Odd charging problem

[Dorsal]

Once in a while (4-5 times in two years) I experience the following. With the engine running fine the ammeter will read 0 and the battery voltage slowly drops. When it gets down near 11.3 Volts it suddenly wakes up, starts charging and everything is fine. Anyone else experience anything like this? Normal operation for me is consistent voltage in the high 12s to low 13s.

[Dave S]

HI Dorsal,

Electrical stuff that only happens sometimes is miserable to diagnose.

A couple ideas.

1) There have been various other folks on the list who have had charging system challenges of one sort or another. Doing a search on "912 Charging" may turn up some ideas.

2) Your normal operating voltage of high 12s ..low 13s may either be a bit low to begin with or the volt meter may not be reading exactly true. Normal voltage should be closer to 14. (I have the onboard and aux alternators....they differ by no more than 0.1-0.2 volts between them; but, they are always running 14 to 14.2 volts unless after startup or at idle.)

3) Dropping voltage is normally indicative of either a high current draw outpacing the charging system or low output for some reason...often the regulator.

4) At face value....the intermittent low fluctuation would appear to be related to the regulator. Back when we had the low tech electro-mechanical regulators on cars...stuff like this happened all the time. This is a solid state system; but, I wouldn't rule out an intermittent fault in the regulator circuit.

Good luck figuring it out....an intermittent deal isn't so easy.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive

[kitfox5v]

Dorsal, Being an old GM tec we used to run in to regulators (exciting) at too low voltages. We always fix the problem with a new regulator. Hope this helps

[Av8r3400]

Fin - I think Kitfox5V is onto something. My 912 does the very same thing. I have a spare regulator that I was going to try, but it is currently borrowed to a friend with an intermittent over-voltage (17-18 volt) problem. I've seen this a couple of times, too.

Replacing the regulator/rectifier is the solution, IMO.

[Dorsal]

Ordered a new one.

[DesertFox4]

I have a spare regulator that I was going to try, but it is currently borrowed to a friend with an intermittent over-voltage (17-18 volt) problem

Av8r3400- Not to hijack this thread but your post reminded me of a series of incidents I experienced a couple years back. My 912S electrical system would intermittently produce an over-voltage during flight. I found no loose wiring anywhere as might be suspected. I replaced the reg/rectifier and it seemed to fix it. Not so. Soon I was again seeing 15.5 (my EIS would trigger at 15) volts on up to 16 or 17 volts.

My response to the warning light during flight was to turn on everything I had to absorb the over-load. I had twin landing lights of 55 watts each and a three strobe Whelen system that together would force it back down to a level that would not activate the warning light.
New regulator/rectifier again seemed to temporarily solve the problem but alas not for long. I even borrowed a friends extra reg./rec. and had the same outcome. Very frustrating. How could I get so many bad regulator/rectifiers in such a short period?

Then on a flight with DanB coming back from Sedona, we touched down at DVT and as I applied the brakes I got smoke rising from the center console. Not really what you want to see anytime but fortunately we were on the ground. Taxi back to the hangar and shut down. During our investigation I pulled the master solenoid back in and a large amount of smoke came from the regulator/rectifier. It was completely toast. Ah, something new. It melted a hole through the potting ressin on the backside of the regulator. After pulling the console apart I found my trim switch power feed wire had abrated against my stainless steel brake lines. The brake lines would flex slightly everytime I apply my brakes and eventially had worn through a very small area of the wire's insulation causing an intermittent dead short. I guess the regulator was over compensating for a the large power useage caused by the short.

It's strange it never blew the breaker. I re-routed the new replacement trim power feed wire so it could not happen again and checked for other wire interferance with the brake lines. After replacing the blown regulator/rectifier the problem has never appeared again.
Maybe your friend's got a short somewhere that makes the regulator over produce. Just a thought.

[Av8r3400]

Steve - not a hijack at all. Very good information, that. I guess it should be something to note: be sure you don't have an electrical fault before just replacing the regulator.

It wonder why the breaker didn't pop or the "smoking" didn't occur earlier???

Would any of our electrical experts care to weigh in if they think a high amp load (like a short) would toast the regulator like that?



(I broke your one long paragraph up, too. Excellent information but was hard to read... )

[DesertFox4]

Thanks Av8r3400, I tend to post like DesertFox6, all one sentence .

[DesertFox6]

I resemble that remark!

"E.T."/DF6