Airconditioner startup surge currents?
Unknown
BriskAir AC (model 57912.621)?
The voltage in the campground here measures typically 116V, and the AC
current nominally changes from about 2 A (fan only) to 8 - 9 A when
the compressor starts, and the voltage dips to 114V. No problem.
However, I'm seeing some occasions where the current jumps to 45A, the
AC fan slows, the compressor hums and fails to start. The line
voltage during these incidents drops to 102 (at power pole) - 104V (in
RV) during this starting surge. I'm on a 30A circuit.
I initially though that the campground's power line was a bit 'soft',
but now I'm not so sure. I suspect that the compressor is attempting
to start under a load, and drawing the extreme current. The travel
trailer is only 19' and the small size may be contributing to short
cycling of the AC and causing this problem. The AC is a non-ducted
model with the standard roof vent mounting.
Any ideas? Fixes? Will it smoke during one of these surges?
................gary
Tom J
<GaryO> wrote in message
news:rdqh6v8t1lcfqkql1...@4ax.com...
> What are the typical startup surge currents for a Dometic
Duo-Therm
> BriskAir AC (model 57912.621)?
>
> The voltage in the campground here measures typically
116V, and the AC
> current nominally changes from about 2 A (fan only) to 8 -
9 A when
> the compressor starts, and the voltage dips to 114V. No
problem.
> However, I'm seeing some occasions where the current jumps
to 45A, the
> AC fan slows, the compressor hums and fails to start. The
line
> voltage during these incidents drops to 102 (at power
pole) - 104V (in
> RV) during this starting surge. I'm on a 30A circuit.
>
> I initially though that the campground's power line was a
bit 'soft',
> but now I'm not so sure.
If you are in a campground for more than overnight that has
power of less than 120 to 130 volts, you are frying
everything in your RV. You need to move to another
campground and never go back to that campground again. 116
volts is never enough for idle voltage.
Tom J
Slaves to Oil
statements of , GaryO <> who spewed them forth from
news:rdqh6v8t1lcfqkql1...@4ax.com:
45Amps, is this the limit of your inverter? Sounds like a short
to me, even with lower voltage the amperage will NOT jump but will
ease upward, unless something active occurs, such as a circuit does
something or such. Possbly a relay may be being activated which in turn
allows a short circuit to suck the amps, I am surprised you don't
have smoke or smell or some indication, but 45amps seems way too high!
Power (watts) = Amps x Volts.
2x114= 228 watts (seems a little high for a fan but...)
9x118= about a 1000 watts (seems reasonable)
45x114 = is a shitload (approx 4000+ watts), too much!!
Sniff around, be careful!!
--
This mail/post has a bad case of Herpes,
did your AntiVirus 'catch it'? ;))
Alan Balmer
<StupidP...@whitehouse.gov> wrote:
>45Amps, is this the limit of your inverter? Sounds like a short
>to me, even with lower voltage the amperage will NOT jump but will
>ease upward,
Even with normal voltage, the amperage will jump when the compressor
starts. After start, it will go back to whatever level it needs for
normal running. If the voltage is too low, it won't start at all, but
will keep trying, pulling a lot of current. Not a short circuit, but
motor windings are a close approximation :-)
Of course, the problem may be something else. The first thing I would
do is get plugged in to a known-good source, and see if the problem
goes away. If not, take a serious look at the compressor.
--
Al Balmer
Balmer Consulting
removebalmerc...@att.net
Chris Bryant
>What are the typical startup surge currents for a Dometic Duo-Therm
>BriskAir AC (model 57912.621)?
To be honest- the actual "surge" current is probably in the
45-50 amp range- but it is so short that it really doesn't matter-
it's only for a very small fraction of a second.
>
>The voltage in the campground here measures typically 116V, and the AC
>current nominally changes from about 2 A (fan only) to 8 - 9 A when
>the compressor starts, and the voltage dips to 114V. No problem.
>However, I'm seeing some occasions where the current jumps to 45A, the
>AC fan slows, the compressor hums and fails to start. The line
>voltage during these incidents drops to 102 (at power pole) - 104V (in
>RV) during this starting surge. I'm on a 30A circuit.
>
>I initially though that the campground's power line was a bit 'soft',
>but now I'm not so sure. I suspect that the compressor is attempting
>to start under a load, and drawing the extreme current. The travel
>trailer is only 19' and the small size may be contributing to short
>cycling of the AC and causing this problem. The AC is a non-ducted
>model with the standard roof vent mounting.
