Electric Motor Guru Question
amdx
It is a shunt field motor.
Please stick with me as I develop the situation.
If you know of better place to ask me question please let me know. (forums?)
I have a shunt field motor that I have been using with a series field
controller. I have been using this on an electric gokart and it has worked
fine for over a year.
Shortly after finishing the wiring and testing (it ran great btw) I realized
I made an error when wiring the shunt.
I wired it so no current flowed in the shunt, The wiring put a 20 ohm
resistor across the shunt. Here's a simplified schematic of the wiring.
The 20 ohm resistor is for current limiting, as I'm overvolting the motor.
http://i395.photobucket.com/albums/p...ringDiagrm.jpg
I wired it properly and the motor ran slower, so I ran the shunt open and
this cause my controller to become defective ( bad day). After I got the
controller fixed I wired it as original (no shunt current) and we have drove
it for a year.
Here's a link showing all three wiring diagrams.
http://i395.photobucket.com/albums/p...arioABCGIF.gif
So, how does this even work with the shunt wired to the 20 ohm resistor
and not current through the shunt? I expect some answer about current
induced by rotor flux, but we'll see.
Next problem, the motor smoked the other day, I pulled it apart and found
the field overheated. The field has 4 poles and is a bit odd. Two poles use
#16 wire and two use #24 wire. The field measures 41 ohms and has not
changed in the last year. I can't tell if the #16 and #25 are series or
parallel, however, I think it is a good guess they are in series because I
think the #16 wire fields would have much less than 41 ohms. The fields do
show opposite magnetic fields as I go around the stator. (Tested with small
magnet on a stick).
Here's a picture of the stator with two different wire sizes.
Note three different color wires in #16 wound field.
http://i395.photobucket.com/albums/p...vam/Stator.jpg
I understand the motor could have compound or interpole windings,
but I don't think either of these are true, based on my measurements.
Here's a diagram of the motor connection.
Only three wires out labeled A2, F1 and F2.
http://i395.photobucket.com/albums/p...2F2F1Motor.jpg
Here's the original motor wiring plate, I don't think it is relevant because
it is clear this motor has been rewound.
So, Why the different size wire in the field?
The #24 wire is overheated at one end of the motor, any idea why
it would have overheated, since I don't battery current through the shunt?
I will be happy to do any more measurements requested if I can.
Any help to enlighten me is appreciated.
Thanks, MikeK
Tim Wescott
> I need some help explaining a motor I have been using for over a year.
> It is a shunt field motor.
> Please stick with me as I develop the situation.
> If you know of better place to ask me question please let me know. (forums?)
> I have a shunt field motor that I have been using with a series field
> controller. I have been using this on an electric gokart and it has worked
> fine for over a year.
> Shortly after finishing the wiring and testing (it ran great btw) I realized
> I made an error when wiring the shunt.
> I wired it so no current flowed in the shunt, The wiring put a 20 ohm
> resistor across the shunt. Here's a simplified schematic of the wiring.
> The 20 ohm resistor is for current limiting, as I'm overvolting the motor.
> http://i395.photobucket.com/albums/p...ringDiagrm.jpg
> I wired it properly and the motor ran slower, so I ran the shunt open and
> this cause my controller to become defective ( bad day). After I got the
> controller fixed I wired it as original (no shunt current) and we have drove
> it for a year.
> Here's a link showing all three wiring diagrams.
> http://i395.photobucket.com/albums/p...arioABCGIF.gif
>
snip
Wiring it with the shunt open is the only way that you could wire it for
no current in the shunt. So you need to specify what you mean when you
say "no current in the shunt".
Your newsgroup agent is mangling the links (mine is just showing what
got posted to the group), photobucket can't find anything. Figuring out
links (tinyURL?) would help a lot, I suspect.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
amdx
"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:HfadndAm062p4PTR...@web-ster.com...
> On 08/16/2010 09:48 AM, amdx wrote:
>> I need some help explaining a motor I have been using for over a year.
>> It is a shunt field motor.
>> Please stick with me as I develop the situation.
>> If you know of better place to ask me question please let me know.
>> (forums?)
>> I have a shunt field motor that I have been using with a series field
>> controller. I have been using this on an electric gokart and it has
>> worked
>> fine for over a year.
>> Shortly after finishing the wiring and testing (it ran great btw) I
>> realized
>> I made an error when wiring the shunt.
>> I wired it so no current flowed in the shunt, The wiring put a 20 ohm
>> resistor across the shunt. Here's a simplified schematic of the wiring.
