Battery Cable Gauge

[Ron Paro]

How is the correct gauge determined when making long battery cables for an electric trolling motor?

I am planning to use a 40# thrust motor with 42 amps as the maximum draw. The cable will be about 12' long, running to a group 24 size, 12 volt deep cycle battery.

Thanks - Ron

[donald branscom]

How is the correct gauge determined when making long battery cables for an electric trolling motor?

I am planning to use a 40# thrust motor with 42 amps as the maximum draw. The cable will be about 12' long, running to a group 24 size, 12 volt deep cycle battery.

Thanks - Ron

I would consult the manufacturer to be absolutely correct.

Probably a #1/0 large multi strand wire.
You will need a special large crimping tool to attach the end fittings.
Impedence will not be factored in unless you go over 20 feet.

[Tylerdurden]

#8 is good #6 is better. You could get by smaller with some voltage drop under load. If going with a permanent install, spend some money on #8 tinned welders wire. Will be plenty. You can series some automotive auto circuit breakers or flip for good DC high current fuse.

[Tylerdurden]

I would consult the manufacturer to be absolutely correct.

Probably a #1/0 large multi strand wire.
You will need a special large crimping tool to attach the end fittings.
Impedence will not be factored in unless you go over 20 feet.

Dude, 1/0 is good for over 150 amps in engine spaces. Crappy #8 will carry almost 50 in the same space and is way cheaper than 1/0.
He only has a 42a ampacity required so 8 will do it.

[Les Schuldt]

Ron,

According to Nigel Calder's "Boatowner's Mechanical and Electrical Manual":

You said that the cable is 12' long. I assume this means the battery is 12' from the motor. (If it's only 6' from the motor, you can go one guage smaller than the below recommendations.)

40 amps through 25' of cable (you have to measure the "round trip") will require 10ga. cable for the 10% voltage drop application (general usage). This assumes good connections and routine maintenance.

However, he recommends going with the 3% drop 4ga.(!!) cable to allow for the marine environment and potential degradation of the connectors. (You may find this too massive to be practical on your motor.) You might wish to compromise between these two sizes, perhaps to 8ga.

He notes that these specs are for SAE rated cables. These same guages can also be used for AWG cable. For a given guage, AWG is approx. 10-15% larger.

Don't forget to put a fuse or breaker as close to the battery as possible.

Les

[Ron Paro]

Donald, Mark, and Les,
Thanks for the quick response! I see that West Marine lists a 6 ga. tin coated cable from Ancor. This is AWG. Sounds like this should work? I will verify with the motor manufacturer as well.

Thanks again - Ron

[George Roberts]

Perhaps the motor directions indicate a proper size.

(8 or 6 seems reasonable - that is a lot of amps.)

[Ron Paro]

George, thanks for the validation!

I checked the Minn Kota site's FAQ, and found the manufacturer's recommended method for calculating the correct gauge.

http://www.minnkotamotors.com/support/faq.asp?pg=general&lp=gb&pt=6

Donald, thanks for the reminder to check the mfr info. I usually would start there, but just didn't think of it this time.

It looks like 8 ga. would be fine, and 6 ga. a little better. I'll go with the 6, and add the fuse box near the battery. Thanks for that tip Les and Mark!

[TMny]

Just to emphasize--the proper crimped connection , and sealing against moisture ingress , makes a vast difference in how long it works well.