Alternator Issues - Suspected Over Voltage

[iamtheari]

I almost posted this in the thread about regretting a decision to upgrade planes. Anyhow, the left engine in the 310 got jealous of the attention the right one was getting from the recent magneto coil meltdown.

The wiring diagram shows that each engine’s alternator has its own voltage regulator and over-voltage protection relay. The over-voltage relays turn off the alternator when the voltage is too high. They can be reset by cycling the field power to the alternator.

The symptoms are that all works fine at idle. Both alternators put out a fair contribution to the airplane’s needs as long as I keep the throttle low. But if the left alternator is turned on when the engine is over ~1000rpm, both alternators turn off. Slowly increasing rpm from idle on the left side, I heard a faint whine in the headset before the alternators shut off. I feel like I saw a high voltage reading on the panel at some point during the test run but I can’t swear to a number. Cycling the field power on each alternator turns it back on, but if the left one is turned on at more than that ~1000rpm point they both shut off again almost immediately. I suspect that the over-voltage relays are tripping due to the left alternator putting out too high a voltage when run at higher speed.

In trying to trace down the problem, I found that the external filter capacitor lead on the left side was broken. I don’t know when that happened. In trying to find out the correct capacitor, though, I was informed that my Hartzell ALT-9522R alternator has an internal filter capacitor so the external one isn’t necessary.

I think that the best experiment would be to swap the two voltage regulators in the plane and see if the issue follows those or stays with the alternator. But it’s winter and I’d rather do some more measurements in the hangar if possible.

Does anyone have specific suggestions that I, a moron with a digital multimeter and only a few major electronics projects to my name (mostly guitar amplifiers, so lots of ~400VDC but not a lot of moving parts), can measure to help decide between ordering either an alternator or a pair of Plane Power voltage regulators?

 

[Jim K]

Have you flown over Peoria, IL recently?

 

[iamtheari]

Have you flown over Peoria, IL recently?

That’s another thread that I considered hijacking with this post. But no, I have not graced your fine skies.

 

[PaulMillner]

I think that the best experiment would be to swap the two voltage regulators in the plane and see if the issue follows those or stays with the alternator. But it’s winter and I’d rather do some more measurements in the hangar if possible.

You can troubleshoot this on the ground, though that's not always the most convenient way. It's likely the left regulator is the trouble... but it *could* be a wiring issue. It's pretty rare for an alternator to go rogue high-voltage all on its own. But, do you have, or can you borrow, a variable voltage DC power supply? Disconnect the battery, hook up the power supply set at 12 volts (assuming a 12 volt airplane, or 24 volts if otherwise). Turn on each charging system in turn, and you should see full voltage on the field terminal, as each regulator strives to cause its alternator to raise the voltage to the system setpoint.

As you raise the voltage to the nominal charging voltage, 14/28, the field voltage on each regulator should drop, as the regulator is satisfied that system voltage is adequate. Push it to 15/30 if you need to... the regulator should definitely try to start regulating by dropping field voltage. I suspect you'll see that the left regulator keeps at close to full output voltage even at 15/30 volts... meaning it's no longer regulating... time for the PlanePower upgrade. Sucks that Hartzell just about doubled prices... maybe there's some lower priced units in someone's inventory.

Paul

 

[iamtheari]

Thanks, Paul. Unfortunately, I don't have a variable voltage power supply available. I'm contemplating other ways to put in voltages between 24 and 30 volts to see how the regulators react. I wonder if the local hardware store has five 6V lantern batteries in stock.

 

[flyingbrit]

For $50 you can get a 30V/10A lab type power supply which can also serve as a battery charger:

https://www.amazon.com/LW-K3010D-Adjustable-Switching-Regulated-Spectrophotometer/dp/B07512KQDW/ref=asc_df_B07512KQDW/?tag=hyprod-20&linkCode=df0&hvadid=241928409996&hvpos=&hvnetw=g&hvrand=6394927802779716739&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9017003&hvtargid=pla-641755143112&mcid=20a3185bb3f13453872f88139f302ada&gclid=EAIaIQobChMI1ZOe-uLkhAMVNltHAR3z1w_LEAQYByABEgKD2vD_BwE&th=1

 

[iamtheari]

Amazon is usually okay but occasionally takes a long time to get stuff to me. The last thing I ordered was placed on January 11 and arrived on February 11, despite showing in stock when I ordered it. So I'll keep that option in my back pocket.

Today, I did 90 minutes of yoga swapping the voltage regulators. Most of that was spent trying to remove a damaged and difficult to reach machine screw, which is now on my desk until I can take it to a taxidermist.

I should have time to do a test run tomorrow and narrow down the cause of the problem.

 

[Dan Thomas]

The wiring diagram shows that each engine’s alternator has its own voltage regulator and over-voltage protection relay. The over-voltage relays turn off the alternator when the voltage is too high. They can be reset by cycling the field power to the alternator.

What year of 310 is this? From the '67-'68 manual:

 

[iamtheari]

What year of 310 is this? From the '67-'68 manual:

It’s a 1976. It has a pair of load-sharing regulators. I don’t know when they changed. My little test did catch the problem appearing on the right side, but intermittent so I was lucky to catch it. So I have a pair of those fancy Plane Power regulators coming my way.