>> The 20 ohm resistor is for current limiting, as I'm overvolting the
>> motor.
http://i395.photobucket.com/albums/pp37/Qmavam/SimplifiedMotorwiringDiagrm.jpg
or
http://tinyurl.com/29o34np
>> I wired it properly and the motor ran slower, so I ran the shunt open and
>> this cause my controller to become defective ( bad day). After I got the
>> controller fixed I wired it as original (no shunt current) and we have
>> drove
>> it for a year.
>> Here's a link showing all three wiring diagrams.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorWiringscenarioABCGIF.giforhttp://tinyurl.com/2cefay4>>>> snip>> Wiring it with the shunt open is the only way that you could wire it forno current in the shunt. So you need to specify what you mean when you say"no current in the shunt".> Or you can connect one end of the shunt to a resistor and the other endof the shunt to the other end of the resistor, then connect one end to B+.Yes it was a mistake, but it worked best this way.> Your newsgroup agent is mangling the links (mine is just showing what gotposted to the group), photobucket can't find anything. Figuring out links(tinyURL?) would help a lot, I suspect.> Thanks, I hope I fixed them. MikeK> -->> Tim Wescott> Wescott Design Services> http://www.wescottdesign.com>> Do you need to implement control loops in software?> "Applied Control Theory for Embedded Systems" was written for you.> See details at http://www.wescottdesign.com/actfes/actfes.html
amdx
I need some help explaining a motor I have been using for over a year.
It is a shunt field motor.
Please stick with me as I develop the situation.
If you know of better place to ask me question please let me know. (forums?)
I have a shunt field motor that I have been using with a series field
controller. I have been using this on an electric gokart and it has worked
fine for over a year.
Shortly after finishing the wiring and testing (it ran great btw) I realized
I made an error when wiring the shunt.
I wired it so no current flowed in the shunt, The wiring put a 20 ohm
resistor across the shunt. Here's a simplified schematic of the wiring.
The 20 ohm resistor is for current limiting, as I'm overvolting the motor.
http://i395.photobucket.com/albums/pp37/Qmavam/SimplifiedMotorwiringDiagrm.jpg
this cause my controller to become defective ( bad day). After I got the
controller fixed I wired it as original (no shunt current) and we have drove
it for a year.
Here's a link showing all three wiring diagrams.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorWiringscenarioABCGIF.gif
So, how does this even work with the shunt wired to the 20 ohm resistor
and not current through the shunt? I expect some answer about current
induced by rotor flux, but we'll see.
Next problem, the motor smoked the other day, I pulled it apart and found
the field overheated. The field has 4 poles and is a bit odd. Two poles use
#16 wire and two use #24 wire. The field measures 41 ohms and has not
changed in the last year. I can't tell if the #16 and #25 are series or
parallel, however, I think it is a good guess they are in series because I
think the #16 wire fields would have much less than 41 ohms. The fields do
show opposite magnetic fields as I go around the stator. (Tested with small
magnet on a stick).
Here's a picture of the stator with two different wire sizes.
Note three different color wires in #16 wound field.
http://i395.photobucket.com/albums/pp37/Qmavam/Stator.jpg
I understand the motor could have compound or interpole windings,
but I don't think either of these are true, based on my measurements.
Here's a diagram of the motor connection.
Only three wires out labeled A2, F1 and F2.
http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
Tim Wescott
I'm not sure why it worked in case A. I think you really had it
connected such that the shunt winding was across the field winding (i.e.
the shunt connected on the opposite side of the motor than you thought).
You could test this by wiring it as in "A" with an ammeter in series
with the resistor -- I expect you'll see current flowing, consistent
with the average voltage out of the PWM.
In case C you turned it from a motor into an inductor, then you put DC
into it. This was a lot like driving your PWM controller straight into
a dead short, and it became dead, shortly.
In case B you were putting _lots_ of current through the field winding.
This makes a motor very tourqey, and slow. The reason is because the
constant of proportionality for torque/amp is proportional to the field
current, and it is (if you get your units right*, and have a lossless
motor) exactly the same as the constant of proportionality for
back-emp/speed.
So, you made that motor constant big which made the back-EMF big, which
means that the motor doesn't have to go very fast to cancel out the
terminal voltage, which means that the motor doesn't go fast.
I'd experiment with putting a resistor in series with your field winding
(what you're calling the shunt), either before the PWM controller
(drawing B with a resistor in there), or after (drawing A with the
resistor moved to the other side of the motor, if drawing A really is
correct). Then I'd experiment with the resistor value. If your field
winding resistance is 40 ohms, I'd start with a 40 or 80 ohm resistor,
and go from there. The bee's knees would be to put a small controllable
supply on the field, with a "gearshift" knob on the dash.
The bigger you make the resistor the more speed you'll get out of the
motor, but the less torque for the input current. It's a tradeoff.
