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Discussion Starter #1
Hey all,

Well I really want to get my Soleq EVCort on the road, I have been trying to design my own
controller but I don't want to have to wait another 6 months or so that it will probably require
for me to finish design, testing and tweaking and that's assuming all goes well.

So I want to try yet another approach with the help of the group. (This is something like Plan E.
:p I gone through in phases Contactor, Rectactor, Mechanical PWM, DIY Controller, etc. )

As some of you may know the EVCort has a GE SepEx motor, and the controller runs at 800Hz with 2
separate banks of 200 Amps each connected to their own inductor before the armature terminal on
the motor. It also has Regen of 200 Amps connected to 1 of those armature branches. The battery
pack is 108V and is intimately tied to the DC-DC and charger and inverter for the A/C.

What I would like to try is to use a low voltage (24-48) low amperage (<100) controller to control
the field. I guess I would need a DC-DC converter for this. And also something like the Curtis
1221 or 1231 to control the armature. I may have to go without Regen until I can either fix my old
controller or build my own.

Now I know that these newer controllers use the higher switching frequency (>15kHz). Would that
cause any problems on either the field or armature? Do I still need to connect it to one or both
(in parallel) of the inductors on the armature?

I know I need the field to be on before the armature so I was thinking of connecting the movement
backwords and having the travel of the accelerator pedal connected with springs and stops to go
from 0 to 100% on the armature controller and then go backwards from 100 - 20?% for field
weakening to get more RPM. Would there be a problem if the current on the field controller went to
Maximum instantly from a microswitch or something on the accelerator? (I think I will physically
limit it with the throw of the pot which I will have to determine the position and then lock it
there at about 20Amps) Normally the field is driven at full battery voltage (nominal 108V) and max
of 20 Amps. Would the current change if I drive it at a lower voltage? Or are 20 Amps 20 Amps?

Also, I suppose the requirements for contactors and precharge, etc. will be the same as any other
series wound arrangement.

I'm sure I am forgetting something so anything else you can think of will be of help.

Thanks all,
Chet Fields

P.S. If someone can come up with the ability to keep the Regen with this setup that would be a
great bonus.

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Discussion Starter #3
Are you going to use a charger? Maybe you could use the charger to control the field.

Another wild idea: Run the charger off a small pack of cheap, high energy batteries (like flooded golf cart batteries). Run the Zilla off a 2nd pack of high power batteries, like A123, to power the armature. Use the charger to run the field and keep the high energy pack charged up.

Another idea: The armature will spend most of its time at 100% PWM, a Zilla might be overkill. What about just switching the power to the armature with a resistor for a moment, and then going direct connection? Then most of the speed/regen control is done with the field. You'll lose the first 1/2 of the rpm range, so you would need a clutch to get moving smoothly.

----- Original Message ----
From: Zeke Yewdall <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Monday, August 20, 2007 2:02:47 PM
Subject: Re: [EVDL] Hodge Podge 108V Sep Ex Controller

Hey, this is exactly what I'm looking at as well. My current
thinking is a Zilla1K for the armature, and series parallel switching
of a small set of batteries to supply current to the field at 24
volts, 48, or 72 volts or something like that. I'm not sure yet, but
I think I might be able to do regen by flipping the field voltage to
the high setting, and letting the current flow through the flyback
diodes on the zilla?, but keep it on the low field voltage setting
most the time (unless I need a higher torque startoff). I haven't
really thought this out in detail yet.... trying to save up some
money for the transmission adaptor right now....







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Discussion Starter #4
--- Chet Fields <[email protected]> wrote:

> Hey all,
>
> Well I really want to get my Soleq EVCort on the

<snip>

> Normally the field is driven
> at full battery voltage (nominal 108V) and max
> of 20 Amps. Would the current change if I drive it
> at a lower voltage? Or are 20 Amps 20 Amps?
>

Hey Chet,

Of course the field current will change if you apply a
lower voltage. Use Ohm's Law. V = I * R. So 20 amps
at 108 volts. Field R = 5.4 Ohms. If you apply 24
volts to the field, you draw 4.4 amps. Which would be
about 22 percent field excitation.

Verify this by putting an Ohmmeter across the field
terminals.


