Alternator Problem! Need Advice or Help

rv969wf · #1 08-11-2007, 12:35 PM

I've been having a problem with my NipponDenso alternator which I cannot figure out.

It all started at around the 350 hour mark since new. Here's what is going on: In day VFR, normally I'm showing 13.5 - 13.8 volts and it's charging around 8 amps. After flying for 30 minutes or so, the voltage falls to 12.4-12.5 with zero amps, NOT charging, then after about 30 minutes it will start trickling up to 1-2 amps with voltage upwards to 12.8 then after a few more minutes I'm up to 13.8 volts and charging 14 amp. After the battery is charged, the amps fall back to around 8. Then here we go again after flying for another 30 minutes, same thing happens over and over. This has been going on for a long time. First I made sure I had good grounds, even ran a ground strap from Alt body to the case, no paint hindering good ground, bare metal ok. I've taken all connections loose to make sure there is no corrosion and sanded all contact points. I even replaced the voltage regulator at around 360 hours. Everything seemed ok for about a 100 more hours till I flew to Oshkosh and the same thing happened over and over and over. The alt now has 510 hour TT. When I take the alt and put it on a test machine, nothing is found even after spinning it for an hour. Can anyone tell me what is going on other than replacing the whole unit with a new one. Any comment would be appreciated.

Build9A · #2 08-11-2007, 12:46 PM

Although it seems that you have checked the fittings and connections. My similar problem was caused by a loose fitting to the voltmeter at the main buss. Another problem I had was the connections at the 60amp breaker. Those things can go south also so maybe replace the 60amp breaker (10-$15).

hevansrv7a · #3 08-11-2007, 12:53 PM

I paid, after turning in the core, about $136 for a replacement for the automotive alternator that came with the FF kit from Van's. Mine was dead, so it was an easier decision. A guy with a Glassair and a similar alternator went through weeks of frustrating debugging before he replaced his. Sometimes you just fix the problem and never find out why it happened. Of course, I know you are an experienced mechanic and will already have done the obvious stuff like checking all the connections, etc. I am not attempting to diagnose yours, merely to suggest that sometimes you get to saying "don't know and don't care" when trying to figure out what is wrong and the solution is clean, fast and cheap. Your mileage may vary. Good luck, AJ.

WilburD2 · #4 08-11-2007, 12:57 PM

AJ, have you checked your battery? A weak cell or one not holding a charge could be messing up the voltage regulator.

plehrke · #5 08-11-2007, 02:12 PM

Quote:

Originally Posted by rv969wf

After flying for 30 minutes or so, the voltage falls to 12.4-12.5 with zero amps, NOT charging, then after about 30 minutes it will start trickling up to 1-2 amps with voltage upwards to 12.8 then after a few more minutes I'm up to 13.8 volts and charging 14 amp. After the battery is charged, the amps fall back to around 8. Then here we go again after flying for another 30 minutes, same thing happens over and over..

Do you have a blast tube to cool the alternator? With it cycling every 30 minutes maybe it gets to hot and shuts down and then when cool it begins working again. I have a blast tube running to mine.

rv969wf · #6 08-11-2007, 05:54 PM

Hey everyone, thanks for the help, everyones comments have given me some places to check. I don't think its a heat issue because it has sometimes but not very often caused problems at start up cold in the winter then it would start working and quit again. I haven't checked the battery for a bad cell yet, it's a couple of years old and seems to be working ok. When the problem first started, my old battery was getting weak so I installed a new one and the problem with the Alt still creeped up on me. Around the 360 hour range when I installed a new internal voltage regulator, "NAPA brand", I also installed new brushes and checked the armature. The old brushs still had plenty of life left on them, but new ones went in while I had the Alt apart. When I find out the problem I'll let everyone know. I will check the buss breaker for problems also. I'm still stumped.

If anyone else has some ideas let me know.

zilik · #7 08-11-2007, 07:29 PM

Quote:

Originally Posted by rv969wf

After flying for 30 minutes or so, the voltage falls to 12.4-12.5 with zero amps, NOT charging, then after about 30 minutes it will start trickling up to 1-2 amps with voltage upwards to 12.8 then after a few more minutes I'm up to 13.8 volts and charging 14 amp.

This is a classic loose wire/bad connection problem. I flew to OSH with exactly the same problem and had checked everyting prior before the flight as it had been acting up for a few weeks prior. This has happened before (over Cuba) and replacing the voltage regulator (internal regulator) seemed to solve the problem, for a while that is. I bought a new unit on Ebay for 40 bucks and gutted the regulator and switched it over to an external unit. Then came the day for the alternator swap and I found that the sudo field wire was loose in the faston conector. I could not see the wire move in the connector but could feel looseness when pushed/pulled. My buddy said it was just the wire shield that was loose. I took no chances and it took the five minutes to replace the connector and all has been good for the last 6-7 hours.

This problem has plagued me on and off since the 135 hour mark and I now have 1000+. If it blinks again the alternator is getting fired and the new gutted, externally regulated unit is going on.

Gary