* If you express your motor constant as Newton-meters/Amp, then with a
bit of light** dimensional analysis you'll find that the motor constant
in Volts/(radians/second) is identical. This isn't just nifty
dimensional analysis tricks: it's the first law of thermodynamics at
work; saying that if you put electrical energy into the thing you have
to get exactly the same mechanical energy out, or visa-versa.
** Hah!
amdx
I new that would be the first response :-) I have checked this several
times,
several ways, and then a year later still questioning it, I checked it
again, by
following the wires, and using an ohm meter.
> You could test this by wiring it as in "A" with an ammeter in series with
> the resistor -- I expect you'll see current flowing, consistent with the
> average voltage out of the PWM.
>
I'm not PWM the shunt current, The plan was to just supply a continuous
dc flow through the 20 ohm dropping resistor. (I'm running a 28volt motor on
48 volts.)
> In case C you turned it from a motor into an inductor, then you put DC
> into it. This was a lot like driving your PWM controller straight into a
> dead short, and it became dead, shortly.
>
I think you are saying with no shunt current the rotor sees no back
emf,
I have several arguements why I don't think that is the case, the easiest is
the controller is current limited, second the fault indicated was on
overvoltage
and it cleared as it should the first time, it didn't clear the second time.
The factory
said it was an overvoltage fault when the got it.
> In case B you were putting _lots_ of current through the field winding.
> This makes a motor very tourqey, and slow. The reason is because the
> constant of proportionality for torque/amp is proportional to the field
> current, and it is (if you get your units right*, and have a lossless
> motor) exactly the same as the constant of proportionality for
> back-emp/speed.
>
_lots_ is a little subjective, it was about 800ma. A 41 ohm shunt resistance
plus 20 ohm resistor is 61 ohms. 48 volts/ 61 ohms = 800ma
> So, you made that motor constant big which made the back-EMF big, which
> means that the motor doesn't have to go very fast to cancel out the
> terminal voltage, which means that the motor doesn't go fast.
>
> I'd experiment with putting a resistor in series with your field winding
> (what you're calling the shunt), either before the PWM controller (drawing
> B with a resistor in there), or after (drawing A with the resistor moved
> to the other side of the motor, if drawing A really is correct). Then I'd
> experiment with the resistor value. If your field winding resistance is
> 40 ohms, I'd start with a 40 or 80 ohm resistor, and go from there. The
> bee's knees would be to put a small controllable supply on the field, with
> a "gearshift" knob on the dash.
I have the bee's knees, I'm thinking I have a 50 ohm reostat on the dash.
I never seemed to have a noticeable effect, but I have the odd hook up.
Here's a video showing my dash, the knob in the upper left of the dash is
on the reostat.
http://www.youtube.com/watch?v=5MKjbXltAew
>
> The bigger you make the resistor the more speed you'll get out of the
> motor, but the less torque for the input current. It's a tradeoff.
Ya, at the moment we have a less powerful series shunt motor, it
does not go as fast but it has more torque, my son likes it better because
it is easier to do spins! (donuts)
Paul Hovnanian P.E.
shunt field and a series field. By mis-wiring the shunt field, it acted
as a series motor.
Two things can happen: 1) A series field motor, unloaded can fail by
overspeed. 2) Even when loaded, the lack of the shunt field will result
in lower back e.m.f and, as a result, higher armature and series field
currents. Which could lead to overheating.
*There are other strange combinations of fields that you might have as
well which, when mis-wired, will behave somewhat like series motors.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Ask not for whom the <CONTROL-G> tolls.
Tim Wescott
> Just a guess. What you have is actually a compound motor*. It has both a
> shunt field and a series field. By mis-wiring the shunt field, it acted
> as a series motor.
>
> Two things can happen: 1) A series field motor, unloaded can fail by
> overspeed. 2) Even when loaded, the lack of the shunt field will result
> in lower back e.m.f and, as a result, higher armature and series field
> currents. Which could lead to overheating.
>
> *There are other strange combinations of fields that you might have as
> well which, when mis-wired, will behave somewhat like series motors.
>
That would certainly explain why there's two different field windings,
wouldn't it?
(I hadn't thought about that. All the motors I've ever controlled have
been permanent magnet DC motors, so I haven't had my nose rubbed in all
the externally-excited motor possibilities).
amdx
"Paul Hovnanian P.E." <Pa...@Hovnanian.com> wrote in message
news:4C69A75D...@Hovnanian.com...
> Just a guess. What you have is actually a compound motor*. It has both a
> shunt field and a series field.
I have been through that thought process and cannot find any logical
way to make that work. This page shows 3 possible combinations
of compound motor wiring, see figure 12-17.
http://zone.ni.com/devzone/cda/ph/p/id/39
If the motor was like A or B, I could see that with a couple of ohm meter
tests.
