What gauge wire to use for 45+A through Y connector?

[erik_m]

I have a system as follows:
72V battery with output never over 45.9A (the max current in the CA is limited to 30A, but I may turn it up to 35A later)
72V, 4110 controller
Cromotor V4

I have a Y connector (the 72V battery is two 36V packs, 20 cells total) which is made of 12 gauge wire, but the phase wires are 10 gauge and the battery wires are 8 gauge. I don't think the 12 gauge wire is fat enough to carry 45A. Should I make a new Y connector with 10 gauge or 8 gauge? The wires on my Y connector are about 30" long. Thank you!

 

[Sunder]

So many variables that it's impossible to say "Xawg" will be fine, unless you so massively overscope it, you might as well just go straight for 00.

Things to consider are:

1. Insulation thermal properties. Difference between current carrying capacity of 60*c insulation and 200*C insulation on same guage is huge
2. Whether the cables are in open air or bunched up
3. How long the cable is
4. How long you put max power through it - You could probably underspec if you just do 30 second hills @ 45amp, but then ride for 10 minutes at a cruisy 10amp.

But long answer short, if the Y connector is already there, and you're not seeing the insulation go white/burnt/brittle over time, you're probably okay. If you really want to be sure, go for a really tough ride and immediately feel the temperature of the wiring. If it's pleasantly warm, it's fine. If it's unpleasant to the touch (usually >60*C) , best change it.

 

[Chalo]

A good rule of thumb to remember is that for every two AWG gauge numbers difference, the conductive area approximately doubles (or halves). So assuming the same length of wire before and after the Y, you could use 10ga for the "trunk" and 12ga for the "branches" and have equivalent resistance along each half.

 

[dogman dan]

I wouldn't hesitate to run 12g silicone. For a run up to 3 feet. But it will be pushing some connectors, such as 45 amps andersons.

 

[erik_m]

12AWG silicone should be fine for 45A, but in practice you want larger cables closer to the controller... so if your batteries have 8 gauge, making the Y out of 8 couldn't hurt. Connectors are usually the weak point. What type do you use?

The connectors on my Y connector are Anderson PowerPole SB50. I have JST-SM for the Halls, bullet connectors for the motor wires on the wheel end, Anderson "SB50 singles" for motor wires at my controller, and all the rest are JST-SM.

 

[erik_m]

Informative replies by all--thank you. The 12 gauge that I have is the gasoline resistant (i.e. non silicone) kind. Before I put flexible wiring conduit over it, I did feel the wire and it never even got warm after a flat, medium power 10 mile ride. I think I will get some 10 gauge silicone and use that, making sure to make my Y connector the correct length this time. The Y connector I have now is about 12" too long, and the excess length is indeed bunched up at the controller with all the controller wires and connectors--I definitely don't want excess heat in that critical area.