Alternator Output

[Blitz]

After about only 10 hours of use on my new 60 Amp alternator for my Yanmar 3GM I noticed that the voltage (via my Victron Battery Monitor) shot up to approx. 15.3 volts at idle! I was running the engine for about 25 minutes at varying RPMs and was monitoring the voltage and amps produced. I was loud near the engine but as I was slowing the engine rpms and letting it idle I noticed my alarm was going off on my battery monitor that the voltage was high. I immediately shut the engine down but was limited on time to do much trouble shooting.

What is the maximum output in volts of an internally regulated alternator?

Also, could this be a symptom of a bad ground to the alternator? Bad diode?


FYI: The batteries are flooded; I have a house bank of approx 260 amp hours and a reserve back of 90 amp hours. The banks are connected only through a Blue Seas Automatic Charging Relay when conditions allow.

 

[Stu Jackson]

While there is no reason to believe the battery monitor was reading incorrectly, you should check the output voltage of the alternator and at the house bank.

Do you have a separate ground for your alternator? Rather than depending on the mount to the engine?

 

[Blitz]

While there is no reason to believe the battery monitor was reading incorrectly, you should check the output voltage of the alternator and at the house bank.

Do you have a separate ground for your alternator? Rather than depending on the mount to the engine?

Thanks Stu, actually I was going to run a seperate ground when I get there later today, then check voltages again. I was thinking that the higher rpms might have caused a problem with case ground.

I was uncertain when I originally installed it in spring exactly where to attach the wire onto the alternator, but I did check resistance between the case and ground and out was ok.

 

[Stu Jackson]

Neil, Maine Sail recommended using the alternator ground terminal whenever installing a higher output alternator. Don't know if that's your issue, sounds more like a regulator issue. An alternator shop could be your answer. Good luck.

 

[Blitz]

The ground terminal is normally labeled E? From memory...

 

[Maine Sail]

Blitz,

If this is a stock Hitachi alt then 15+ is way to high. What is the alternator sensing a battery or the alt itself? Do you have an additional sense wire custom installed or is it fully stock? There is no external regulator on your boat, correct? This is a REAL Hitachi, not an "imitation" Hitachi / el cheapo?

Hitachi's on Yanmar engines are regulated to 14.3V +/- 0.3V, 14.4V +/- 0.3V or 14.5V +/- 0.3V..Even at the high end of the error range you're looking at a max of 14.8V but they are normally 14.3V - 14.5V when I measure them.. The Hitachi alts are a good alternator but the eBay type knock offs, not so much...

 

[Blitz]

Mainesail,

It's most likely a knock off, internally regulated from spider marine. No sensing wire so it's sensing itself I assume. I do not have an external regulator.

Spider quickly told me to send it back so they could test it. I just wanted to make sure a bad ground of some sort didn't cause a problem. Wasn't exactly sure where to attach the ground cable to alternator since original alternator was only case grounded.

I was getting a rock steady 14.5 volts during most of my run time yesterday since I was closely monitoring it. It was only during my last few moments of run time I noted the high voltage.

Thanks again for your help,

Neal

 

[Blitz]

As an update I received a replacement Alternator under warranty and again only after short use (less than 1 hour) the replacement Hitachi 12 Volt 60 Amp Alternator (yes - it's a knock off) seems to be outputting voltage too high. I recorded a volatge reading of greater than 15 volts (15.45 volts noted before shutdown) again after warm up and running the alternator on my second day of use.

I just got a messege back from supplier that there was nothing wrong with the original alternator

Wiring is good at both ends. Seperate ground was installed to ensure good ground. Temperature in engine compartment was not excessive - any suggestions?