Nippon Denso tests good, panel indicates overvoltage

[flytoboat]

I had the same alternator with over voltage problems. I believe the main problem is high resistance somewhere in the Alt Field circuit path. In my case it was the 5 amp breaker switch.

[rv7charlie]

A reminder; the alternator spec'd does not have a field terminal. It's an internally regulated alternator. It does have an IG terminal, which must go high to make the alternator 'turn on', but it is not a field terminal. The field windings are internally connected to the internal regulator.

It *does* have an 'S' (sense) terminal, which *might* cause issues if it's connected and there's high resistance in that path.

Charlie

[cojaken]

I wanted to thank everyone who provided input and potentially help others by sharing the final outcome.

As shared earlier, the alternator giving the over voltage was a Nippon Denso as supplied by Vans about 10 years ago. The problem occurred at about 120 tach hours. The only connections to the alternator were the IGN and B terminals and it had worked well until this issue. Due to the fact that only the IGN and B terminals were connected, I surmised that the only problem could be with the internal regulator, whereas if the S terminal was connected I may have been looking at continuity and resistance in that connection. I believe this regulator has a fixed set point at 14.5V.

O'Reilly's and Advance Auto tested the alternator and internal regulator and reported it was good. An alternator shop later tested it and reported the regulator was bad.

I decided to buy a re-manufactured alternator from Denso which is the new name for the original manufacturer. These alternators are not made new by them any more. The alternator I believe is the closest replacement is part # 210-0637 http://densoautoparts.com 1987 Suzuki Samurai. I hoped the best quality re-manufacture would come from the original manufacturer.

I did have to file 3mm off the bracket the alternator mounts to, but I believe this was probably due to inaccuracy in the alternator housing casting rather than a different spec.

I ground ran the engine yesterday and flew it today with no overvoltage issues at all. I am not sure if my logic was correct but the result seems to be good. Incidentally, a replacement regulator can be purchased here: https://store.alternatorparts.com/part-in253.aspx and costs about 1/3 of the price of the re-manufactured alternator. I will buy one and keep the original alternator as a backup since it had such low hours.

[MCA]

Glad to hear you were able to resolve the issue. Sometimes those intermittent gremlins can be really hard to find!

[BillL]

Originally Posted by cojaken

I hoped the best quality re-manufacture would come from the original manufacturer.

IMO - You chose . . . . wisely.