That's a great chart, Scott---thanks for the link.
And it makes it clear why 4 or 2 ga can be too small for a lot of us while on a golf cart it might be just fine. Let's say you're drawing under 100amps continuous and the round-trip distance from your pack to your controller is just 10 feet, the chart shows that 4ga would be fine for a 3% voltage drop. And if one is fine with up to another 3% in efficiency loss, it could be fine.
But let's say we might draw 150amps continuous at speed and the high current path length is more like 15feet round trip between the controller and battery---for that, the chart recommends 0 or 1ga.
Even accepting 3% voltage loss may be too much compromise given it will translate directly into efficiency loss. With my 16+ft main high current path, I use 1/0 cable---it's cheap enough and there were neither space, nor weight concerns that made it the wrong choice. My controller-to-motor cabling also uses 1/0 cable given I could easily see 200amps into the motor for a minute or 2 at least when trying to, e.g., catch a wave with my boat. J
You never want cabling or high resistance with lugs to cause key elements to overheat---not battery posts, not the controller and not the motor. Always be sure your contact resistances are low. Do that by running at full clip for a long enough time to generate heat, then stop and check all connections for heat. With my 1920 Milburn Electric car, I've had bad lug connections cause lead-acid battery posts to instantly turn into a pool of lead with current draw between 100-150amps. I also found a bad connection behind the original Amp/Amp-hour gauge after arriving home one time after a 2 mile jaunt only to find the glass at the front of the gauge was wa-a-a-ay too hot to touch…
Anyway, enough about this---thanks for the link to the great chart.
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Tuesday, May 9, 2017 1:43 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Choosing the Correct Wire Size for a DC Circuit
Here is a link to Blue Sea Systems website when choosing wire size. There are interesting products and reading too.
https://www.bluesea.com/resources/1437
Scott
Posted by: "Myles Twete" <matwete@comcast.net>
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