>
>Any ideas? Fixes? Will it smoke during one of these surges?
It should be off for at least 3 minutes- if it is shutting off
and trying to restart in a shorter time, then it is a short cycling
problem. I would start by removing the filter, running the A/C and
feeling in the return area for any cold air leaking back into the
return- if you find any, plug the leak. Also check the orientation of
the thermostat capillary tube- it should be sensing the return air (of
course).
This model should use a PTC device along with a start
capacitor for a start circuit- either one of these could be bad- if it
isn't short cycling, I would probably go ahead and replace both-
should be under $20- you can check this circuit by clamping an amp
probe over the wires to it and seeing if you get any reading- you
should on start, but not run.
--
Chris Bryant
Bryant RV Services- http://www.bryantrv.com
Cass
It very much DOES matter if the circuit cannot supply the required
current -even for a fraction of a second
The supply has to be able to supply whatever current is required for the
compressor to start in addition to the fan.
You can look on the compressor and somewhere, you will find a rating for
L.R.A. That abbreviation is for locked-rotor amperage to overcome the
inertia of a static rotor and get up to speed. Even though it lasts for a
fraction of a second, the circuit must be capable of supplying that required
current.
If not, you are going to get problems.
Cass
Cass
"Chris Bryant" <Bryan...@cfl.rr.com> wrote in message
news:31ci6v8i43umu8ibe...@4ax.com...
Morton
--
Tryna
25 miles west of Palm Springs
www.saltontheroad.com
"Cass" <BYE_OSAMAca...@galaxycorp.com> wrote in message
news:b4bkmd$f2o$0...@pita.alt.net...
> Chris,
>
> It very much DOES matter if the circuit cannot supply the required
> current -even for a fraction of a second
The starting capacitor, which is an energy storage device, will provide the
starting current for a time that is dependent on its size. So if sized
correctly this will happen and the following statement is incorrect.
>
> The supply has to be able to supply whatever current is required for the
> compressor to start in addition to the fan.
>
> Snip
> Cass
The following is correct.
> > To be honest- the actual "surge" current is probably in the
> > 45-50 amp range- but it is so short that it really doesn't matter-
> > it's only for a very small fraction of a second.
> >
As is the following!!!
> > This model should use a PTC device along with a start
> > capacitor for a start circuit- either one of these could be bad- if it
> > isn't short cycling, I would probably go ahead and replace both-
> > should be under $20- you can check this circuit by clamping an amp
> > probe over the wires to it and seeing if you get any reading- you
> > should on start, but not run.
> >
> >
> > --
> > Chris Bryant
> > Bryant RV Services- http://www.bryantrv.com
Al
Cass
Believe that if you wish.
While you are believing that, figure out how many joules a typical rv
air-condtioner requires to supply say, 50 to 75 amperes.
Now, contemplate how many farads one would need to supply that amount of
energy.
Also, contemplate the fact that the rotor doesn't instantly go from a rest
state to a working r.p.m.
Anyway, be sure that your wiring and supply can supply what is required. If
you are relying on something as tenuous as a starting capacitor without
regard to supply capacity and wiring gauge and length, you are absolutely
begging for trouble.
Cass
"Morton" <tmorton7...@earthlink.net> wrote in message
news:zxeaa.8248$gF3.8...@newsread1.prod.itd.earthlink.net...
Yofuri
the phase of the starter winding current to increase starting torque. All
the starting current is provided by the AC input; there is no free lunch.
Rick
"Morton" <tmorton7...@earthlink.net> wrote in message
news:zxeaa.8248$gF3.8...@newsread1.prod.itd.earthlink.net...
>
>
Lone Haranguer
> --
> Tryna
> 25 miles west of Palm Springs
>
> www.saltontheroad.com
> "Cass" <BYE_OSAMAca...@galaxycorp.com> wrote in message
> news:b4bkmd$f2o$0...@pita.alt.net...
>
>>Chris,
>>
>>It very much DOES matter if the circuit cannot supply the required
>>current -even for a fraction of a second
>
>
> The starting capacitor, which is an energy storage device, will provide the
> starting current for a time that is dependent on its size. So if sized
> correctly this will happen and the following statement is incorrect.
