Battery Not Charging with Engines

U ONT 2?

New Member
Sep 9, 2018
6
Boat Info
1995 370 Sundancer DA
Engines
330 HP 454 cid Mercruisers
I have a 95 370 Sundancer and the voltage on the Starboard is always low. I have had the alternators tested and are working properly, but had to come home the other night holding the Emergency Start button to charge the Starboard engine. Once I plugged into shore power and the AC converter charged the battery all was fine, except the Starboard engine voltage is higher at idle than at or above 1,000 rpm.
Does anyone know where I can find a wiring diagram showing from the alternators to the ignition switches?

Thanks
UONT2?
 
I would yank your batteries and get them tested....... sounds like one (or more) might have a bad cell.

Always start with the simple stuff.
 
Agree with Little Ducky. A hydometer cost $5.00 at Autozone! If ALL cells are good. Next step would be to put a multimeter on the batteries with and without the engines running and check to see if you see a voltage increase.
I think i get 14 volts when my engines are running
 
NWMDC
Remove the cable and load test your batteries before you go any further.
 
I just bought one of these on Amazon. Different model, same concept. $35 to keep me from hauling 5 batteries to be tested.
 
I just bought one of these on Amazon. Different model, same concept. $35 to keep me from hauling 5 batteries to be tested.
Thanks, I'll try that, but when I test voltage with my meter it's about 13.8 vdc without the engine running When I start both engines the on the starboard engine voltage drops and continues to drop until it starved my house on low voltage.
 
Thanks, I'll try that, but when I test voltage with my meter it's about 13.8 vdc without the engine running When I start both engines the on the starboard engine voltage drops and continues to drop until it starved my house on low voltage.
Volts are different than amps. Start with what the guys mentioned, above. Is it absolutely the problem? Maybe not. But this is the proper sequence to diagnose.

FYI, a battery shouldn't read that high with the engine off. Either your meter is wrong, or you took the reading too quickly after turning the engine off. Try again, but run a few 12V items for 10 minutes and then take the reading.

Also, you should disconnect any batteries that are wired in parrallel before testing them - either V or A.
 
I think it's a bad isolator because here are the following test results. I turned of the ac converter and ran the fridge on house battery and the bilge blowers for 10 minutes the Port 12.9 volts and the Starboard (house battery) battery was 12.7 volts.
I started Starboard engine only, and the Port engine battery increased to over 14.6 volts and the starboard slowly decreased. I stopped the Starboard engine and started the Port engine. The port battery dropped down to a more normal charge of 13.9 volts and the Starboard battery remained 12.7 volts.
When both engines were started the Port battery goes higher and the Starboard continues to drop in voltage with the fridge and blowers on.
I'm thinking somehow the voltage is sensing the higher voltage of the Port battery and reducing the output to the Starboard alternator.
I have tested and moved batteries with the results
 
Sorry I forgot the second f in ac converter off
 
This is from a 370 aft cabin, but it should be close if not spot on.
 

Attachments

  • 370 engine dc wiring.pdf
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never liked that wiring , combining 2 alt thru 1 isolator .
should have atleast 1 motor system dedicated to itself. use the isol on the other engine .
Should you happen to lose the isol, you on battery power only,You could move a alt feed from #1 alt, and hard wire it to #1 isol output
 
Last edited:
never liked that wiring , combining 2 alt thru 1 isolator .
should have atleast 1 motor system dedicated to itself. use the isol on the other engine .
Should you happen to lose the isol, you on battery power only,You could move a alt feed from #1 alt, and hard wire it to #1 isol output
I agree.
I removed Battery 2 (House Batteries & Starboard) from the isolator and bolted the two wires together and that helped when I don't have the AC Converter on. So I think I also have a second issue with the AC converter.
 

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