The Stovebolt Site Forums The Shop Area The Electrical Bay starter to ammeter fuse

what size fuse would i use? 20 amp? 30 amp? 50 amp?

53 3\4 ton 12v with alternator

thanks
rolf

Fuse the circuit to the maximum output of the alternator plus 10%. For instance- - - - a 55 amp alternator would need about a 60 amp fuse, etc. After a long cranking session to clear a flood situation, etc., the alternator will go to full output for a short time to replenish the battery drain. If the fuse isn't capable of handling full output of the alternator the fuse will blow. It will still burn out and protect the wire harness in a dead-short situation. Use at least 10 gauge wire from the alternator to the ammeter and the same from the ammeter to the battery cable terminal. 8 gauge is better if you can find it.
Jerry

thanks hotrod

As usual Jerry is spot on. The only thing I would add is where this fuse should be located. I suggest placing it at the output lug of the generator/alternator. I use a fuseable link which I made up to fit my application. I also carry a spare because if it opens I can clear the short, replace the link, and get back on the road.

I'd locate the fuse holder or fuse link at the battery cable terminal of the starter, in the wire to the ammeter so it protects the whole circuit, including the ammeter, fuse block, etc., not just the alternator stator. That's where most manufacturers place a fusible link. Quite often, there are multiple fuse linked circuits to essential functions like headlights, ignition switch, charging system, etc., but the old stovebolts weren't wired that way from the factory.
Jerry

Good info there again. I noticed on my painless wiring on my roadster, they included an additional feed wire from the alternator to the fuse panel. Seems 8 gauge wire is more expensive than two lesser gauge wires. Some of those 100 watt alternators that run all the power window and AC blowers and high amp stereos needs some big wires. Don't over fuse the wire though and don't use a fusable link next to anything that can melt or burn.

ok
good info.
so i would use a fuse between alternator and ammeter and a fusible link between starter and ammeter.

have i got this right?

having a hard time finding a inline fuse holder with #10 wire.
going to check an rv store next.

thanks

rgie, I don't think you need both a fuse and a fusible link in the same circuit

Bill

There's a reason the manufacturers use fuse links instead of big fuses. If they're needed, there's a major short somewhere which will require at least a little wiring harness repair. As long as there's a "weak link" somewhere in the system to protect the rest of the circuit, the closer to the battery it is, the better. Having a fuse at, or near the alternator really isn't necessary.

Fuses don't do anything to protect individual parts- - - -they simply prevent wiring harness fires if something shorts out. Always fuse to protect the wire. 5-7 amp for 18 gauge, 10 for 16 Ga., 15 for 14 Ga., etc.

If you really want to add a fuse at or near the alternator, check with a shop that sells window-rattling sound systems. They have huge wires and big fuse holders for wiring subwoofer amplifiers that should carry alternator current with no problems.
Jerry

thanks jerry.
thanks bill.

i'll do the fusible link between the starter and the ammeter.
just to confirm-it's a 10 ga so it gets a 12ga link.

thanks again guys

rolf

That sounds like a plan. You might want to check the link with the alternator putting out a heavy charge to be sure it's not getting warm to the touch. If it is, you're operating pretty close to its maximum capacity. That would probably only happen if you're recharging a very low battery. Be sure you make a good, very low-resistance splice between the fuse link and the main harness wire. I prefer to do a "Western Union Splice", where about 2 inches of each wire is stripped of insulation and wrapped tightly over the other wire, then soldered and covered with a piece of shrink tubing. It gives a virtually zero-resistance splice, much better than any crimped connector can provide.
Jerry

I always wanted to know why a fusible link instead of a fuse. This is the best reason I have seen...now if I could just get myself to like them...that will be another day. Thanks Jerry