>
house. Ask a knowledgeable employee to prescribe the right kit
for the size of the problem. I put a kit on my freezer when I
first bought it so it could be started by my 800 watt inverter,
even if the batteries were not fully charged.
I believe that was 8 years ago and it has worked fine.
LZ
Tom Shaw
wires you clamp it over a wire.
It doesn't work if you clamp over both.
TS
"Morton" <tmorton7...@earthlink.net> wrote in message
news:zxeaa.8248$gF3.8...@newsread1.prod.itd.earthlink.net...
>
>
Tom Shaw
TS
"Yofuri" <yof...@oakharbor.net> wrote in message
news:v6j22pq...@corp.supernews.com...
Unknown
<Bryan...@cfl.rr.com> wrote:
>GaryO <> wrote:
>
>>What are the typical startup surge currents for a Dometic Duo-Therm
>>BriskAir AC (model 57912.621)?
>
> To be honest- the actual "surge" current is probably in the
>45-50 amp range- but it is so short that it really doesn't matter-
>it's only for a very small fraction of a second.
It seems to be lasting much longer than a fraction of a second. I'm
able to see it easily with a Fluke 32 clamp-on ammeter. The fan speed
drop is quite audible - almost to a stop. This doesn't happen all the
time, just 10-30% of the time. Other times it starts correctly.
I was actually clipped onto the main power line to the RV, so the 2A
idle included a loafing inverter, and other miscellaneous small loads.
>>The voltage in the campground here measures typically 116V, and the AC
>>current nominally changes from about 2 A (fan only) to 8 - 9 A when
>>the compressor starts, and the voltage dips to 114V. No problem.
>>However, I'm seeing some occasions where the current jumps to 45A, the
>>AC fan slows, the compressor hums and fails to start. The line
>>voltage during these incidents drops to 102 (at power pole) - 104V (in
>>RV) during this starting surge. I'm on a 30A circuit.
>>
>>I initially though that the campground's power line was a bit 'soft',
>>but now I'm not so sure. I suspect that the compressor is attempting
>>to start under a load, and drawing the extreme current. The travel
>>trailer is only 19' and the small size may be contributing to short
>>cycling of the AC and causing this problem. The AC is a non-ducted
>>model with the standard roof vent mounting.
>>
>>Any ideas? Fixes? Will it smoke during one of these surges?
>
> It should be off for at least 3 minutes- if it is shutting off
>and trying to restart in a shorter time, then it is a short cycling
>problem.
The off time has typically been much shorter than 3 minutes.
>I would start by removing the filter, running the A/C and
>feeling in the return area for any cold air leaking back into the
>return- if you find any, plug the leak. Also check the orientation of
>the thermostat capillary tube- it should be sensing the return air (of
>course).
I think I may have spotted the problem. I removed the inside
cover/plenum to check for air leaks, and found some gaps in the output
"duct" which may be allowing some air leakage - I covered these with
duct tape. But I think the bigger issue is the placement of the
thermostat's capillary tube. The end of it is jammed into the
evaporator! :-( Initially I thought it was the freeze sensor, but I
can find no other capillary tube emanating from the switch/control
assembly. What is the correct placement for this tube?
I did measure 20-30 degree output air temperatures with the inside
cover removed and the AC on high, so I don't suspect a low charge
situation.
> This model should use a PTC device along with a start
>capacitor for a start circuit- either one of these could be bad- if it
>isn't short cycling, I would probably go ahead and replace both-
>should be under $20- you can check this circuit by clamping an amp
>probe over the wires to it and seeing if you get any reading- you
>should on start, but not run.
Where is this located? Under the shroud on the roof?
................gary
Chris Bryant
<<..>>
<<..>>
>I think I may have spotted the problem. I removed the inside
>cover/plenum to check for air leaks, and found some gaps in the output
>"duct" which may be allowing some air leakage - I covered these with
>duct tape. But I think the bigger issue is the placement of the
>thermostat's capillary tube. The end of it is jammed into the
>evaporator! :-( Initially I thought it was the freeze sensor, but I
>can find no other capillary tube emanating from the switch/control
>assembly. What is the correct placement for this tube?
It basically just needs to be in the return air flow- the
should be a spot to hold the tube in the sheet metal of the inside
assembly right at the front- it is just a small piece bent at a 90°
angle with a hole through it.
