DC controller common terminal

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DC controller common terminal

Electric Vehicle Discussion List mailing list
This question refers to a non-road EV, but I think it's applicable to road
EVs too.

I recently bought an Alltrax controller for my Elec-trac tractor.  Like most
(all?) DC controllers, it has 3 high power terminals.  In this case they're
B-, M-, and B+M+ (actually marked just B+ but described as the B+M+
terminal).

The printed manual with it contains the following intriguing warning.  It's
printed in boldface type and underlined text (in parentheses, quotated,
capital letters ... no, wait, that's something else).

"Connect the motor leads as shown, making sure that you connect the B+ power
lead from the contactor and the A1 motor lead AT the B+ terminal of the
controller.  This is important for proper controller operation."

I read this as meaning that I should NOT, say, run a single cable from the
contactor "downstream" side to the controller B+M+ terminal, and then
connect the motor A1 lead to the contactor at that "downstream" terminal.

Instead, the motor A1 lead should be extended to the controller B+M+
terminal, so that there are 2 lugs on that controller terminal.

View following with a monospaced font such as Courier:

RIGHT:
               |---------------------
               |                    |
               |                  Motor
           B-  |M-  B+M+            |
 |---------()  -()   ()--------------
 -                   |
---                  |
 -                   |
---                  |
 |___________________|

Battery    Controller              Motor


WRONG:

               |---------------------
               |                    |
               |                  Motor
           B-  |M-  B+M+            |
 |---------()  -()   ()             |
 -                   |              |
---                  |              |
 -                   |              |
---                  |              |
 |___________________|______________|

Battery    Controller              Motor

I've previously connected DC controllers the "wrong" way -- that is,
connecting the motor lead to the contactor when it made for a shorter motor
lead.  It seemed to work fine.  

I guess my ignorance is showing here.  Can someone explain why connecting
the motor directly to the common controller terminal, not some other
terminal feeding it, would be  "important for proper controller operation"?

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: DC controller common terminal

Electric Vehicle Discussion List mailing list
The battery is not the only thing that supplies current to the motor.
The switching of the controller connects the motor to the battery for a
period of time,
followed by a period where the "freewheel" (diode or transistor) inside
the controller
carries all the current, also during the time that the motor is
connected to the battery,
it is not just the battery but also the capacitors in the controller
that provide the current.
Wiring the motor to the contactor instead of to the controller itself,
creates a large loop
and increases the inductance which can affect the operation of the
controller, besides creating
a lot of noise from the high frequent switching and the large "antenna"
loop created by the
wiring conncted to different points.
Some people even twist the motor leads together to minimize the
effective area inside the
loop created by the two motor leads, to further reduce the noise
radiated from the
output of the controller.
especially nearby sensing wires such as throttle control or sensor
inputs can be affected
by hundreds of volts fast-switching nearby and generating large amounts
of noise due to
improper wiring.

-----Original Message-----
From: EV [mailto:[hidden email]] On Behalf Of EVDL
Administrator via EV
Sent: Saturday, December 16, 2017 10:32 PM
To: [hidden email]
Cc: EVDL Administrator
Subject: [EVDL] DC controller common terminal

This question refers to a non-road EV, but I think it's applicable to
road EVs too.

I recently bought an Alltrax controller for my Elec-trac tractor.  Like
most
(all?) DC controllers, it has 3 high power terminals.  In this case
they're B-, M-, and B+M+ (actually marked just B+ but described as the
B+M+ terminal).

The printed manual with it contains the following intriguing warning.
It's printed in boldface type and underlined text (in parentheses,
quotated, capital letters ... no, wait, that's something else).

"Connect the motor leads as shown, making sure that you connect the B+
power lead from the contactor and the A1 motor lead AT the B+ terminal
of the controller.  This is important for proper controller operation."

I read this as meaning that I should NOT, say, run a single cable from
the contactor "downstream" side to the controller B+M+ terminal, and
then connect the motor A1 lead to the contactor at that "downstream"
terminal.

Instead, the motor A1 lead should be extended to the controller B+M+
terminal, so that there are 2 lugs on that controller terminal.

