Alternator over-charging the battery

[amxpro]

My 94 c280 is having an issue with overcharging the battery. It has caused several issues; the car is hard to start, and when it does, the engine surges, no response from accel pedal, both hi-beam bulbs burned out, the radio will turn off and on, etc.. can anyone share some info on the charging system with me, or has anyone run into this problem? I tested the charging system here at home, and found 17.6 volts at the battery, at idle.. any help is appreciated...

[strictlyspeakin]

There is an overvoltage protection on the back of the alternator. Sounds like it burned out. try a search on OVP here. Should get some good hits

[navaidrule]

You have a very odd problem.
1. Measuring 17.6 V at the battery is very strange. It suggests the battery is disconnected or defective.
In normal operation the battery voltage is needed to exite the alternator so must have been connected at some stage but does as act as a 'sink' and will regulate the voltage to about a maximim of 14
2. The voltage regulator at the rear of the alternator is easily replaced, if necessary. No need to remove the alternator just ensure battery is disconnected.
3. I would also make sure the connections to the battery are clean and secure as a temporary disconnect here, after alternator excitation, will play havic with the cars electrics.

Joe

[Sulaco]

You have a very odd problem.
1. Measuring 17.6 V at the battery is very strange. It suggests the battery is disconnected or defective.
In normal operation the battery voltage is needed to exite the alternator so must have been connected at some stage but does as act as a 'sink' and will regulate the voltage to about a maximim of 14
2. The voltage regulator at the rear of the alternator is easily replaced, if necessary. No need to remove the alternator just ensure battery is disconnected.
3. I would also make sure the connections to the battery are clean and secure as a temporary disconnect here, after alternator excitation, will play havic with the cars electrics.

Joe

he's exactly right. Your alternator should NEVER send 17 volts anywhere, as that could result in massive failures elsewhere. Check your voltage relay, as stated, which is mounted INSIDE the alternator. It's not hard to replace, however. And it's like $12.

This happened in my C280 once. The extra voltage would cause my ABS to not work, my headlight bulbs blew out once I tried to switch to bright, my radio would randomly stop working. All kinds of weird problems.

Your OVP (over voltage protection) relay is designed to stop stuff like this from happening, but it can only do it's job for so long. If it fries and is stuck closed, it can kill ALOT of expensive things on down the line. If it fries and is stuck open, your car will not crank no matter what you do.

[amxpro]

Thanks for all the info. I pulled the voltage regulator, and it was smoked, i also found the field windings in the alternator had burned slightly. Installed a new alternator w/ regulator, and now happily charging at 13.5 volts. It appears the OVP relay is working fine. I will replace both high beam bulbs, and retest just to make sure system is good. Thanks again !!!

[amxpro]

Thanks for all the info Joe. I pulled the voltage regulator, and it was smoked, I also found the field windings in the alternator had burned slightly. Installed a new alternator w/ regulator, and now happily charging at 13.5 volts. It appears the OVP relay is working fine. I will replace both high beam bulbs, and retest just to make sure system is good. Thanks again !!!

[taz069]

Had just the opposite here mine was undervoltage. And yes the alternator was the culperate. Glad you found the prob!! Read some more post's and chime in glad to have ya. See ya soon