# Gang of Controllers



## dougingraham (Jul 26, 2011)

If the controllers were designed for it you could conceivably parallel them. I dont know of any designed this way. The switching would have to be synchronized between the devices and there would have to be considerations for the load sharing. It is not practical to place controllers in series to increase the voltage capability. You have to use higher voltage rated power switches. MOSFETs for voltages up to around 200 to 250 and IGBTs above that.

The 72 volts is easy. The 1500 amps is quite a bit more difficult. Your best bet is to get a 2000A capable Zilla. The other option that comes to mind is an Evnetics Shiva which would be massive overkill.


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## Qer (May 7, 2008)

The only practical way to run more than one controller is to let each power a separate motor, for example a siamese motor powered by two controller - one controller per motor half.

Considering your limit with the available controllers on the market is 2x3000 Amps at more than 400 Volt that setup should be quite sufficient for most vehicles.


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## oddpowers (Dec 9, 2008)

Thanks for not pointing out how stupid the question was!! I kinda figured that was the case, But just had to ask.
This leads me into another question. I hear so folks talking about continous amp rating VS Peak. I only need the 1500 amp for about 10 seconds. Does that help with my options?


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## dougingraham (Jul 26, 2011)

With the controllers that can do 1500 amps, all are water cooled and I doubt they would make 1500 amps for even 10 seconds without the water cooling.

So you are drag racing. Why only 72 volts? This is only 108kw (145 HP) into the motor. And 1500 amps is quite a lot more difficult to deal with than 1000 amps. If you go to 192 volts at 1000 amps you would see 192kw (257 HP) into the motor. With a single motor you can even do 288 volts at 1000 amps and see peak power into the motor of 288 kw (386 HP). Or like Qer points out use two motors and one really big controller or two controllers to obtain the equivalent of lots of amps.


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## oddpowers (Dec 9, 2008)

The max I could go is 144v. I have 12 PC680 odyssey batteries. I'm afraid the voltage sag would be so much, my 60ft time would be terrible.

So if I ran 144v, A 700 amp controller would be all I need to get the max out of the batteries?

I thought the max these batteries would give was 680 amps. Whats wrong with my calculation?
144v @ 680 amps = 97.920 KW
72V @ 1360 amps = 97.920 KW


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## oddpowers (Dec 9, 2008)

Thanks for you guys help, btw!


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## frodus (Apr 12, 2008)

oddpowers said:


> The max I could go is 144v. I have 12 PC680 odyssey batteries. I'm afraid the voltage sag would be so much, my 60ft time would be terrible.
> 
> So if I ran 144v, A 700 amp controller would be all I need to get the max out of the batteries?
> 
> ...


You forgot the sag..... It won't be 144V. I'd be surprised if you could even get 680A out of that cell for longer than a few seconds before it sagged low enough to start damaging the battery. 

Unfortunately I can't find a datasheet that shows the sag voltages of the battery. I would imaging it would be under 1.5VPC, or somewhere around 8-9V. Lets say its 9V, that would make 144V become 108V. 108V * 680A = ~73kw or so. I wouldn't expect the life to be very long if you kept doing that.


Read this:
http://evdl.awardspace.com/voltage%20sag,%20peukerts%20effect/


One thing to note though, controllers are rated by motor side amperage. Look at them as power converters. Watts in = Watts out. I realize there are losses, but for clarity, imagine there are none. If you have 108V and 680A coming into the controller, you have 73kw. At low RPM, the controller duty cycle is low, so if you did have a 1500A controller, you could be outputting 1500A. As the duty cycle and RPM increase, the Amperage will fall off.


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## oddpowers (Dec 9, 2008)

Thanks Frodus!

After reading the link you posted, I think I understand the sage issue (maybe )

But what I surely don't understand is this:

If you have 108V and 680A coming into the controller, you have 73kw. At low RPM, the controller duty cycle is low, so if you did have a 1500A controller, you could be outputting 1500A.

If I have 680a in how do I get 1500a out?


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## Duncan (Dec 8, 2008)

oddpowers said:


> Thanks Frodus!
> 
> After reading the link you posted, I think I understand the sage issue (maybe )
> 
> ...