I have checked it is not wired like that.
If it was like C I could ohm that out also.
I have checked it is not wired like that either.
It is wired just like this url shows.
http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
>By mis-wiring the shunt field, it acted
> as a series motor.
This is not possible because the shunt has a very high resistance,
41 ohms. The motor will draw 100s of amps.
> Two things can happen: 1) A series field motor, unloaded can fail by
> overspeed. 2) Even when loaded, the lack of the shunt field will result
> in lower back e.m.f and, as a result, higher armature and series field
> currents. Which could lead to overheating.
>
> *There are other strange combinations of fields that you might have as
> well which, when mis-wired, will behave somewhat like series motors.
>
Please look at this drawing, the motor only has three wires out, labeled
F2, F1 and A2, logicaly F2 is connected to A1 internally. Oh darn I see
in parentheses I have A2 it should be A1
For clearity, A1, A2 is armature and F1, F2 is field.
http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
Thanks for your thoughts, I have been through this thing
trying to find some connection other than what is in the above drawing
and what you see is all I can find.
MikeK
Paul Hovnanian P.E.
>
> "Paul Hovnanian P.E." <Pa...@Hovnanian.com> wrote in message
> news:4C69A75D...@Hovnanian.com...
> > Just a guess. What you have is actually a compound motor*. It has both a
> > shunt field and a series field.
>
> I have been through that thought process and cannot find any logical
> way to make that work. This page shows 3 possible combinations
> of compound motor wiring, see figure 12-17.
> http://zone.ni.com/devzone/cda/ph/p/id/39
> If the motor was like A or B, I could see that with a couple of ohm meter
> tests.
> I have checked it is not wired like that.
> If it was like C I could ohm that out also.
> I have checked it is not wired like that either.
> It is wired just like this url shows.
> http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
>
> >By mis-wiring the shunt field, it acted
> > as a series motor.
>
> This is not possible because the shunt has a very high resistance,
> 41 ohms. The motor will draw 100s of amps.
The armature may draw that, but that current doesn't have to pass
through the 41 ohm field.
> > Two things can happen: 1) A series field motor, unloaded can fail by
> > overspeed. 2) Even when loaded, the lack of the shunt field will result
> > in lower back e.m.f and, as a result, higher armature and series field
> > currents. Which could lead to overheating.
> >
>
> > *There are other strange combinations of fields that you might have as
> > well which, when mis-wired, will behave somewhat like series motors.
> >
> Please look at this drawing, the motor only has three wires out, labeled
> F2, F1 and A2, logicaly F2 is connected to A1 internally. Oh darn I see
> in parentheses I have A2 it should be A1
> For clearity, A1, A2 is armature and F1, F2 is field.
You know this how? By using an ohmmeter on the external connections?
That may not reveal a second series field. In a previous post, you
stated that you took the motor apart and found two diffecet field
windings on 4 poles. So, your drawing below doesn't seem to reflect the
motors innards.
> http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
> Thanks for your thoughts, I have been through this thing
> trying to find some connection other than what is in the above drawing
> and what you see is all I can find.
How many brushes does this motor have?
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
If God is perfect then why did He create discontinuous functions?
amdx
I did some more measurements and I'm much closer to the answer.
It looks like I do have a compound motor, couldn't tell with my ohm meter,
I had to measure 0.01 and 0.001 ohms. I used a constant current source
to measure between leads to get the new info. I have a new drawing with
a description of estimated turns and length of each turns to find the
resistance of each coil. The numbers don't work out, off by a factor of 15.
However by energizing the leads I find a magnetic field on one set of coils
but not the other. So now I'm certain of a separate series field.
I have a drawing with the two possible compound wiring scenarios.
I don't know a way to figure out which scenario I have.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorseriesshuntField.jpg
Thanks, MikeK
PS. I still need to go back and see how this fits with my improper wiring
that worked so well.
Tim Wescott
> Hi guys, and thanks for the help.
> I did some more measurements and I'm much closer to the answer.
> It looks like I do have a compound motor, couldn't tell with my ohm meter,
> I had to measure 0.01 and 0.001 ohms. I used a constant current source
> to measure between leads to get the new info. I have a new drawing with
> a description of estimated turns and length of each turns to find the
> resistance of each coil. The numbers don't work out, off by a factor of 15.
> However by energizing the leads I find a magnetic field on one set of coils
> but not the other. So now I'm certain of a separate series field.
> I have a drawing with the two possible compound wiring scenarios.
> I don't know a way to figure out which scenario I have.