<<..>>
>> This model should use a PTC device along with a start
>>capacitor for a start circuit- either one of these could be bad- if it
>>isn't short cycling, I would probably go ahead and replace both-
>>should be under $20- you can check this circuit by clamping an amp
>>probe over the wires to it and seeing if you get any reading- you
>>should on start, but not run.
>
>Where is this located? Under the shroud on the roof?
Yes- should be in a box with the run capacitor under the
shroud on the roof unit.
It is possible that it came without a start device, in which
case adding a capacitor/ptc would be a very good thing.
Cass
Cass
"Morton" <tmorton7...@earthlink.net> wrote in message
news:zxeaa.8248$gF3.8...@newsread1.prod.itd.earthlink.net...
>
>
Unknown
<Bryan...@cfl.rr.com> wrote:
>GaryO <> wrote:
><<..>>
>>I think I may have spotted the problem. I removed the inside
>>cover/plenum to check for air leaks, and found some gaps in the output
>>"duct" which may be allowing some air leakage - I covered these with
>>duct tape. But I think the bigger issue is the placement of the
>>thermostat's capillary tube. The end of it is jammed into the
>>evaporator! :-( Initially I thought it was the freeze sensor, but I
>>can find no other capillary tube emanating from the switch/control
>>assembly. What is the correct placement for this tube?
>
> It basically just needs to be in the return air flow- the
>should be a spot to hold the tube in the sheet metal of the inside
>assembly right at the front- it is just a small piece bent at a 90°
>angle with a hole through it.
I think I see the item you are referring to. It has a small plastic
bushing inserted in the hole. I'll try placing it in there.
The AC has been running fine now since I pulled the capillary tube out
of the evaporator. The big startup surges are gone, and the off cycle
time is now much longer. It seems to be running as designed! :-)
One thing which I find odd, is that there is no sort of assembly to
properly support and hold the air filter in place. It looks if the
filter should become dirty or restrictive, it could be easily sucked
up into the unit against the evaporator coil.
I also see a small opening (1.5" - 2" hole) at the edge of the
evaporator, on the curb side. Is this normal, or should I cover it
with duct tape?
><<..>>
>>> This model should use a PTC device along with a start
>>>capacitor for a start circuit- either one of these could be bad- if it
>>>isn't short cycling, I would probably go ahead and replace both-
>>>should be under $20- you can check this circuit by clamping an amp
>>>probe over the wires to it and seeing if you get any reading- you
>>>should on start, but not run.
>>
>>Where is this located? Under the shroud on the roof?
>
> Yes- should be in a box with the run capacitor under the
>shroud on the roof unit.
> It is possible that it came without a start device, in which
>case adding a capacitor/ptc would be a very good thing.
Is there any way to check this other than by climbing on the roof?
The 3-step ladder I have with me just won't quite allow for rooftop
access. I do see a gazillion numbers on the AC which are visible by
removing the filter and inside airbox assembly. Could one of these
indicate the presence of a capacitor & ptc device?
................gary
Neon John
>What are the typical startup surge currents for a Dometic Duo-Therm
>BriskAir AC (model 57912.621)?
>
>The voltage in the campground here measures typically 116V, and the AC
>current nominally changes from about 2 A (fan only) to 8 - 9 A when
>the compressor starts, and the voltage dips to 114V. No problem.
>However, I'm seeing some occasions where the current jumps to 45A, the
>AC fan slows, the compressor hums and fails to start. The line
>voltage during these incidents drops to 102 (at power pole) - 104V (in
>RV) during this starting surge. I'm on a 30A circuit.
The peak starting current will be a little less than the locked rotor current
or LRA. the LRA of the compressor is expressed on the nameplate. You can
pull the cover off and look if you really want to know. there will be an
"LRA" with a number beside it on the nameplate. I'm going to guess about 50
amps.
You can calculate the impedance of the campground supply from the information
you have provided. The formula is:
impedance = delta voltage/delta current. Your voltage drops from 116 volts to
114 volts when you draw, let's average your numbers and say, 8.5 amps. the
delta voltage is 2 volts and the delta amps is 8.5 so 2/8.5 = 0.235 ohms.
This quite "soft". Typically I'd expect the impedance at the end of you RV
power cable to be 0.03 or less.
