Battery Cable Size, Power Loss

[LewTwo]

This may fall under "everyone already knew that" and if so then some one tell me and I will delete this thread.
I am moving the battery from the front of my bike to the back. I already have 7 feet of 14 gauge copper, silicon ruber insulated battery cable on hand but my question was "is this sufficiently large or should I order some 10 gauge cable"? So I began trolling the internet looking for answers and found this page:
https://www.altestore.com/howto/wire-sizing-tool-for-12-24-and-48-volt-dc-systems-a106/
It seemed to have the information I was looking for but I wanted to know what the difference between cable sizes was and more importantly how much switching cable size would affect the real world outcome ... or at least a guestimate. So I put together a spreadsheet to compare cable size with specific battery parameters. Lastly it calculates the difference in speed due to cable loss (if I got all the formulas correct).

One can change the input parameters (yellow cells) for a given battery and controler to determine the voltage loss across a specific distance. Add the nominal rated speed for those power parameters gives the real world speed loss as well. In this case I am looking at moving the battery about 4 cable feet (max) for my 15 Amp Controller and 36 Volt 350 watt motor. That is going to cost me 0.334 MPH. Using a 12 gauge cable would only recover 0.124 MPH or 7.5 watts. I think that I will use the 14 gauge cable I have on hand.

Comments, corrections and criticisms welcomed.View attachment Power Cable Loss.xls

 

[motomech]

I don't know if that chart is applicable for silicone cabling. You are not using copper are you?
At any rate, 14 gauge is fine for that low-power system.
On the only hand, the Turnigy silicone stuff is really inexpensive at HK, the 12 guage for your bike would be less than $10.
But if you don't need anything else, I wouldn't sweat it.
10AWG is huge and clumsey to work with.

 

[LewTwo]

I don't know if that chart is applicable for silicone cabling. You are not using copper are you?

Point taken and corrected. Yes, if I did not have it on hand then I would probably gone for 12 Ga.

 

[docw009]

I've always done it this way. Correct me if I'm wrong.

14G copper wire, per powerstream.com is .002525 ohm per foot. So four feet is a resistance of .0101 ohm. Current x resistance is voltage drop, so 15A x .01 ohm is .15 volts. You will drop that voltage in both power and ground feeds, so you lose twice that or .30 volts. Watts lost in heating of the wires is 4.5 watts. calculated by (square of current) x (resistance) or 225A x.020 ohm.

12G is .001585 ohm per foot and a 4 foot one way run loses .19 volts with 15A

10G is .000990 ohm per foot and a 4 foot one way run loses .12 volt with 15A

 

[Toorbough ULL-Zeveigh]

Correct me if I'm wrong.

:wink:

hint:
the bigger the gauge the less the voltage drop.
not more.

14G copper wire, per powerstream.com is .002525 ohm per foot. So four feet is a resistance of .0101 ohm. Current x resistance is voltage drop, so 15A x .01 ohm is .15 volts. You will drop that voltage in both power and ground feeds, so you lose twice that or .30 volts. Watts lost in heating of the wires is 4.5 watts. calculated by (square of current) x (resistance) or 225A x.020 ohm.

12G is .001585 ohm per foot and a 4 foot one way run loses .19 volts with 15A

10G is .000990 ohm per foot and a 4 foot one way run loses .12 volt with 15A

 

[liveforphysics]

I don't know if that chart is applicable for silicone cabling. You are not using copper are you?
At any rate, 14 gauge is fine for that low-power system.
On the only hand, the Turnigy silicone stuff is really inexpensive at HK, the 12 guage for your bike would be less than $10.
But if you don't need anything else, I wouldn't sweat it.
10AWG is huge and clumsey to work with.

Silicone insulation wires crack propagate right down to the base conductors from almost any surface defects/scratches. It's notch-sensative just like glass, so sleeve it in something of you're going to use it.

 

[LewTwo]

Silicone insulation wires crack propagate right down to the base conductors from almost any surface defects/scratches. It's notch-sensative just like glass, so sleeve it in something of you're going to use it.

Did that already ... TechFlex 1/8 Inch PET Expandable Braided Sleeving https://www.amazon.com/gp/B00H2R9YWY
A tad tight but it makes for a neat cable.
Though I have to say the insulation is so soft and pliable that I can not imagine it cracking.
https://www.amazon.com/gp/B00CUKRN8A

 

[vk4bxi]

Nice work in progress. But remember as you reduce circuit resistance you also increase fault current. You may have to relook at fusing/ circuit breaker ratings. Most breakers run out of "steam" above 5kA

Bob

 

[amberwolf]

Though I have to say the insulation is so soft and pliable that I can not imagine it cracking.

Pressure from a thinner wire along a thicker one can cause a split, or even something squeezing a single wire.

Somewhere around here I have the remains of a controller, sent to me to use for parts, because when it was shipped to the original owner the silicone-insulated phase and battery cables were wrapped around it and then it was packed in a box with some other items (themselves in their own cardboard "wrappings", so no direct item-to-item pressure but still pressing the cables against the controller's surface and fins).

The battery cables were paired together inside a (non-shrunk) heatshrink sleeve, as were the phase wires in their own sleeve, preventing the original owner from seeing the pinched-insulation damage, where it had torn a sort of diamond-ish shaped flap in two of the phase wires, right next to each other (looked as if they were squeezed against each other, but there were no marks on the insulation itself other than the tears, and just cable marks on the inside of the outer sleeving, and no marks on the outside of the outer sleeving).

Since they didnt' see that, when they hooked it up to power and motor and tried a test ride, it almost immediately blew FETs in the two phases.


Before that, I thought the silicone stuff would be a great idea in stuff that might get hot...but decided against it after that. For myself I mostly (re)use whatever wire I have lying around anyway, often from old power cords and extension cables.

 

[LewTwo]

Nice work in progress. But remember as you reduce circuit resistance you also increase fault current. You may have to relook at fusing/ circuit breaker ratings. Most breakers run out of "steam" above 5kA

At the moment the battery has about 6 inches (15 cm) of cable. So I am actually lengthening it. ... and I don't think this kit has any fuses or circuit breaker unless there is something hidden under the shrink wrap.