyre
ground" <TutAm...@theheartofthecheopspyramid.hol> wrote:
>On Sun, 26 May 2002 12:18:20 GMT, tom__ma...@hotmail.com (Tom
>MacIntyre) Gave us:
>
>>I am referring to watching the screen, and monitoring the B+, so as to
>>see what the differences are. I am curious about these things. I don't
>>consider a TV power supply as working properly when the picture is
>>shrunken up and vibrating. Normally these supplies don't stay stable
>>below 70 volts AC, but this one supply was good to 30 volts, with full
>>horizontal and vertical deflection, and full B+.
>>
>>Ripple will show up on the screen anyway. I am not trying to say that
>>my eye replaces test equipment, I am trying to say that it verifies
>>and enhances what the test equipment tells me.
>>
>30 volts is pretty darn low for an AC fed switcher.
Yes. It was well outside of anything I ever saw.
>
> We make a military computer supply that has AC DC, and internal
>Battery hookups. It can auto switch between them, and auto switches
>AC line as well, so one can run it from 85VAC all the way up thru
>265VAC no problem. The AC is auto switched at around 137 volts to the
>second circuit for the 137-265 range. We generally test them to
>operate down to 85 volts, but we don't test much to see if they
>continue working below that figure.
The Sencore variac we have will get up close to 150 volts, and almost
any supply we see will handle that, linear or switching. Exceptions
are supplies using the 2SD1092/2SD1294 as the regulator, if memory
serves me.
Tom
w_tom
motor since we were developing coefficients for formulas
applicable to each motor. I don't remember if loading was
constant torque or if the loading was variable and measured.
This was many decades ago. Even back then, it was considered
old technology which is why many EEs today are not required to
take a 200 or 300 level course on electric motors?
Induction motors were definitely one of the motors tested.
They are a most classic example of increased current with
decreased voltage.
"Tut AmongUs @ the hole in the ground" wrote:
> Was there any load involved?
>
> Next question: Is it an induction motor.
Bob Penoyer
<tgra...@bigpond.net.au> wrote:
>Hey Bob,
>I suggest you go check your university textbooks before you continue to make
>an even bigger fool of yourself then you already have.
Based on other posts of yours, I admit that I misjudged both you and
your knowledge. Mea culpa.
However, it's interesting that the graphic that you posted elsewhere
came not from a university textbook but from an engineering handbook.
Maybe it would have been no use to check my old textbooks--or yours.
Tom Grayson
Actually I was the only book I could find in a hurry. My old faithfull,
"Electric Machines" by Fitzgerald, Kingsley and Kusko has been lost in a
move somewhere ( much to my dissapointment) but it did go into a lot of
detail about these things.
BTY appology accepted with grace. no hard feelings.
"Bob Penoyer" <rpen...@NOSPAMieee.org> wrote in message
news:15q2fu005mo1bsfen...@4ax.com...
Lane Lewis
When a brownout occurs most likely the compressor will stall and will
cause the built in overload protection to cut out. As long as the compressor
can remain running it should be OK. This is just from practical experience.
Note that if the motor continues running in a brownout condition it will run
hotter. This is just from practical experience but I have also seen other
motors run cooler in a low voltage situation. Many water pump motors that
have been wired for 220 and then run accidentily for years on 110v with no
ill effects. But the load characteristics of compressors and umpeller type
water pumps are different. Hope this helps clarify the situation.
Computer power supplies using poor quality components or design or both can
result in spike damage to the power supply or the motherboard or both.
I don't have a degree in anything and it probably shows but 30 yrs out in
the field sure beats arguing over degrees anytime.
Lane
Tom Grayson
I have nothing but respect for the Old electricians with the "Runs on the
Board" so to speak.
As a graduate Engineer it was just those types that gave me a lot of the
practical knowledge I now have.
I know Motors well, Just not Refrigeration motors, to any extent. thanks for
the insight.
"Lane Lewis" <myn...@hotmail.com> wrote in message
news:72fI8.14477$Np5....@nwrddc01.gnilink.net...
Tom Grayson
Tom
"AC/DCdude17" <Je...@prontoREMOVETHISmail.com> wrote in message
news:3CF09D2A...@prontoREMOVETHISmail.com...
> X-No-Archive: Yes
>
> Looking at the voltage chart, it is obvious that slight overvoltage is
> beneficial, but undervoltage has detrimental effects. I believe this is
why you
> won't see induction motors(excluding super cheapo residential grade stuff)
of
> these ratings: 120V, 240V, 480V. Motors are rated with these voltages:
115V,
> 230V and 460V. So if you connect it to lines with nominal voltage higher
than
> motor voltage you can assume that motor is fed at name plate voltage after
> including voltage sag in consideration or with slightly higher voltage.