View following with a monospaced font such as Courier:

RIGHT:
               |---------------------
               |                    |
               |                  Motor
           B-  |M-  B+M+            |
 |---------()  -()   ()--------------
 -                   |
---                  |
 -                   |
---                  |
 |___________________|

Battery    Controller              Motor


WRONG:

               |---------------------
               |                    |
               |                  Motor
           B-  |M-  B+M+            |
 |---------()  -()   ()             |
 -                   |              |
---                  |              |
 -                   |              |
---                  |              |
 |___________________|______________|

Battery    Controller              Motor

I've previously connected DC controllers the "wrong" way -- that is,
connecting the motor lead to the contactor when it made for a shorter
motor lead.  It seemed to work fine.  

I guess my ignorance is showing here.  Can someone explain why
connecting the motor directly to the common controller terminal, not
some other terminal feeding it, would be  "important for proper
controller operation"?

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL
Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = =
= = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not reach me.
To send a private message, please obtain my email address from the
webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


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Re: DC controller common terminal

Electric Vehicle Discussion List mailing list
With these controllers, it is essential that the field be reversed and that the armature be connected directly to the controller’s B+ and A2 terminals, because the plug diode inside is connected to these terminals. Some vehicles, especially those previously using older, resistor-type controllers, may reverse the motor armature rather than the field winding.

Sent from my iPhone

> On Dec 17, 2017, at 1:36 AM, Cor van de Water via EV <[hidden email]> wrote:
>
> The battery is not the only thing that supplies current to the motor.
> The switching of the controller connects the motor to the battery for a
> period of time,
> followed by a period where the "freewheel" (diode or transistor) inside
> the controller
> carries all the current, also during the time that the motor is
> connected to the battery,
> it is not just the battery but also the capacitors in the controller
> that provide the current.
> Wiring the motor to the contactor instead of to the controller itself,
> creates a large loop
> and increases the inductance which can affect the operation of the
> controller, besides creating
> a lot of noise from the high frequent switching and the large "antenna"
> loop created by the
> wiring conncted to different points.
> Some people even twist the motor leads together to minimize the
> effective area inside the
> loop created by the two motor leads, to further reduce the noise
> radiated from the
> output of the controller.
> especially nearby sensing wires such as throttle control or sensor
> inputs can be affected
> by hundreds of volts fast-switching nearby and generating large amounts
> of noise due to
> improper wiring.
>
> -----Original Message-----
> From: EV [mailto:[hidden email]] On Behalf Of EVDL
> Administrator via EV
> Sent: Saturday, December 16, 2017 10:32 PM
> To: [hidden email]
> Cc: EVDL Administrator
> Subject: [EVDL] DC controller common terminal
>
> This question refers to a non-road EV, but I think it's applicable to
> road EVs too.
>
> I recently bought an Alltrax controller for my Elec-trac tractor.  Like
> most
> (all?) DC controllers, it has 3 high power terminals.  In this case
> they're B-, M-, and B+M+ (actually marked just B+ but described as the
> B+M+ terminal).
>
> The printed manual with it contains the following intriguing warning.
> It's printed in boldface type and underlined text (in parentheses,
> quotated, capital letters ... no, wait, that's something else).
>
> "Connect the motor leads as shown, making sure that you connect the B+
> power lead from the contactor and the A1 motor lead AT the B+ terminal
> of the controller.  This is important for proper controller operation."
>
> I read this as meaning that I should NOT, say, run a single cable from
> the contactor "downstream" side to the controller B+M+ terminal, and
> then connect the motor A1 lead to the contactor at that "downstream"
> terminal.
>
> Instead, the motor A1 lead should be extended to the controller B+M+
> terminal, so that there are 2 lugs on that controller terminal.
>
> View following with a monospaced font such as Courier:
>
> RIGHT:
>               |---------------------
>               |                    |
>               |                  Motor
>           B-  |M-  B+M+            |
> |---------()  -()   ()--------------
> -                   |
> ---                  |
> -                   |
> ---                  |
> |___________________|
>
> Battery    Controller              Motor
>
>
> WRONG:
>
>               |---------------------
>               |                    |
>               |                  Motor
>           B-  |M-  B+M+            |
> |---------()  -()   ()             |
> -                   |              |
> ---                  |              |
> -                   |              |
> ---                  |              |
> |___________________|______________|
>
> Battery    Controller              Motor
>
> I've previously connected DC controllers the "wrong" way -- that is,
> connecting the motor lead to the contactor when it made for a shorter
> motor lead.  It seemed to work fine.  
>
> I guess my ignorance is showing here.  Can someone explain why
> connecting the motor directly to the common controller terminal, not
> some other terminal feeding it, would be  "important for proper
> controller operation"?
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL
> Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = =
> = = = = = = = = = = = =
> Note: mail sent to "evpost" and "etpost" addresses will not reach me.
> To send a private message, please obtain my email address from the
> webpage http://www.evdl.org/help/ .
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> Please discuss EV drag racing at NEDRA
> (http://groups.yahoo.com/group/NEDRA)
>
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
>

