 ### Network # Rewinding DC motor

A

#### amdx

Jan 1, 1970
0
Hi guys and Sylvia,
I'm rewinding a 4 pole compound motor so it is a series motor.
It had two series fields and two shunt fields.
Motor info 2hp, 28volt, 62 amps.
It has been suggested that when I go from two fields to four
that I should reduce the turn count on each field.
My thinking (guess) is that I want to have the same inductance
in four fields that I had in the original two fields.
MikeK

A

#### amdx

Jan 1, 1970
0
total nonsense, you first need to count the turns on the old field,
work out the total amp turns, and wind the new field to give the same
total if you want the same full load speed. If you want less speed
then you need more turns.

The old field has 17 turns on each field. For a total of 34 turns for two
poles.
These two fields were wired in parallel. When you say "work out the total
amp turns"

Is that amp/turns per pole?

Since the two poles are is parallel that would be 1/2 times amp/turns or (.5
x amps)/17turns

And, what wiring scheme should I use: all in series, all in parallel,
parallel
two and put in series with the other parallel two?

T

#### Tim Williams

Jan 1, 1970
0
amdx said:
Is that amp/turns per pole?

Amp-turns is amp-turns, not amps per turn.

Tim

A

#### amdx

Jan 1, 1970
0
Tim Williams said:
Amp-turns is amp-turns, not amps per turn.

Tim
Ya, I did that wrong, thanks.
So is that amp-turns per pole?
The two coils are in parallel so only 1/2 of the motor current
would go through each coil.
Thanks, MikeK

J

#### Jamie

Jan 1, 1970
0
amdx said:
Hi guys and Sylvia,
I'm rewinding a 4 pole compound motor so it is a series motor.
It had two series fields and two shunt fields.
Motor info 2hp, 28volt, 62 amps.
It has been suggested that when I go from two fields to four
that I should reduce the turn count on each field.
My thinking (guess) is that I want to have the same inductance
in four fields that I had in the original two fields.
MikeK
You'll reduce your RPM by half if that is the case.

T

#### Tim Williams

Jan 1, 1970
0
amdx said:
So is that amp-turns per pole?
The two coils are in parallel so only 1/2 of the motor current
would go through each coil.

As long as they have equal resistance, current will be shared equally.
This is equivalent to a series connection with half the turns of
double-thick wire. They probably did this to save on the trouble of
winding such beefy "wire".

Apparently, golf cart motors have single turns of rectangular copper going
through the rotor and stator. Lots of amps.

Tim

A

#### amdx

Jan 1, 1970
0
The old field has 17 turns on each field. For a total of 34 turns for two
poles.
These two fields were wired in parallel. When you say "work out the total
amp turns"

Is that amp/turns per pole?

Since the two poles are is parallel that would be 1/2 times amp/turns or
(.5
x amps)/17turns

And, what wiring scheme should I use: all in series, all in parallel,
parallel
two and put in series with the other parallel two?

there should be two windings on each pole, series and shunt, you now
seem to have only one.

I'll try again.
I have a compound 4 pole motor. Two of the poles are series fields with
17 turns, these two are wired in parallel. The other two poles are shunt
fields
and wound with many (100s) of turns. These are wired in series.
Each pole has only one winding on it.
Secondly poles come in pairs, so a four pole
motor has 2 pole pairs, opposite each other.

This is correct.
Each pole pair needs to be considered as independent from the other
pole pair. Magneticaly the poles of a pair are in series so the amp turns
add up. eg: 17 turns at 1amp for each pole equals 34amp turns in total.

But, these are in parallel so the current is divided, that would make it,
1/2amp x 17turns x 2 poles = 17 amp-turns.
I think?

Someone on a forum suggested that shunt fields commonly have equal amp-turns
as the series field, so winding the new series fields the same as the
original would
give similar torque and rpm.
So, if I wire the two new 17 turn poles in parallel and put those in series
with
original two 17 turn parallel poles I should have 1/2 amp through each pole
of
17 turns, this equals 8.5 amp-turns. With 4 poles x 8.5 amp-turns I would
end
up with 34 amp-turns. I think this would be equal to the original series and
shunt fields as far as amp-turns.

What do you think?
Thanks, MikeK

A

#### amdx

Jan 1, 1970
0
Jamie said:
You'll reduce your RPM by half if that is the case.
Ok, I see that now, it would increase the CEMF, slowing the motor.
As I stated in another post, "someone on a forum suggested that
shunt fields commonly have equal amp-turns as the series field"
If I assume that, then I would get back closer to the original, if
I wind the two new series fields the same as the original, put them
in parallel as the original, and then wire these in series with the
original.
Feeble attempt to show that in ascii.

___l___
( (
( (
( (
l______l
___l___
( (
( (
( (
l______l
l
Hmm... Is this the same as putting two in series and parallel that
with two more in series.
___l___
( (
( (
( (
l l
1 1
( (
( (
( (
l______l
l
Thanks for helping,
MikeK

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