The Infamous Back EMF Problem with Basic ESC R3

Hi All,

I’m facing a problem with my custom-built ROV. I’m powering the ROV from the surface using this power supply.

Every time I stop the thrusters somehow quickly not gradually, the OV protection kicks in and reboot the power supply due to regenerative breaking built-in the ESC, and the raspberry pi reboots subsequently.

I read so many topics about this issue with no apparent fix. The only fix was reported by another forum member using some diodes (Flyback Diodes I guess) but he/she didn’t share how it was connected.

Did anyone else get this to work? The issue is bugging me in my dreams.

Hi @mamdouh,

I’m curious what kind of tether you’re using for this. Low voltage DC is quite poorly suited to providing power at a distance, so I’m interested in how much voltage drop you’re experiencing.

Out of interest, is this occurring in the water? Previously we’ve found that

I don’t expect flyback diodes would work well for a brushless DC motor without being integrated into the controller, although it’s been a while since I last worked with diode designs, and I’m not super familiar with how the ESC’s regenerative braking operates, so I may be mistaken.

Some other diode options I can think of would be using one or more Zener or TVS diodes to avoid the over-voltage, but it may be difficult to get a suitable power rating. Alternatively it may be possible to use an “ideal diode” in series with the power wire to each ESC, but adding a barrier against reverse current doesn’t provide anywhere for the power to dissipate, so could potentially cause some extra ESC heating or something (I’m not certain what would occur).

Some previous recommendations:

Hi @EliotBR

I’m using 8-AWG OFC cable from this company The total length of my tether is 12 meters or around 40 ft. I used Blue Robotics’s voltage drop calculator before buying it with roughly a 1-volt drop. BTW It is thicker than the standard 8 AWG.
I had the old R1 Afro ESCs with the same setup and didn’t face such a problem.

Out of interest, is this occurring in the water?

Yes, but it’s more pronounced on air due to more violent breaking.

If any possible extremely short and small voltage spikes are a concern for your particularly sensitive equipment, I recommend using either a different ESC or adding a power filter.

Can you guide me to a recommended power filter? Changing the ESCs at this point is quite difficult.

Friend of mine suggested to use this diode in series with the output of the power supply. Would it help?

I’m not sure what’s available commercially, so I don’t have particular recommendations. Perhaps try searching for “low-pass RC filter”. It’s possible you may need to design one yourself, but there are many resources available, and it’s a very simple circuit (just a resistor and capacitor).

As above,

I’m unsure what the losses would be with the diode you’ve linked to, and I’m unsure whether it could cause issues with the ESC, but if power losses are low and the ESC is capable of handling the voltage spikes without getting overheated or damaged then it would indeed help.

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Wait, I’m wondering if the thrusters have such a large counter-EMF on the instantaneous dynamics. My suggestion is to increase the capacitance. We are using a VICOR module with 25V 6800uf capacitors.

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An RC filter is a series resistor and a parallel (decoupling) capacitor, so “increase the capacitance” would be half of that, just with less ability to tune the frequency response (which may still be acceptable for this use-case). Decoupling capacitors effectively act as fast-response small batteries, which can indeed help to reduce voltage spikes :slight_smile:

Before settling on a particular solution it would be worth investigating the magnitude of the voltage spikes. A very rapid deceleration could potentially have a brief but somewhat large voltage spike, so even if sufficient capacitance was added to absorb the excess energy the components could still fail if the spike goes above their voltage rating.

Hi @MMMMK,
Can you share the VICOR Module part number and the circuit connection diagrams?. This problem is driving us crazy.

@EliotBR I don’t have previous experience with low-pass RC filters, Can you share a ready made module or guide to building one.

Also, I’d like to thank you all for your help. I really appreciate it.

As above:

These lecture slides were the first result when I searched for “RC filter”.

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