Alternator Not Charging (Enough)?

ssokol · #1 07-21-2017, 09:28 AM

Greetings Folks,

I seem to have some sort of charging issue with my RV-6A. It has a 35a Denso alternator which appears to be making power as the voltage on the Dynon SkyView reads 14 - 14.1. However, the Dynon also indicates a drain of -1 to -3 amps. I thought perhaps it was the battery so I replaced it (new Odyssey 680) but it did not appear to help.

This morning I did a test. Charged up the Odyssey to full using a 2 amp charger. Flew for ~40 minutes, with the Dynon indicating -3 throughout the flight. After landing I put the battery back on the charger and waited. After 30 minutes it was still not showing full.

My first guess would be the alternator, but it's putting out the right voltage. It has an integrated regulator so I can't point the finger at the reg. Anyone have a guess what this might be? Is it possible for an alternator to fail in some weird way that it can make rated voltage but not push enough amperage to both run the systems and charge the battery?

Thanks!

Steve

Jesse · #2 07-21-2017, 09:39 AM

I wouldn't be surprised with the amperage being off just a little bit in reading. If it's sitting at 14+ volts the battery is staying close to full. My experience with trickle chargers is that they charge for quite a while before sensing the battery is full even if it is full to start with.

ssokol · #3 07-21-2017, 10:10 AM

I should have mentioned that I noticed the problem when I was unable to re-start the airplane after a short flight. The battery wouldn't spin the prop / mags fast enough to light it off. A buddy put a jump pack on it and it fired right up, so it wasn't a hot start issue.

This happened a couple of times. So I ordered the new battery...

rv7charlie · #4 07-21-2017, 10:56 AM

Multiple thoughts:

Make yourself a test harness. Clip directly on the battery + & - terminals, & run the leads into the cockpit. Check voltage with a known-good, accurate digital voltmeter. Then check at the same point, in flight, with all electrical loads off, then with all normally used electronics on and operating. With a 35A alternator, you might have enough electrical load in the plane to pull charge voltage *at the battery terminals* below what's needed for full charging.

You need close to 14.3 volts to reliably/fully charge an SLA battery (Odyssey, etc). Any resistance losses between the alternator's B lead and the battery's + terminal, *OR* between the alternator's case and the battery's - terminal, will reduce the charge voltage at the battery, where it matters. I've had corroded battery terminals prevent charging, even when the circuit would start the plane. With SLA batteries, you may not see the nasty white foamy powder common on automotive battery terminals, but if you unbolt the connection, the copper/brass terminals can have a layer of corrosion that has high resistance. Same can apply to the wire/terminal interface, which is almost impossible to inspect directly.

Amp readings are tough to interpret from a distance, without knowing exactly how the current sensor is installed (there are at least three ways to configure a current reading system).

snopercod · #5 07-21-2017, 11:04 AM

Quote:

Originally Posted by ssokol

... it's putting out the right voltage.

I guess that depends upon the battery. My recombinant gas sealed lead acid battery requires 14.6V +/- 0.2V.

JonJay · #6 07-21-2017, 11:18 AM

Odyssey publishes a minimum charging Amperage of 6A. I can not find a minimum voltage but I would assume anything above 12.8v, the published full charge voltage.
My B&C SD8 charges the PC680 just fine at 13.8v.

rv7charlie · #7 07-21-2017, 12:04 PM

Jon,

Try looking here:
http://www.odysseybattery.com/docume...M-002_1214.pdf

12.8 V won't fully charge a 12V lead acid battery; neither flooded nor AGM.

FasGlas · #8 07-21-2017, 12:29 PM

If a diode or two burned out the ALT will still put out voltage and little amperage. Easy to take it to a local autoparts store that tests ALT's. The machine will put a load on the output and check the AMP's out.

JonJay · #9 07-21-2017, 01:36 PM

Quote:

Originally Posted by rv7charlie

Jon,

Try looking here:
http://www.odysseybattery.com/docume...M-002_1214.pdf

12.8 V won't fully charge a 12V lead acid battery; neither flooded nor AGM.

Thank you. They also warn that the charge voltage should not be lower than 13.2v or battery life could suffer.

texdog · #10 07-21-2017, 02:18 PM

I just went down this road and the alternator was the problem. I replaced the plane power with a Nippon Denso and everything is happy now. 12 hour trip and everything is working. If you are reading 12 volts at the battery with engine and alternator running, it is basically battery voltage. I'm not an expert but it worked for me. You can spend money replacing parts but check the voltage.