To check our math lets use the same formula to compute the starting voltage
drop problem. If your voltage drops from 114 to 104 during starting and the
LRA is about 50 amps, then 10/50 = 0.2 ohms. Given the estimated numbers,
this is quite good agreement. Since the voltage at the pole and the RV is
practically the same, one may assume that the CG wiring is where the excess
impedance (softness) is.
Your AC is obviously on the edge. I know that mine will start at 104 volts
but probably won't at 100. I imagine your voltage varies that much as the
load on the whole park changes so sometimes your AC will start and sometimes
it won't.
>
>I initially though that the campground's power line was a bit 'soft',
>but now I'm not so sure. I suspect that the compressor is attempting
>to start under a load, and drawing the extreme current. The travel
>trailer is only 19' and the small size may be contributing to short
>cycling of the AC and causing this problem. The AC is a non-ducted
>model with the standard roof vent mounting.
>
>Any ideas? Fixes? Will it smoke during one of these surges?
Last question first, yes this situation poses a risk for the AC. It isn't
that the motor will necessarily be harmed by the low voltage - it probably
won't. The problem is that after so many operations the Klixon thermal
overload breaker in the compressor will weld its contacts on one of the
no-start events. When that happens, the LRA current will flow until something
gives. Hopefully the RV breaker but maybe the compressor winding.
Fixes? Best bet is to move. If you can't do that then you'll need to do
something to boost your voltage. You can buy one of those very expensive
autotransformers from $CW$ or equiv.
If you're handy you can build something very cheaply. All you really need to
do is boost your voltage about 10 volts. To do that you simply need to obtain
a 10 volt, 30 amp transformer, hook the 120 volt primary to the RV power and
hook the secondary in SERIES with the RV supply, observing the polarity so
that the voltages add.
You can get such a transformer surplus for $20 or so from places like
http://www.meci.com. Mount it in a metal box along with a switch to cut it in
and out of the circuit (30 amp DPDT switch from Lowe's, etc - about $6) and
install it near the breaker panel. When the supply voltage is low, flip the
switch to boost the voltage 10 or 12 volts. When it isn't, flip the switch
the other way and switch the transformer out of the circuit. If you're
interested in doing this I can supply you with a circuit sketch. Of course,
if you're not comfortable twisting wires together then the autotransformer
from $CW$ would be appropriate. (I suppose that disclaimer is necessary for
those who don't know how to do things but criticize those who do....)
There is another option you might want to check into. There is a gadget
available called a hard start kit or "kick starter" that attaches to the
compressor terminals and generates additional torque in the motor. This
device helps tight compressors or compressors operating on low voltage to
start. The device is available from HVAC supply stores and costs <$30. A
kick starter is a good thing in general to have on the AC because it also
lowers the peak starting current. It will let you run on lower supply voltage
or at the end of longer extension cords. It is a simple 2 wire device that
simply clips to the compressor terminals.
For voltage as low as you're reporting this would merely be a patch to cover
over the real problem. But it will be useful for other CGs with higher
voltage. Also reduces light dimming when the compressor starts.
John
---
John De Armond
johngdDO...@bellsouth.net
http://bellsouthpwp.net/j/o/johngd/
Cleveland, Occupied TN
Cass
locked rotor amperage as the peak starting current of the fan needs to be
considered.
Cass
"Neon John" <johngdDO...@bellsouth.net> wrote in message
news:l57o6voou5j6bce83...@4ax.com...
Chris Bryant
<<..>>
>> It basically just needs to be in the return air flow- the
>>should be a spot to hold the tube in the sheet metal of the inside
>>assembly right at the front- it is just a small piece bent at a 90°
>>angle with a hole through it.
>
>I think I see the item you are referring to. It has a small plastic
>bushing inserted in the hole. I'll try placing it in there.
Yep- that's the place.
>
>The AC has been running fine now since I pulled the capillary tube out
>of the evaporator. The big startup surges are gone, and the off cycle
>time is now much longer. It seems to be running as designed! :-)
I would bet that this has been the trouble all along- even
with the proper start circuit, if the compressor tries to restart to
quickly it will draw a huge amount of current.
>One thing which I find odd, is that there is no sort of assembly to
>properly support and hold the air filter in place. It looks if the
>filter should become dirty or restrictive, it could be easily sucked
>up into the unit against the evaporator coil.
Use three rubber bands running sideways between the posts that
stick up on either side of the grill.
