Way too much voltage!!

seth6025 · May 21, 2009

Had my boat out for the first time and I noticed the Volt meter was off the charts. It started blowing fuses to my lights and bildge pump so I unhooked the battery. Thought I was ok then, but after that my volt gage was all over the place and the gage itself started to get hot and fog the glass?? What is going on??

blktout67 · May 21, 2009

Re: Way too much voltage!!

i would start at the alternator i have seen them put out to much voltage when there going bad you can take it to any autozone or krgns and have them check it. it could also be your voltage regulator has gone bad

seth6025 · May 21, 2009

Re: Way too much voltage!!

Thanks, I will check that out

j_martin · May 21, 2009

Re: Way too much voltage!!

First, it would help to know what engine you have.

Second, the battery may be the only voltage regulator in the system (common on low output outboards) Disconnecting the battery is absolutely the worst thing you could do.

hope it helps
John

seth6025 · May 21, 2009

Re: Way too much voltage!!

It is a 1978 80 hp mercury outboard....What could it do by disconnecting the battery?

jimg984 · May 21, 2009

Re: Way too much voltage!!

disconnecting battery would fry the rectifier which is part of the charging system,,, probably was bad anyways causing the problem

Silvertip · May 21, 2009

Re: Way too much voltage!!

The alternator output is unregulated without a battery and it simply, for lack of a better term, runs away. If the system has a regulator or regulator/rectifier you damage those components as well. Some of those are very expensive. You never run an electric start outboard without a battery. Since this is an outboard, the alternator is not a conventional alternator like you would find in a car. It consists of a stator under the flywheel. Magnets in the flywheel spin past the poles of the stator thus generating AC power. The rectifier changes the AC voltage to DC. Therefore there is nothing you can take to an auto store to have them check. The sales people would very likely give you a deer in the headlights look as they wouldn't have a clue what they are looking at.

blktout67 · May 21, 2009

Re: Way too much voltage!!

so what would happen if the battery is bad and he had to change it out would it still fry the system. i have never herd of anything like that before i have owned a lot of old hot rods and some old bikes but kinda new to boating im just trying to learn about something i haven't herd of yet thanks

blktout67 · May 21, 2009

Re: Way too much voltage!!

cool thanks for explaining that to me.it is very good knowledge to know if i ever
buy a outboard motor.i did not want him to unhook the battier and i did not relies there was that big of a difference in the charging systems from a i/o and a outboard this is why i really like the board i learn something new everyday thanks everyone

seth6025 · May 21, 2009

Re: Way too much voltage!!

Thanks alot for all the info...I will look at changing the rectifer/regulator....This is a very good site to learn....Thanks again

Barnacle_Bill · May 21, 2009

Re: Way too much voltage!!

Here is how to test the rectifier.

Testing Merc?s square rectifier

If you use an analog meter set it on the RX1000 scale.
If using a digital meter, set it on the diode symbol.

1. Disconnect the battery leads.
2. Disconnect all wires on the rectifier.
3. Connect the red test lead to ground and the black lead alternately to terminals A and C.
The meter should show continuity.
4. Connect the black lead to gound and the red lead alternately to terminals A and C.
The meter should not show continuity.
5. Connect the black lead to terminal B and the red lead alternately to terminals A and C.
The meter should show continuity.
6. Connect the red lead to terminal B and the black lead alternately to terminals A and C.
The meter should not show continuity.
7. Replace the rectifier if you do not get correct readings.

j_martin · May 21, 2009

Re: Way too much voltage!!

seth6025 said:
Thanks alot for all the info...I will look at changing the rectifer/regulator....This is a very good site to learn....Thanks again

Slow down and understand what you have.

It is a 9 or 16 amp stator, limited by design to that current. (AC)

Next in the system is a rectifier, which converts it to DC.

There is no voltage regulator. Between a little lighting, instruments, and the ability of the battery to accept a slight overcharge, none is needed.

If you don't maintain the battery, eventually the water in the electrolyte is hydrolized, converted to oxygen and hydrogen and lost. The battery fails at that time, and nothing is now limiting the voltage, so it will rise out of control.

The only thing wrong with your system is the battery is bad. Replace it and maintain it regularly from now on to prevent this in the future.

hope it helps
John

jimg984 · May 22, 2009

Re: Way too much voltage!!

yes, bad battery could cause this, also corrided connections on battery, ground included, also charring circuit is likely. the starter takes a big current draw so it may go thru bad connection. where as the charring ciruit is a small draw and may not feed thru those connections...had problems with this

seth6025 · May 26, 2009

Re: Way too much voltage!!

Ok well I checked my Rectifier and it shows good. I guess my next step is to get a new battery...hope that is the problem. Thanks for the info on how to check the rectifier

Way too much voltage!!

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