80s mercury classic 50 overcharging

[GradyWhiteFisher204]

I recently got this classic 50 on a bass tracker that is charging around 17v while cruising. I'e heard bad rectifier could be the cause. Also battery could be the cause. The battery is a maxx-29dc that tests good. But also have heard that these motors aren't supposed to use "maintenance free" batteries. Could this be the cause? And is there a way to test the rectifier to see if it' the problem. Any help is appreciated.

 

[GA_Boater]

If you have a maintenance free battery, pry off the caps and fill it with distilled water to the rings.

Just because it's called maintenance free doesn't mean it can't be maintained. The caps do pry off to check the water level a few times during the season.

And the next battery you get, find one with caps. With no regulator, you only have a rectifier, the battery acts as the regulator and the water boils away.

BTW - 17 volts is only a skosh high for a non-regulated charging system.

 

[GradyWhiteFisher204]

So with the battery full is this 17v normal or something I should worry about.

 

[GA_Boater]

In my opinion, if you keep it full - No worries.

 

[Scott Danforth]

turning the radio up helps too

 

[GA_Boater]

The motor only has a 6 amp charging system and any electrical load helps divert what little excess power it has from the battery. But too much load and the battery won't be maintained.

I run a radio and 2 fish finders and the battery is kept charged. I also don't let the battery run down as in if I'm working on the motor and using the starter more than normal, onto the charger she goes. 6 amps won't charge a low battery unless you run around the lake for a long time. Wrapping the pull rope around the flywheel and yanking is tiresome.

 

[GradyWhiteFisher204]

Thanks for the input

 

[QBhoy]

Hi

how do you know it’s 17v ? Is this from the dash gauge or verified at battery with a meter ? Gauges tend to lie like Pinocchio most of the time.

 

[GradyWhiteFisher204]

Verified with volt meter on fish finder and with a MAC multimeter

 

[Redbarron%%]

You can upgrade to a MOSFET rectifier/regulator that will limit the voltage to 14.8 VDC and cost less than 25 bucks.
You can also use a Chinesium Yamaha unit .
The Chinese copy of the Ducati regulator was $28.00
Iboats probabley has the PWC regulators or search for MOSFET rectifier/regulator.
The one I bought is good for 60 amps so the 16 amps my coil can ut out won;t overheat it (probably)
The maintenance free batteries don't soak up the excess power boiling the water out like a regular lead acid batter (to the same extent anyway)
CDI recommends not using maintenance free batteries for this reason.
Personally I recommend a good regulator.
You can install a rectifier/regulator in place of your straight regulator. but the one I bought is too big to fit in the same space so in my Sport Jet I mounted off the engine where I had space on a bulkhead and it is cooler than on the engine

 

[merc850]

I put a regulator in my motor last year, the regulator is a Mercury one that I had lying around and I bolted it to the front cowl support (I think it should be grounded). This gives me 13.5 v constantly.

 

[QBhoy]

Ok. Being honest I wouldn’t worry too much about it. Loads of amps would be more of a worry.
Do you have anything you can use to put a bit of load on the system ? If you have a 12v socket, try plugging in a cheap 12v heater or something to see what happens. It’s likely that once you’ve started the engine and especially if she fires up quickly...you have very little load on the charging system and it’s just doing what stator/rectifier systems do. They are pretty rough and ready systems. I’d imagine it won’t be 17 volts when you are running flat out ? Or is it ? That might be different.

 

[Redbarron%%]

Even the CDI Rectifier/Regulator will go over voltage when the battery is fully charged and the power from the stator coil is not dissipated elsewhere.If it goes high enough it can kill the Rev Limiter etc.
Adding 12 volt load will reduce the voltage or adding a MOSFET rectifier and regulator will do the same thing.
Electronics has progressed since the 90's.
Since these alternators have no regulating field and put out the voltage and current determined only by it's internal resistance and magnetic power the external regulator does not effect this, but rather loads the system to do the job.
The SCRs in the old unit do not work fast enough etc to control this, but the MOSFETS are up to the job.
The modern Rectifier/regulators used in motorcycles and PWC will easily handle this task.
Iboats may have a unit for PWCs that will work. Many motorcycle regulators will work as well, but have three input coil wires and you just use two of them and you are A-OK