# Re: [EVDL] Series wiring of two series motors



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Wire them in series.
Since you are direct drive, the motor rpm will be low, and the backemf of
the two combined motors isnt likely to get near to your pack voltage.
Wiring in series is also easier on your controller as there is greater
inductance, resistance and back-emf, and lower cruising motor-side current.

It doesn't matter which order you wire the armatures and fields, as long as
they are all wired with the corret polarity.

Matt 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Steve Condie
Sent: Friday, 12 June 2009 10:58 AM
To: [email protected]
Subject: [EVDL] Series wiring of two series motors


I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
rear wheel. I've got a single 144 volt Logisystems controller, and one
reversing contactor. I've been mulling over whether to connect the motors
to the controller in series or in parallel ( I don't plan to shift between
the two.) It occurred to me that if I wired them in series, I could either
wire up motor 1, then move over to motor 2, so the circuit went
armature/field/armature/field, or I could wire the two armatures in series,
then the two fields - a/a/f/f/ (or vice versa). I'm trying to figure out if
that creates a problem somehow. It seems, since they're all in series, that
it shouldn't, but I have a nagging feeling that I'm missing something. (The
advantage of doing it that way is that a single reversing contactor then can
reverse both motors.)
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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Nope, there's nothing wrong with going armature/armature/field/field.
It's the current that matters.

You would have a problem if the voltage difference between armature
and field was high enough to cause breakdown, but that would take far
more than 144V.

-Morgan LaMoore



> Steve Condie <[email protected]> wrote:
> >
> > I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
> > rear wheel. I've got a single 144 volt Logisystems controller, and =
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Uh, not "direct drive" but single speed reduction. Doesn't automatically
mean low RPM ?

> Wire them in series.
> Since you are direct drive, the motor rpm will be low, and the backemf of
> the two combined motors isnt likely to get near to your pack voltage.
> Wiring in series is also easier on your controller as there is greater
> inductance, resistance and back-emf, and lower cruising motor-side current.

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

You snipped a bit to much Jeff.
In the original email, steve stated: 
"I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
rear wheel."

Which I took to mean true direct drive, rather than single ratio reduction.
If it isn't true direct drive, then yes wed need more info....Steve?

Matt

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Jeff Shanab
Sent: Saturday, 13 June 2009 10:26 AM
To: [email protected]
Subject: Re: [EVDL] Series wiring of two series motors


Uh, not "direct drive" but single speed reduction. Doesn't automatically
mean low RPM ?

> Wire them in series.
> Since you are direct drive, the motor rpm will be low, and the backemf 
> of the two combined motors isnt likely to get near to your pack voltage.
> Wiring in series is also easier on your controller as there is greater 
> inductance, resistance and back-emf, and lower cruising motor-side
current.

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

<<<< You snipped a bit to much Jeff.
In the original email, steve stated:
"I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
rear wheel."

Which I took to mean true direct drive, rather than single ratio reduction.
If it isn't true direct drive, then yes wed need more info....Steve? >>>>

If it set up as originally manufactured, there would be a single ratio 
reduction by belt drive to each rear wheel.


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

When you wire two series motors in series, you lose tractive effort quicker
when one wheel spins, analogous to a differential without positraction.

Two series motors wired in parallel will direct the most tractive energy to
wheel that still has traction which is a beneficial result. 

In any case, all series motors require overspeed detection and speed limiting
or shut down when this speed is exceeded. 






On Fri, 12 Jun 2009 19:26:11 -0700, Jeff Shanab wrote
> Uh, not "direct drive" but single speed reduction. Doesn't automatically
> mean low RPM ?
> 
> > Wire them in series.
> > Since you are direct drive, the motor rpm will be low, and the backemf of
> > the two combined motors isnt likely to get near to your pack voltage.
> > Wiring in series is also easier on your controller as there is greater
> > inductance, resistance and back-emf, and lower cruising motor-side current.
> 
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*



> Steve Condie wrote:
> > I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
> > rear wheel. I've got a single 144 volt Logisystems controller, and one
> > reversing contactor. I've been mulling over whether to connect the motors
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Yes, the Tropica has two motors, each driving a rear wheel through a toothed
belt with about 4:1 reduction. 