>
>
>
> Tom Grayson wrote:
>
> > I know that we are not supposed to post images here but I will do so at
the
> > risk of further flaming, The attached picture is from " Standard
Handbook
> > for Electrical Engineers" by Fink and Beaty, Eleventh Edition, It is
dated
> > 1978 but I do not really think AC motor theory has changed any in the
> > intervening years.
> >
> > I draw your attention the part where it says that at 90% rated voltage
the
> > full load current increases by 11%
>
Michael Buchholz
"Pctchrisgibson" <pctchri...@aol.comma> schrieb im Newsbeitrag
news:20020525170054...@mb-fj.aol.com...
Maybe some advice from a simple german electrican:
An (AC, async.) Electric motor is a inductive load, so, given a fixed
fequency, the
winding alone acts linear.
But:
at decreasing voltage the motor will rotate slower, so the reverse induction
will be less, resulting in a slightly higher current und the Coil.
Maybe 'till the point of burning the Winding by overheating.
Yust my 2 cent, Michael.
Villy Kruse
>>He seems to be saying that as the motor gets less and less voltage to
>>operate, the load of the compressor drags the motor into locked rotor
>>condition, and, therefore, more current, to the point of destruction.
>>
>
>I think that he thinks a motor will draw more current as the voltage drops in
>order to keep the power the same. The reason I say that, is because that is
>what he said ! He thinks a motor is a constant power device.
which it basically is, as long as the rotational speed is kept constant,
or nearly constant, and it will be for normal async AC motors as long as
the voltage is kept high enough to prevent the motor from stalling.
Villy
w_tom
daestrom
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
Your premise is that an AC induction motor (refrigerator) slows down
proportionally with line voltage. Nope. Wrong. Incorrect. Simple DC
motor (shunt wound) will do that, but AC induction motors are different
things. As voltage is dropped, motor torque will drop. This will increase
the slip. This will increase rotor currents until the torque generated is
again in equilibrium with the load. The increase is faster than the speed
drop. So for a slight drop in speed, the rotor currents rise quickly and
torque is restored.
Dropping the voltage by 10% will not drop the speed by 10%. It may only
drop 2-3%.
A change in compressor speed of 2-3% only changes the power needed to drive
it by 2-3%. If the motor is to continue running, it will have to draw more
current, not less as voltage drops.
With voltage dropping faster than the power required of the load, current
must (and actually does) rise. Running a AC induction motor at low voltage
is a sure way to running it hotter. Even centrifugal pumps, whose power
requirements drop with speed^3, overheat because the speed doesn't drop
anywhere near linearly with voltage.
daestrom
w_tom
included as necessary for a properly designed machine. Brand
name manufacturers with good reputations don't use MBA
philosophies of price to obtain their supplies. Those same
overseas manufacturers must instead provide different power
supplies designed for 'value' because better computer brands
purchase using engineering principals. For example, what is
the actual ESR and actual temperature rating for that
electrolytic capacitor? But when those overseas manufacturers
sell to a clone market - where most who recommend don't even
understand electrical basics - then many required
specifications are forgotten. Many clone system builders only
understand the philosophies taught in business school - where
the only criteria is price - the product be damned. Better
brand name systems do not purchase same products from those
overseas manufacturers because engineering - not accounting -
performs the analysis.
From Intel:
> 3.1 AC Input Requirements:
> The power supply shall be capable of supplying full rated
> output power over two input voltage ranges rated 100-127 VAC
> and 200-240 VAC RMS nominal. ... The power supply must be
> able to start up under peak loading at 90 VAC.
It does not matter if "computers rarely load their supplies
at full rated load." A computer's power supply must "be able"
to startup at full load. Just another reason why brand name
computer systems demand better power supplies.
Lets say a clone builder has a 250 watt supply that does not
startup at full load or causes power intermittents. No
problem. Since most who buy and even "recommend" supplies
don't know any of this nor electrical basics, then the naive
instead recommend 350 and 400 watt supplies to solve their
problem.
Those who regard themselves as knowledgeable can't hear any
of this - since reasons for the problems are irrelevant if the
problem is eliminated. Overseas power supply builders 'feed'
on the ignorance of so many clone computer assemblers.
If any appliance creates a voltage so low as to 'trip' a
properly designed computer, then the structure has serious
wiring problems (maybe another one of those awful stablok wire
connections or aluminum wiring) or the offending appliance may
be a fire threat to humans. No safe and 'powering on'
appliance must cause a 25% voltage drop on a branch circuit.
