12 volt electrical gremlins

DanW

I anchored out this weekend and came across a new problem. It started with my radio randomly turning off and then when I went to sleep, I could hear the refrigerator cycling on and off. I watched the voltmeter and it would show 11.9 volts and the fridge would try to start and voltage dropped to around 7-8 volts before the fridge would stop it’s cycle and the radio would turn off. The voltmeter would then return to around the same - 11.9 to 12.2. This cycle repeated itself every 2-3 minutes or so before I just turned everything off for the night because I was afraid something would be damaged. It doesn’t matter what 12 volt item I try to use, the same thing happens. Flush the toilet and the voltage drops to 7 volts and then returns to normal after. 

This only happens on the batteries. If I run the generator or connect to shore power and turn on the battery charger, all 12 volt items behave normally and there’s no voltage drop. I did a little research and think maybe a bad ground? I checked battery and negative bus in the bilge and didn’t see an obvious problem. This is probably over my head and I will have to find a boat electrician, but I thought I would see if anyone has any ideas so I don’t sound completely crazy when I explain this to the mechanic. 

Thanks,
Dan

LaRea

Sounds like your house battery is kaput.  How old is it? 

When you unplug from shore power, the battery should be putting out around 12.8 volts.  If the voltage is only 11.9 volts, the battery is dead.  When the fridge tries to turn on the compressor, it pulls the voltage so low that the radio can't run.

If the battery is older than 3-4 years, replace it.  If that doesn't fix the problem, maybe your battery charger is shot. 

Ian

I agree with @LaRea, battery on the way out, can’t take the load.

LaRea

If your battery charger is the original from 2002, you're lucky it works at all.  From what we've seen here on the forum, chargers from that era typically last 10 years, maybe 15.  

DanW

The charger and batteries were replaced last year. But I just got the boat back from the mechanic for other issues. I wonder if he didn’t plug the boat in while he had it and and killed the batteries? I’ll have someone load test them. Thanks!