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Capacitors or diodes on RC speed controllers (ESC)?

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compet17:
I do have a nice RC model of a Super Constellation (40 years old now) and I want to convert that from gasoline engines to electric... So I need to have long power lines from the batteries to the motors.
Long power lines on the motor side of the ESC are not a problem but putting 4 ESCs into the fuselage close to the batteries could cause heat problems.
On the other side, placing the ESC close to the motor where cooling is easy, requires long battery cables.

Speed controllers (ESC's) for RC models always have pretty large capacitors connected to the battery input side. These capacitors are primarily used to suppress voltage transients generated by the fast swichting of the MOSFETs. These transients are especially bad on the battery input side because they can be high enough to destroy the FETs.
Transients also exist on the motor side but the circuits are designed to handle that.

The question is this: When I use longer battery cables, I will get more powerful noise and I will have to add more capacitors to handle that. This is a common practise among RC builders.
My idea is to use suppressor diodes instead or additional to the capacitors. They are lighter and smaller and cheaper.

Is there something that speaks against those diodes?

Siwastaja:
Definitely place the controllers near motors, run battery DC wires. Not only you have one power wire less, these wires carry DC so less EMI (given that the controller has proper capacitors), and also run at higher voltage and lower current than the motors. (At speeds less than full, motor wires carry lower voltage and higher current).

Battery itself has quite some inductance in it already, making the wires longer should not cause a big difference unless the design is already marginal. I understand the cheap ESCs save costs in capacitance; then add the missing capacitance to fix them. There's really no way around it as far as I know. Hopefully the ESCs already use enough low-inductance DC link capacitors (such as ceramic caps) so that only thing left is to add a larger electrolytic for damping. Maybe post an image of the ESC PCB so we can make some guesses?

I do not know of any way to solve the problem with diodes. Where would you connect the diodes and why and how do you think it would help?

exe:
Can you please provide a schematic and photos for your setup?

Niklas:
It depends on the current. I have not been active with RC flying for little over 10 years, but there were limitations on wire length, both on the motor and battery sides, on the brushless speed controllers back then. The LiPos were on the way in, but for the high currents needed for the F5b and F5f gliders we still used pushed and matched NiMh cells. The electrolytic capacitors are not fast enough, so an additional varistor at the controller's battery input could be an option. The current in the battery wires is far from DC and make sure to tie the wires together to minimize inductance and radiated emissions.

compet17:
My idea was to add so called "suppressor diodes" on the battery side of the ESC between the + and - wires to clamp down any voltage spikes higher than the allowed voltage range.
That's what all the input capacitors do.... reducing the overvoltage created by the fast switching of the MOSFETs. The suppressor diodes act like z-diodes but they are much faster and can handle more powerful spikes. I would add two diodes in parallel with opposite polarities. In fact the reverse diode could be a normal diode, clamping reverse spikes at 0.7V already.

Mounting the ESC close to the motor saves a lot of wire, thats a benefit. But all RC forums warn of long battery cables because of the said inductance effects. But you are certainly right when you say that a good ESC should be immune to that by design. The problem is.... what is a good ESC and what not? :-//

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