2 controllers in paralell for one hub motor, is it possible?

Electric Motors and Controllers
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endonuclease
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2 controllers in paralell for one hub motor, is it possible?

Post by endonuclease » Nov 13, 2017 6:02 am

Hi, I recently got me a Crystalyte H4080 motor. I run this on a Crystalyte 72 volt 45 A sensor/sensor-less controller (I run it in sensor-less mode and works well). But the case is that I now have two such identical regulators, after I removed two blown MOSFETS (an identical regulator from my previous ebike) and soldered back two new MOSFETs of the same type. The question is perhaps hard to answer, cause I have not found anything on the web or youtube about this scenario.

But here's the question: Is it possible to connect these two identical regulators in parallell to one hub motor ?, to double the current from max 45 A to max 90 A ? They will of course self-synchronize (in sensor-less mode)....... But if it is possible; should I run both controllers in a sensor-less mode, or in sensor-mode ? I can't see any trouble about anything "backfiring" from one controller into the other because they are connected in parallell and the current (let's say at 60A will divide in a Y-connection).

I must emphasize that I'm NOT going to use two hubs, only ONE motor. And ONE speed regulator, because the voltage from the regulator will be the same into each controller through a Y-splitter into both controllers, but the CURRENT out/in to the controllers will get "splitted" on the output side.

So if you can imagine a circuit as a water pipe mesh; the voltage is the pressure in the "pipe-mesh" and the current is the "water-flow". I know mediokre electronics and can't see any dangers, but perhaps there is someone with deeper insight that will see a problem. I've also thought about using diodes, but then the controllers won't get feedback from the hub to synchronize...

Thanks,
Endunuclease

Clyte H4080, 72v nominal 20Ah, 45A (hopefully 65A with two parallell controllers (shared output = 32,5 A per controller and very little heat) if this works, and will make it possible to connect an extra battery in parallell later).

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amberwolf
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by amberwolf » Nov 14, 2017 2:43 am

If it was a 6-phase motor, you could do two controllers like that. There's an ongoing recent thread about such a motor / controller setup under that name, and another older thread about it (by 12p3phPMDC

But a regular 3phase motor won't work that way, because the controllers won't operate with identical timing, and they won't synchronize, so at some point in the controllers' commutations of the motor, you'll be shorting battery to ground between the FETs of the different controllers, and parts will probably fail (probably spectacularly).


You can try it out and see what happens, but I don't recommend it.


Now, if you were to disconnect the gate drive of one controller from it's MCU, and connect it to the other controller's MCU, so that one controller drives both power stages, it might work. But if there is enough delay (long enough wires, enough inductance and/or capacitance in the path, etc), that could still have enough difference between power stage timings to cause problems. If there's enough dead time between switchings it won't cause a shoot-thru (battery short) but it could cause excessive heating.



You can't use diodes anywhere in the phase wires to or from the controllers, because current has to flow both directions thru each phase to be able to drive the motor.


there's other threads about two contorllers and one motor, if it helps, though there's no testing in them to verify that I recall. This search
https://endless-sphere.com/forums/searc ... mit=Search
finds some of them; most results aren't relevant but you can see from the titles which ones are.

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fechter
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by fechter » Nov 14, 2017 11:01 am

I've seen it done before without smoke, but I didn't think it would work. The PWM timing between controllers will never be in sync unless you run a sync line between them and use one as a remote. Better to just get a bigger controller.
"One test is worth a thousand opinions"

endonuclease
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by endonuclease » Nov 15, 2017 8:54 am

Yes, by a second thought, I totally agree..... Just a de-synchronization of a few milli-seconds will perhaps be tolerated by the controllers, but the battery will be also shorted in those fractions of milliseconds - something that can't be good at all for the battery. Especially when you think of the rpm of perhaps 600-700 at max speed (82 km/h). The the battery will short-out more than 700 times each minute.....That battery won't last for a long period (shorting out 10 times each second)....Then perhaps it would be better to modify the Controller...(?) I've even been reluctant to use regenerative breaking because of the battery life-time....

Endonuclease


Crystalyte H4080 motor. 72v 20Ah LiFePO4 battery, 1500-2000 charges (capable of 65A). Crystalyte sensorless 72v 45A Controller.

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fechter
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by fechter » Nov 15, 2017 9:14 am

Depending on the controller, it's often possible to increase the current capacity by installing better FETs and beefing up the traces.

Most controllers that support regen can be programmed for regen level. Just use a lower level if you're worried about it. Even at a low level, it really helps the brakes.
"One test is worth a thousand opinions"

endonuclease
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by endonuclease » Nov 16, 2017 2:16 am

Yeah, I can experiment with the oldest controller and see if I can change the FET's into those Crystalyte are using in the controlller for the CROWN motor (60A or 90A). And I can also check out if some of the capacitors need to be changed.

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John in CR
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Re: 2 controllers in paralell for one hub motor, is it possi

Post by John in CR » Nov 16, 2017 4:34 am

You could do it by separating the individual strands of the windings at both ends, and terminating both ends as 2 groups of separate windings. Seems like a waste of time to me when I can easily get a 90A controller. Plus it's a bad idea anyway, since 90A is too much for that motor anyway unless it's pushing a light load on flat terrain avoiding repetitive hard launches, so peak current is very short in duration. Heat in the windings goes up by the square of current, so if you double the current, heat goes up 4X.

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