One test I would often demonstrate on clone computers uses
20K generated by leather slippers on dry days. Some computers
were so poorly constructed that a painful static shock would
crash them. Any properly constructed computer chassis also
can be shocked in every corner and not crash the system.
What I demonstrate is solved by 'single point grounding' a
motherboard to chassis. Once single point grounded, then
static shock no longer crashed these computers. No computer,
properly constructed, need by crashed when 20K volt transients
are applied to the chassis.
Computer power supplies also must withstand 2000 volts
common mode and 1000 volts differential mode. But again, no
such transient must exist on household AC power. If 2000 volt
transients are crashing the computer, then the household
already has had many unnecessary electronic appliance
failures.
"Tut AmongUs @ the hole in the ground" wrote:
>
> On Fri, 24 May 2002 14:08:46 -0400, w_tom <w_t...@usa.net> Gave us:
>
> > There is no reason for any argument because Pctchrisgibson
> >is very much correct. For example, a computer by design must
> >withstand 2000 volts common mode transients. Look at that
> >number. Yes, thousands. A computer must not only work just
> >fine, but must even startup when at 100% load even when the
> >120 VAC is at 90.
>
> That is not true. Computers rarely load their supplies at full
> rated load. Most are less than half for consumers. If thy fill it
> out, their little mini-towers barely fully tax the supply at start-up,
> much less during running.
>
> It is correct, however, that it must succeed in starting at lower
> than normal low line conditions.
>
> > That is voltage so low that incandescent
> >lamps would be at less than 50% intensity.
> >
> > Those requirements are what any properly designed power
> >supply must do. However, to sell power supplies to MBA
> >mentalities for less than $100, then many of those functions
> >required in a power supply are forgotten. A computer power
> >supply should be one of the most robust appliances in the
> >house. But then too many clone builders cut costs without any
> >idea of why their clone machine cost less than a brand name
> >machine.
> >
>
> You do realize that these "brand name" machine builders get their
> thousand upon thousands of power supplies for their systems from the
> same power supply houses in taiwan and china, don't you?
>
> You don't actually think that these machines are manufactured here,
> do you? System integration, maybe. Parts come from Asia though.
>
> Even the "good" supplies" come from Asia as that is how good
> economies produce. Companies aren't dummies. Contract manufacturing
> is the rule of the day, and quality does not suffer with a god design
> team. I recommend "Enermax" supplies for PCs.
>
> If our company made standard PC supplies, I'd recommend ours, of
> course. We do not, however.
>
> > If refrigerators created so much spikes and harmonics, then
> >dimmer switches would be replaced daily before there was even
> >an IBM PC. Those who claim electrical threats from
> >refrigerators or other household appliances do so only from
> >theory - have not been tempered by experiences in reality.
>
> Turn on transients could presumably cause a brown out drop out or
> reset of a PC that just happened to be plugged into the wrong leg of
> the household circuit, and it *has* been documented.
>
> Most modern houses are wired well enough that the kitchen runs don't
> cause those problems as much, and of course, compressor technology has
> advanced to the point where apartment refrigerators use what small bar
> fridges used to use. They don't have the same start up requisites as
> well.
>
> >If
> >any appliance can damage a computer, then that appliance must
> >be removed immediately as a threat to human safety.
>
> I do not understand why the role the PC plays is as the "canary" in
> this scenario, but... ok.
>
> > The human
> >easily knows that appliance is defective because he is
> >replacing GFCI, dimmer switches, IR proximity detectors,
> >electronic timer switches, on-off lamps, and microwave ovens
> >daily.
>
> There are analysers for power lines available.
>
> >
> > Pctchrisgibson has accurately defanged another urban myth
> >about spikes, brownouts, computers, and household appliances.
> >
> That fact is that if a spike is big enough to generate a magnetic
> pulse that extends beyond the PC's power supply, it resets at the
> motherboard level in the form of a latch-up, even if the rails are
> still up, the PC crashes from the spike getting through. Try placing
> a taser near your PC's case while it is "up",and tap the arc a few
> times avery couple minutes while you work, and see how long it takes
> for it to latch up the box.
>
> EMI/EMP goes beyond power lines.
Pctchrisgibson
>proportionally with line voltage. Nope. Wrong. Incorrect. Simple DC
>motor (shunt wound) will do that, but AC induction motors are different
>things. As voltage is dropped, motor torque will drop. This will increase
>the slip. This will increase rotor currents until the torque generated is
>again in equilibrium with the load. The increase is faster than the speed
>drop. So for a slight drop in speed, the rotor currents rise quickly and
>torque is restored.