> http://i395.photobucket.com/albums/pp37/Qmavam/MotorseriesshuntField.jpg
This would certainly explain why the "wrong" connection of the 20 ohm
resistor worked, but not why the controller blew with the "open coil"
version -- unless that was just happenstance.
amdx
> On 08/16/2010 07:17 PM, amdx wrote:
>> Hi guys, and thanks for the help.
>> I did some more measurements and I'm much closer to the answer.
>> It looks like I do have a compound motor, couldn't tell with my ohm
>> meter,
>> I had to measure 0.01 and 0.001 ohms. I used a constant current source
>> to measure between leads to get the new info. I have a new drawing with
>> a description of estimated turns and length of each turns to find the
>> resistance of each coil. The numbers don't work out, off by a factor of
>> 15.
>> However by energizing the leads I find a magnetic field on one set of
>> coils
>> but not the other. So now I'm certain of a separate series field.
>> I have a drawing with the two possible compound wiring scenarios.
>> I don't know a way to figure out which scenario I have.
>> http://i395.photobucket.com/albums/pp37/Qmavam/MotorseriesshuntField.jpg
>
> This would certainly explain why the "wrong" connection of the 20 ohm
> resistor worked, but not why the controller blew with the "open coil"
> version -- unless that was just happenstance.
>
given to me,
after someone disassembled a military lift. To him a 28 volt dc motor was
junk,
it was just what I was looking for at the time.
As far as blowing the controller, I'll never know.
So know I have figured out that I have a Short Shunt Compound Motor.
Here's the method I used,
http://i395.photobucket.com/albums/pp37/Qmavam/MotorLongShortShuntTest.jpg
At the end you see I have one more question about the motor.
Is it a cumulative compound or a differential compound motor?
Here's a diagram showing that is just the difference in polarity of the
wiring.
http://i395.photobucket.com/albums/pp37/Qmavam/CumulativeandDifferentialMotor.jpg
I cannot see the connections in the stator so I've tested the magnetic
fields with current
flowing. I'm pretty confused by the data, I will post it later and see if
anyone can decipher it.
Thanks, MikeK
amdx
"amdx" <am...@knology.net> wrote in message
news:90a16$4c6b071a$18ec6dd7$16...@KNOLOGY.NET...
Now I want to know if my motor a cumulative compound or a differential
compound motor?
Here's a picture showing the polarity of the magnetic fields of the motor
when I apply current.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorMagneticFields.jpg
The fields are reversed leading me to think the motor is wired as a
differential compound motor,
and not a cumulative compound motor.
But I have no confidence in that opinion.
Anyone have any ideas?
Any other tests I could do for more info?
This link shows the polarity difference between the two styles.
http://i395.photobucket.com/albums/pp37/Qmavam/CumulativeandDifferentialMotor.jpg
Thanks, MikeK
Jamie
it sounds like you have a compound motor ? In which case, you can use
the motor with out the series winding and directly connect to the
armature, this of course implies that you connect the field in parallel
to the same A1 and A2 wires where the motor will operate the same
direction AC/DC, or, you can connect the series field S+, S- in series
with A+ and A-, with the field connected to a + and - line you'll get a
motor that has torque enhancement. If you alternate the S+ and S- series
field with the armature field, you get Speed enhancement but a softer
bottom end torque.. This is because the series field is with in the
shunt field and that is counteracting with the Field's strength.. This
type of motor is good for auto field weakening/strengthening effects
with out the drive electronics doing this to the shunt field to give
the enhancements to the motor you're looking for.
In DC shunt motors, weakening the field yields more speed but less
torque where as, strengthening it will yield the torque and lessen the
speed..
In today's DC shunt drive electronics comes auto field weakening so the
need for compound motors are not so prevalent any more, they still can
be employed to enhance it even more, also, problems exist in
reversing the direction in a compound motor. In order to maintain torque
enhancement in compound motors when changing directions, you must
reverse the S+ and S- leads that are joined to the A+ and A1 leads,
other wise, you'll be doing the opposite to the shunt field... Older
technology reversed these types of motors by connected these leads to a
reversing contactor, rated for the load along with the armature leads to
maintain the effects on the motor they are looking for, speed or
torque in either direction.
In today's world where new drive electronics are connected to such
motors, most of the time the series fields are not used.. They are
capped and tapped off...
In your case, if you were not concerned about reversing the
motor, you can connect the wires this way..
S+..S- to A+..A-
The shunt field should be connected like this.
F+ to S+ and F- to A-
and you would have a single + and - power drive source that also connects
to + to the (F+,S+) and - to the (F-,A-)
This will give you a clock rotation looking into the face/shaft
drive of the motor with torque enhancement.
This will give you a constant torque with the series field varying the
field to adjust torque demand verses speed demand naturally..
