# Dual Controllers One Motor?



## Qer (May 7, 2008)

I'd say that unless the controllers are made for cooperation it's probably not a good idea.

AC controllers has to work in perfect sync, otherwise they will short circuit each other and burn up.

Not so sure about how DC-controllers will work, it will probably be very depending on how they're constructed. Since they're PWMing the power it might work, but since the induction in the motor will be part of the formula odd things might happen when two controllers PWM against the same inductor. If you're really lucky it will work smoothly, if you're not as lucky the ride might get jerky and awkward (especially at full acceleration and/or low rpm) and if you're unlucky your controllers will be toast.

Note, this is conclusions made from my experience in electricity, not from experience of EV:s. However, induction is tricky and since they change behavior by frequency things will go odd with two unsynchronized PWM's which probably will lead to interference and sudden power spikes and jerks in the acceleration etc. If there's a way to synchronize them so that they're always fired off at the same time things will work better, but if one shuts off before the other, the one still active will get a power spike that can lead to a burned out controller and even a runaway situation.

Generally I'd say that one controller is a much safer way to go.


----------



## Madmac (Mar 14, 2008)

In the case of PWM DC motor drive...

Imagine both controllers set to 50% or half power. The motor receives power for half the time and is off for the other half.

Now imagine both controllers being out of step by being exactly opposite, while one is on half the time the other is off.

The motor will get power from one controller and then the other, there will be no period when it is not powered. Ignoring any current limit the motor will be powered all the time and run at full power.

If the controllers run at almost the same frequency then they will drift in and out of phase at the beat frequency and the power will vary from half to full power.

In reality the current limits will shut down the controllers when the motor takes too much current and make the motor erratic.

Madmac.


----------



## frodus (Apr 12, 2008)

Controllers aren't modular... They've got their own control loops for voltage and current (and some have loops for motor RPM). 

The issue is, you can't sync the PWM as stated above. Even if you have the same throttle input, you can't even guarantee that the PWM is going to be the EXACT same percent. You'll be missing more than hitting. This is why the boards on the controllers are carefully made so that all the FET's are gated at the same time. if they're not, and one is out of time, they can fry.


----------



## Bouche (Jul 9, 2008)

Got it.

I did a little research on PWM and how a controller delivers power. It makes sense to me now why it can't work.

Thanks for information.


----------



## peggus (Feb 18, 2008)

Ah, a little knowledge is a dangerous thing! It does work if you do it right. It has even been done in the past using cutii, Google "battery blaster glenn roach". What you need is an inductor between each controller and the motor. Incidentally a series motor contains 4 large inductors, also known as the field winding. They are usually connected in series but you can break them up into two parallell coils. This requires some modification to the motor, you'll have to drill holes and install terminals for the split field winding.


----------



## Tubularfab (Sep 25, 2008)

I've been contemplating something similar myself, but in a slightly different case. I am soon going to have a Sevcon SC2000 controller, which was made to run dual 500 amp channels for dual motor drive. As I recall Sevcon spent a lot of time making sure both channels were completely in sync, specially when it came to the regen braking. I'm wondering if I can run both channels in parallel for one 1000 amp controller. I'd think they would share one internal clock and pulse perfectly in sync...


----------



## piotrsko (Dec 9, 2007)

As I recall Sevcon spent a lot of time making sure both channels were completely in sync, specially when it came to the regen braking. I'm wondering if I can run both channels in parallel for one 1000 amp controller. I'd think they would share one internal clock and pulse perfectly in sync...



Not sure how to test except for running two motors and checking to see if the phases are in sync with an Oscilloscope using the x-y and seeing if it makes the 45 degree Lissajous pattern all the time. Like everybody else stated off phasing makes they electron angry


----------



## fugdabug (Jul 14, 2008)

Get a copy of "Electric Motors and Control Techniques" by Irving M. Gottleib, ISBN 0-07-024012-4 (pbk. version) Amazon books has it for about (US$)16.47 plus shpg. IF you don't have a heavy math background or whatever it doesn't matter! It just means you have to re-read a bit and you will come to understand what is being said and how it is applied... Learn all you can, newb or not, educate yourself...


----------