>
Yep that's what I thought. But experiments with fridges did not seem to bear
this out. I did some "asking of questions" with a fridge engineer and he says
that these motors are deliberately designed with a very a high slip capability,
he had no idea why. Perhaps this explains it ? Result is that while loaded,
lower voltage does indeed slow them down. They actually seem much more
concerned with the voltage than the frequency.
Chris
Robert Richter
A high slip means you can start under load.
Pctchrisgibson
>
It also means if you load the motor up the speed will drop.
Chris
w_tom
starts posting by insulting others.
This cheap Deer power supply, so common in clone computers,
does not use Nichicon capacitors. It uses electrolytic
capacitors that are smaller by volume than equivalent Nichicon
capacitors. Long before anyone thought of sticking a penis
into someone else to create you, we observed how that
capacitor volume a strong indication of cheaper parts in
failing power supplies. Back then, the Mallory capacitors of
same spec had larger volume and never failed.
Is that capacitor really rated for 85 degrees or is the
average of all capacitors in the batch only good for 85
degrees? Clone manufacturers have all kinds of tricks to
purchase same value parts that cost less. But when selling to
a company of engineers, they can't play all those tricks.
Clone computer assemblers typically don't have a clue and
therefore purchase based upon price.
Clone manufacturers routinely use cheaper parts compared to
brand name machines. It is why clone computers fail so much
more often, and worse, operate less stable.
Before you start insulting, maybe you could learn some basic
engineering principals such as sticking to the facts. In the
meantime, it is well acknowledged where our designs must work
reliably, clone computers fail too often. Failure typically
because the design is based mostly on price. We don't have
power problems with brand name systems and power supplies.
Clone owners will constantly recommend things like UPSes and
separate AC circuits because failure for them is too common.
One need stop insulting and only look at the many missing
functions in those clone power supplies to appreciate reasons
for failure. Then one learns everyone else was really
smarter.
"Tut AmongUs @ the hole in the ground" wrote:
>
> On Mon, 27 May 2002 11:39:50 -0400, w_tom <w_t...@usa.net> Gave us:
>
> > Brand name machines typically require that functions be
> >included as necessary for a properly designed machine. Brand
> >name manufacturers with good reputations don't use MBA
> >philosophies of price to obtain their supplies.
>
> You ain't real bright, are ya? No MBA OR Technical degree.
> Fact is, yes, they do.
>
> >Those same
> >overseas manufacturers must instead provide different power
> >supplies designed for 'value' because better computer brands
> >purchase using engineering principals.
>
> Boy, they led you down the path. Gateway supplies cost about ten
> bucks each, maybe twenty, and come from guess where? Same supply
> house, off the same shelf, out of the same build.
>
> What? You thing they snip a cap here, snip a filter there?
> Yer nuts. A switcher either is compliant to a spec or isn't, there is
> no in between.
>
> > For example, what is
> >the actual ESR and actual temperature rating for that
> >electrolytic capacitor?
>
> Most any PC you open up is going to have nichi-con (sp)
> electrolytics in them. Most I have seen use 105C caps.
> Nichi-con is a very good maker, and they don't cut corners. The
> lifespan of a chinese electronic component maker is directly
> proportional to whether or not they are making what they claim they
> are making.
>
> > But when those overseas manufacturers
> >sell to a clone market - where most who recommend don't even
> >understand electrical basics - then many required
> >specifications are forgotten.
>
> You are full of shit. Most of those companies are controlled from
> over here. Our makers in china make the exact supplies that we
> design, period. How could they be our contract manufacturers
> otherwise? Doh!
>
> > Many clone system builders only
> >understand the philosophies taught in business school - where
> >the only criteria is price - the product be damned.
>
> The power supply industry is very competitive, both over here and
> over there. Spec conformance, price, and quality have always been the
> only criteria for staying in business. $10 dollars worth of part
> placed properly makes more money than $10 worth of parts that don't do
> the job. Again, you falter.
>
> Yer lost. There are standards that must be held by makers before
> they can even put a single pallet on a container ship.
>
> Do you always make shit up as you go along?
>
> > Better
> >brand name systems do not purchase same products from those
> >overseas manufacturers because engineering - not accounting -
> >performs the analysis.
>
> You are lost. If it says that it is ATX compliant, you can pretty
> much bet that it is, or that if it isn't, you won't see it around
> long. Duh. Do you even know how economies work?
>
> >
> > From Intel:
> >> 3.1 AC Input Requirements:
> >> The power supply shall be capable of supplying full rated
> >> output power over two input voltage ranges rated 100-127 VAC
> >> and 200-240 VAC RMS nominal. ... The power supply must be
> >> able to start up under peak loading at 90 VAC.