Most people do not wire a DC shunt motor this way, most practices place
the shunt field at a fixed DC source.. This will give you lots of torque
at the bottom end and soften as the speed increase.. The series field
can help adjust for this..
have a good day..
Jamie
your motor is differential acting only if for example, the Series field
is weakening the shunt field.
If you do not have the series at the same polarity as the field, you
are in differential mode (reducing field strength as current increases
through the series field)
And of course, less overall field means less torque and more speed but
does serve for some nice tension mode starts for some applications.
amdx
"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:I7Gao.1101$cE1...@newsfe18.iad...
Did you type that opposite of what you meant to say?
I would think in a differential the shunt would weaken the series field,
since that is the adjustable field.
> If you do not have the series at the same polarity as the field, you are
> in differential mode (reducing field strength as current increases
> through the series field)
I think you mean (through the shunt field)
> And of course, less overall field means less torque and more speed but
> does serve for some nice tension mode starts for some applications.
I think you are saying put zero current through shunt to have a spinning
wheel
start and then for top speed turn shunt current to maximum.
Thanks, MikeK
amdx
Yes, I believe I have a differential compound motor, for a the
reasons
stated in the above posts.
>In which case, you can use the motor with out the series winding and
>directly connect to the armature, this of course implies that you connect
>the field in parallel to the same A1 and A2 wires where the motor will
>operate the same direction AC/DC, or, you can connect the series field S+,
>S- in series with A+ and A-, with the field connected to a + and - line
>you'll get a motor that has torque enhancement. If you alternate the S+ and
>S- series field with the armature field, you get Speed enhancement but a
>softer bottom end torque.. This is because the series field is with in the
>shunt field and that is counteracting with the Field's strength.. This type
>of motor is good for auto field weakening/strengthening effects with out
>the drive electronics doing this to the shunt field to give
> the enhancements to the motor you're looking for.
You missed some of my earlier posts where I stated I only
have three connections
to the is motor A2, F1 and F2 .which I think is internally
connected to A1.
The drawing an the left side of this page is what I think I
have. Although the polarity
of the shunt may be reversed. I should have labeled coil A as
the series field and
coil B as the shunt Field.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorseriesshuntField.jpg
I think we need to clear up this terminology series field and
shunt field.
The little knowledge I have would be from golfcart motors. Most are
series field
motors. They are wired so the field and the armature are in
series. All the current that
flows in the armature must also flow through the series field. They
have large studs to
the series field to go to a reverse switch to change rotation of the
motor.
In my motor the connections are all hardwired, sleaved and
varnished in place so
I can't really see what connects to what. Hence all the juming
through hoops to get
this thing figured out.
So have you got the series and shunt terminology backwards or am
I about to
relearn what I thought I already knew?
Thanks, MikeK
amdx
"Paul Hovnanian P.E." <Pa...@Hovnanian.com> wrote in message
> amdx wrote:
>>
>> "Paul Hovnanian P.E." <Pa...@Hovnanian.com> wrote in message
>> news:4C69A75D...@Hovnanian.com...
>> > Just a guess. What you have is actually a compound motor*. It has both
>> > a
>> > shunt field and a series field.
>>
>> I have been through that thought process and cannot find any logical
>> way to make that work. This page shows 3 possible combinations
>> of compound motor wiring, see figure 12-17.
>> http://zone.ni.com/devzone/cda/ph/p/id/39
>> If the motor was like A or B, I could see that with a couple of ohm meter
>> tests.
>> I have checked it is not wired like that.
>> If it was like C I could ohm that out also.
>> I have checked it is not wired like that either.
>> It is wired just like this url shows.
>> http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
>>
>> >By mis-wiring the shunt field, it acted
>> > as a series motor.
>>
>> This is not possible because the shunt has a very high resistance,
>> 41 ohms. The motor will draw 100s of amps.
>
> The armature may draw that, but that current doesn't have to pass
> through the 41 ohm field.
I agree, but what he said was (as I read it) I turned my shunt into a
series
field that would mean the same current that goes through the armature would
necessarily go through the (41 ohm) shunt. Hence my answer.
>> > Two things can happen: 1) A series field motor, unloaded can fail by
>> > overspeed. 2) Even when loaded, the lack of the shunt field will result
>> > in lower back e.m.f and, as a result, higher armature and series field
>> > currents. Which could lead to overheating.
>> >
>>
>> > *There are other strange combinations of fields that you might have as
>> > well which, when mis-wired, will behave somewhat like series motors.
>> >
>> Please look at this drawing, the motor only has three wires out,
>> labeled
>> F2, F1 and A2, logicaly F2 is connected to A1 internally. Oh darn I see
>> in parentheses I have A2 it should be A1
>> For clearity, A1, A2 is armature and F1, F2 is field.
>
> You know this how? By using an ohmmeter on the external connections?
