Is 12.5 volts right?

[barak888@msn.com]

I have a Merc Black Max about a 1985. I recently took my boat in for service. I told the mechanic that I didn’t think it was charging correctly. He checked it out, and said the engine was pushing out12.5 volts, and that was correct. This seems low to me. Is this correct? And if not, where should I look first to correct the problem? Any help is much appreciated.

 

[TwoBallScrewBall]

Re: Is 12.5 volts right?

With the alternator spinning, you should see mid-14 volts. 12.5 will not charge your system sufficiently. My first guess would be the alternator.

 

[ndemge]

Re: Is 12.5 volts right?

Yeah, alternator is not charging.<br /><br />Easy way to check alternator, is check voltage before starting, then check voltage after starting. If it's the same, or lower after starting, it's dead.<br /><br />12.5 is about a 50% discharged battery, 12.7 being full charge

 

[Peter J Fraser]

Re: Is 12.5 volts right?

With engine running you should have 13.8 to 14.5 vdc at battery terminals otherwise you are not getting sufficient charge. Be wary though because I have just been through some grief with an alternator that showed 14 volts. Should be OK BUT it had a faulty regulator that had correct voltage but low output (no amps) so we had a battery going flat each week.<br />If possible you may need to place an ammeter in series with alternator output to check current.<br />Good luck<br /><br />Peter

 

[JB]

Re: Is 12.5 volts right?

Yeah. What those guys said.

 

[18rabbit]

Re: Is 12.5 volts right?

Yeah. What JB said. <br /><br />And this…<br /><br />I am having my alternators rebuilt, one at a time. When I went to pick up the first one, I had the shop put it on their tester, spin it, applied a load to it, then adjusted the voltage…all under my supervision. Will do the same with the second one.<br /><br />Don’t know if you alternator will allow for an adjustment to the voltage, if so start there. Some places will test your alternator for free.

 

[barak888@msn.com]

Re: Is 12.5 volts right?

Thanks for all the info, but I don’t think this engine has an alternator. <br />I believe it has a stator, a rectifier, and a voltage regulator. I have already replaced the voltage regulator. That didn’t work, and you can’t return electrical parts. That was a costly mistake. I can’t afford another one like that.<br />

 

[Dunaruna]

Re: Is 12.5 volts right?

Barak888, the stator under the flywheel produces AC current and the rectifier changes it to DC to charge the battery. <br /><br />You should have minimum 13.5v at battery @1500rpm with no load(lights etc. off).<br /><br />Try posting in the merc section with more detail about your motor - you might get more specific replys from people who have your model.<br /><br />Aldo