>
> No shit. Now guess what all those supply makers over in China make
> their supplies conform to? Or else!
> >
> > It does not matter if "computers rarely load their supplies
> >at full rated load." A computer's power supply must "be able"
> >to startup at full load. Just another reason why brand name
> >computer systems demand better power supplies.
> >
> That's silly. What aspect of "brand name system" has a greater
> power requisite than a home built system? NONE.
>
> As far as starting it at full load, no shit, I know it has to "be
> able to". I also know that what he said was that it DOES start that
> way, and THAT is what I banged him on. It only starts that way if
> that load is there. It doesn't start into full load in use, it barely
> sees that at all in its life in a normal computer. Period.
>
> > Lets say a clone builder has a 250 watt supply that does not
> >startup at full load or causes power intermittents.
>
> Then he doesn't have a compliant supply. I doubt he would continue
> with it.
>
> Yer an idiot. As I previously stated, the clone builders and the
> Gateways use the SAME chinese manufacturers for their hardware, in
> almost every case. Those manufacturers want to stay in business. It
> is in their best interest to make what they claim to be making.
>
> It is not and cannot be called a "PC supply" UNLESS it complies with
> the ATX spec. If it doesn't it is substandard, and falls OUTSIDE the
> parameters for any of your statements.
>
> >No
> >problem. Since most who buy and even "recommend" supplies
> >don't know any of this nor electrical basics, then the naive
> >instead recommend 350 and 400 watt supplies to solve their
> >problem.
> >
> Huh? You are lost. The engineers that put together a chassis to run
> a system know exactly what their power requisites are.
>
> Joe Blow System builder shops do to. They have reputations to
> uphold with police, fire, and business communities, all of which buy
> hundreds of systems from them, and they have to know what is required
> to run a given system setup. You are making shit up, again.
>
> Obviously, a dual P4 CPU MOBO with an NVIDIA GPU card and four hard
> drives is going to need a beefier supply than a P1 mini tower with one
> hd and a 4 MB video card.
>
> > Those who regard themselves as knowledgeable can't hear any
> >of this - since reasons for the problems are irrelevant if the
> >problem is eliminated. Overseas power supply builders 'feed'
> >on the ignorance of so many clone computer assemblers.
>
> Yer nuts. Most ma and pa PC shops have sensible enough owners that
> they find their sources at the same places as do the slightly larger
> franchise based small PC shops do.
>
> Like I said, you are uninformed, hopelessly it seems.
> Brand name PC makers get their hardware from china, just like we do.
> If a clone shop wants to stay in business, he must have viable
> hardware, period! YOU WERE BRAINWASHED BY SOMEONE THAT TOLD YOU THAT
> "CLONE MAKERS" CUT CORNERS. I ask: WHERE? Get a clue?
>
> In fact, the motherboard I put in my box from ASUS is orders of
> magnitude better than ANY mobo installed in ANY Gateway machine EVER
> built.
>
> You have no clue as to how these brand name machine builders
> economize. Their mobos are the bottom lime offerings, compared to
> what one sees in a PC shop from the same makers. That $120 mobo would
> cost hundreds of dollars if it were made here, in the US. For the
> parts alone.
>
> >
> > If any appliance creates a voltage so low as to 'trip' a
> >properly designed computer, then the structure has serious
> >wiring problems (maybe another one of those awful stablok wire
> >connections or aluminum wiring) or the offending appliance may
> >be a fire threat to humans.
>
> Whatever. I as much as said that it would be wiring configuration
> related.
>
> > No safe and 'powering on'
> >appliance must cause a 25% voltage drop on a branch circuit.
> >
>
> No shit. Old fridge compressors used to be able to though, as their
> start currents were so high. Not a problem any more. Kitchen
> circuits are better designed too. Your oven, dryer, full AC... all of
> these things no longer pose problems of that nature.
>
> > One test I would often demonstrate on clone computers uses
> >20K generated by leather slippers on dry days. Some computers
> >were so poorly constructed that a painful static shock would
> >crash them. Any properly constructed computer chassis also
> >can be shocked in every corner and not crash the system.
>
> ESD can and will crash ANY computer at the right instance.
>
> Generally all metal enclosed, properly grounded systems have just as
> good a Faraday cage as any other, and would have just as good ESD
> resilience. To say that Gateway has a better cage on their chassis
> case than does a clone case, is ridiculous.
>
> >
> > What I demonstrate is solved by 'single point grounding' a
> >motherboard to chassis. Once single point grounded, then
> >static shock no longer crashed these computers.