> That may not reveal a second series field. In a previous post, you
> stated that you took the motor apart and found two diffecet field
> windings on 4 poles.
I have since that post got additional info, I now know the motor is
a differential compound motor.
>So, your drawing below doesn't seem to reflect the
> motors innards.
Ya, I guess that's just for simplicity of drawing.
>> http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
>> Thanks for your thoughts, I have been through this thing
>> trying to find some connection other than what is in the above drawing
>> and what you see is all I can find.
> How many brushes does this motor have?
The motor has 4 sets of brushes and each set has two brushes (more surface).
Thanks, MikeK
Jamie
You don't operate the shunt field in series with any counter
parts of the Series field or armature..
The field is either operated by a fixed DC source or to the
same source as what drives your armature.
I'll make an attempt to graph it.
Connected like most are on systems that use compound machines.
Fixed Field supply >>>> (+)---------field------------(-)
Drive Feed(+)>>(S+)--(S-)--(A+)--(A-)<<<<<DriveFeed(-);
--- Now those that use a single source ----
Drive Feed(+)>>>>>>>>(+)-----Field----------(-)<<<<<<<DriveFeed(-);
Drive Feed(+)>>(S+)--(S-)----(A+)-----(A-)<<<<<<<<DriveFeed(-);
The above two examples are accumulative because it adds to the Shunt
field's current which increases the strength due to the series being
physically in the area of the shunt field.
Reverse the (S) leads and you get differential because it weakens
the shunt field.
Most use the accumulative configurations because they are looking for
torque when current builds in the series and armature leads. This will
contribute to the Shunt field.
And you do not operate the shunt field of a compound motor in series
with anything else of the motor.. There could be a resistor to reduce
its strength in series from where ever its getting the supply from..
Such motors that operate what looks to be the shunt field in series is
exactly that, A series motor and does not employ a shunt field. Also,
the shunt field wire size is always smaller than the armature leads.
That's because only a small amount of DC current passes through the
shunt compared to the armature.. Motors with series fields should have
the same size leads as the armature because it has to be able to handle
the current of the armature.
Now, I don't know where the confusion was in my first post..
P.S.
A compound motor will turn if you try to run it as a series only
motor, but be aware that it most likely will not perform as expected
because the series field in a compound motor isn't nothing like that
found in series motor. The series field in compound motors are designed
to shift the Shunt field alittle and not create the equal effects of a
shunt field.
amdx
I Agree.
>
> The field is either operated by a fixed DC source or to the
> same source as what drives your armature.
>
I assume your still discussing the shunt field.
There are many sources that discuss adjusting the shunt field current.
So it would not always be operated by a fixed DC source.
Here's one.
"Control is obtained by weakening the shunt-field current of the dc motor
to increase speed and to reduce output torque for a given armature current."
http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee3/bdeee3_1-1.aspx
> I'll make an attempt to graph it.
> Connected like most are on systems that use compound machines.
>
> Fixed Field supply >>>> (+)---------field------------(-)
>
> Drive Feed(+)>>(S+)--(S-)--(A+)--(A-)<<<<<DriveFeed(-);
>
Yes, ok.
> --- Now those that use a single source ----
> Drive Feed(+)>>>>>>>>(+)-----Field----------(-)<<<<<<<DriveFeed(-);
>
>
> Drive Feed(+)>>(S+)--(S-)----(A+)-----(A-)<<<<<<<<DriveFeed(-);
>
Yes varying the current to the shunt field.
and also the series field/armature.
> The above two examples are accumulative because it adds to the Shunt
> field's current which increases the strength due to the series being
> physically in the area of the shunt field.
>
I don't see why it adds to the shunt fields current? (Maybe you meant shunt
fields field.)
The overall field may be increased though.
You might straighten me out on that :-)
> Reverse the (S) leads and you get differential because it weakens
> the shunt field.
>
Ok
> Most use the accumulative configurations because they are looking for
> torque when current builds in the series and armature leads. This will
> contribute to the Shunt field.
>
> And you do not operate the shunt field of a compound motor in series
> with anything else of the motor.. There could be a resistor to reduce its
> strength in series from where ever its getting the supply from..
>
Ah, there we go.
> Such motors that operate what looks to be the shunt field in series is
> exactly that, A series motor and does not employ a shunt field. Also, the
> shunt field wire size is always smaller than the armature leads. That's
> because only a small amount of DC current passes through the shunt
> compared to the armature.. Motors with series fields should have the same
> size leads as the armature because it has to be able to handle the current
> of the armature.
>
> Now, I don't know where the confusion was in my first post..
>
I had to go back and look :-)
Ok, I'll take all the blame for my confusion.
