Distance between ESC and motor


Hello everyone here !

First of all, thank you Pacificmeister for all your work and what you share, it really helps !

I read that long wires between controller and motor could increase ESC temperature and affect ESC lifetime.

Does anyone notice this phenomenon ?
Is there a way to mesure it ?
Should we add capacitors ?

Bonne journée,

(Please apologise my english it’s a french one !)


The distance from battery to esc should be as short as possible to avoid voltage spikes.
The longer distance you have the more capacitor you will need.
The distance from esc to motor can be long, no problem. /Jan


The longer the distance the more power you will lose and heat you could potentially gain with electronics. You must oversize the wiring from what you think is required as longer wires dramatically reduces the current your can put through it. If you have 6-8’ wire from motor to ESC you should be using 8awg for sure to eliminate this issue.
the link you show, the first comment there answers the common issue “captain MoMo”.

Poor soldering, and most users to way to small of connectors like 4mm or 5mm. Really, you should have 5.5 - 6.5mm connectors that are rated for 100A++. We are using 8awg 100% copper, with high end 6mm bullet connectors rated for 200A. This costs an extra $15 for all the connectors, but they are made for 8awg wire and then you know the wiring will not be an issue.

Check this calculator for wire length, current and volts it will tell you what you need as minimum: http://www.solar-wind.co.uk/cable-sizing-DC-cables.html


You are right for 2 reasons (at least) :

  • Long wires from battery to motor generate voltage spikes
  • Long wires from ESC to motor “it smoothes the current, thus reducing noise/interference.”

I read again the first page of this discussion RCGroups.com : too long battery wires can kill ESC over time, i simply misunderstood it.

Here is a copy of the text :

Solution I
Keep battery wires short, lengthen the ESC-motor wires.
That’s hardly critical because there’s already a lot of wire in the coils in the motor itself. If the motor-ESC wire eventually gets too long, it will not harm motor and/or controller. May cause interference though, give the motor-ESC wires a twist. Always a good idea to do that anyway.
And on the motorside wire-inductance is a good thing, together with PWM frequency and flyback diodes it smoothes the current, thus reducing noise/interference.

Motorside: voltage chopping and smoothing of current

Some ESC manufacturers advise against lengthening the wires motorside. But that’s only because motor wires have a tough insulating varnish/resin coating that has to be removed before soldering. Use the aspirin trick mentioned in opening post:
(Re)winding and building motors (sticky)

Noise from the motorwires is hardly an issue, here induction is good, in combination with PWM frequency it smoothes the current.

But what if you can not extend the motor wires?

Solution II & rules of thumb, calculation spreadsheet
If you have to lengthen the battery wires, for whatever reason, add extra electrolytic capacitors in parallel with ESC, never in series with ESC. As a rule of thumb, for every 4inch/10cm extra length/distance between battery and ESC, add an 220uF extra capacitance near the controller (electrolytic condensators, voltage the same as the capacitors already installed, low ESR type) (Ludwich Retzbach, German e-flight author&editor, the ‘R’ in LRK).
Better to use several smaller caps (in parallel) instead of one biggie. Smaller caps can shed more heat and total inductance will be lower (inductance per cap is lower and those inductances are paralled to boot ). See attached pictures below.
Also keep the positive and negative wires as close to each other as possible by taping them together (twisting the wires will give extra length!). When the wires are close to each other then the series inductance will be reduced, because the current is going in opposite directions in each wire (and therefore producing opposite polarity magnetic fields which cancel out). For example, 13AWG wires separated from each other by 1 inch have about 4 times higher inductance than if they are bound together. (Bruce Abbott in www.rcgroups.com/forums/showthread.php?p=11594609#post11594609)
Remove insulation of one of the wires???

Extra capacity based on current and wire length, calculation spreadsheet

Influence of ESC max.current rating on choice of capacitance


Capacitor type
The main spec you need is low impedance and low ESR (Equivalent Series Resistance). I think the only thing you will find at radio shack will be general purpose caps, not low ESR. The ESR value of a cap is not printed on it, you will have to look up the manufacturers spec sheet. The Rubicon ZL series mentioned in the Schulze instructions is a good one and is available from newark/farnell. The Panasonic FM series is another good low impedance cap and is available from digikey

You would want the voltage rating on the caps to be significantly higher than the battery voltage. Same voltage rating as the manufacturer installed caps. Higher voltage rating is no problem. (thanks jeffs555).
If you try it with longer wires and no extra low esr caps it may work for a while, but the longer wires put an extra load on the original cap. The extra load shortens the life of the original cap and it will eventually fail, probably catastrophically. (thanks jeffs555, from www.rcgroups.com/forums/showthread.php?p=11996840#post11996840.

Capacitor polarity/orientation!
Electrolytic capacitors, like batteries, have a (+) and (-) lead! Solder them in the wrong way and they will got hot, pop open or even explode. Nasty fumes and stains from the liquid. Don’t ask how I know

How & where (not) to add extra capacitors (English and German)
www.matthias-schulze-elektronik.de/guide/gfutc-de.pdf (English)
YGE controllers, extra capacitors and their location, nice pics, click to enlarge:

All capacitors as close as possible to ESC board, direct across plus and minus terminals.
Not distributed along the battery wires!.
Capacitors near/on battery are useless, the battery itself already is a huge capacitor.
By distributing them along the wires between battery and ESC they will be less efficient, or useless. All the afforementioned does is add extra weight, and extra points of failure.

Battery to ESC, cable length issue