>
> No shit, Sherlock.
>
> > No computer,
> >properly constructed, need by crashed when 20K volt transients
> >are applied to the chassis.
>
> I don't think your kV numbers are right, or very reliably generated,
> but whatever you say.
>
> >
> > Computer power supplies also must withstand 2000 volts
> >common mode and 1000 volts differential mode. But again, no
> >such transient must exist on household AC power. If 2000 volt
> >transients are crashing the computer, then the household
> >already has had many unnecessary electronic appliance
> >failures.
> >
> No shit, but the computer's power supply being from a brand name
> maker or from a PC shop is NOT a valid reason for it happening.
>
> In today's clone builder world, case selection is an important part
> of the build. Many cases come with El Cheapo power supplies in them.
> that's fine as they are capable of doing the shit mobo, shit setup
> basic get online consumer PC (Your basic Gateway or brand name box
> fits this genre, btw).
>
> A power user box is different. It starts with a tower case that has
> no supply in it, and the mobo, and all other devices are usually high
> end. Both my mobo and my vid card suggest high end, high output power
> supplies. My PC is better than ANY PC that you could buy from ANY
> "brand name" maker at ANY time for the same cash.
>
> My $2000 has bought orders of magnitude better hardware than ANY
> "brand name" maker could make.
>
> BTW, these "brand name" PCs are called "clones" too, dumbass.
> Anything that isn't an IBM box is called a clone as they were the
> first builders of the PC. Gateway, and Compaq, HP, and all the other
> "brand name" makers are "clone" builders. You need to bone up.
Robert Richter
> >A high slip means you can start under load.
> >
>
> It also means if you load the motor up the speed will drop.
>
> Chris
Not sure whose post to put this under, but here is some experimenting
I did:
I separated out the compressor on a fridge so that the impedance
limited fan motors would play a factor, as they very definitely will
go down in current with decreased voltage. These measurement are
compressor only, not total fridge current.
At steady state,
121V 4.14A
110V 3.79A
100V 3.56A
90V 3.48A
80V 3.48A
70V 3.72A
62 5.2A
60 Stalled
With the fridge compressor off, and the pressures given time to
equalize, I started at 120V and got 4.4A; then I adjusted the variac
to 110V and as I was adjusting voltage current went up to 4.6A at
110V. As I was getting ready for another adjustment, the current was
dropping on my meter, so I waited, and it went from 4.6 to about 3.8
as shown above, so it appears that startup is closer to 100% load. I
was surprised that at steadu state. I had to get the voltage as low as
I did before current increased. Perhaps a warmer fridge has a heavier
load, but don't quote me on this.
Anything below 107V failed to start the compressor. I paid attention
to the 22A startup current dropping the output of the variac. A
brown-out doesn't appear serious on a compressor that is already
running as opposed to a fridge that is cold and then warms up enough
to need a start.
Pctchrisgibson
The figures you show above agree quite closely with those I got (except roughly
double voltage and half current cause I'm in UK).
I don't know why this happens, motors are definitely not my strong point, but I
do know what I measured, and now, it seems, what you also measured.
No-one believes me ! Maybe fridge motors are a law unto themselves, maybe
theory is not quite what it should be. I don't know, I just know that fridge
current does indeed drop as the voltage drops until it gets close to stall.
That's what I said in my original post and was greeted with insults and
questions about my qualifications. Ah well.
Chris
Robert Richter
I apologize for "It is possible to get a degree in electrical
engineering and not know a thing about motors" and anything else I may
have said. My statement is technically true, however; these courses
are not required. I was a little surprised with the test results;
most motors start increasing in current rather quickly with a drop in
voltage. Maybe fridge makers got tired of fridges being easily burned
out and decided to make them a little more robust to brown-outs.
daestrom
> Not sure whose post to put this under, but here is some experimenting
> I did:
>
> I separated out the compressor on a fridge so that the impedance
> limited fan motors would play a factor, as they very definitely will
> go down in current with decreased voltage. These measurement are
> compressor only, not total fridge current.
>
> At steady state,
> 121V 4.14A
> 110V 3.79A
> 100V 3.56A
> 90V 3.48A
> 80V 3.48A
> 70V 3.72A
> 62 5.2A
> 60 Stalled
Interesting data. Now, if we divide the voltage by the current, we get
ohmic value for the circuit.
> 121V / 4.14A = 29.22
> 110V / 3.79A = 29.02
> 100V / 3.56A = 28.09
> 90V / 3.48A = 25.86
> 80V / 3.48A = 22.99
> 70V / 3.72A = 18.82
> 62 / 5.2A = 11.92
Although the current decays with voltage, it doesn't drop as fast as ohm's
law would predict. Without details about pf, we can't determine if hp
rises/drops/stays put.
