volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

[chris0061]

Hello all and hope your all getting pumped for the boating season. I am. The last run last year my volt gauge was reading 16 volts and actually fried a new battery. I just dewinterized today and put on a alternator that I new was good the last time I ran it and still the same thing so I put it on battery number two and it is old and may be fried but it kept running but wouldn't charge the battery. Batteries were stored indoors all winter. I"ll take the old alternator to the shop and have them test it but is there any way something else could make it all of a sudden run 16 volts. I haven't put a volt meeter to it yet but it did fry a new battery last fall.

 

[stylesabu]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

1st double check voltage with volt meter, but 16 volts will take out a battery if exposed to that voltage for extend periods of time.next where is your voltage regulator, this is what controls voltage output. when or if this ever happens again after you repair,turn on every ting electrical to try to "use" excess voltage. if both alts do same thing, I belt they both test fine that you have a short in the wirirng. i'll tell you how to check that after we find out about regulator and alternator

 

[Silvertip]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

Shorts blow fuses so don't bother looking for one. If there was a short that DIDN"T blow a fuse, breaker, or fusable link, then the voltage would have been pulled down significantly from 16 volts. What you need to do first is check the accuracy of the voltmeters your are using. Even new batteries have been known to fail so don't rush to blame the alternator. It is highly unlikely that both alternators have bad regulators but it is certainly possible.

 

[stylesabu]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

i could be wrong as most of my expiriance comes from automotive field.but old chrysler regulators field controls were ground side not positive side. and I realize most alternators have internal regulators. So it might not be a shorted wire( and I did mean shorted to ground) which I agree most people don't realize a shorted neg control need can cause a problem.. so I stand corrected, but wanted to state where I saw basing my info from. Had Silvertip replied first, I would not have disagreed. but 1960"s mopars used ground to control alternator output. and I did say to double check your readings. and I stated that I doubt both alts bad, and a 1981 boat could have an external regulator, no?

 

[Silvertip]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

When it comes to electronics, whether it is a voltage regulator or a radio, they can fail due to an internal component that "shorted" (using the term very loosely). Diodes for example can go bad and lose their blocking ability so if one measured with an ohm meter it would show continuity in both directions. In the boating world shorts are generally considered short to ground which is why I suggested not looking for shorts. Whether a regulator is internal or external, they either work or they don't and when they fail they generally fail to charge or undercharge, not overcharge. Most auto stores can check an external regulator. They can also check an alternator whether it has an internal regulator or not. Since this boat is powered by a 30 year old GM engine with who knows alternator at this point, it is a pretty fair assumption that it would not have a MOPAR alternator or regulator.

 

[Boatist]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

In 1981 many boats had external regulators.
Question how many wires connect to the Alternator?
GM used 3 wires, the big 10 gauge wire usually red that goes to the battery or starter solenoid Battery side.
Then two smaller wires that Connect to the field and relay that go to the external voltage regulator.
If the field wire is shorted to ground the alternator will charge at it full output all the time.
I have see this many times when the field line shorted to the manifold.

If the alternator only has one wire then the voltage regulator is inside the alternator and nothing external will affect the alternator output.

So check the voltage at the battery and at the alternator output with a voltage meter first.
If it is 16 volts or higher and it has 3 wires follow the wire connected to the F terminal. Make sure it does not have any spots where the insulation is rubbed off or melted by the exhaust manifold.
If the wire is good then it is probably a bad external voltage regulator. The one I had that was bad was only about $10 from an alternator rebuild shop. The Marine Dealer wanted about $35 back in year 1990.

My Factory service manual had very detailed checks and test to find the problem with a Volt Ohm Meter.

Good luck and please tell us what you find.

 

[chris0061]

Re: volt guage reading 16 volts Sea ray 245 260 mercruiser 1981

I'll drop the old alternator off and have it bench tested if the regulator is bad I'll throw a new one on there and see what happens. Thanks for all the reply