Re: [electricboats] Fuse Setup for 10KW Thunderstruck motor on 28FT Herreshoff

Hi rholden;

Before you spend any money, spend some time watching the youtube videos from Pacific Yacht Systems. Sit through the multi-part electrical systems seminar. You'll get a quick overview of most of the issues.

A quick summary to answer your question about fuses:

The fuse (or circuit breaker) protects the wire. Each wire can withstand a certain amount of power being transmitted through it before it is likely to fail. "Failing" means catastrophically melting and setting fire to your boat so you want to avoid that. Your goal as you design your electrical system is to have a fuse between the power source and the load for almost every wire in your system (there are exceptions for the alternator on the motor and a few other specific things). Because the fuse protects the wire you want the fuse physically located as close as you can to the power source.

You also want to size the wires you're using so they're appropriate for the load. Each load in your system will have a maximum draw rated in amps. The wire should be rated to carry MORE than that amount of amps. The tradeoff is cost; the larger the wire, the higher the cost. You COULD run battery cable to every load in your boat and you'd have a super-safe boat. But the cost (and weight) will kill you.

So you design your system in reverse. Start with the load. Let's say you have an electric motor that can draw up to 200 amps at 48V. You need a wire that can carry MORE than 200 amps. Doing the calculations you'll end up with AWG 2/0 wire. One end of the wire is connected to the motor controller. The other is connected to the source - your battery bank. Close to the source, you should have a fuse rated at more than 200 amps, but less than the carrying capacity of the wire. (You may end up with a 200 amp fuse for all sorts of reasons, and you'll probably be ok running the motor at 200 amps but you'd build in some margin for error if you had a 250 amp fuse in that circuit instead).

Generally speaking you want 1 fuse for every load. Practically speaking that means that you will connect a fuse box or circuit breaker panel to your source; you'll fuse the wire from the source to the panel, and then fuse each wire from the box/panel to its load.

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