Boat Gauge

What gauge wire do I need to use?

Ok I am working on putting together a small electric motor on a bicycle and powering it with a couple of old boat batteries. So I need to wire the two batteries together and then to an on/off and to the motor itself. Do I use the same gauge at each point in the circuit and whether yes or no, what/which gauge/s should I use?
Oh sorry. If you come back, the motor will have a ~22 amp draw.
Oh, ok. If you happen to come back again (heh), I do not need to use a lower gauge where I connect the 2 batteries together? Do you think 10 gauge will be plenty safe?

yes, you should use the same gauge throughout. But the size depends on the size of the motor. If the motor draws 10 amps max, then you should use a wire that will cause you to lose well less than 1 volt. The length of wire is short, perhaps 5 ft max. At 10 amps, 0.1 volt (conservative, well less than 1v) is 0.01 ohms. at 5 ft, that is 0.002 ohms per ft. #12 wire meets that spec.

But there were a lot of guesses. 10 amps may be high, 0.1 volt drop is very conservative.

#16 is 0.004 ohms/ft, so at 5 ft that is 0.02 ohms, and at 10 amps that is 0.2 volts drop, still very small.

So, for 10 amps, use #16 wire. Wire is cheap, and #16 is pretty small, so I see no reason to go any thinner, even if your current is lower.

edit. At 20 amps, just double the drops listed above. So for 5 ft total length, #16 would have a 0.4 volts drop. OK, but if you can use #14 wire, use that instead. Or if the total length is more than 5 ft, go up a size.

wire gage tables:

http://www.powerstream.com/Wire_Size.htm

.

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