# Dual controllers



## frodus (Apr 12, 2008)

no

controllers have to be precisely timed so that the FET's (or igbt's in some controllers) switch on and off at the EXACT same time. If they're not in sync, then they won't work. It would be nearly impossible to get them both to sync.


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## bblocher (Jul 30, 2008)

Yeah since they would need to be run in series to double the voltage. Not possible without the controllers supporting such a feature.

Two in parallel for increased amps is something I'd like to see documented. I've heard of a build or two doing it but not sure if it's cut and dry hook it up or if something custom was done. Not sure if the you can get "feedback" for lack of a better word from one controller to another and if that would cause issues. That is one controller is firing while the other is not since they aren't sync'd.


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## rmay635703 (Oct 23, 2008)

There is only one way I know of to put more voltage in a car than the controller can handle. Typically though this technique is used on electric scooters.

Anyway your controller is rated for 72v and up to a certain amperage. If that amperage is well below the limit when you are at cruising speed you can put in a cutoff in front of the controller going to the motor.

Basically you can wire some batteries through contactors between your controller and the motor. My car has survived this test a few times but my F/R contactor shuts off when I let off the accellerator and I only tested adding 12v.

You need to be carefull with this because the car needs to be moving before your thow the contactor set to put the batteries in line or you may send so much amperage through that your controller fries.

Also I highly doubt you could safely double your pack this way but you could add maybe 36v if you get large contactors and your controller is rated at a high enough amperage. You also would have to get the car up to speed flat out before throwing the contactors so the amperage level isn't too high and there is enough back emf to counteract the added voltage.

You would need to take care that your motor doesn't overspeed also, depending of coarse on how your car is geared and what speed you are currently able to muster.

Personally 12v-16v is the safest level to use one of these at but I have heard of others getting away with more, all depends on your motor and controller.

Good Luck


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## frodus (Apr 12, 2008)

bblocher said:


> Yeah since they would need to be run in series to double the voltage. Not possible without the controllers supporting such a feature.
> 
> Two in parallel for increased amps is something I'd like to see documented. I've heard of a build or two doing it but not sure if it's cut and dry hook it up or if something custom was done. Not sure if the you can get "feedback" for lack of a better word from one controller to another and if that would cause issues. That is one controller is firing while the other is not since they aren't sync'd.


 
ITS VERY VERY HARD to put controllers in series OR parallel... they have to gate at the same exact time... and I mean EXACT... at whatever sqitching frequency the controller is at. If they don't, you will likely let the magic smoke out of your controllers. This is why controllers are built as one unit, so they can precisely control the gates of each FET or IGBT and isolate from noise and external variables.

To go up in voltage, you have to have higher voltage FET/IGBT's, Capacitors and Diodes... amongst other things.


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## icebeater (Jan 21, 2009)

frodus - when you say it's hard to do in parallel, are you thinking about running one motor off two controllers - which is probably impossible? But ... with 2 motors, each with their own controller, surely running them in parallel wouldn't be any more tricky than running two battery packs?


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## frodus (Apr 12, 2008)

you cannot series or parallel the output of the controller.

One controller per motor is the best idea... but you can't just connect their outputs to get more current (parallel) or higher voltage (series).


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## icebeater (Jan 21, 2009)

frodus said:


> you cannot series or parallel the output of the controller.


Thanks Travis - understood! When it comes to the (battery) input though, two controllers could be connected in parallel to the same battery pack, right? As long as they powered separate (unconnected) motors. Wouldn't they'd just draw twice the current? (if they were identical setups.)

David


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## frodus (Apr 12, 2008)

parallel battery packs are ok... just as long as each controller has their own motor.

To get the maximum power out of each controller, you would need a battery pack that could support it. i.e. if you had 2 50kw controllers, you would need a battery pack that could supply 100kw peak.


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## DavidDymaxion (Dec 1, 2008)

In theory, if you rewound and rewired the motor (might require a 2nd commutator to handle all the current) you could get the same power with twice the current (2I) at 72 V as the current I at 144 V. It would be the same effect as doubled voltage. Big but, though: If one controller ever failed (or even was not exactly equal to the other as the pedal moved), the fields in the motor could go horribly out of balance and the motor could arc itself to death.

A much better and safer plan is to get a controller and motor up to 144 Volts, or use 2 separate motors.


xtreme cartz said:


> Is it possible to wire two controllers and double the motor voltage? For example, I want to use two 72 volt Alltrax controllers for 144 volts.


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## major (Apr 4, 2008)

DavidDymaxion said:


> In theory, you could power 1 pair of field coils and 2 brushes with one controller, and the other pairs with a second controller. It would be the same effect as doubled voltage.


Hi David,

This is incorrect. It would not be the same as doubling the voltage. In the 4 pole motor, the two brush pairs are in parallel with each other. And the 4 pole wave armatures are self equalizing, meaning that there is essentially a short in the armature itself between the two brush contact points of brushes of same polarity. So, if those brush pairs do not have exactly the same potential, you'll get high currents is some of the armature coils. 

You could run two field coils from one source and two from another, but have to have a node before the armature (or brush) connection. But I do not recommend it.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

In the practical world, you are absolutely right! I glossed over some details. I certainly wouldn't advocate it, but theoretically you could rewind/rewire the motor so two controllers delivering twice the current would be the same (to first order, anyways) as half the current at twice the voltage. You can think of different ways to this goal: Thicker armature wire, or rewire the motor so 72 V powers 1/2 of the wire length it used to (might require dual commutators to handle the current). Anyway, the real point was theoretically you could do it, but it isn't practical. Using 2 motors is much better.


major said:


> Hi David,
> 
> This is incorrect. It would not be the same as doubling the voltage. In the 4 pole motor, the two brush pairs are in parallel with each other. And the 4 pole wave armatures are self equalizing, meaning that there is essentially a short in the armature itself between the two brush contact points of brushes of same polarity. So, if those brush pairs do not have exactly the same potential, you'll get high currents is some of the armature coils.
> 
> ...


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