View Full Version : Weak Alternator/wiring

07-26-2013, 06:24 PM
Boat would not start last Sunday. Figured either two bad batteries or dead alternator. Took batts home, slow charged until battery tender said good.

Put back in boat this afternoon, boat cranked right up off either battery. Test alternator, getting 14v at alternator with just engine running. If I turn on the tower lights (biggest load I have) it runs about 13.6v at 1500 rpm. These lights will sometimes pop their 30 amp breaker so I guess that is about their draw. 30amps, 13.6v @1500rpm seems ok.

Part 2- I do not like the cheap crimp on ring terminal on the alternator, nor the small wire (was getting warm on the test above). Would like to upsize the wire.

Looks like I could run a new wire straight to the battery terminal on the starter- anyone know if I can do this? I'm assuming the smaller red wire on that post is the battery connection for the electronics on the back of the engine.http://img.tapatalk.com/d/13/07/27/apahu2et.jpg

07-26-2013, 06:28 PM
Pic of terminal on starter.http://img.tapatalk.com/d/13/07/27/dezapyhe.jpg

07-26-2013, 06:51 PM
I don't think this would be a good idea as you would bypass the 50amp breaker. I had the same issue and just took a wire brush to all connectors and terminals now works great.

07-26-2013, 06:57 PM
You added the lights and extra battery? You can't add to the alternator's load without increasing the gauge of the charging lead and cabling. Your charging lead getting warm says you need heavier wire- the voltage drop causes the batteries to charge to a lower voltage, not 13.6 or whatever they normally are at rest after a full charge.

It's not the ring terminal that's causing this, it's the fact that you added things to a charging system that was never designed for what you added. You need to analyze the current demand of everything in your boat and if this exceeds your alternator's charging capacity, you need to upgrade that, too.

07-27-2013, 02:40 PM
Spooky- I was wondering if the alternator output goes through the 50 amp breaker. This doesn't seem ideal since the alternator is rated for 80 or 90 amps! Maybe the best solution is to add a breaker properly sized for the alternator and run the cable directly to the starter post.

Whoa Jim, Innocent until proven guilty, right? :D

I bought the boat the way it is now, with dual batteries and the tower lights, so don't shoot me. :D

I disagree with loads determining the size of the alternator wiring. It doesn't matter if you have 2 batteries or 12, the alternator wire should be sized to the alternators rated output.

Also, a zinc plated ring terminal is a time bomb in the bilge of a boat. It should be stainless.

I agree regarding sizing the alternator to the loads. We have had this boat for 3 years and this is the first time we have ever experienced a dead battery. The dual batteries are for backup, not because I tie up at the sandbar and like to blow everyones eardrums for 5 hours.

So back to the issue at hand, including a properly rated circuit breaker, any reason not to run the alternator output wire straight to the starter post?

07-27-2013, 03:59 PM
That circuit breaker is not on the alternator wire. It doesn't seem as though MC installed circuit breakers on any of the alternator leads going to the battery/battery isolators.

I just upgraded my alternator to battery isolator wire and wires from the isolator to the batteries to 6 gauge wire. I also added a 100 amp circuit breaker between the alternator and the isolator.

I believe the wire going to the starter solenoid has a fusible link on it and is 8 gauge wire.