Voltage Spikes on amp gauge

[Ian Cameron]

I just bought a older Cal 39. Recently, my amp gauge started jumping violently from 12 to 16 volts every several seconds and the RPM gauge needle does the same from 0 to maximum. It only happens after 1,000 RPM, slower everything is fine. I believe the alternator is 200 amp and regulator is basic, not a smart one. The problem seemed to coincide with removing the second belt off the alternator (suggested by a mechanic who said it was redundant when he surveyed the Perkins engine). I put it back on but the spiking remain. Any suggestions?

[btrayfors]

Belt might be slipping.

Redundant 2nd belt with a 200A alternator??? Unless your first belt is a serpentine, I'd say the 2nd isn't redundant at all.

If you have a multimeter handy, you might measure the voltage at the alternator output terminal or, if that's not easy, at the battery terminals to verify that the voltage is really spiking. Could be just a bad connection somewhere.

Bill

[44'cruisingcat]

You see voltage spikes on an amp gauge?

[delmarrey]

Originally Posted by 44'cruisingcat

You see voltage spikes on an amp gauge?

I'm sure he means a voltmeter.

But even at that 16 volts is too high and with the tach jumping too. Assuming it's a alt driven tach I'd be looking for a short in the alternator or some where. And yeah, you should be using two belts or you're going to loose the one you have, under a load. The alt brushes may be arcing.

[Ex-Calif]

Originally Posted by delmarrey

I'm sure he means a voltmeter.

But even at that 16 volts is too high and with the tach jumping too. Assuming it's a alt driven tach I'd be looking for a short in the alternator or some where. And yeah, you should be using two belts or you're going to loose the one you have, under a load. The alt brushes may be arcing.

Depends on how the 200 amp alternator is regulated (internal or not) but I would look for a wiring fault (intermittent open), likely where the tach sgnal and field wire are colocated in a plug or j-strip.

This connection could have been damaged or disturbed when taking the belt off. I failed the tach wire changing a belt on my boat.

[edfoster]

Spikes and jumps in the amp gauge or tach. can happen if things were reconnected to the wrong side of a ground shunt. Sometimes things get disconnected and or removed before the sale of a boat. Make sure accessory items linked to the battery management system are connected properly.

[Florida Mike]

It sounds like you're voltage regulator is shutting down and not maintaining a minimal field car. Without this minimal field current the alternator stops charging and then abruptly starts again. I traced a similar problem on a friend's boat. It turned out to be the voltage regulator had a small resistor burnt out. This resistor was designed to feed a minimal amount of field and current to the alternator. The fix that we use was to put a small lightbulb ( dash light ) jumped across the regulator. Just my two cents, Mike.