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Maximum cable lengths between VESC, battery pack and motor?

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sandersesurf
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Maximum cable lengths between VESC, battery pack and motor?

Currently building an electric surfboard, Im using a 100/250 VESC, 65161 Flipsky waterproof motor, 18S battery pack (75.6Vdc peak) . Currently redesigning my cooling system and want to use a passive heat sink located at the rear bottom of the board near the motor. The battery pack is in a waterproof case located at the top front of the board for weight balance reasons, this would result in the cables between the ESC and battery pack being about 1.5 meters apart.

I've read various conflicting statements regarding max cable lengths and battery/ESC/motor placements. Larger size cable is an easy issue to mitigate power losses, i'm curious if a 1.5m space between battery pack and ESC would be too large of a distance for the ESC to handle? Potential issues being voltage spikes in the phase wires rising higher than the capacitors can handle?

Any clarity would be appreciated!

electricfox
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It's better to have longer phasewires than longer batterywires. It's good that you are only using 18S and not max 22S. You can/should add same type of capacitors in same amount or better double amount of the VESC 100250 has, as close as possible to the VESC. 

vadicus
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Power or heat losses via battery wires wouldn't be your primary concern, not at 1.5m anyway, provided you sized them up right for the amount of current you are planning to run and the ambient temperature expected. 8AWG silicon wire or similar would be more than sufficient for 100-150A in most cases. The issue with longer battery wires is the parasitic inductance added on the DC link that increases the chances of voltage spikes that kill mosfets the closer you run it to the mosfet voltage rating. The DC link capacitors are there to smooth out the DC power during switching. One simple thing you can do is twist the battery wire together - this actually helps to reduce the parasitic inductance. As Electricfox mentioned, running at least 10-15% below the mosfet voltage also helps to ensure reliability of the system. It's also a good practice to twist/bundle the phase wires together if they are long to reduce the amount of noise they produce and keep analog and digital signals away from high power sources such as battery and phases wires. 

 

 

NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)

bww129
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One (relatively) easy way to reduce wiring inductance is to use multiple closely spaced conductor pairs for power/ground. For example, a star quad cable has 4 conductors tightly spaced. Put power/ground on opposing wires for reduced inductance. You can extrapolate this to a higher number of conductor pairs but it all depends on your use case.