By the magic of buck converters!

My motor has a "resistance" of about 15mOhms
So 15v will drive 1000amps - when the motor is stationary

Start - 0 rpm
Motor - 15v - 1000amps = 15,000watts
Battery 150v - 100amps = 15,000watts

1000rpm - motor has 30v Back EMF
Motor - 15v + 30v (45v) - 1000amps = 45,000watts
Battery 150v - 300amps = 45,000watts

2000rpm - motor has 60v Back EMF
Motor - 15v + 60v (75v) - 1000amps = 75,000watts
Battery 150v - 500amps = 75,000watts

It does this because the converter is rapidly switching the power on and off
The battery "sees" the average at that voltage
the motor "sees" the average at its voltage

It's lovely!


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## John Metric (Feb 26, 2009)

oddpowers said:


> Thanks Frodus!
> 
> After reading the link you posted, I think I understand the sage issue (maybe )
> 
> ...


I have a number of good charts on this topic on both of my DIY links below my name.

This one is from DC Plasma Build Thread showing a twin zilla2k-EHV making 2X2000=4000 motor amps from only 500 battery amps.


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## Qer (May 7, 2008)

This is why it usually pays off increasing battery voltage too.

Today you have 12 12 Volt batteries connected in two strings that are parallel, ie 72 Volt, right? If the motor pulls 500 Amps at 36 Volt it means that you get 250 Amps at 72 Volt in the battery end (I'm ignoring the sag here to keep things simple), but since the batteries are separated in two strings each string sees half of that, 125 Amps.

If you connect the batteries in one long string you get 144 Volt instead so the 500 Amps at 36 Volt becomes 125 Amps at 144 Volt, ie the same current (and thus the same sag) per battery! Nothing is lost by rearranging the batteries for a higher voltage (provided the controller can take the voltage).

What you gain with higher voltage is, however, higher possible RPM. A motor will cause a back-EMF that is depending on the RPM, higher RPM means higher back-EMF. When back-EMF starts to get close to pack voltage, current will start to drop off (since the controller can only decrease the voltage, never increase it) so your pack voltage limits top RPM. Higher pack voltage equals higher top RPM.

This is true up to around 200 Volt. After that you don't benefit from increased voltage since the motor can't handle higher voltages anyway and if you keep rising the voltage despite this you'll only decrease the efficiency of the system.

This is why the Soliton S1 cuts down the max motor current from 1000 Amps to "mere" 900 Amps at somewhere around 300-ish Volts (don't remember exactly when, but it's mentioned in the manual); at higher voltages the switching losses starts to become a problem and the controller lowers the motor current to protect itself.

You should, imo, definitely go for 144 Volt if you can. At least if your controller, charger etc can handle it.


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## oddpowers (Dec 9, 2008)

Qer said:


> Today you have 12 12 Volt batteries connected in two strings that are parallel, ie 72 Volt, right? If the motor pulls 500 Amps at 36 Volt it means that you get 250 Amps at 72 Volt in the battery end (I'm ignoring the sag here to keep things simple), but since the batteries are separated in two strings each string sees half of that, 125 Amps.
> 
> If you connect the batteries in one long string you get 144 Volt instead so the 500 Amps at 36 Volt becomes 125 Amps at 144 Volt, ie the same current (and thus the same sag) per battery! Nothing is lost by rearranging the batteries for a higher voltage (provided the controller can take the voltage).


Thanks, this makes sense. I really would like to stay @ 72 volts for now. So with what you said above, will I benefit from using 2- 72 volt pack verses one 72v pack? If so, is it enough to overcome the weight of the second pack? (about 93lbs)

Right now I'm in the low 10's with my older PC925s (single pack). This year I'm trying to break into the 9's on 72v. I was just using a contactor the last 2 years, and have managed to toast the contactor. So I'm not trying to figure out a way to NOT spend 2k on a controller.


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## Qer (May 7, 2008)

oddpowers said:


> will I benefit from using 2- 72 volt pack verses one 72v pack?


THAT I can not tell you...


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