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I was wondering if I could upgrade my current bldc motor controller (three phase motor)(*) to a higher wattage/output power by doing the following modifications:

  • Replace mosfets with higher power rates ones (higher amps, lower Rds(on), equal or higher voltage rating )
  • replace shunt with much thicker one (and recalibrate)
  • Improve cooling of mosfets (bigger heatsink, perhaps some activate cooling with eg a fan)
  • use thicker wires/leads on the pcb to account for the higher amperage

Would these mods enable me to increase the power output of the controller by for example 3 times (if I choose mosfets that can handle the required amount of amps/ can handle the voltage and potential voltage spikes(Note: I will keep the battery voltage the exact same as before the mod, I am currently using 84volt (20s)))?

Would I need to make any other mods in order for this to work (other than the ones I've mentioned above in the list? For example would there be other components I would need to replace because the original components will likely not be able to handle the increased amps?

Would there theoretically be a limit to how much I can increase the power output using these modifications (for example would it be doable to increase the power output 10 fold if I choose the right components? I know this won't be very practical since I'll need much more cooling and much thicker wires but it's more of a theoretical question) and what would be the issue causing this limit ? (ignoring possible issues like not being able to fit enough mosfets in the controller, the controller becoming too heavy etc.)

*info about the controller/setup: It's a 72v-84v 1000-1200w (three phase) BLDC motor controller (rotor position determined using 3 hall sensors). The motor is an outrunner with permanent magnets in the rotor. Currently has a shunt mod increasing the power to perhaps 1400watt. The battery is 10p20s.

If anything is unclear/incomplete about my explanation please let me know and I'll try to clarify.

Thank you very much!

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I was wondering if I could upgrade my current bldc motor controller (three phase motor) to a higher wattage/output power by doing the following modifications:

Probably - but it depends to some extent on the application and how sophisticated the controller is. I could attempt a point by point response but essentially they are broadly covered below for 3X increase in power, and at 10X VESC is almost certainly an attractive choice.

You mention "a current shunt" suggesting that gross motor current rather than phase currents is being sensed, which in turn suggests that the controller is 'not too magic', which is good in this case.

If the controller is NOT using FOC control and trying to implement deep magic, as modern advanced controllers do, thn more and bigger of the same may well be good enough. If the controller used advanced methods to implement vector control and if the motor + controller were designed to work together then some of the magic may need recasting to make things work as well.

A FOC controller will usually use current sensors in at least 2 phases (the theory being that the third phase can be inferred) and the latest VESC iteration uses sensors in all 3 phases as Benjamin Vetter has concluded that the difference between theory and practice is greater in practice than in theory.

All that said, if you are going from 1+ kW to 3 - 5 kW load you would probably benefit from a FOC based control strategy. If you are willing to change MOSFETS, shunt, heatsinks and more then implementing an open source VESC ESC may do you major favours.

My recent SE EE answer here provides links to various VESC related sources.

There is another open source ESC that was popular a few years before VESC gained popularity. It uses a processor costing about $1 in 1's whereas the VESC MPU is "somewhat more". I'm 'out of country' at present but can look up details in a week or so if of interest.

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  • \$\begingroup\$ Thank you for the interesting info/your answer! I'd definitely be interested in some more details regarding the open source ESC you mention in the last paragraph. Would be great if you could send some info when you have the time. Thank you! \$\endgroup\$ – Maarten -Monica for president Mar 7 '20 at 13:51
  • \$\begingroup\$ @Maarten-Monicaforpresident As noted above, this SE EE answer of mine : electronics.stackexchange.com/a/484438/3288 provides links to older and newer versions of VESC and other related links. \$\endgroup\$ – Russell McMahon Mar 7 '20 at 23:27
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What you haven't mentioned is what you will do with the extra power.

As you plan to increase the current capability, you will increase the available torque. (Assuming, of course, the motor can take the extra heating). This will improve acceleration or hill climbing ability (assuming a road vehicle) but won't by itself allow any higher speed.

If that is useful to you : go ahead.

Keeping the voltage the same is probably a good idea; finding higher voltage MOSFETs would be feasible; ensuring the MOSFET drivers and the rest of the circuitry were up to the task is another matter.

Without increasing voltage, you won't significantly increase speed. Unless you also either change the motor (for one with a higher speed constant Kv) or you change the gearing arrangements (smaller sprocket on a bicycle, larger wheels, coarser pitch propeller, whatever). Those will increase speed at the same voltage ... but require higher current to maintain even the same torque. As a rough guide, if you increase speed by 20%, expect to need 40% more torque and current.

So, make sure the basic physics work for you before improving the wrong parameter.

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  • \$\begingroup\$ Thank you for the info! Could you please elaborate on why it is that if you increase the kV rating of the motor (by rewinding it I assume) to gain a higher speed at the same voltage... you would require more current to maintain the same torque? Thank you! My thinking is that even with different kv motor you would need same wattage to reach a certain speed (with the vehicle) so if you keep the same voltage (battery) and need same power output how come the the amount of amps needs to be higher? Is the controller or perhaps the motor less efficient after increasing kv? Or am I missing something? \$\endgroup\$ – Maarten -Monica for president Mar 7 '20 at 13:53
  • \$\begingroup\$ Because the product of Kv (radians/second/V) and Kt (Nm/A) = 1. (because V * I = Power = Nm * radians/sec). If you run at a higher speed (same V, higher Kv) you need a higher power output (NOT the same power) and that can only come from extra current because you kept the same voltage. \$\endgroup\$ – user_1818839 Mar 7 '20 at 17:38

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