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Re: DC controller common terminal

Electric Vehicle Discussion List mailing list
Cor, Paul, thanks for the replies!  I forgot about the freeewheeling
diode(s).

So I'll connect it the way the manual says.

Still ...

I recall some discussion years ago about fixed frequency 15kHz+ Curtis
controllers having trouble with current limiting on large, low inductance
motors.  It caused the combination to have jerky starts, or worse.  The way
Lee Hart explained it was that the low resistance meant that the current
didn't have time to decay enough when the chopping transistors were off
(because it was a very short time), so the current just kept rising insead
of being properly limited.

If that were the crucial factor here, I would think that extra resistance in
the motor loop would HELP.  But obviously not, because we're always advised
to keep the motor leads as short as possible.

I hate to sound dense (even though I am), but while I can understand that
connecting the motor lead at the contactor (or other point ahead of the
controller common terminal) could change the way the controller "sees" the
motor, I still don't fully understand what specific problems that might
cause.  Maybe the earlier discussion about motor loop impedance / resistance
isn't relevant here?

Thanks again!

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me.  To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


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Re: DC controller common terminal

Electric Vehicle Discussion List mailing list
In reply to this post by Electric Vehicle Discussion List mailing list
Increasing inductance slows down the ramp up of current, so adding inductance to a motor with too low inductance helps to get better current limit, especially on controllers with low switching speed where a single step will cause so big current change that it can damage the controller.This is entirely different from the addition of a physical loop of wire, even though that also adds inductance, because a physical distance between the two wires or even a wire running without the "return" current running right next to it, will act as antenna, spewing the switching noise into the air and possibly disrupting the operation of sensitive circuits in the controller but certainly killing your radio reception and possibly someone else's which is illegal.
The addition of inductance is what i have done on my previous EV truck which had a low speed EV100 controller and a large 11 inch motor. I could fit 3 loops of the motor cable through a large microwave transformer core. But i kept the motor cables close together.
Do not add resistance in the motor loop, as that only increases losses.Hope this clarifies.Cor


Sent from my T-Mobile 4G LTE Device
-------- Original message --------From: EVDL Administrator via EV <[hidden email]> Date: 12/17/17  9:13 AM  (GMT-08:00) To: Electric Vehicle Discussion List <[hidden email]> Cc: EVDL Administrator <[hidden email]> Subject: Re: [EVDL] DC controller common terminal
Cor, Paul, thanks for the replies!  I forgot about the freeewheeling
diode(s).

So I'll connect it the way the manual says.

Still ...

I recall some discussion years ago about fixed frequency 15kHz+ Curtis
controllers having trouble with current limiting on large, low inductance
motors.  It caused the combination to have jerky starts, or worse.  The way
Lee Hart explained it was that the low resistance meant that the current
didn't have time to decay enough when the chopping transistors were off
(because it was a very short time), so the current just kept rising insead
of being properly limited.

If that were the crucial factor here, I would think that extra resistance in
the motor loop would HELP.  But obviously not, because we're always advised
to keep the motor leads as short as possible.

I hate to sound dense (even though I am), but while I can understand that
connecting the motor lead at the contactor (or other point ahead of the
controller common terminal) could change the way the controller "sees" the
motor, I still don't fully understand what specific problems that might
cause.  Maybe the earlier discussion about motor loop impedance / resistance
isn't relevant here?

Thanks again!

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me.  To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


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