Jeff M


<snip>
> Thanks all,
> Chet Fields




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Discussion Starter #5
--- Jeff Major <[email protected]> wrote:

> --- Chet Fields <[email protected]> wrote:
>
> > Hey all,
> >
> > Well I really want to get my Soleq EVCort on the
>
> <snip>
>
> > Normally the field is driven
> > at full battery voltage (nominal 108V) and max
> > of 20 Amps. Would the current change if I drive it
> > at a lower voltage? Or are 20 Amps 20 Amps?
> >

> Hey Chet,
>
> Of course the field current will change if you apply a
> lower voltage. Use Ohm's Law. V = I * R. So 20 amps
> at 108 volts. Field R = 5.4 Ohms. If you apply 24
> volts to the field, you draw 4.4 amps. Which would be
> about 22 percent field excitation.

I'm sorry I guess I forgot to mention that a chopper is used on the field and I'm not sure what
the max duty cycle is. I will need to measure the resistance and I do also have a spec sheet on
the motor that has that figure on it. I need to find it though.

So, what I was trying to ask is if the resistance is say, 2 ohms I would need to have 40 volts
average, which would be ~83% duty cycle on a 48 volt controller, but a 36 volt controller would
not be enough to produce the full 20 Amps. In other words it would also not be necessary to have a
controller rated at greater than 48 volts. What is important is that the controller is capable of
producing the 20 Amps max at something less than its 100% duty cycle. Correct?

Thanks again,

Chet

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Discussion Starter #6
--- Chet Fields <[email protected]> wrote:

>
> --- Jeff Major <[email protected]> wrote:
>
> >
--- Chet Fields <[email protected]> wrote:
> >
> > > Hey all,
> > >
> > > Well I really want to get my Soleq EVCort on the
> >
> > <snip>
> >
> > > Normally the field is driven
> > > at full battery voltage (nominal 108V) and max
> > > of 20 Amps. Would the current change if I drive
> it
> > > at a lower voltage? Or are 20 Amps 20 Amps?
> > >
>
> > Hey Chet,
> >
> > Of course the field current will change if you
> apply a
> > lower voltage. Use Ohm's Law. V = I * R. So 20
> amps
> > at 108 volts. Field R = 5.4 Ohms. If you apply
> 24
> > volts to the field, you draw 4.4 amps. Which
> would be
> > about 22 percent field excitation.
>
> I'm sorry I guess I forgot to mention that a chopper
> is used on the field and I'm not sure what
> the max duty cycle is. I will need to measure the
> resistance and I do also have a spec sheet on
> the motor that has that figure on it. I need to find
> it though.
>
> So, what I was trying to ask is if the resistance is
> say, 2 ohms I would need to have 40 volts
> average, which would be ~83% duty cycle on a 48 volt
> controller, but a 36 volt controller would
> not be enough to produce the full 20 Amps. In other
> words it would also not be necessary to have a
> controller rated at greater than 48 volts. What is
> important is that the controller is capable of
> producing the 20 Amps max at something less than its
> 100% duty cycle. Correct?
>
> Thanks again,
>
> Chet
>
O.K. Chet,

I think I see where you're going. What is important
is the field is Amps. And Ohm's law tells you what
voltage to apply to the field to get those Amps. If
you use a chopper to drive the field, then the chopper
has to be rated for its source voltage. If that is
the 108 volt battery, you need a 108 volt chopper.
You then adjust the duty cycle to get your desired
field voltage and consequent current. If you're going
to use a different source voltage for your field
chopper, then it would have to be a high enough
voltage to give you the output voltage to drive 20
amps at the field resistance at the 100% or maximum
duty cycle.

Jeff M




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Discussion Starter #7
Chet Fields wrote:
> Well I really want to get my Soleq EVCort on the road. I have been
> trying to design my own controller but I don't want to have to wait
> another 6 months or so that it will probably require for me to finish
> design, testing and tweaking and that's assuming all goes well.
>
> So I want to try yet another approach with the help of the group.
> As some of you may know the EVCort has a GE SepEx motor, and the
> controller runs at 800Hz with 2 separate banks of 200 Amps each
> connected to their own inductor before the armature terminal on
> the motor. It also has Regen of 200 Amps connected to 1 of those
> armature branches. The battery pack is 108V and is intimately tied
> to the DC-DC and charger and inverter for the A/C.
>
> What I would like to try is to use a low voltage (24-48) low amperage
> (<100) controller to control the field. I guess I would need a DC-DC
> converter for this.

First:
------
What exactly is wrong with your present Soleq do-it-all controller
package? Which of its subsections are still working -- DC/DC, inverter
for the A/C, motor field, motor armature, instrumentation, or battery
charger?

