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Starboard alternator over charging

My starboard alternator on my 2006 cummins 6bta 270hp is over charging. It´s a 3 wire plug 105 amp. The tac pick up is not being used. It´s charging at 17volts. Soon as you crank the engine the volts start to climb to 17volts

So far I have taken the alt. to a respected alt shop. He told me the alt. was in perfect working condition. Reinstalled, same issue. Changed the battery´s thinking I might have a dead cell, no change. Replaced the alt with the port alt. no change. Change the pig tale, check all my wiring, test tested all systems with my volt meter. Everything looks good so far. But still over charging

I haven´t been able to find any diodes that I have been reading about to check or change.

Please let me know if you have had this problem or know of a soulition.

Thank you Joe

Joe E wrote:Starboard alternator over charging

My starboard alternator on my 2006 cummins 6bta 270hp is over charging. It´s a 3 wire plug 105 amp. The tac pick up is not being used. It´s charging at 17volts. Soon as you crank the engine the volts start to climb to 17volts

So far I have taken the alt. to a respected alt shop. He told me the alt. was in perfect working condition. Reinstalled, same issue. Changed the battery´s thinking I might have a dead cell, no change. Replaced the alt with the port alt. no change. Change the pig tale, check all my wiring, test tested all systems with my volt meter. Everything looks good so far. But still over charging

I haven´t been able to find any diodes that I have been reading about to check or change.

The alternator generates AC power... Dynamos generate DC power... As batteries are DC the AC from the alternator needs to be changed to DC... This is called rectifying... The diodes are part of the rectifier which is in the alternator... The fact that you switched the alternators between your 2 engines and the "problem" didn't move or change places should tell you that there's nothing wrong with the alternator itself...

17 Volts with no load sounds about right... Questions: how exactly are you measuring the voltage?!... On the alternator or at the battery?!... Is the alternator fully connected?!... Is your volt meter accurate?!... What does the other alternator show when measured exactly the same way?!...

At this point, with no further information, I would be inclined to suspect something in the wiring... For example a loose or corroded wire which basically causes your alternator to work without a load... First measure the Voltage in the batteries BEFORE your start up the engines... Make a note of the measured Voltage... Then start the engines and measure the Voltage output of both alternators at their respective batteries... I suspect that the "good" alternator will show roughly 14 Volts whereas the "bad" alternator will show roughly the same Voltage as your first (engines not running) measurement... This will confirm the wiring issue...

Replaced the alt with the port alt

Bad Gauge?

It's a wiring issue, I just need to figure out what is either causing back feeding or not exciting the signal wire. The system is being monitored by 3 different volt meters, analog on the dash, multi meter on the DC panel and a hand held multi meter. All of the above options have been performed. Still chasing the issue. Joe

Joe , cummins alternators are a weak link..I keep a spare on board..I had an overcharging issue and found a diode had called it quits..alternator guy fixed it no charge..swap in a spare get that one fixed..rotate..repeat. The exciter takes a bit to kick in as well to get her to charge at low rpms just goose it and it should kick in..BH

Not sure if you fixed your voltage issue, but my alternator had the same symptoms a few years ago. I can tell you how I fixed it -- but not why it was fixed... I was following wires looking for clues when I discovered a diode crimped in line with the yellow exciter wire. It was located about 1 foot from the alternator, buried in the corrugated plastic wire protector. It was covered with yellow shrink wrap -- very hard to see. I replaced it with a new one -- failed again. I jumped it out and the alternator has been working ever since -- with no obvious reverse current issues. I just wish I knew why!