First I'm using a PWM motor controller, it varies the current through
motor. I never thought of that as controlling the series field current,
just the current through the armature. Most of that is because for the year
I have been using the motor I didn't know it had a series field.
I thought I had this;
http://i395.photobucket.com/albums/pp37/Qmavam/A2F2F1Motor.jpg
The motor has three wires out labeled F2, F1 and A2. F2 to A2 is
very low ohm and F1 to A2 is 41 ohms. This led me to think I only
had a shunt field.
Now I understand I have a compound motor with only one external
connection to the series field and only one external connection to the
shunt field. Like this;
http://i395.photobucket.com/albums/pp37/Qmavam/MotorShortshunt.jpg
> P.S.
> A compound motor will turn if you try to run it as a series only motor,
> but be aware that it most likely will not perform as expected
> because the series field in a compound motor isn't nothing like that
> found in series motor. The series field in compound motors are designed
> to shift the Shunt field alittle and not create the equal effects of a
> shunt field.
>
Ok good to know, although I will never try to run my motor with an open
field coil again. The first and last time I did it I blew my motor
controller.
Maybe coincidence but it shut down with a fault and after clearing the
fault
we ran it again this time the fault never cleared.
Thank you very much for taking your time to help me.
MikeK
Jamie
now you understand :)
Yes, you have a motor that looks like is designed for one direction.
you connect F1 to the F2 via a R if you want to control the shunt field
strength or, just couple them together for full power which makes it a
2 wire motor then.
That motor looks like it'll operate on DC/AC,like a universal motor
the other side of the shunt field seems to be tied with the A2
connection. which I find common in systems where the motor is expected
to have the A2 tied to a common point and not on an output of a bridged
drive.
Have a good..
amdx
Actually the other side of the shunt field is tied to the brush and the
shunt field
current has to go through the armature along with the series field current.
As shown here.
http://i395.photobucket.com/albums/pp37/Qmavam/MotorShortshunt.jpg
Thanks again, MikeK
JosephKK
From the looks of the stator windings it is compound wound with a
compensating winding.
I would have to take the stator apart more to figure it out correctly.
What information is there to had on the manufacturers nameplate?
JosephKK
>
>"Paul Hovnanian P.E." <Pa...@Hovnanian.com> wrote in message
>news:4C69A75D...@Hovnanian.com...
>> Just a guess. What you have is actually a compound motor*. It has both a
>> shunt field and a series field.
>
> I have been through that thought process and cannot find any logical
>way to make that work. This page shows 3 possible combinations
>of compound motor wiring, see figure 12-17.
>http://zone.ni.com/devzone/cda/ph/p/id/39
Judging from the stator photograph, it must be "C" or a variation of
it
>If the motor was like A or B, I could see that with a couple of ohm meter
>tests.
>I have checked it is not wired like that.
>If it was like C I could ohm that out also.
>I have checked it is not wired like that either.
Since you are not getting to the internal connections you cannot rule
that out.
JosephKK
Much clearer. That still does not account for all the brushes. Ples
show us how they work out.
JosephKK
Ok, let's reference this into things you might reasonably do:
The stator photograph shows three windings, can you pry out just where
they are connected? How are the brushes connected to all this? It
may be quite strange. It is really important to have a full
connection diagram of all the windings, brushes and well just
everything, including polarities (aiding vs opposing in terms of
armature current). Please provide the best you can.
JosephKK
There are three stator windings from the insulation colors in the
photo. You have stated that thereare 4 brush positions (which matches
the stator photo), how is it all connected?
amdx
"JosephKK" <quiett...@yahoo.com> wrote in message
news:35o376pupgcniikvc...@4ax.com...
Hi Joseph,
Thanks for your input, I don't know what all I've put in this thread, but
the bottom line is the motor had overheated wires. At this point I have
removed all the windings. My plan is to rewind it as a series motor.
It is a four pole motor two were series fields and two were shunt fields.
I want to make all four poles series.
I will be starting a new thread asking whether inductance is a proper
way to figure out the new turns count.
Thanks again, Mike.
JosephKK
And the quick answer in normally no. MMF and gap energy vs
torque-speed properties. I really recommend compound wound if you can
get through the calculations. Say 75% series and 25% shunt MMF
average over the speed range. Great bottom end torque without giving
up all the top end torque.
Don Kelly
------------------------------------------------------------------
This motor appears to be a 2 pole shunt motor with interpoles.
Typically a compound motor will have series and shunt fields on the same
poles. Interpoles between the normal poles, if used, will have series
windings. However interpoles are generally quite narrow (and as I recall,
the picture of the field didn't show this) so that they only affect the
coils being switched by the commutator in order to eliminate arcing at the
brushes under heavy load.
--
Don Kelly
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