>
>I also see a small opening (1.5" - 2" hole) at the edge of the
>evaporator, on the curb side. Is this normal, or should I cover it
>with duct tape?
That's normal - if it is what I think it is, it is an opening
for a freeze control used in ducted applications. The freeze switch
clamps on to the evaporator tubing, but you can just ignore it.
<<..>>
>>>Where is this located? Under the shroud on the roof?
>>
>> Yes- should be in a box with the run capacitor under the
>>shroud on the roof unit.
>> It is possible that it came without a start device, in which
>>case adding a capacitor/ptc would be a very good thing.
>
>Is there any way to check this other than by climbing on the roof?
>The 3-step ladder I have with me just won't quite allow for rooftop
>access. I do see a gazillion numbers on the AC which are visible by
>removing the filter and inside airbox assembly. Could one of these
>indicate the presence of a capacitor & ptc device?
I'm afraid you have to get on the roof to see it. The numbers
probably would tell whether it has a start device, but I'm not
positive. FWIW, even though my parts breakdowns say "optional" for
your model, I have never seen a DuoTherm without the start circuit
(I've seen lots of Colemans, though).
Unknown
<Bryan...@cfl.rr.com> wrote:
>GaryO <> wrote:
><<..>>
>>The AC has been running fine now since I pulled the capillary tube out
>>of the evaporator. The big startup surges are gone, and the off cycle
>>time is now much longer. It seems to be running as designed! :-)
>
> I would bet that this has been the trouble all along- even
>with the proper start circuit, if the compressor tries to restart to
>quickly it will draw a huge amount of current.
I think you are right. The AC seemed to run afterwards. I don't
understand why someone decided to insert it into the evaporator -
maybe it was having an evaporator freezing problem at some point in
its history, and this was a poor attempt to solve it.
>>One thing which I find odd, is that there is no sort of assembly to
>>properly support and hold the air filter in place. It looks if the
>>filter should become dirty or restrictive, it could be easily sucked
>>up into the unit against the evaporator coil.
>
> Use three rubber bands running sideways between the posts that
>stick up on either side of the grill.
Simple but effective I guess. :^)
>>I also see a small opening (1.5" - 2" hole) at the edge of the
>>evaporator, on the curb side. Is this normal, or should I cover it
>>with duct tape?
>
> That's normal - if it is what I think it is, it is an opening
>for a freeze control used in ducted applications. The freeze switch
>clamps on to the evaporator tubing, but you can just ignore it.
Mine is not ducted, so I guess it has no freeze sensor.
><<..>>
>>>>Where is this located? Under the shroud on the roof?
>>>
>>> Yes- should be in a box with the run capacitor under the
>>>shroud on the roof unit.
>>> It is possible that it came without a start device, in which
>>>case adding a capacitor/ptc would be a very good thing.
>>
>>Is there any way to check this other than by climbing on the roof?
>>The 3-step ladder I have with me just won't quite allow for rooftop
>>access. I do see a gazillion numbers on the AC which are visible by
>>removing the filter and inside airbox assembly. Could one of these
>>indicate the presence of a capacitor & ptc device?
>
> I'm afraid you have to get on the roof to see it. The numbers
>probably would tell whether it has a start device, but I'm not
>positive. FWIW, even though my parts breakdowns say "optional" for
>your model, I have never seen a DuoTherm without the start circuit
>(I've seen lots of Colemans, though).
Thanks for all your help. My ability to access this newsgroup was
somewhat limited for the last several weeks while I was camping in the
middle of nowhere.
I'll add this to my list of thinks to do/check this spring. I was in
Florida for the last 6 weeks :-) and just got home to PA tonight :-( .
The weather here is still below freezing at night :-( so it looks like
I will be winterizing the unit tomorrow. I'm running the heater in
the storage lot tonight! I had to move some snow in order to park it
in the lot!
...........gary
Unknown
<johngdDO...@bellsouth.net> wrote:
>On Fri, 07 Mar 2003 14:31:18 -0500, GaryO <> wrote:
>
>>What are the typical startup surge currents for a Dometic Duo-Therm
>>BriskAir AC (model 57912.621)?
>>
>>The voltage in the campground here measures typically 116V, and the AC
>>current nominally changes from about 2 A (fan only) to 8 - 9 A when
>>the compressor starts, and the voltage dips to 114V. No problem.
