Strange Electrical Problem

[Michigan_SAN]

I’ve been struggling with an electrical issue on my ‘02 Super Air Nautique for several weeks now and could use some help. The issue is that after startup, the voltage gauge will be sitting at or slightly below 12V. When I check the voltage at the battery with it running I measure about 12.5V (the gauge is consistently 0.7V lower than the battery). If I raise the RPM with the voltage at this level, I soon smell the alternator belt burning and find little bits of belt rubber flung onto the back of the engine hatch. If I let it idle long enough, the voltage eventually comes up to 13.5V on the gauge or 14.2V at the battery. Once this happens, I can cruise around just fine. No belt smoke. The time it seems to take for the voltage to increase while sitting at idle seems linked to how far down the batteries have been drained. If I’ve been sitting with the engine off and radio on for an hour, it might take 10 mins at idle for the voltage to come up. If the boat just sat overnight then it might only take 10-15 seconds. I’ve seemingly confirmed this by drawing down one battery only, starting on that battery and seeing a low voltage, but then switching to the other battery and immediately seeing to voltage jump up to 13.5V. Switching back and the voltage drops again. At idle you can also hear the engine load up/slow down when the voltage drops and then unload/speed up when the voltage goes up. I’ve tried switching the batteries (1<->2) and the low voltage behavior followed the discharged battery. Things I’ve tried:

- New 50 amp alternator
- New 100 amp alternator with the upgrade kit from Nautiqueparts.com
- New PCM belts
- Tightened the alternator belt
- 2 new batteries (old ones tested good but replaced them anyway because they were >5yrs old, didn’t help)

None have fixed the problem. I’ve also measured current output of the 100A alternator just after start when the voltage is low and it’s only putting out about 30A. The battery is receiving 10-15A during this time as well. It seems that for some reason the alternator is under enormous load for some time during startup but for the life of me I can’t figure out why.

Anybody seen this before or have any ideas?

[jpwhit]

You've got a low resistive short somewhere. I don't have any idea how your boat is wired, so I can't be specific, but you need to disconnect different parts of the electrical system in a systematic fashion to isolate the location of the issue.

[Michigan_SAN]

You've got a low resistive short somewhere. I don't have any idea how your boat is wired, so I can't be specific, but you need to disconnect different parts of the electrical system in a systematic fashion to isolate the location of the issue.

Really don’t like the sound of that. If I had a short, wouldn’t my measured current out of the alternator be really high? It’s rated at 100A and it only puts out 30-40A. What about the fact that the condition always eventually clears itself given enough time? That doesn’t seem like the way a short would behave. I’d like to be really really sure there’s a needle in the haystack before I go looking for it.

[jpwhit]

Not if the short is resistive, as opposed to an absolute short of zero ohms. Sounds like you have a short of around a 0.5 ohm given you measured 30 amps out of alternator and only 10-15 amps going into the battery. The other 20ish amps is turning into heat at the short. Otherwise, where is that missing amperage going?

The reason it gets better, is the battery and the short are both drawing power right after startup that adds up to a big load on the alternator. Once the battery replenishes the energy needed to start the motor, then that load drops. It's probably the load of the short combined with the load of the battery charging that's causing the issue right after startup.

At least this is the only thing I can think of that would explain the symptoms you're describing.

[bturner]

I like where JP is going and he's typically spot on with electrical.

On a 22 YO boat I would start with the tried and true battery cable inspection, cleaning and tightening method. You may be able to power through the start cycle but charging is a different story. Jeff mentioned inspecting/replacing battery cables in another thread due to corrosion that you can't see that occurs in the cable jacketing. I have seen that before as well. Another thing you could try would be to carefully feel the cables during this condition to see if they're getting warm during this cycle. This would indicate increased resistance in the cable.

Older boats are known for bad grounds and the environment these boats operate in are ripe for corrosion issues.

The belt issue sounds more like a separate issue more related to alignment to me. The only time I've seen that is with a froze alternator or tensioner / idler pully.

[jpwhit]

The belt issue sounds more like a separate issue more related to alignment to me. The only time I've seen that is with a froze alternator or tensioner / idler pully.

You're probably right that there are issues with the belt alignments, tensioners and/or worn pulleys, etc.... But the problems are likely related in the sense that the the whole belt system has to be in pretty tip top shape not to slip when an alternator is under pretty heavy load.

[Michigan_SAN]

I think I’ve solved it. I decided to replace the battery cables and my Perko switch based on the results of this post describing a similar issue: https://www.planetnautique.com/vb5/f...r-wasted/page2

My voltage gauge now sits at about 12.5-13V at start up but jumps up to 14V with a little bump of the throttle. As a test, I ran a battery down with the radio for an hour, started up the boat, and then soon got up to cruising speed and everything was fine, no smoking belt like before.

I also cut off the insulation from all the old cables expecting to find some corrosion somewhere however they looked pretty good. One cable did have about 1/3 of its strands broken right at the battery clamp terminal. I’m thinking that was probably the issue. Anyway, thanks all for the help.