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Started my engine for the second time in two weeks and noticed battery voltage had dropped from 12.43 to 11.33 after 37 minutes of run time. I charged this new battery back to full charge 12.8 volts and ran engine again for 25 minutes and voltage dropped off again to 11.46. It appears the battery is not charging. I'm not sure what the best way to troubleshoot the charging system would be and the Aerovee manual has nothing in it about a failure to charge. Could I have a bad voltage regulator? Can someone tell me the best way to troubleshoot problem with a volt/ohm meter. Thanks for any help or suggestions.

Mike
Onex #0038 AeroVee #0406

if you mean you ran the engine at idle or slightly above then you will not have charged the battery. the permanent magnet alternator does not put out a charge until the rpm is above around 22 or 2500 rpm. I found this while sorting out the tuning on the aerocarb. in flight there is plenty of power but on the ground not so much.

My EIS has a warning light when the battery voltage drops below 12.0. The light is usually blinking during engine warmup.

Last summer I thought I had a voltage regulator failure...it turned out to be a loose connection at the battery terminal.

If you run the engine up to 3000 rpm your volt meter should show in the high 12s - low 13s.

Thanks to all. I did run engine at 2000 + rpm in short 1 to 2 min cycles. What output should I see from the two leads from the pm alternator that connect to the voltage regulator (20 amps ac at 2000 rpm, 0 amps at 1000 rpm)? I also have a MGL E-1 connected and have the low voltage alarm set to 12 volts. All connections are OK. First thing I checked. I have an ammeter(VDO) with internal shunt, but not sure of best way to connect it. I can also check DC amps from center feed going to battery pos terminal, but it doesn't sound like I'll get any reading at low rpm. Maybe I'm chasing my tail here, but I'm concerned that with enough voltage drop that the secondary ignition could stop functioning. Isn't there a simple way to test the charging system components?

752mr wrote:Isn't there a simple way to test the charging system components?

Fly it!

Sorry to sound snarky, couldn't resist, but that will really be the best way. Remember, the battery will not even charge until you get up into the low 13 volts. Most battery tenders run about 13.2 volts. You won't see that until you are at flying RPM's.

During your Aerovee ground setup, if you want to run the engine briefly at WOT - which is OK for a short time - make it a check off item to view the voltage output. If you are unhappy with the number, be sure and double check the voltage with a good voltmeter. Those tenths of volts will matter.

On the ground, even during WOT you will still see lower voltage than in the air because the battery is recovering from the cranking drain. Be happy that the number is rising. That will mean the full amperage of the alternator is starting to recover the battery. The voltage will slowly rise as the battery charge builds. In the air, don't expect to see above 14 volts, more like 13.8 max.

It takes a good long flight for the battery to recharge - and reach max voltage - with the Aerovee alternator. If you fly 30 minutes at a time you will not recover to a full charge. An hour at normal cruise seems to be more than enough however.

Here are some plots of recent flights. Add 2.2 volts to the plot numbers. The MGL tool I use for the Enigma records the raw data not the calibrated displayed number.

The First is for about a one hour cruise flight and the second is for some pattern work. Note the steady drop in max voltage in the pattern work plot.

Thank you very much Bob. The plots explain the situation as it is. I'll wait until my reg and inspection are complete and just fly it.

752mr wrote:Started my engine for the second time in two weeks and noticed battery voltage had dropped from 12.43 to 11.33 after 37 minutes of run time. I charged this new battery back to full charge 12.8 volts and ran engine again for 25 minutes and voltage dropped off again to 11.46. It appears the battery is not charging. I'm not sure what the best way to troubleshoot the charging system would be and the Aerovee manual has nothing in it about a failure to charge. Could I have a bad voltage regulator? Can someone tell me the best way to troubleshoot problem with a volt/ohm meter. Thanks for any help or suggestions.

Mike
Onex #0038 AeroVee #0406

I hate to bring this up Mike, but if you're running your engine for that long on the ground prior to breaking in the rings and cylinders, you're not doing your engine any favors. You really need to run the engine HARD for a while to seat the rings and that can only be done in an engine test cell or flying. Running your engine for 25 or 37 minutes on the ground is a great way to glaze cylinders which may cause you more engine work later. Do yourself a favor and limit ground runs to making sure your carb is properly adjusted, whatever taxi operations you need to do, and then get flying! The harder your run your engine at first the better.

With regards to your charging issue, I agree with Bob here. You won't get good numbers on the ground because of all the starting you do (drains the battery), and in order for the alternator to work it has to be spinning pretty fast. I normally don't see anything over 12.6-12.8 volts until I'm flying, but after I'm in the air, I see 14.5-15.0 volts thorough my MGL. I look at the AeroVee alternator as more of an old school generator; i.e., the faster it spins, the more power it produces. On the good side of things, if you do take off and see your voltage is still only in the mid 12's (volts), even a small battery will provide plenty of power for you to leisurely come back and land. Most Sonexes have minimal amperage draw from radios, EFIS displays, etc, so you'll be fine.

Thanks Mike. I appreciate your input. It appears I don't really have a charging issue. I was able to get carb adjusted and check timing of secondary ignition. To my surprise the timing showed off only 30 rpm, so I didn't try to adjust it. I have a couple of minor oil leaks to deal with. The oil temperature when running at 2500 rpm never went above 112F and oil pressure at 900 rpm was 18 psi and 52 psi at 2500 rpm. Is this about the norm? Outside air temp 69F , no baffling on engine yet and no cowling.

Buddy, I've been fighting oil pressure issues for years on my engine. Maybe it's best you ask someone else! :) (Just kidding...I'll try to help)

Actually, those numbers seem fine. As a general rule of thumb you will want your oil pressure to be at or above 40 psi at cruise RPMs (3000-3200), but you won't be able to know what yours is going to be until you get your plane up in the air, fly it at those power settings and let the oil warm up. It's very common to see high oil pressure on the ground at first with the oil being "cold" (viscous) and pressure dropping a little as the oil warms up and thins out.

Oil pressure has been a highly debated issue for a long time. Many VW engine builders go by the "10 psi per 1000 rpm" rule, and I've heard some people beliving cruise oil pressure is okay all the way down to 25 or so psi. Personally, I would go with the Sonex company standard that you want your pressure at 40 psi in cruise (3200 rpm), but again, I've had talks with the factory and there's no hard set rule that this number has to be followed. In the end, it's up to the person flying!

Regardless, don't be surprised if you see high(er) oil pressure at first, and then have it drop a little as oil temperatures rise. Obviously, if you're up flying and pressure drops well below a safe level, it's going to be best to land and troubleshoot on the ground.

It sounds like you're getting close! Keep us up to date on how things go from here! Keep it up and you'll be airborne in no time!

The "rule of thumb" of 10 psi per 1000 rpm is for auto use. The front bearing of an aero engine demands plenty of oil...I would not want less than 40 psi in cruise flight.

Also, don't worry too much about whether your secondary ignition is working or not. I flew all the way to Crossville and back to Kansas City on just the magnetos...and the engine ran better! I now routinely shut the secondary off in flight and usually see lower CHTs as a result.