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Suggestions for Alternator Dropping off?

R

rwelsh

Member
I have an RV-8 (O-360) that after five years had my alternator (Plane Power) drop off at 1.5 hours into a 6 hour flight. The amps went to zero while i watched my voltage slowly continue to drop down to 12.2 volts (approx. 25 min). Then, alternator came back on by itself, starting at approximately 45 amps until it started getting the battery charged back up then ran normal at approximately 9 amps and 13.8 volts. It never faulted the circuit breaker which is set at 6 amps.

Return flight it cycled 2 -3 times and seemed to shorten run length with each cycle. I was hopping it was my master switch (cheapest replacement item) but replaced with no change. I sent Plane power unit to Hatzel because it only had 320 hours (but was out of warranty). They tested on bench under load and said it worked perfectly but they also suspected a "thermal" issue and send me a new voltage regulator. Still the same alternator drop off problem after 45 -60 minutes.

In full disclosure this entire problem started after I had a dead battery and charged the Odyssey PC680 battery up with a borrowed charger.

Since re-installing my tested Plan Power Alternator i have:
*Contacted Stein Air for ideas (they provided all components & Elec Schematic) *Contacted Vertical Power Tech support (circuit breaker is performed by VP)
*Purchase a new Plane Power Alternator/VR and installed
*Checked all wires for continuity
*Ran a separate ground wire from ground buss to alternator mounting bracket
*My A&P removed wiring to Vert. Power, installed new wire harness/connector and installed in-line fuse.

I am currently awaiting a new 60 amp fuse (current fuse looks and test good), a new shunt, and a new battery. However, any suggestions will be greatly appreciated.
 
There was another recent example on VAF where the alternator wiring tested OK... but it actually wasn't. It turned out that there was a bad crimp within the B-lead, so you might try replacing that wire and terminals. It's relatively easy to do.

Otherwise it seems that you've covered all of the obvious things and assume that the alternator belt has been checked.
 
As Paul suggested, check B-lead terminations, 3 pin control connector pins, and lastly - if you have a split battery master (batt/alt); check it.
 
Check the whole field circuit

I once had a bad fuse. Not blown, but bad. It would sometimes pass current normally and sometimes give up to a couple ohms of resistance. Everything else in the wiring was solid, and the intermittent resistance was very difficult to replicate on the ground. That one took a while to figure out.
 
PaulvS said:
There was another recent example on VAF where the alternator wiring tested OK... but it actually wasn't. It turned out that there was a bad crimp within the B-lead, so you might try replacing that wire and terminals. It's relatively easy to do.

Otherwise it seems that you've covered all of the obvious things and assume that the alternator belt has been checked.
Click to expand...

That was not a 0 output problem that Pete experienced. It was a lower voltage issue due to excessive resistance- 13.7 vs 14.2 or something like that. Seems clear from the symptoms posted that the alt stopped producing output in this case. If your volts drop to 12.2, you can pretty much be assured that your alternator has stopped doing it's thing.
 
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The 3 pin connector going into the PP alt is somewhat nototorious for bad crimps on the pins inside the connector shell. Suggest starting there.
 
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lr172 said:
The 3 pin connector going into the PP alt is somewhat nototorious for bad crimps on the pins inside the connector shell. Suggest starting there.
Click to expand...

PP Doesn't put the wire support grommets in the connector, so the pins can fatigue and crack, leading to intermittent operation. Disconnect the plug and pull on the wires. If they are good, put some RTV in the back of the hole to support the wires.
 

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Alternator problem solved

Thanks for everyone's suggestions!

I had already ordered a new battery and 60 amp fuse so both of these were installed. I still had the same problem with alternator dropping off but run time was now shortened to approximately 30 minutes.

I had previously checked continuity of all alternator wiring but my neighbor friend (A&P) instructed me to check ohms not just continuity. The third wire tested was large gauge power wire from alternator and it tested at 5300 ohms! After removing the rubber boot and shrink wrap insulation we could see the wire was burnt and corroded at the alternator terminal.

The wire was repaired and plane has now flown about 7 hours with any alternator problems!!
 
rwelsh said:
The third wire tested was large gauge power wire from alternator and it tested at 5300 ohms! After removing the rubber boot and shrink wrap insulation we could see the wire was burnt and corroded at the alternator terminal.
Click to expand...

What sort of wire? Tefzel, or welding cable?
 
wire type

The problem wire was the large gauge power wire from the alternator (with ring terminal and shrink wrap done by Vans)
 
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