View Single Post
Old 07-30-2010, 02:46 PM   #3614 (permalink)
MPaulHolmes's Avatar
Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
Posts: 3,832

Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
Thanks: 1,368
Thanked 1,119 Times in 734 Posts
Hi Jack! So, sometimes they are in series, and sometimes in parallel... What would happen if they are in series:
How does the wiring work? Battery pack + goes to Post1 of motor 1, then Post 2 of motor 1 goes to post 1 of motor 2, and then post 2 of Motor 2 goes to motor-? Each motor would see half of the pwmDuty*pack voltage? It would have greater inductance because there are more coils, so the PI loop might behave a little different. The change of current would be a little slower. But it might not be that big of a deal. I don't see a difficulty with series, but I've never tried it.

How about parallel?
Motor controller M- goes to post 2 of motor 1 and motor 2. Battery pack + goes to post 1 of motor1 and motor 2, right? Now, the pwmDuty*pack voltage would be the same for both, but the current would have to be twice what it normally would be with a single motor to get the same torque for each one. I don't see why the controller would have a problem running 2 at the same time. Would the equivalent inductance be half? I think so. So, the current could change fast, so you might have to program your PI loop to be slower changing to account for this case. Or, you could change the PI values on the fly depending on if the motors are in series or parallel.

Now, how about switching between the 2... It seems like some subtleties could creep in if you aren't careful. If there is a moment when neither motor is connected when switching between parallel and series, you could have dwffy's problem if the throttle was nonzero.
kits and boards
  Reply With Quote