Merc 1400 high voltage problem

[rustyscrew]

OK I am stumped. I have read a lot of the other threads on this topic. Check it out:

I have a 1978 Merc 1400 (I-6). Last week I was checking the voltage on the starter battery and saw that it read over 17 volts when we were running at a medium RPM. This was concerning, but everything ran fine so we ran home ok. Back at the boatyard, it wouldn't start and after a lot of diagnosing (and reading your excellent forum!) I found that the starter wire had shorted to the GAS TANK. Scary. I fixed that and everything runs great- But I am still getting high voltage.

I removed the rectifier and tested it per the directions in the manual and it was faulty. (I did the same procedure on a new one to confirm that I was doing it right...and the new one tested good). So I took your forum's advice and replaced the rectifier with one from radio shack (50V, 20A). I just tested it and again everything runs great, but I still get high voltage. I forgot to look at the tach, but with the warmup lever up I was at 16.95 volts.

I don't think I have a voltage regulator on that model. Some entries said that since the amperage is low, it isn't a problem unless it is boiling your battery. A mercury mechanic I spoke with said "no- if its 17 volts its overcharging". I just replaced both of my batteries and I really don't want to damage them.

Any thoughts on how I should proceed?

Also, this is particularly pesky because I installed a battery combiner and it has an overcharge lockout that essentially keeps the batteries isolated all of the time!

Is it possible to install a voltage regulator, or should I just load it up to drop the voltage?

Sorry about all the questions...but I am needing to get this thing working...it is my work boat.

thanks!!

 

[rustyscrew]

Re: Merc 1400 high voltage problem

I just saw another person's entry with the same problem.

They recommend replacing the rectifier with a regulator "194-5279". I wonder if this will work for me. Does this really REPLACE the rectifier?


I just tested the voltage again. At 2500 RPM's the voltage slowly creeps up. It was at 17.5 when I finally turned it off.

Its a new battery, I cleaned all of the connections from the rectifier back to the battery, replaced the rectifier and still have the problem. Would a regulator just be a band-aid for a another problem...like resistance in the stator?

thanks.

 

[Laddies]

Re: Merc 1400 high voltage problem

rusty, that regulater will fix your problem

 

[rustyscrew]

Re: Merc 1400 high voltage problem

thanks laddies, I am going to try the regulator. I just wanted to avoid throwing money at a problem, until I was certain it would work. Thanks to your forum the rectifier was only a $3.50 item.

so I am guessing that old engines have destroyed a lot of batteries over the years. The amperage output of my rectifier was 7.5 amps, so its low enough compared to modern alternators that it probably took some time to burn them out. Hopefully the regulator will prolong the life of my batttery.

Keep you posted.

 

[Texasmark]

Re: Merc 1400 high voltage problem

Sounds like you are on top of it rusty. You didn't say anything, nor made any assumptions that weren't true as far as I am concerned.

The only thing I don't know is if the regulator contains the rectifiers also.....just a minute and I'll look.

Service manual for later model 75 thru 125's shows 2 yellow wires coming from the stator (under the flywheel) to the regulator. So the rectifiers are in the regulator module.........makes sense.

Therefore if you get a regulator, you don't need your $3.50 rectifier you bought and if you try to use it, your regulator won't work. It needs ac inputs to work.

Now, these regulators are setup to control 12 to 16 amp alternators on the newer engines. So it might not work, but it might (should I guess) work. Don't know till you try. With only 7.5 amperes max out of your alternator (per your measurement), the regulator current limit will probably be wide open most of the time. The voltage clamp however should work just fine and your charge voltage should be around 14v at low rpm's and up to 14.5 ish at WOT.

Mark