Motor Wire Gauge VS Power

I have an electric bike and I noticed that the motor has noticeably thinner wires than the controller. I heard somewhere that heavier gauge wire can help you get more power out of the motor. I am wondering if this is true.

All wire has some amount of resistance; the thicker the wire, the less resistance. Resistance is per length of wire, usually expressed as ohms per 1000 feet or something like that. Passing current across a resistance causes a voltage drop, which is lost as heat.

Making a wire longer increases ​its resistance just like making it skinnier. But the long thick wire would have less tendency to heat up, because the same power loss is spread out over more mass and area.

Consider that the traces on the circuit board inside your controller, and the tiny legs of the power transistors in it, carry the same current as your battery and motor wires. It works because those conductive paths are short. If your motor's phase leads are longer than necessary, you can shorten them and accomplish the same thing as if you'd fattened them up.

Consider also that the leads going into the axle of your hub motor are very likely not the most significant bottleneck in terms of either voltage drop or heat accumulation. If you drive your motor harder with more volts and amps until it fails, it probably won't be the phase leads that fail first. So reducing resistance in the phase leads would likely only increase the load on the part that is at the greatest risk of failure.

I wouldn't worry about it too much it's a pain to run new wire into the motors for too little benefit.

Anyway if you're getting the idea that your system isn't powerful enough you need a more powerful motor, controller, and battery. That will solve the problem.

Even if you don't run it all the way thru the hub axle, running larger wires from the controller to the motor helps a lot. There's still higher resistance in the short section left, but much less, and the copper mass of the bigger wires right next to it helps wick that away. I melted my connectors together being a little undersized and too tightly bundled together, and it happened slowly enough (like over a year) that I didn't notice it until one heavy load uphill climb finally finished it. Since upsizing the phase wires to the axle, doing uglier but better airflow loose bundling, and direct crimps with no plugs everything runs cool even on hour long WOT sessions. It won't be that you will notice a giant jump in power, but you increase how long you can hold full power.

Like this.... my local uphill heat buildup test ride route

[youtube]FQAOSU6-LgY[/youtube]

some people should learn more about electrical wiring before they give bad advice. good luck.

I'm guessing you mean me, tho it's hard to tell with the weird passive "some people" thing, but there is nothing bad about that advice. It would be best of course to replace the wire all the way thru the axle, but if you can't, limiting the heat build up by running larger wire as far as you can is miles better than skinny wire the whole way. It's not like its going to suddenly allow so much extra current thru that the remaining thin section is going to go poof, and the extra copper mass does help draw away the heat from that area.
EDIT ... I would love to hear what you see as a negative there... it's not some miracle way to more power, but it stops one of the top failures of ebikes that came into our shop, which was the phase wires melting together from extended hill climbing, usually near the crappy bullet connectors where it switched from the larger controller wires to the smaller phase wires inside the smashed together rats nest of wires in the compartment where they stuff controllers on most turnkey bikes.

If the motor wires are getting hot there may be some benefit to using a heavier gauge. The primary improvement will be a reduction in wire heating. The power involved to heat the wires is a small fraction of that provided to the motor, so performance changes in the motor will generally not be noticeable. But it is important to avoid overheating the wiring.

Note that if the motor is getting hot you have a bigger problem and you may need to limit power to the motor. Increasing the wire size could make motor heating worse and lead to additional heat in the motor.

Edited mine as you were posting that and agreed, if the resistance of ones hot phase wires are all that's keeping a hot motor from cooking.. you have bigger system problems.

The wire is teflon and ok with getting hot plus it cools rapidly. The hack of heavier gauge wire down to the hub itself is cool but really if you find that NECESSARY you need a more powerful or lower geared setup.

Thanks for all the advice. I was just curious about the wires. I am already building a new bike because I want more a more powerful motor. 48v 1000w Direct Drive. I will also be replacing my current bikes 36v 500w motor with a 36v 500w geared bafang motor

Def building a second more powerful one is the best plan!

And it's a moot point now, but I can't agree with your last point Flat Tire. It won't always be the case of course, but on mine, it became necessary when they melted down. It wasn't an optional upgrade, but I didn't need a bigger controller or a higher wattage motor, or different gearing, but just to get rid of the phase wire bottleneck.
It was the same on many ebikes that I had to repair, where the controller/motor combo was fine, but the bad bullets and small wire couldn't take it. On the ones that did it, they uniformly failed within a foot of the controller, usually where they are crammed together exiting the controller location, and never at the hub end.
So my personal experience is that there are many fine working controller/motor combos out there hobbled by small phase wires that an easy low dollar fix will take care of.

Thicker wires have less resistance, so they can transfer more power without heating up. Heat = wasted energy. In theory thicker wires would give you more power, because less heat was created so you have more power to make the wheel accelerate. But soldering and connecting points increase resistance, if you can't manage to replace the entire phase wire, the point where you soldered the thick and thin wires together will make lots of resistance, because lead and tin in the soldering wire is a worse conductor than copper. I just finished replacing my phase wires, the stock wasn't that thin, and I soldered 10 awg cables to the stock phase wires, but even the 10 awg cables were warm, so you could imagine how hot those stock phase wires was. I had to increase the hole from 10,5 mm to 13 mm, but I was able to pull 7 AWG (!!!) wires through the axle. I hope that it makes difference in power end efficiency. I had to remove the sillicone from the wires and I applied heat shrink tubes so they are thinner at the motor. I hope that it won't melt, it says 125°C on it and 200°C on the silicone, so not much difference.
Btw I had to lengthen the axle to fit into my motorcycle fork, I was worried, tired so at AM 2:30 that's what came into my mind and I welded them together.

Anyway, why do my phase wires look burnt and why only 2?