# Transwarp9 and ADC FB1-4001A in series?



## kerrymann (Feb 17, 2011)

Hypothetical question for the motor gurus. Can you run a Transwarp9 and ADC FB1-4001A in series?

My Miata currently has a ADC FB-4001A and have been thinking about going to dual motors later in the future. At this point I don't have the battery pack to bother but I have a first generation Transwarp9 sitting on the bench and plenty of power left in my Soliton. Originally I was keeping an eye open for another warp 9 to have 2 motors that are well matched. However I was wondering what would happen if I ran the ADC and the W9 in series with them physically coupled together? The motors are similar but there are differences that will give the motors different impedance. 

If the motors weren't physically tied together wiring them in series would lead to a unstable system which would end up sending more power to the motor with the least physical resistance (correct me if I am wrong here). But even if the motors were perfectly matched this would be the case.

Physically coupling the motors together means they will always have the same RPM. Then the differences in the motors means it would be stable but that they will output different power levels. This means one motor would be providing a larger share of the shaft power. If the difference is small then that is not a big deal (which is the case for everyone running dual W9s). However if they are different enough and one motor takes 95% of the power then there is no sense in bothering with the second motor. I don't know how different these two motors really are but my guess is that the difference would not be that great, More like 45/55? But that is just a guess and why I am asking the hypothetical question for you motor gurus.

Happy holidays!


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## major (Apr 4, 2008)

kerrymann said:


> Hypothetical question for the motor gurus. Can you run a Transwarp9 and ADC FB1-4001A in series?
> 
> My Miata currently has a ADC FB-4001A and have been thinking about going to dual motors later in the future. At this point I don't have the battery pack to bother but I have a first generation Transwarp9 sitting on the bench and plenty of power left in my Soliton. Originally I was keeping an eye open for another warp 9 to have 2 motors that are well matched. However I was wondering what would happen if I ran the ADC and the W9 in series with them physically coupled together? The motors are similar but there are differences that will give the motors different inductance.
> 
> ...


Hi ker,

I can't remember ever having done it, but I don't see a problem. You'll be limited to the thermal rating of the lesser of the two. The current will be the same in both motors. Each will produce torque, likely different values, but so what? The torque just adds to the common shaft. The applied voltage to the series connected motors is set by the controller and will divide according to the respective machine constants. Shouldn't be a problem. 

Since the current is equal for the motors, the power split will be in proportion to the voltage division. Unlikely to be equal power, but I don't see a problem if the motors were somewhat close in rated speed, power and voltage to start with.

major


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## kerrymann (Feb 17, 2011)

major said:


> Hi ker,
> 
> I can't remember ever having done it, but I don't see a problem. You'll be limited to the thermal rating of the lesser of the two. The current will be the same in both motors. Each will produce torque, likely different values, but so what? The torque just adds to the common shaft. The applied voltage to the series connected motors is set by the controller and will divide according to the respective machine constants. Shouldn't be a problem.
> 
> ...


Thanks Major,
Not knowing the real differences between the two motors I didn't know how big the power split would be. It's good to know that since they are both 9" motors with almost identical voltage and nameplate ratings it should be close enough. 

For my reference how would you determine the power split? At low RPMs I think it would be the resistance of the winding's? And then at higher RPMs the split would be based on the back EMF of the two designs?

Kerry


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## major (Apr 4, 2008)

kerrymann said:


> For my reference how would you determine the power split? At low RPMs I think it would be the resistance of the winding's? And then at higher RPMs the split would be based on the back EMF of the two designs?


Yep. And it shows as the individual motor terminal voltage. It happens automatically kinda like a voltage divider circuit. So you don't have to determine it. You can measure it if you want to know. It will take care of itself. 

To calculate it ahead of time, you would need to know the design parameters of both motors like the number of armature conductors, resistance, magnetization curve, etc. Or it might be possible to guestimate the voltage split using the characteristic curves. I'm unsure of the benefit of doing this.

Since the current is the same, the power is in proportion to the motor voltage. If motor 1 takes 60V and #2 takes 40V of a 100V applied to the pair, then motor #1 produces 60% of the total power or 50% more than motor #2. This is obviously an approximation using the assumption that the 2 motors have equal efficiency.


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## kerrymann (Feb 17, 2011)

major said:


> Yep. And it shows as the individual motor terminal voltage. It happens automatically kinda like a voltage divider circuit. So you don't have to determine it. You can measure it if you want to know. It will take care of itself.
> 
> To calculate it ahead of time, you would need to know the design parameters of both motors like the number of armature conductors, resistance, magnetization curve, etc. Or it might be possible to guestimate the voltage split using the characteristic curves. I'm unsure of the benefit of doing this.
> 
> Since the current is the same, the power is in proportion to the motor voltage. If motor 1 takes 60V and #2 takes 40V of a 100V applied to the pair, then motor #1 produces 60% of the total power or 50% more than motor #2. This is obviously an approximation using the assumption that the 2 motors have equal efficiency.


Thanks Major,
My thinking in the benefit in checking is 2 reasons: 

#1: I am always curious and want to understand as much as I can. 
#2: To see how severe the voltage split is. 

If I do bump my pack voltage from 240V to 310V (the max voltage for 1000amps on the Soliton1) and I apply 310VDC across the motors and they both take half then they will both be *happy* at 155VDC (neglecting losses and sag). But if it is a 40/60 split then one motor is going to see 186V at which point I have probably zorched the motor. If the voltage division is any more severe then using the ADC isn't worth even trying and I'll keep my eye open for another WP9. 

I just looked through the motor curves for both motors (thx for the idea). I found a ADC curve at 75VDC CCW that had advanced timing I THINK, but not sure, and no idea how much. Then Netgain's curve at 72VDC CCW rotation. I picked 3000 rpm and 3500rpm and here is what I found

ADC 3000rpm, 185amps, 28ftlbs, 75VDC
WP9 3000rpm, 220amps, 25ftlbs, 72VDC

ADC 3500rpm, 155amps, 20ftlbs, 75VDC
WP9 3500rpm, 180amps, 22ftlbs, 72VDC

That puts it at a ~45/55 which probably has as much to do about differences in test equipment, set-up sensor error, etc). So it will be fine (just as you said it would be). If/when I try it I'll measure the individual motor under load and sneak up on the voltage limits (not to mention timing, brushes, etc).


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