If most of these are working, it makes sense to leave it in the car, and
just add a (temporary?) replacement for the non-working sections.

Field
-----
If the field supply is not working: Measure the resistance of the field
winding. You have a sepex motor, so its field will be wound for
something less than full pack voltage. It would also help a lot to find
out the range of field currents that a working Soleq Evcort controller
applied.

You can get fancy, but all you really need for the field is a big
rheostat. The field only uses 1-2% of the total motor power, so the
field rheostat will only dissipate something like 100-200 watts when the
motor is delivering 10-20 kw. This takes a fist-sized rheostat and maybe
a small fan, but that's all.

You basically want to control this rheostat manually, via the
accelerator pedal. Set it up for full field current at minimum throttle,
and progressively less field current as you press down on the pedal.

Armature
--------
If the armature controller isn't working, you can use a Curtis 1221 or
1231 in its place. You'll probably lose regen, but it will work.

Regen will "sort of" work. For example, you can wire the brake light
switch to cut off the potbox to the Curtis controller so it is fully
off, but the big field rheostat is still providing power to the field.
Now you can control regen while one foot is on the brake and the other
foot controls the accelerator pedal to control field current. The motor
becomes a generator and produces more than the pack voltage. The
MOSFET's parasitic diodes in the Curtis controller will conduct, and
regen current will flow back into the batteries. This type of regen
won't be as smooth or well-controlled as the Soleq controller, but might
be acceptable.

> Now I know that these newer controllers use the higher switching
> frequency (>15kHz). Would that cause any problems on either the
> field or armature?

No. The motor will generate more heat on the higher frequency, but it
also has fan cooling to deal with it.

> Do I still need to connect it to one or both
> (in parallel) of the inductors on the armature?

Keep the existing armature inductors, since they're already there and
the Curtis will work better with the extra inductance. Just feel them
after a drive to see if they're getting too hot. Since they were built
for the Soleq 800 Hz controller, they may have too much core loss at the
15 KHz Curtis operating frequency.

> I know I need the field to be on before the armature so I was thinking
> of connecting the movement backwords and having the travel of the
> accelerator pedal connected with springs and stops to go from 0 to
> 100% on the armature controller and then go backwards from 100 - 20?%
> for field weakening to get more RPM.

Yes, that's the right idea.

> Would there be a problem if the current on the field controller
> went to Maximum instantly from a microswitch or something on the
> accelerator?

The field is just a big inductor. It would destroy a microswitch (as
they can't handle the peak current when on, nor the peak voltage spike
when it switched off).

You will need at least some minimum resistance in series with the field
rather than hitting it with full pack voltage. It is probably about a
30v winding, so at 108v it would burn out in a minute or less.

> Normally the field is driven at full battery voltage (nominal 108V)
> and max of 20 Amps.

This sounds wrong, Chet. 108v at 20a is 2160 watts, which is way too
much power for that field winding for more than a few seconds.

But I could see it being wound for 30v, and drawing 20a max (i.e. field
resistance R = 30v/20a = 15 ohms). This is 600 watts, which it could
probably handle for a minute or so with a blower on the motor. The Soleq
would have gotten this with a switchmode field controller that steps
108v at 6a down to 30v at 20a.

> Also, I suppose the requirements for contactors and precharge, etc.
> will be the same as any other series wound arrangement.

Yes. Just follow what Curtis recommends in their manuals (as a minimum).

--
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net


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Discussion Starter #8
--- Lee Hart <[email protected]> wrote:

> First:
> ------
> What exactly is wrong with your present Soleq do-it-all
> controller
> package? Which of its subsections are still working -- DC/DC,
> inverter
> for the A/C, motor field, motor armature, instrumentation, or
> battery
> charger?
>

It is the main controller, field and armature that isn't working.

>
> Field
> -----
> You can get fancy, but all you really need for the field is a big
> rheostat. The field only uses 1-2% of the total motor power, so
> the field rheostat will only dissipate something like 100-200
> watts when the
> motor is delivering 10-20 kw. This takes a fist-sized rheostat
> and maybe a small fan, but that's all.

Thanks, Lee. This is much simpler than having to use a special
DC-DC converter and a lower voltage / lower amperage controller.
I'll starting surfing to find one right away.