>>However, I'm seeing some occasions where the current jumps to 45A, the
>>AC fan slows, the compressor hums and fails to start. The line
>>voltage during these incidents drops to 102 (at power pole) - 104V (in
>>RV) during this starting surge. I'm on a 30A circuit.
>
>The peak starting current will be a little less than the locked rotor current
>or LRA. the LRA of the compressor is expressed on the nameplate. You can
>pull the cover off and look if you really want to know. there will be an
>"LRA" with a number beside it on the nameplate. I'm going to guess about 50
>amps.
I'll have to check for this when I climb on the roof. This seems to
agree with the currents I was measuring.
>You can calculate the impedance of the campground supply from the information
>you have provided. The formula is:
>
>impedance = delta voltage/delta current. Your voltage drops from 116 volts to
>114 volts when you draw, let's average your numbers and say, 8.5 amps. the
>delta voltage is 2 volts and the delta amps is 8.5 so 2/8.5 = 0.235 ohms.
>This quite "soft". Typically I'd expect the impedance at the end of you RV
>power cable to be 0.03 or less.
I guess being on vacation, I must have turned my brain off. I should
have though of this, but I had no reference for "good" values. Is
there something in the electrical code which covers this? Campground
power supplies are so variable, unfortunately.
I think the actual "delta I" is more like 6.5A. This would give 0.31
ohms, which is even worse.
>To check our math lets use the same formula to compute the starting voltage
>drop problem. If your voltage drops from 114 to 104 during starting and the
>LRA is about 50 amps, then 10/50 = 0.2 ohms. Given the estimated numbers,
>this is quite good agreement. Since the voltage at the pole and the RV is
>practically the same, one may assume that the CG wiring is where the excess
>impedance (softness) is.
Yeah, but the campgrounds always say that it is the power company's
fault.
>Your AC is obviously on the edge. I know that mine will start at 104 volts
>but probably won't at 100. I imagine your voltage varies that much as the
>load on the whole park changes so sometimes your AC will start and sometimes
>it won't.
Fortunately it only drops this low when attempting to pull 45A. This
does not seem to be the normal situation, unless the compressor is
short cycling, as mine was.
>>I initially though that the campground's power line was a bit 'soft',
>>but now I'm not so sure. I suspect that the compressor is attempting
>>to start under a load, and drawing the extreme current. The travel
>>trailer is only 19' and the small size may be contributing to short
>>cycling of the AC and causing this problem. The AC is a non-ducted
>>model with the standard roof vent mounting.
>>
>>Any ideas? Fixes? Will it smoke during one of these surges?
>
>Last question first, yes this situation poses a risk for the AC. It isn't
>that the motor will necessarily be harmed by the low voltage - it probably
>won't. The problem is that after so many operations the Klixon thermal
>overload breaker in the compressor will weld its contacts on one of the
>no-start events. When that happens, the LRA current will flow until something
>gives. Hopefully the RV breaker but maybe the compressor winding.
Would you know if the Klixon breaker is accessible and replaceable? I
don't know how long this problem has been going on - but I suspect
some time. If replaceable, I just may replace it for peace of mind.
>Fixes? Best bet is to move. If you can't do that then you'll need to do
>something to boost your voltage. You can buy one of those very expensive
>autotransformers from $CW$ or equiv.
I've already "moved", as I'm now back home. :-( I've seen the
autotransformer in the CW catalog. It looks to be $$, large, and
heavy. No thanks.
>If you're handy you can build something very cheaply. All you really need to
>do is boost your voltage about 10 volts. To do that you simply need to obtain
>a 10 volt, 30 amp transformer, hook the 120 volt primary to the RV power and
>hook the secondary in SERIES with the RV supply, observing the polarity so
>that the voltages add.
>
>You can get such a transformer surplus for $20 or so from places like
>http://www.meci.com. Mount it in a metal box along with a switch to cut it in
>and out of the circuit (30 amp DPDT switch from Lowe's, etc - about $6) and
>install it near the breaker panel. When the supply voltage is low, flip the
>switch to boost the voltage 10 or 12 volts. When it isn't, flip the switch
>the other way and switch the transformer out of the circuit. If you're
>interested in doing this I can supply you with a circuit sketch. Of course,
>if you're not comfortable twisting wires together then the autotransformer
>from $CW$ would be appropriate. (I suppose that disclaimer is necessary for
>those who don't know how to do things but criticize those who do....)