Given, as someone posted, these motors are high-slip, they would have poor
speed regulation with changes in voltage. So a brownout would slow a motor
and reduce the hp requirements. I had seen a very-high slip motor used for
variable speed service. By chopping the AC sine-wave with SCR's, but *NOT*
changing the frequency, the system was able to get a wide speed range. But
the units did heat up when running at low speeds (either the current draw,
slower fan speed, or high harmonics, don't know which).
>
> With the fridge compressor off, and the pressures given time to
> equalize, I started at 120V and got 4.4A; then I adjusted the variac
> to 110V and as I was adjusting voltage current went up to 4.6A at
> 110V. As I was getting ready for another adjustment, the current was
> dropping on my meter, so I waited, and it went from 4.6 to about 3.8
> as shown above, so it appears that startup is closer to 100% load. I
> was surprised that at steadu state. I had to get the voltage as low as
> I did before current increased. Perhaps a warmer fridge has a heavier
> load, but don't quote me on this.
The suction pressure would be higher, and the discharge may also be higher
so it is difficult to tell for sure. Higher Freon flow may be the
determining factor.
Nice experiment
daestrom
Lane Lewis
amperage almost three times as much. Somewhere along the line manufactures
decided you did not need a big compressor and started putting smaller ones
in. The only caveat seams to be that the new ones take longer to cool down.
Also I haven't checked but the new ones could be rotary instead of the old
piston type.
Lane
Pctchrisgibson
>engineering and not know a thing about motors" and anything else I may
>have said. My statement is technically true, however; these courses
>are not required. I was a little surprised with the test results;
>most motors start increasing in current rather quickly with a drop in
>voltage. Maybe fridge makers got tired of fridges being easily burned
>out and decided to make them a little more robust to brown-outs.
>
Apology accepted.
I would, however, like to know why and how this happens in fridge motors.
There's obviously something very different about their construction. None of
the stationary power tools at our workshop exhibit this "feature" and they are
basically the same type of motor. They all operate as you state they should.
ie, lower the voltage, the loaded speed remains the same and the current
increases.
With a fridge the effect isn't marginal, it is so pronounced you could almost
use a variac as a vari-speed control.
Chris
eh...@bellatlantic.net
But doesn't this (i.e., predicting using ohm's law) ignore
the effect of back emf?
daestrom
ohm's
> > law would predict.
>
> But doesn't this (i.e., predicting using ohm's law) ignore
> the effect of back emf?
Yes, exactly. Others had posted that current would drop in a linear fashion
with voltage (i.e. predicted by ohm's law). Some of us were arguing that
this is wrong (because it ignores back-emf) and that current would normally
rise in a AC induction motor. BUT, another gentleman ran the actual
experiment and posted the data.
Apparently, these motors are very high slip. This is done by using
high-resistance in the rotor circuit. The effect is to shift the pull-out
torque point closer to 0 RPM. This may have been done to provide better
starting of the compressor while it still has head-pressure against it. A
side-effect is that the have poor regulation with voltage variations.
I have actually seen this used once for variable-speed control, but not
often.
daestrom
Pctchrisgibson
>Yes, exactly. Others had posted that current would drop in a linear fashion
>with voltage (i.e. predicted by ohm's law).
>
I think the original confusion arose because one poster said a fridge
compressor was a constant load irrespective of voltage. Whilst the original
posters were referring to "motor" (knowing that a fridge compressor motor was
being referred to - perhaps if the term "fridge compressor motor" had been used
throughout it would have been removed the confusion - OK I'll take the blame
for that one :) others assumed they meant *all* motors. I think !
Chris
Lane Lewis
in the piston type stays the same while the rotary load will decrease with
slower RPM.
The same phenomena happens with a direct displacement waterpump as
opposed to a centrifugal pump. The direct displacement pump motor will burn
up in a low voltage situation but not the centrifugal. I think we can now
see its a mechanical problem as much as a motor problem. There is just to
much load for the motor to handle in a low voltage situation. Piston pump
motors overload and burn up and rotary and centrifugal pump motors go into a
reduced current situation.
Lane
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
news:20020529193033...@mb-mi.aol.com...
Lane Lewis
slows down as opposed to a piston type. Thats why your getting the reduced
current. But a piston type compressor will still have the same load in a low
voltage situation and the current will rise.
Lane
"Tut AmongUs @ the hole in the ground"
<TutAm...@theheartofthecheopspyramid.hol> wrote in message
news:p7b8fuss40k9hs0s1...@4ax.com...
