Electrical Gremlins

cmelt2003

All last year, and this year, I have had issues with my voltage gauge. I don't know really where to start with what I see with it. I guess I'll start with what I see when I get to the boat.

After any amount of time away from the boat, it's always on shore power, and the batteries are always charging. The starting battery is new this year, house battery 2 or 3 years old. 

I'll run the blower for 5 minutes before starting the boat, while it is on shore power. Disconnect shore, turn all the breakers off etc, then start the boat.

Right after starting the boat, the voltage gauge will normally show between 10 and 11. If I turn the blower off, it may show a little higher. I'll head out, and while running about 1600-1800 rpms, the gauge may jump up to between 11 and 12 with blower on, right about 12 with it off.

When I am at plane speed, between 3500-4000 rpms, blower off, gauge will show between 12-13, but will randomly drop down to 10, and wildly fluctuate between 10 and almost 13. 

I suspect a loose ground or connection somewhere, but I am stumped. I haven't checked the voltage output from the alternator, but before I start disconnecting and pulling wires and testing things, I wanted to reach out the the best group of boaters around. 

Any and all suggestions welcome! Thanks!

Black_Diamond

Always start with the ground..then start at the 'problem' and work backwards.  

frodo13056

Usually, alternator output is around 13.8 volts (charging volts) which is what your gauge should show with the engine running and no load on the 12 volt system. As you add load, you expect to see the voltage drop and running the blower is a fairly large draw (amps) on the system so you should see your charging volts drop around 1 volt so you should see around 12.8 volts on the gauge. My guess is that you either have a loose / worn drive belt or the alternator could be on its way out. I didn't see what boat you have but if you have a battery switch that you can manually connect up one or both batteries or switch them off , most older battery switches would "break before make" meaning that if you throw the switch while the engine is running (alternator outputting voltage) that the switch would disconnect from both batteries, then make the new connection - like if you switched from battery 1 to Battery 2 or switched to both. When this would happen, damage to the output diodes in the alternator would occur since the alternator would be producing voltage but that voltage would have no place to go when the switch was repositioned - even if it only took a second to reposition the switch. I'm not 100% sure but most newer switches are "make before break" - make the new connection before breaking the old connection so that you could not damage the alternator. I'd buy a cheapie digital volt meter, plug it into the cigarette lighter and watch that for awhile and see if it mirrors your gauge. You can find these on e-bay for $4-$6 if you do a search for "cigeratte lighter voltage indicator" or something along those lines. Also, the more demand you place on your 12 volt system, the more the alternator draw, the harder it is for the engine to spin the alternator which would cause voltage variances if the belt was slipping. From your description, my guess is the drive belt rather than an "electrical gremlin". When was the last time the drive belt was replaced? easy check is to look at the underside and if it is very shiney, it's slipping. Also, you can do a "reverse" bend on the belt and if you see cracks, it's time for a new belt. Remember, a too tight belt is worse than a belt that is not tight enough. Too tight and you can easily fry alternator shaft and or water pump shaft bearings. Let us know what you find!

cmelt2003

Gremlin found and resolved! Long story short, was tinkering in engine compartment yesterday double checking ground connections, etc, when I gave up. Was going to take boat to pumpout, and turned the key, short engine turnover, then nothing. I mean nothing... no beeps, radio, gauges, etc. Figured I blew a fuse or something. Took the dash apart,couldn't find any blown fuses. Laid in the engine compartment, tracing wires, etc, until I traced the wiring back from the alternator back to the starboard side, towards the back of the engine, about half way down. Whole connection point was loose. That's gotta be why it would look normal some times, and horrible others. Took it apart, tightened it, and then tightened it back to the solenoid (at least that what I think it is) that it was connected to. After tightening it back up, gauge reads exactly as described in the previous post by frodo. Now my only concern is that one of the wires that was connected is actually cut in 2, and I was wondering if anyone knew what it went to (orange on in picture). Everything else seems to be working fine now.

mvn

On my boat, the heavy gauge orange wire is the output from the alternator.  In your case, you may have either a charging relay or an isolator added, in which case the orange wire could have been replaced.

Mark

cmelt2003

Well, that's my next task, to resplice that wire.