overcharging ?

[holmes61]

hi all
i have a mariner 40 hp outboard and tested the charging system and on high revs it is pushing out 18 volts i understand that a 12v system can charge up to 14.5 volts so is my rectifier gone any help would be great

[simonl]

how did you measure it?
What voltage at lower revs?

[holmes61]

hi thanks for reply
i have a volt reader on boat and volts start at 14 at low revs

[simonl]

Has it changed? What was it previously?
Where is that voltage measured? Have you measured at the battery with a voltmeter?
How big is the battery? Does it get warm? Does it emit bubbles in the cells (if you can see them)
Unlikely to be a rectifier issue - that is unlikely to increase the voltage. I don't know what the circuit consists of - it could have a voltage regulator that's packed up. Pence to replace if you're handy with a soldering iron

[Pikey Dave]

Stick a multimeter on the battery terminals with the engine running & measure the voltage there.

[jeffstevens763@g]

charge output of 40hp Page: 1 - iboats Boating Forums | 137031

for info

[Last Tango]

You didn't say how old the engine is. Older engines only had a rectifier and no regulator. Basically used the battery to regulate the voltage, boils them a bit but the idea was, you could always top them up. Seeing 18 volts (floating) on this would be normal
This setup shouldn't be used with sealed leisure batteries as it will quickly destroy them.

I think it was about 1990 (I could be wrong) that everyone started fitting regulators to their charging systems to facilitate the use of leisure/gel batteries. Should show about 14.3 volts "on load".