> On Tue, 28 May 2002 23:51:25 GMT, "Lane Lewis" <myn...@hotmail.com>
> Gave us:
>
> >Also I haven't checked but the new ones could be rotary instead of the
old
> >piston type.
>
>
> Of course they are.
Matthew & Cali-Linn Beasley
displacement. These should have nearly flat torque curves...
The only part that is easier for the motor is that there isn't a cyclical
load. No sudden compression to come up against.
"Lane Lewis" <myn...@hotmail.com> wrote in message
news:ffeJ8.42006$R_4....@nwrddc02.gnilink.net...
daestrom
load
> in the piston type stays the same while the rotary load will decrease with
> slower RPM.
> The same phenomena happens with a direct displacement waterpump as
> opposed to a centrifugal pump. The direct displacement pump motor will
burn
> up in a low voltage situation but not the centrifugal. I think we can now
> see its a mechanical problem as much as a motor problem. There is just to
> much load for the motor to handle in a low voltage situation. Piston pump
> motors overload and burn up and rotary and centrifugal pump motors go into
a
> reduced current situation.
>
> Lane
>
The 'load' on centrifugal pumps varies only with speed and the discharge
conditions. If you vary the voltage, the load on such pumps will only go
down IF the speed drops. Standard motors do not slow down more than a few
percent (like maybe 5%) when running on low voltage. Induction-motor driven
centrifugal pumps can, and often do burn up if run on low voltage.
From the experiments others have run, I believe the 'fridge motor is not
"standard". It apparently has a higher than normal rotor resistance, and
thus poor speed regulation with variations in voltage.
daestrom
art
You might consider refresher.
Art.
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
> >Can you please tell me which university you studied Electrical
Engineering
> >at ?
> >
>
> I'll give you benifit of the doubt and assume you are asking a serious
question
> in which case I will answer University of Manchester Institute of Science
and
> Technology. UK.
>
> If it was an attempt at sarcasm I will reply by saying you clearly have so
> little knowledge that you're not worth discussin the matter with. Anyone
who
> think an electric motor exhibits negative resistance characteristics has a
> serious issue with his basic electrical theory.
>
> Chris
>
>
art
with arogant people.
Art.
"w_tom" <w_t...@usa.net> wrote in message news:3CF2496A...@usa.net...
art
Art.
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
> >So do I :-)
> >That said, my motor doesn't seem to have inversely proportional
> >relationship between its voltage and current. This is my result from
> >actual experiment.
> >
> >when V running is 121V, I running is 9.03A
> >
> >when Vrunning is 106V, Irunning is 7.5A
> >
>
> And that is what you *will* find if you actually try the experiment.
>
> Chris
>
>
Pctchrisgibson
>Nicely done Michael, close enough. That is my two Canadian cent..... Heck
>with arogant people.
>Art.
>
Except you're both wrong.
Chris
Pctchrisgibson
>Take a look at http://24.82.35.119/IvsE_AC_Motors.pdf
>You might consider refresher.
>Art.
>
You should read the rest of the thread then you'll realise it was resolved. We
all finally agreed that a fridge DOES draw less current at reduced voltage
which is what I originally said. Sort your attitude out.
Chris
John Gilmer
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
I don't recall that being definitely established.
art
right. Did you take a pick at the address I posted, any conclusions (not
about my attitude).
Art
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
art
>(Motor) It is *not* a constant power device. This is true, following that
you can draw your conclusions. If the load will require constant power motor
will deliver that power, requiring more current. Now the rest depends on the
fridge, point of cycle it is in, type of the compressor.
Art.
"Pctchrisgibson" <pctchri...@aol.comma> wrote in message
news:20020610033403...@mb-cp.aol.com...
Pctchrisgibson
Like I said..... Go and read the ENTIRE thread not a small part of it. You
know.... like ALL of it. You'll realise "motor" means fridge compressor motor.
Chris
Pctchrisgibson
Well two posters (me being one of them) ran tests on fridges and the
measurements bore that out. Another poster (a motor engineer) explained why it
happened.
Chris
Rob
number in the context of phsors, anyway? If the V and the I are not in
phase, and also the V and I are not liearly coupled, why would we even care
about "positive" or "negative" impedances, or the try to compare the
magnitudes only of two phasors?
Bung
Life is non-linear.
"art" <art...@hotmail.com> wrote in message
news:GOWM8.212336$xS2.16...@news1.calgary.shaw.ca...
Pctchrisgibson
>Are we comparing apples with apples here?
>
No we're not. Some posters jumped in halfway through without reading the full
thread.
Chris