longer battery wires or longer motor wires

zblad

1 mW
Joined
Apr 18, 2016
Messages
15
I thought i read somewhere that long battery wires cause issues with the vesc. So i am wondering if a person is better off having long motor wires or long battery wires. I want my batteries mounted in the center of the board along with the vesc but that means my motor wires will have to be about a foot long, will that cause issues?
 
Either one can be as long as you want you just need to make sure they're the appropriate gauge (thickness).

Go with 10 gauge unless you're running an unusually large amount of power.
 
@flat tire, are you certain about this?

I think I also read here that you should if needed to choose, make phase wires from controller/esc longer then from battery to controller/esc. But I can't seem to remember the reasoning for that. Nor did my search come up with anything meaningful.

Could it be that phase wires are at the most 2 out of 3 powered up, and constantly chaninging? While battery current is constant?
 
Phase wires the shorter (lenght) as possible.

Batt wire the bigger( diameter) as possible.

Also the less loop in wires as you can.. you wnat to reduce the inductance the more you can!

Inductance make fet to heat and short...

Good caps with low ESR on the batt setion input the closer as possible to the cotroller help too.

i remember that Luke or maybe someone else here said if it woudl be possible to put the controller right next to the motor it would be best...

But all that have more importantce if you run a low inductance (high kv) motor...

Controller blow more when driving low inductance motor ( high kv).. and i can stand on that too as my experience are also the same way

Doc
 
spinningmagnets said:
Battery to controller should be short and fat. The motor phase wires can be much longer...

Do you know the reasoning for that? I've had this in the back of my mind for couple of days but are still not able to remember why that is.
 
WTF. Is drbass's post invisible to everyone except me? He mentions inductance as a reason to keep phase wires as short as possible and is the only one to back up his claims.

For my part, I just assumed current-carrying capacity / resistance was the only important aspect to the cables, but of course there's more.
 
As an example without any understanding of why, I recall a guy who built a toy dirigible (filled with helium) that could fit in a pickup truck bed (6 feet long?), with the battery that he held in his hand. It had a motor driving a propeller on it, and a steering control, so he could "fly" it into the wind, or any direction he wanted. I believe it would "fly" about twenty feet above him.

When he had two wires from the battery up to the tiny controller in the dirigible, and three very short wires from the controller to the motor...he had lots of problems.

His forum said to make the battery to controllers wires short, basically right next to each other....and then run three wires that are twenty feet long up to the motor. Worked fine after that.

When the long run of wires were only two of them, it was cheaper, and that's why he tried that first. Apparently inductance isn't an issue on the three motor phase wires, and they can be very long.
 
I read years ago that battery wires should be short. And I've tried to stick to that in my builds, but within reason.
Quality capacitors on the battery wires deal with the majority of issues caused by the inductance.

Shortening the battery wire by 2cm on a skate board probably won't have any appreciable benefit.
 
Long motor wires only cause harm in the form of copper losses, since increased inductance from the motor wires makes the load the controller "sees" easier on the controller. Not only is it good to make the battery leads short, but the routing of the wires should be done in a way to minimize the size of the loop enclosed within the pathway of the electrical flow (including the batteries themselves. That's because a larger loop increases inductance, as does the wire itself. Inductance slows the electrical pulses, and the capacitors have to work harder to provide the even flow of electricity to the controller.

Minimal length and least resistance of all wiring is the ideal to minimize wasted battery energy in the form of heat in the wires. If you have to choose, then longer phase wires to keep the battery leads shorter is better. When deciding on the wire gauge keep in mind that the alternating current going to a BLDC motor has higher peaks than the battery leads due to the inherent shape of the waveform. Since heat losses go up by the square of current, you'll find that with phase and battery wires of the same gauge, the phase wires will get hotter (meaning more losses)...that is if they are both shielded from the cooling effects of air flow, because 3 wires of the same gauge shed heat faster than 2. The Chinese use bigger gauge on the battery leads than phase wires, but I suspect that's more for fire prevention than efficiency, since a short in the battery leads is dangerous while the spindly phase wires they often use only risk a breakdown.

I learned this lesson from an early ebike build where I used doubled up 12ga for both the battery and phase wires, and while the phase wires had somewhat better cooling, they were always hotter than my battery leads. Now I use oversized wire for everything, since I value performance over a bit of extra weight from wiring in order to minimize voltage drop.
 
John,

I couldn't explain better than you. :wink:

Sometime, French to english translation are not my best in technical stuff.

Doc
 
that woud be great to have Biff explanations too.

He designed the new 2013+ Hugh performance Zero motor.

Doc
 
just wanted to say thanks to everyone for posting. I received my VESC and yesterday and didnt realize they use 10awg wire for the battery and phase wires. I plan on running 8s do you think 10awg is overkill? I am fine with using 10awg wire but the motor i am using is a sk3 213kv motor and the wires on it dont seem very thick at all when compared to the 10awg.
 
Here's the way to view the battery / controller / motor cable length tradeoff:

1) Keep battery wires as short as feasible, and keep them paired to reduce inductance.

2) Extend motor wires if necessary, keeping them together as well.

3) Always use appropriate wire gauges for the currents involved, and keep lengths to a minimum to reduce losses.

Adding wire length (inductance) in battery to controller wiring is very bad for the controller. It causes increased ripple in the capacitor bank currents and increased spikes in the FET voltages during switching, which causes capacitor and FET heating and reduces the FET voltage margins. FET voltage spikes can cause reduced device life or even rapid failure. Capacitors are not tolerant of heating and are easily damaged.

Adding inductance in the motor wiring is not a problem. The motor is already an inductor, and slightly increasing the inductance of the motor actually makes the waveforms easier for the controller to manage. Low inductance motors are a problem that is often solved by adding inductance.

There may be special cases that are different, such as unfortunate resonance conditions or extremely excessive cable lengths. A controller may be designed for long battery cables by having an extra large capacitor bank and using high ripple current capacitors, but this adds cost and bulk to the controller.
 
zblad said:
just wanted to say thanks to everyone for posting. I received my VESC and yesterday and didnt realize they use 10awg wire for the battery and phase wires. I plan on running 8s do you think 10awg is overkill? I am fine with using 10awg wire but the motor i am using is a sk3 213kv motor and the wires on it dont seem very thick at all when compared to the 10awg.


From my experience 10AWG can take 100A easy [youtube]0DhzWPoSYoQ[/youtube]

Doc
 
Alan B said:
Here's the way to view the battery / controller / motor cable length tradeoff:

1) Keep battery wires as short as feasible, and keep them paired to reduce inductance.

2) Extend motor wires if necessary, keeping them together as well.

3) Always use appropriate wire gauges for the currents involved, and keep lengths to a minimum to reduce losses.

Adding wire length (inductance) in battery to controller wiring is very bad for the controller. It causes increased ripple in the capacitor bank currents and increased spikes in the FET voltages during switching, which causes capacitor and FET heating and reduces the FET voltage margins. FET voltage spikes can cause reduced device life or even rapid failure. Capacitors are not tolerant of heating and are easily damaged.

Adding inductance in the motor wiring is not a problem. The motor is already an inductor, and slightly increasing the inductance of the motor actually makes the waveforms easier for the controller to manage. Low inductance motors are a problem that is often solved by adding inductance.

There may be special cases that are different, such as unfortunate resonance conditions or extremely excessive cable lengths. A controller may be designed for long battery cables by having an extra large capacitor bank and using high ripple current capacitors, but this adds cost and bulk to the controller.
Thanks Alan. Really interesting thread and post!
 
Back
Top