Mercury charging issue.

[davez104]

Hi all,

I've got a 1990 model 135HP Merc V6. I had it out last week and the battery ran flat after a day or so. While the motor is running it appears to be making some charge as the lights are brighter and the volt reading on the sounder slowly climbs. But try to use the bilge pump or trim the motor and the sounder cuts out on low voltage. Even after a half hour run back to the ramp there was not a lot of charge in the battery.

What actually does the charging on these motors? Is it the stator or is that only part of the ignition circuit? Is there any way I can test the amperage being output and roughly what should it be? Is there a regulator or something under the cowling that could be causing problems.

I've checked the wiring and can't find any obvious problems, but if I could test the output from the motor then I could narrow down the search area.

Cheers,
Dave.

[Skusto]

how old is the battery? by the sounds of it it could also be your battery thats not holding charge? maybe take the battery out and put it onto a charger check for volts if all good then maybe put it into a car or back in ya boat and use ya trim and sounder and all that and see if it holds charge?

[davez104]

The battery wouldn't be 12 months old, but has not been looked after real well, so could be the issue. I did charge it up yesterday, ran the motor with it for a few minutes then left it sit till about an hour ago. It still has enough in it to operate trim without sounding slow. I'll see how it sounds tomorrow. The battery was my first thought and I hoped that was all it was.

Cheers,
Dave.

[Owen]

A: Put a volt meter on your battery with the motor off.
Should be 12 volts, but probably won't be in your case.
B: Then start motor and test again.
Should be 13-14 volts.

If A < 12v but B > 12 volts your charging circuit is at least working.

Some outboard charging systems are marginal at best, so better to charge it fully on a charger.
Get yourself a hydrometer from supercheap or spmewhere and test the cells too.

Quite likely theres a dead cell so it'll never hold a charge.

[davez104]

Thanks. I might bung it on the charger in the morning for a while then take it to the local auto sparkies and get them to test it.

[davez104]

I think I can rule out the battery. It still holds charge a week later.

I fired it up just a moment ago, the multimeter read 12.3V before I started then 12.4V when it was running. This very slowly increased as I let it run, ending up at around 12.7V after a couple of minutes.

So again, what does the charging on these motors and what is likely to need replacing? I can see myself getting a quote for new 4 banger if this looks like being an expensive fix.

Cheers,
Dave.

[dreemon]

It might only be the rectifer, but its the charging coils are under the flywheel and can be costly but no where near a new 4 st

[davez104]

Thanks for that. I'll have to have a think about it. The problem I have is that I'm 200k's from the nearest outboard mechanic, which makes it a right royal pain to get the problem diagnosed in the first place. I also want to put a new motor on the old girl, but didn't want to stretch the budget until the end of next year. The current motor is 20 years old and I was hoping she would keep steaming till then.

Thanks again,
Dave.