Too long battery/ESC power wires will kill ESC over time

Hi,

I ran across this thread, and thought it would be worth sharing, especially with multicopters. I had been moving my ESC’s farther from the flight controller/ magnetometer to help with noise, to do this I was using longer power wires.

I am not sure how critical this is but like I said I thought it was worth sharing. here is a link to a thread with the info

too long battery wires will kill ESC over time: precautions,
http://www.rcgroups.com/forums/showthread.php?t=952523&highlight=batteri+cabl+too+long+kill+esc+over+time

John

Yes I am always surprised how many folks don’t know that

It is worth noting there is a lot of misinformation in that thread.

In most cases the issue is for people using small battery capacity and long large scale 3D planes with thin wires (as they are trying to save weight). As long as you are using decent gauge wires and extending the power supply side and your power source is of a decent size and C rating (not normally an issue for multirotor guys) then you will not have a problem till you start making your wires longer than 1.5-2m. Considering the size of most multirotors this is never going to be an issue (and I use a 1300mm Octo). The issue is further reduced if you go up in voltage, as most multirotors with long arms (over 500mm long arms, so a wheelbase of 1000mm or greater) are on 6S, it simply is not an issue unless you plan on running 18AWG wire to your ESC’s…

Extending the wires on the motor side is definitely the wrong thing to do despite the arguments that are often made about it as you will reduce motor efficiency as you start adding more resistance to the motor windings and start putting the phases out of balance. A high quality motor not only has identical numbers of turns used with near identical lengths of wire for the windings, they are also balanced in resistance by shortening the motor leads with the higher resistance (this is also why you should not cut your motor leads on high quality motors).

What’s this all boil down too, unless you are building large multirotor (1000mm plus) then you have nothing to worry about, if you are then make sure you go up a gauge in your power feed wires to the ESC’s, don’t change the length of your motor wires and if you are really concerned, replace the capacitors on the ESC with a couple of high quality ones (add a couple in parallel is better than one large one).

Admittedly I don’t trust the thermal compound/tape or the heat-sink on any of the ESC’s I buy, so I always replace these on my large birds as well as replacing the capacitors for larger ones of much higher quality and voltage, this adds significant reliability and longevity to the ESC’s and has nothing to do with the compensating for wire lengths.

While we are here it is also worth noting that placing the ESC’s heat-sink directly in the propwash not only increases its lifespan, it adds a significant increase in both efficiency and max RPM, this can be in the order of 15% for some ESC’s but normally equates to around 5-7% on most decent ESC’s (changing the heat-sink and thermal transfer compound/tape further adds to this in the order of 2-5%).

I should also mention that in the thread there is not one example nor could they show one of a ESC failing due to a capacitor failing from long wires yet it is shown efficiency is lost due to lengthening the motor wires…

You mention replacing the ESC’s capacitor with a higher quality one. What constitutes “higher quality” in electrolytic capacitors? Or would you use something other than electrolytics? And would increasing the capacitance beyond what was provided by the stock capacitor be of any benefit?

Thanks, I had been wondering about this, if it really was a problem. thanks again for the answer.

[quote=“Redemptioner”]It is worth noting there is a lot of misinformation in that thread.

In most cases the issue is for people using small battery capacity and long large scale 3D planes with thin wires (as they are trying to save weight). As long as you are using decent gauge wires and extending the power supply side and your power source is of a decent size and C rating (not normally an issue for multirotor guys) then you will not have a problem till you start making your wires longer than 1.5-2m. Considering the size of most multirotors this is never going to be an issue (and I use a 1300mm Octo). The issue is further reduced if you go up in voltage, as most multirotors with long arms (over 500mm long arms, so a wheelbase of 1000mm or greater) are on 6S, it simply is not an issue unless you plan on running 18AWG wire to your ESC’s…

Extending the wires on the motor side is definitely the wrong thing to do despite the arguments that are often made about it as you will reduce motor efficiency as you start adding more resistance to the motor windings and start putting the phases out of balance. A high quality motor not only has identical numbers of turns used with near identical lengths of wire for the windings, they are also balanced in resistance by shortening the motor leads with the higher resistance (this is also why you should not cut your motor leads on high quality motors).

What’s this all boil down too, unless you are building large multirotor (1000mm plus) then you have nothing to worry about, if you are then make sure you go up a gauge in your power feed wires to the ESC’s, don’t change the length of your motor wires and if you are really concerned, replace the capacitors on the ESC with a couple of high quality ones (add a couple in parallel is better than one large one).

Admittedly I don’t trust the thermal compound/tape or the heat-sink on any of the ESC’s I buy, so I always replace these on my large birds as well as replacing the capacitors for larger ones of much higher quality and voltage, this adds significant reliability and longevity to the ESC’s and has nothing to do with the compensating for wire lengths.

While we are here it is also worth noting that placing the ESC’s heat-sink directly in the propwash not only increases its lifespan, it adds a significant increase in both efficiency and max RPM, this can be in the order of 15% for some ESC’s but normally equates to around 5-7% on most decent ESC’s (changing the heat-sink and thermal transfer compound/tape further adds to this in the order of 2-5%).[/quote]

I think you could go with electrolytic caps of a higher temperature and lower ESR rating or even better, (I think, I am not 100% sure) you could replace them with low ESR tantalum capacitor’s. I am not 100% sure about the tantalum caps but I have seen them used on one set of ESC’s I have.