[dabney]

On the way back from OSH my RV6A with an O360A1A started to experience something I had not seen before. Here are the details. The battery is new this year. When I flip the battery switch on for start my voltmeter typically reads 12. 2 or 3, somewhere in that range. It starts in a couple of turns no problem. I turn on all my radios, instruments etc and the voltage remains the same. During taxi it remains the same. As soon as I apply full power for takeoff the voltage goes to 14.2 or so and stays there the entire flight. That was until coming home from OSH. On the last two legs across the hot desert SW into SoCal the voltage started to fluctuate from the normal 14.- down to as low as 12.2 or 3. Then it would go back up to 13.-- or 14.-- then back to 12.--However, it never went below 12 during the 2.7 hour leg. I watched it closely thinking I might have to shed some load if the battery was being discharged but that never happened.

I was wondering if the very high OAT was to blame hurting the performance of the alternator. When the weather cooled off back home I took it out for a flight around the pattern. Same indications prior to takeoff and after takeoff. During the 15-20 flight at 75% power I had a steady 14+ on the gauge. Normal. I thought the problem was over. Wrong..As soon as I pulled the power back to descend and land the voltage dropped into the 12's.

Has anyone encountered a situation like this. I am thinking my alternator is about ready to fail. Or is the gauge the problem? What should I do to troubleshoot this problem??

 

[Bevan]

More info is needed.

Internally regulated?

Do you have a cooling blast tube to the alternator?

Perhaps the regulator is not handling the heat very well.

If it is externally regulated, where is the regulator located?

Is the battery located on the firewall or inside the cockpit?

I'm no expert but they will chime in soon.

Bevan

 

[turbo]

i have been running the automotive alternator for years. when it had been acting up like that i was told it was the ic diode. it would only act up when hot. tested at the parts store it would be ok. when i told them that my 'mechanic' said it was the ic diode, bingo, they would replace it under warranty.

funny thing is, now it is over charging a bit, so i am running some lights to keep it around 14.4 or so. i have a spare on hand if needed. if it keeps up i will bring it back when i get back to florida and say the ic diode is going bad. bingo, yes sir, we can warranty that for you.

i also keep a spare starter on the shelf in case that acts up. cleared for take off.

do some testing at different parts of the circuit, alternator, bus, battery ect. see were the loss is coming from. good luck.

 

[Walt]

One thing you can be sure of, mechanical/electrical problems don't miraculously "heal" themselves, failure is immenent.

You may have a wiring problem or the alternator/regulator may be failing. If you end up replacing the alt/reg do yourself a favor and get an aircraft unit like B&C or plane-power.

First thing is pull the cowls and check all the wiring and connections, then report back with some of the additional info that Beven referred to.

 

[Jerry Cochran]

Could it be..

,,,the alternator belt slipping sporadically? FWIW.

 

[walkman]

i have been running the automotive alternator for years. when it had been acting up like that i was told it was the ic diode. it would only act up when hot. tested at the parts store it would be ok. when i told them that my 'mechanic' said it was the ic diode, bingo, they would replace it under warranty.

funny thing is, now it is over charging a bit, so i am running some lights to keep it around 14.4 or so. i have a spare on hand if needed. if it keeps up i will bring it back when i get back to florida and say the ic diode is going bad. bingo, yes sir, we can warranty that for you.

i also keep a spare starter on the shelf in case that acts up. cleared for take off.

do some testing at different parts of the circuit, alternator, bus, battery ect. see were the loss is coming from. good luck.

Is that government cut?

 

[turbo]

yes, miami. returning from key west @ 1,000'. one of the nicest flight in florida.

 

[Neal@F14]

Sounds very much like the voltage regulator (don't matter whether internal or external) is failing. If your RV-6 was built using the Van's-supplied small Nippon-Denso alternator with external regulator like mine was... the regulator is probably the small square metal can with one red wire coming out, and one screw terminal on it. This is a Mopar-style external regulator, and mine also failed in the mode that it was still charging, but only letting the alternator put out 11.8-12.2 volts. I replaced my regulator with the Ford-style external unit and it's now been charging rock-solid at 14.3v +/- 0.1v.