You snipped a bit to much Jeff.
In the original email, steve stated: 
"I'm restoring a Tropica, with two 6.7 inch series motors, one driving each
rear wheel."

Which I took to mean true direct drive, rather than single ratio reduction.
If it isn't true direct drive, then yes wed need more info....Steve?


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Lee, you left out the one combination I was wondering about: What if you
wire the two armatures in series, and the fields in series, and then wired
the two sets in parallel? I'm thinking it should be like wiring two series
motors in parallel, but I wonder if other factors would cause a problem? 
(It would allow reversing both motors with a single reversing contactor.)

Also, would keeping the armatures in series but shifting the fields from
series to parallel have the same effect as shifting both motors (series
wired) from series to parallel?




> Lee Hart wrote:
> >
> > Steve Condie wrote:
> >> I'm restoring a Tropica, with two 6.7 inch series motors, one driving
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*



> Steve Condie wrote:
> > Lee, you left out the one combination I was wondering about: What if
> > you wire the two armatures in series, and the fields in series, and
> > then wired the two sets in parallel?
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Thanks, Lee. I always know I will get a knowledgible and understandable
explanation from you!

This has me intrigued:

> Also, would keeping the armatures in series but shifting the fields
> from series to parallel have the same effect as shifting both motors
> (series wired) from series to parallel?

Not quite. Switching just the fields between series/parallel gives you 
the same armature voltage in both cases, but 1/2 and full field 
strength. It is a smaller change than switching both fields and 
armatures between series/parallel.

I'm curious because the Tropica is set up to go about 60 mph at 72V - which
is where it sits running the two motors in series off of a 144V controller. 
I'd like a little more top end to be available, but obviously don't need or
want 144V going to both motors (as is the theoretical top end if the motors
are wired in parallel.) If setting it up so a series/parallel shift of just
the fields would increase the top speed by 50% - or even less - that would
be great. A complete series/parallel shift cuts the amps - and hence torque
- by half. Would the torque be cut by less than half with just a field
shift? And I'm confused (again.) Is fields in series faster but weaker? 
Or is it fields in parallel that has that effect? I freely admit - I don't
understand field weakening. It's kind of like magic to me.
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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

>> Switching just the fields between series/parallel gives you the
>> same armature voltage in both cases, but 1/2 and full field 
>> strength. It is a smaller change than switching both fields and 
>> armatures between series/parallel.



> Steve Condie wrote:
> > the Tropica is set up to go about 60 mph at 72V --
> > which is where it sits running the two motors in series off of a 144V
> > controller. I'd like a little more top end to be available, but
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

Maybe this will take the "magic" out of field weakening..... 
Assuming it does not blow up, the top speed of a DC motor is limited by the
point at which the back EMF (the spinning motor acting as a generator
producing a voltage opposite to the applied voltage referred to as "back"
ElectroMotive Force) balances the load and windage losses. If you reduce
the field, the motor becomes weaker, but it also becomes a worse generator,
allowing an increase in speed, but at the cost of torque available to drive
a load.
Stephen Chapman





> Steve Condie wrote:
> >
> > Thanks, Lee. I always know I will get a knowledgible and understandable
> > explanation from you!
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*

I think Jerry Dycus wrote about using field weakening in his contactor
controlled 3 wheeler; IIRC he put 12 inches of 12 gauge wire in parallel
with his field and saw about 25% increase in speed in either a golf cart or
6" series wound motor. Using that method, what sort of current would the
weakening shunt see? (Thinking in terms of how big the SPST contactors
would have to be.) And would winding the 12 gauge wires in coils around
iron rods address the inductance problem?

There is one more possibility now that I think on it: Keep your motors 
wired the same, but add field weakening resistors across each field. 
This adds 2 big resistors, and 2 big SPST contactors. You need to make 
sure the controller is fully on before closing those contactors, because 
it will see much less motor inductance, and its current limiting may not 
work.


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*



> Jeff Major wrote:
> > Lee,
> > Did you mean to say "with both fields in parallel" ?
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*



> Lee Hart wrote:
> >
> > 2. Armatures in parallel, fields in parallel.
> >
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Series wiring of two series motors*



> Jeff Major<[email protected]> wrote:
> >
> > Hi Steve,
> >
> ...


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