People get confused on picking the right size wires to feed a camping house battery from an alternator dc dc charger. Things like total circuit length, voltage drop, the right DC ampacity charts, etc. So I made a quick video for a Tacoma on finding the right wire size.
Video of wire sizing for 2nd battery alternator charging
- Thread starter Dave in AZ
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Advocate I
Thanks Dave.
I’m in the (soon) process of doing this very thing. From my limited understanding (my mind operates in the mechanical realm, not the black-magic of electricity lol) and somewhat of a WAG, I purchased #4awg. I expect the run to be less than 20’
Something I find that I need to be mindful and not forget/ overlook is circuit protection. Perhaps another video explaining what, where and sizing?
I’m in the (soon) process of doing this very thing. From my limited understanding (my mind operates in the mechanical realm, not the black-magic of electricity lol) and somewhat of a WAG, I purchased #4awg. I expect the run to be less than 20’
Something I find that I need to be mindful and not forget/ overlook is circuit protection. Perhaps another video explaining what, where and sizing?
4awg is even better, and for a 20ft run, 40ft circuit, the right choice, nice!
Good idea on video, fuse sizing is easy to mess up. In meantime, here is a general ruleset:
1. Size the wire to be able to carry the max possible amps your load could demand continuously.
2. Put a fuse or circuit breaker on wire TO PROTECT THE WIRE, at 125% of the wire rating. Round up if needed to find an available fuse size to no more than 150%. Place it near the power source side of wire run, on the positive.
3. If you want to also protect your load device, you can reduce fuse size to the device amps limit, if you will be able to stay under that for actual use. But this can lead to nuisance trips if you bump up to max load sometimes.
4. Motors are different, consult the NEC.
5. Look at each part of system, wire and busses, and think, "If everything that feeds power to this wire/bus fed power at once, despite any fuse of CB to stop that, would it exceed 120% of this wire/bus amperage rating?" If so, increase size of wire/bus.