> Armature
> --------
> Regen will "sort of" work. For example, you can wire the brake
> light
> switch to cut off the potbox to the Curtis controller so it is
> fully
> off, but the big field rheostat is still providing power to the
> field.
> Now you can control regen while one foot is on the brake and the
> other
> foot controls the accelerator pedal to control field current. The
> motor
> becomes a generator and produces more than the pack voltage. The
> MOSFET's parasitic diodes in the Curtis controller will conduct,
> and
> regen current will flow back into the batteries. This type of
> regen
> won't be as smooth or well-controlled as the Soleq controller,
> but might be acceptable.

Ok, I hope I understand this correctly. Using this setup, if I
instead of releasing the accelerator pedal apply enough brake to
turn on the brake light, this would kill the pot input to the
armature controller and then I would slowly release the accelerator
to apply increasing field down to base speed. Is this as far as
regen will occur? I might want to put this field controller slider
on the stick shift handle. That would allow my feet to behave like
normal. (I don't normally drive with left foot on brake.)

> You will need at least some minimum resistance in series with the
> field
> rather than hitting it with full pack voltage. It is probably
> about a
> 30v winding, so at 108v it would burn out in a minute or less.

But if it really takes about 30 volts to run the the field at 20
Amps that would mean that 78 volts are being dropped by the
rheostat and at 20 amps wouldn't that be like 2340 watts? I would
need a rheostat capable of dissipating this much power, correct?

> > Normally the field is driven at full battery voltage (nominal
> 108V) and max of 20 Amps.
>
> This sounds wrong, Chet. 108v at 20a is 2160 watts, which is way
> too
> much power for that field winding for more than a few seconds.
>
> But I could see it being wound for 30v, and drawing 20a max (i.e.
> field
> resistance R = 30v/20a = 15 ohms). This is 600 watts, which it
> could
> probably handle for a minute or so with a blower on the motor.
> The Soleq
> would have gotten this with a switchmode field controller that
> steps
> 108v at 6a down to 30v at 20a.

Yes, Although it is connected directly to the full battery voltage
of 108V it does have a field chopper. So I guess it would be at
about a 30% duty cycle or so at maximum field current.

Thanks,
Chet

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Discussion Starter #9
--- Chet Fields <[email protected]> wrote:

> But if it really takes about 30 volts to run the the field at 20
> Amps that would mean that 78 volts are being dropped by the
> rheostat and at 20 amps wouldn't that be like 2340 watts? I would
> need a rheostat capable of dissipating this much power, correct?

Sorry, didn't have enough coffee yet or something. I should have
asked >wouldn't that be like 1560 watts?<

I haven't been able to find a rheostat capable of that much
dissipation for under $500. Anyone have a source for a 20Amp 108V
rheostat?

Thanks,
Chet

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Discussion Starter #10
Chet Fields wrote:

>
> I haven't been able to find a rheostat capable of that much
> dissipation for under $500. Anyone have a source for a 20Amp 108V
> rheostat?

---------------------------
Harbor Freight has a battery tester with a carbon pile rheostat
at a very reasonable price. My bad memory says 500 Amps (not
continuous, I's sure!)

John in Sylmar, CA
PV EV

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Discussion Starter #11
You don't want to put full pack voltage on it. Just tap the pack for 30
volts to run the field.

> Stephen Paschke
> DAR, ERISA, Plan Review, and IPI/ICTMS support,
>TIAA-CREF Denver
> Senior Consultant
> Keane, Inc.
> Office 303-607-2993
> Cell 303-204-9280
[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Chet Fields
Sent: Monday, August 27, 2007 10:29 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Hodge Podge 108V Sep Ex Controller

--- Chet Fields <[email protected]> wrote:

> But if it really takes about 30 volts to run the the field at 20
> Amps that would mean that 78 volts are being dropped by the
> rheostat and at 20 amps wouldn't that be like 2340 watts? I would
> need a rheostat capable of dissipating this much power, correct?

Sorry, didn't have enough coffee yet or something. I should have
asked >wouldn't that be like 1560 watts?<

I haven't been able to find a rheostat capable of that much
dissipation for under $500. Anyone have a source for a 20Amp 108V
rheostat?

Thanks,
Chet

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Discussion Starter #12
Ok, that makes sense. My only concern is the imbalance in the
batteries it might cause. Can I over time, move the connection
around the pack and have the voltage range float? Or does the -
have to correspond to B- on the armature?

