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Length of power wires from Lipo to ESC - questions.


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I have a big old vintage plane which I have converted to Lipo power - two problems

1) the only way to swap batteries is to take off the wing, however the major mod’s required to make a battery hatch are too much of a fag so I’ll live with that.

2) once the battery is installed, even before the wing is banded on the motor is “live”.

   As I have before, I intend to put a break in one of the wires between the Lipo and the ESC -  the circuit being completed either with a shorted XT60, or 2 x 4mm female plugs sticking out of the side of the fuselage - the circuit being completed by 2 male 4mms wired together. 
Now - my concern/worry. Previously I have ended up with both power wires to the ESC near enough the same length ( to a mm or 2 anyway ). Due to problems with the installation there will be a significant difference in the lengths of the +ve and -ve wires between the Lipo and the ESC. WILL THIS CAUSE ANY PROBLEMS ? ? ?

Many thanks in advance. 

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The total length of LiPo to ESC wires can be an issue. Long wires can create surge voltage spikes which will overwork the input capacitors on the ESC causing them to fail which will then wreck the ESC itself.

The set up will work with long wires but the longer they are the sooner the ESC will fail.

 

The best advice it to keep the length no longer than the combined length of the wires already attached to the LIPo and ESC but there is quite a bit of tolerance. If the wires are really long, say over 500 mm then it is possible to add appropriate extra capacitors but they have to have the same voltage spec as those in the ESC.

 

The wires from the ESC to motor can be as long as you like. The only limits being weight and voltage drop. 

Edited by Simon Chaddock
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I echo the above. I put high value capacitors of the correct low Z type on the ESCs in my Mossie since the wires were extended. On the second flight attempt an ESC half died on take off and the model was badly damaged. I have now only extended the ESC to motor wiring which is OK to do. The ESCs are now in the fus and get little cooling but that is less of a problem.

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19 hours ago, Martin McIntosh said:

I echo the above. I put high value capacitors of the correct low Z type on the ESCs in my Mossie since the wires were extended. On the second flight attempt an ESC half died on take off and the model was badly damaged. I have now only extended the ESC to motor wiring which is OK to do. The ESCs are now in the fus and get little cooling but that is less of a problem.

Could you elaborate of the make and model of the ESC's please (it appears not all ESC's suffer this issue)? 

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Does the same thing apply to the cables from the esc to the motor.  To aid balance I had to move the esc.  Originally the battery was on top of the esc but as the fuselage is thin it was a push fit and removing the battery was difficult.  I have moved the esc to be behind the battery and this way the esc is not covered and the battery comes out ok.  I have used standard length 20 cm leads but could trim them a little if necessary.  The cable from battery to esc is short and the standard size.

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It can depend on the quality of the components used and the duty it is under but all ESCs can suffer from this electrical spike effect. It comes down to how often and how strong the spikes are.  A 30A 4s ESC but running at 15A on 2s is likely to be able to handle longer battery wires and for longer than if it is used at its maximum rated amps and voltage.

Some quad ESCs do not have any smoothing capacitors but the layout of a quad means the battery to ESC wires will be really short.

 

Julian

It s only the input to the ESC that is voltage delicate. The output electronics are robust and the motor is completely unaffected by any likely voltage spike.

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Just as an aside, if the ESC to motor wires are to be lengthened, as in the case of a two or four motor set up, it is a good idea to make them up from heavier duty cable to reduce losses, which at that low voltage can be considerable. (power loss = I squared R), hence mains is transmitted at a very high voltage to reduce the current.

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