Mitsubishi 60amp alternator

[fieldbaren]

I bought a RV6A last October the builder told me the alternator was old and would have to be replaced in the future. I decided to replace it when the voltage would vary between 13.2 and
13.6 volts. This is the third RV that I have had and normally I would expect to see from about 13.8 and 14.3 volts I replaced it with a similar rebuilt Mitsubishi internally regulated alternator.
It is a 60 amp which should be more than adequate. I put a 470 ohm resistor inline where normally an incandescent light would be. Start up was fine showing 14.1 volts then it went down to 13.8volts during runup. after takeoff it went down to 13.7 volts. then I noticed it went down further upon loading up by turning on the strobe and landing lights; at that point I was drawing
20 amps the voltage, it went down to 13.2. If I reduced the load it would go back up to 13.8.
So if any of you have any ideas I would appreciate a response. By the way my AI mechanic said that was normal; Really??

 

[Walt]

Not normal, 14.2 is 'normal'.

 

[mechmike]

Depends where you're measuring the voltage from. The alt may be putting out the voltage but if the wire size is too small that goes to the + terminal on the alt, you'll get a significant voltage drop as you load up the system.

1) Run a temporary wire to the + stud of the alt and hook it to a digital volt meter in the cabin. Negative should go to your battery. If it shows 14.2 - 14.6 then the internal reg is all good

2) If the above test shows good, you need to do voltage drop tests on the + side as well as the - side while under load.
Really the + side testing should go all the way from the + stud of the alt to the + bus bar and again to the + of the battery

Mike

 

[fieldbaren]

Depends where you're measuring the voltage from. The alt may be putting out the voltage but if the wire size is too that goes to the + terminal on the alt, you'll get a significant voltage drop as you load up the system.

1) Run a temporary wire to the + stud of the alt and hook it to a digital volt meter in the cabin. Negative should go to your battery. If it shows 14.2 - 14.6 then the internal reg is all good

2) If the above test shows good, you need to do voltage drop tests on the + side as well as the - side while under load.
Really the + side testing should go all the way from the + stud of the alt to the + bus bar and again to the + of the battery

Mike

Thank you Mike. I’ll give it a try.
Marc B

 

[fieldbaren]

Problem solved. The wire from the output of the alternator had a loose connection. Tightened the nut and now charging 13.8 to 14.2 volts. Thank you Mike for your input.
Marc B

 

[paulsmeds]

This forum is great! My 6A new to me 2 years ago also has a Mitsubishi alternator but I think just a 40 AMP. You describe my experience exactly. Idle 14.3 then more RPM and more load drops to 13.1 in cruise. However I'm fully electrically loaded up while idling. I'm not sure why it drops to 13.1 when up around 2400 RPM and stays there. Not that it matters, next time the cowling is off I'm looking for a loose connection! What's kept me from looking into it as my 2+ year Odyssey PC680 battery is strong and never had an issue... almost as if it likes the lower charging voltage.