--- "Paschke, Stephen" <[email protected]> wrote:

> You don't want to put full pack voltage on it. Just tap the pack
> for 30
> volts to run the field.
>
> > Stephen Paschke

> --- Chet Fields <[email protected]> wrote:
>
> > But if it really takes about 30 volts to run the the field at
> 20
> > Amps that would mean that 78 volts are being dropped by the
> > rheostat and at 20 amps wouldn't that be like 2340 watts? I
> would
> > need a rheostat capable of dissipating this much power,
> correct?
>
> Sorry, didn't have enough coffee yet or something. I should have
> asked >wouldn't that be like 1560 watts?<
>
> I haven't been able to find a rheostat capable of that much
> dissipation for under $500. Anyone have a source for a 20Amp 108V
> rheostat?
>
> Thanks,
> Chet

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Discussion Starter #13
I think you can move it around. Using Lee Hart's battery balancer would
probably solve that problem


> Stephen Paschke
> DAR, ERISA, Plan Review, and IPI/ICTMS support,
>TIAA-CREF Denver
> Senior Consultant
> Keane, Inc.
> Office 303-607-2993
> Cell 303-204-9280
[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Chet Fields
Sent: Monday, August 27, 2007 12:00 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Hodge Podge 108V Sep Ex Controller

Ok, that makes sense. My only concern is the imbalance in the
batteries it might cause. Can I over time, move the connection
around the pack and have the voltage range float? Or does the -
have to correspond to B- on the armature?

--- "Paschke, Stephen" <[email protected]> wrote:

> You don't want to put full pack voltage on it. Just tap the pack
> for 30
> volts to run the field.
>
> > Stephen Paschke

> --- Chet Fields <[email protected]> wrote:
>
> > But if it really takes about 30 volts to run the the field at
> 20
> > Amps that would mean that 78 volts are being dropped by the
> > rheostat and at 20 amps wouldn't that be like 2340 watts? I
> would
> > need a rheostat capable of dissipating this much power,
> correct?
>
> Sorry, didn't have enough coffee yet or something. I should have
> asked >wouldn't that be like 1560 watts?<
>
> I haven't been able to find a rheostat capable of that much
> dissipation for under $500. Anyone have a source for a 20Amp 108V
> rheostat?
>
> Thanks,
> Chet

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Discussion Starter #14
Got that covered. Already have it on order and was planning on
using it anyway.

--- "Paschke, Stephen" <[email protected]> wrote:

> I think you can move it around. Using Lee Hart's battery
> balancer would
> probably solve that problem
>
> > Stephen Paschke

> -----Original Message-----

> Ok, that makes sense. My only concern is the imbalance in the
> batteries it might cause. Can I over time, move the connection
> around the pack and have the voltage range float? Or does the -
> have to correspond to B- on the armature?
>
>
--- "Paschke, Stephen" <[email protected]> wrote:
>
> > You don't want to put full pack voltage on it. Just tap the
> pack for 30 volts to run the field.
> >
> > > Stephen Paschke

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Discussion Starter #15
Chet Fields wrote:
>
> --- Chet Fields <[email protected]> wrote:
>
> > But if it really takes about 30 volts to run the the field at 20
> > Amps that would mean that 78 volts are being dropped by the
> > rheostat and at 20 amps wouldn't that be like 2340 watts? I would
> > need a rheostat capable of dissipating this much power, correct?
>
> Sorry, didn't have enough coffee yet or something. I should have
> asked >wouldn't that be like 1560 watts?<
>
> I haven't been able to find a rheostat capable of that much
> dissipation for under $500. Anyone have a source for a 20Amp 108V
> rheostat?

That's why I started out by asking what your field resistance actually
is. And, if you had any measurements from a working Soleq on what the
normal range of field voltages (or currents are). From this, we can
calculate the wattage for the field rheostat.

This is also why I noted that a fan on the rheostat may be necessary.
You are unlikely to run the field at full power for any length of time.
The same goes for the field rheostat. Its peak power may be 1 KW or
more, but the average will be a lot less. You size the rheostat for the
average power it must dissipate -- not the peak.

Finally, if the Soleq never runs the field at full pack voltage, then
you can put a fixed resistor in series with the rheostat to handle the
max-current situation, so all of the power isn't dissipated in the
rheostat alone.

--
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net


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Discussion Starter #16
Paschke, Stephen wrote:
> I think you can move it around. Using Lee Hart's battery balancer
> would probably solve that problem

No, I think this would be a poor use for a balancer.

