Rapid Fluctuation in Battery Voltage With Engine Running

[PDReynolds]

Hi All,
An unusual situation seems to have developed. When I am under power, my battery voltage will rapidly fluctuate between 13.5 and 14.5 volts - a cycle time of about .5 seconds. (As noted at the DC panel Boat and a Victron digital monitor for my house batteries) . The boat is a 2006 423 with a Yanmar 55 HP engine. Batteries are new this year. I am starting to look to the alternator, but looking for input on this. Recently I tightened the alternator belt as it was a bit loose. Problem is still present.

Thanks,
Peter

 

[KD3PC]

voltage regulator, likely built in to the alternator - unless a Previous Owner went with an aftermarket, outboard unit.

 

[PDReynolds]

The engine has the Original Hitachi alternator with 600 hours.

 

[Don S/V ILLusion]

Before getting too deep in the guessing game, have you removed, cleaned and secured all connections in the circuit for the voltage monitor and charging system?

 

[markwbird]

Normally when the voltage regulator goes the voltage increase and decreases with engine RPM's. Your symptoms could be a bad connection. They could also be the voltage regulator.

 

[jviss]

I'm betting a bad ground.

 

[Maine Sail]

First check & clean all connections in the alternator circuit..

 

[Benny17441]

Your voltage seems to oscillate within an acceptable range so I would venture to guess that your problem lies with a faulty connection.

 

[Ron20324]

Might those changes be related to some other piece of equipment cycling on/off or off/on?