Actually, I've considered making one from my old Magnetek converter
and a SPDT relay. Should be quite easy, but I'm not so sure that I
want to add another large gadget to the RV (due to limited storage
space and weight), unless low voltage and AC operation becomes a more
common problem for me. I only used the AC about a week out of the
last 6 weeks - and that was primarily for humidity reduction. I
generally just use the TurboMaxx Fan.
>There is another option you might want to check into. There is a gadget
>available called a hard start kit or "kick starter" that attaches to the
>compressor terminals and generates additional torque in the motor. This
>device helps tight compressors or compressors operating on low voltage to
>start. The device is available from HVAC supply stores and costs <$30. A
>kick starter is a good thing in general to have on the AC because it also
>lowers the peak starting current. It will let you run on lower supply voltage
>or at the end of longer extension cords. It is a simple 2 wire device that
>simply clips to the compressor terminals.
Is this the same item which Chris was referring to? A capacitor and a
PTC?
>For voltage as low as you're reporting this would merely be a patch to cover
>over the real problem. But it will be useful for other CGs with higher
>voltage. Also reduces light dimming when the compressor starts.
Light dimming? My lighting is all 12V! The battery makes for an
excellent brownout protector. :-)
...........gary
Neon John
>On Wed, 12 Mar 2003 22:33:09 -0500, Neon John
><johngdDO...@bellsouth.net> wrote:
>
>>Last question first, yes this situation poses a risk for the AC. It isn't
>>that the motor will necessarily be harmed by the low voltage - it probably
>>won't. The problem is that after so many operations the Klixon thermal
>>overload breaker in the compressor will weld its contacts on one of the
>>no-start events. When that happens, the LRA current will flow until something
>>gives. Hopefully the RV breaker but maybe the compressor winding.
>
>Would you know if the Klixon breaker is accessible and replaceable? I
>don't know how long this problem has been going on - but I suspect
>some time. If replaceable, I just may replace it for peace of mind.
Almost always this round black device is located in the compressor terminal
box. Just pop the box cover and there it is. If you're lucky there will be a
Klixon number on the device. If you're unlucky it will be a house number. If
you can't find the Klixon part number, I recommend getting one directly from
the Mfr, as many times the house numbered parts are custom-tailored for the
application. I would NOT trust a cross-referenced general purpose part for
this application.
>>There is another option you might want to check into. There is a gadget
>>available called a hard start kit or "kick starter" that attaches to the
>>compressor terminals and generates additional torque in the motor. This
>>device helps tight compressors or compressors operating on low voltage to
>>start. The device is available from HVAC supply stores and costs <$30. A
>>kick starter is a good thing in general to have on the AC because it also
>>lowers the peak starting current. It will let you run on lower supply voltage
>>or at the end of longer extension cords. It is a simple 2 wire device that
>>simply clips to the compressor terminals.
>
>Is this the same item which Chris was referring to? A capacitor and a
>PTC?
yep, same thing. The original Kick Starter brand used a capacitor and a
mechanical potential relay but all the ones I've purchased in the last couple
of years have been solid state. Frankly, I like the mechanical ones better.
The PTC solid state ones require a bit of time to cool off and reset. If you
try to restart too soon, the kickstarter won't have any effect. The downside
of the mechanical one is that orientation matters.
>
>>For voltage as low as you're reporting this would merely be a patch to cover
>>over the real problem. But it will be useful for other CGs with higher
>>voltage. Also reduces light dimming when the compressor starts.
>
>Light dimming? My lighting is all 12V! The battery makes for an
>excellent brownout protector. :-)
Well yeah, if your converter design leaves the battery in the circuit. Mine
does. My mother's MH's magnetek converter doesn't. When AC is applied the
relay transfers the 12 volt lighting from the battery to the rectifier.
Lights very much DO dim with (not so) heavy loads like the AC starting or
using the microwave. Annoying. Didn't know which kind you had, which is why
I mentioned it.
Unknown
Actually, my original converter was the Magnetek 6332 which used a 12V
switchover relay. I've replaced it with the 7345RU which no longer
uses this relay - the full converter output is applied directly to the
battery & house circuits.
Thanks for the advice. I'll be looking for the Klixon breaker and
replace it for safety sake. I'll also verify that the capacitor and
ptc device which Chris referred to is actually installed, and install
one if it's not.
...........gary