Chet has a sepex motor. The way you control its speed (and regenerative
braking) is by varying the field voltage. You can't effectively do this
by switching taps on the battery. The field draws enough current to
unbalance the pack. Switching such a highly inductive load will cause
arcing problems with the switching devices used. Finally, you could
easily wind up with momentary loss of field current, which is *very* bad
for the armature.

--
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #17
--- Lee Hart <[email protected]> wrote:

> Chet Fields wrote:
>
> > But if it really takes about 30 volts to run the the field at
> > 20 Amps that would mean that 78 volts are being dropped by the
> > rheostat and at 20 amps wouldn't that be like 1560 watts? I
> > would need a rheostat capable of dissipating this much power,
> > correct?

> That's why I started out by asking what your field resistance
> actually
> is. And, if you had any measurements from a working Soleq on what
> the
> normal range of field voltages (or currents are). From this, we
> can calculate the wattage for the field rheostat.

Well, I received a copy of the GE Motor specifications from Barry
Reicher and then misplaced them but a quick call to him helped
determine that the field resistance is: 4 x .0025 ohms on the main
field and 4 x .0024 ohms on the common field. Now, I really have
only a vague clue as to what that means exactly. Apparently, a part
of the field is in series with the armature and part is SepEx. Kind
of like a compound motor. The armature is .0087 ohms. Now it seems
to me like that is very low resistance in the field.

In talking to Barry, he thought that perhaps there is some kind of
interaction between the field and the armature or something that
would create some kind of back EMF and increase the resistance of
the field. If the field resistance is really only 10 milliohms then
full pack voltage would create over 11,000 amps!! So now I am even
more confused then before. :( I need to spend the time and try and
measure the resistance directly. But if it is sort of dynamic then
that will be a bit more complicated.

> This is also why I noted that a fan on the rheostat may be
> necessary. You are unlikely to run the field at full power for
> any length of time.
> The same goes for the field rheostat. Its peak power may be 1 KW
> or
> more, but the average will be a lot less. You size the rheostat
> for the average power it must dissipate -- not the peak.
>
> Finally, if the Soleq never runs the field at full pack voltage,
> then
> you can put a fixed resistor in series with the rheostat to
> handle the max-current situation, so all of the power isn't
> dissipated in the rheostat alone.

Now that makes sense as well. That way it can be connected to the
full pack and not cause imbalance issues.

Chet

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Discussion Starter #19
Hi Chet,

A few comments inserted....

--- Chet Fields <[email protected]> wrote:

> Well, I received a copy of the GE Motor
> specifications from Barry
> Reicher and then misplaced them but a quick call to
> him helped
> determine that the field resistance is: 4 x .0025
> ohms on the main
> field and 4 x .0024 ohms on the common field. Now, I
> really have
> only a vague clue as to what that means exactly.

My guess is that he gave you the figures from a series
wound motor, not a sepex. And it most likely is
"comm" not "common", meaning the comm coil winding
which is on the interpoles and in the armature
circuit.

Did you not tell me you measured the field resistance
at 2 Ohms?

> Apparently, a part
> of the field is in series with the armature and part
> is SepEx. Kind
> of like a compound motor. The armature is .0087
> ohms. Now it seems
> to me like that is very low resistance in the field.
>
>
> In talking to Barry, he thought that perhaps there
> is some kind of
> interaction between the field and the armature or
> something that
> would create some kind of back EMF and increase the
> resistance of
> the field.

Possible for a transient, but should not interact with
what you're doing. Field control pretty much is a
steady state type of thing.

> If the field resistance is really only 10
> milliohms then
> full pack voltage would create over 11,000 amps!! So
> now I am even
> more confused then before. :( I need to spend the
> time and try and
> measure the resistance directly. But if it is sort
> of dynamic then
> that will be a bit more complicated.

Should be a simple resistance measurement.

My opinions,

Jeff M

>
> Chet
>




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Discussion Starter #20
--- Morgan LaMoore <[email protected]> wrote:

> It makes sense that the field is such low
> resistance. Any power dissipated
> in the field is waste heat; field resistance should
> be as low as possible to
> increase efficiency. Only field current matters to
> motor operation. High
> current at low voltage means less wasted power.

Hey Morgan,

This is an incorrect statement. It is the mmf, or
ampere-turns. Not field current. So a shunt coil
with a high resistance can provide the same amp-turns
as a series coil with low resistance with the same
watts, provided they have the same amount of copper.

Jeff M


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