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dekky111

Well Known Member
RV7-A with 40A alternator, LR-3 controller, Odyssey PC680 battery.

Have been noting amperage spikes to 25-35a that are intermittent. Today noted EIS voltage spikes to 15.2 V. Normally runs ~ 14.6V at cruise. Am I looking at a battery or regulator problem? Any guesses?
 
Spikes

Could be regulator high temp. Got the same problem and looking to run cooling scat tube to the regulator and see if that fixes the problem.
 
Check the bus voltage sense line between the bus and the LR3. An intermittent break in that line will cause the symptoms described.
 
I'm having similar issues.

http://www.vansairforce.com/community/showthread.php?t=107239

Do you have a blast tube pointed at the regulator? I do not. I read it doesn't matter... But now I'm thinking it does if you run hard. If someone says they haven't needed one in 700hrs. Then they state they like to fly at 150kts saving fuel... Different sorry on my plane! I fly 185kts+ everywhere.

Replacing alternator and directing blast tube Monday. (We'll see?)

Does your amps drop to zero or negative before the spikes? If the alternator is cutting out and ships power comes from the battery. Battery draws down then the alternator jumps back on line and jolts the battery with some juice?
 
Small voltage fluctuations above 14-15v (although not normal with the B&C alt/regulator) would not cause large amperage swings on it own. Large amperage swings can be caused as noted above if the alternator is dropping off line then coming back on and re-charging the battery (not what you described), a short or bad battery.

Of course verifying indications and all connections are secure (not sure what you have for a V/A meter) would be the first thing.
 
Last edited:
Walt,

Thanks for posting. Your statement about that battery just made a lightbulb go off in my head! Gonna switch out the battery today before messing with the alternator.

Thanks again,

Scott
 
rzbill said:
Check the bus voltage sense line between the bus and the LR3. An intermittent break in that line will cause the symptoms described.
Click to expand...

+1, And . . the other side of that is the ground. Be sure grounds are secure out to the alternator too. Think how your voltage is measured and how the alternator senses it. Your wiring diagram and knowing your specific connection will help greatly.
 
Spikes

I had exactly the same issues last year. The molex plug that goes into the alternator had a loose pin. Fixed that and supported the wire better and have not had a issue since.
 
Appreciated

Thanks for all your replies: 18 degrees in the hangar right now. Will get to work on it tomorrow:)
 
It is highly unlikely that a battery would cause voltage or amperage swings. The problem is more likely a bad connection in the voltage regulator circuit.
Joe Gores
 
Check fuses

If your system uses automotive blade type fuses, even slight oxidation on the fuse blades of the voltage sense circuit can cause what you are describing.

Just remove and replace or push the fuse in and out a few times might temporarily get your voltage back to normal. If it proves to be the case, memorize the location of the fuse by feel as you might need to do it in flight some time if your voltage starts to ramp up.

I wish somebody made copper plated fuses.
 
Tool for low resistance measurements.

When it comes to flight worthy I don't like to guess. It might happen, but hoping that a part replacement will fix something (especially an intermittent issue) is not a definitive plan. Here is a low resistance tool that can be used with a standard VOM to test the circuit from end to end and see if there is a connection issue. Hook up and wiggle everything to see if it changes.

Regarding connection corrosion, I use a dielectric grease for this purpose. GM had some stuff years back and it would keep the surfaces bright. Bulb sockets on my old truck exposed to salt were a constant problem. I filled the sockets with this grease and never had that issue again. I got it at a truck stop.

http://www.aeroelectric.com/articles/LowOhmsAdapter_3.pdf

Happy hunting. Let us know what you find, there are all too many alternator issues. I have put over a million miles on 8 road vehicles, all of which exceeded 100,000 miles, and never had an alternator failure. The only one that failed was a regulator on my Kubota tractor after 4000 hours.
 
Do you have an APRS transmitter? I've seen several planes indicate large ammeter changes like that when the APRS transmits.
 
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