Electrical System "Shutdown"

Have you measured the current draw of the landing light circuits off the battery with the engine off?

Brushes worn on alternator. That would be my first check. Just replace them. You can find them at Napa. For Motorola alternator


Sent from my iPhone using SuperCub.Org

I had precisely the same problem.

I bought a used 0-320 core that came with that alternator, but no regulator, so I bought the InterAv regulator and installed both. It would discharge if the bus was pulling anything over about 12 amps. So, if I had the radio on, the transponder and the strobes, it would result in a dead battery in about 90 minutes while flying. (the Whelen strobe power supply draws about 10 amps all by itself, if I recall). Belts were replaced, wiring scrutinized, amp gauges consulted and finally the alternator was removed and bench tested and found to be fit and hardy.

I replaced the regulator and overvoltage relay with a Plane Power R1224. It is a PMA replacement for the InterAv regulator and includes an over voltage relay and can be adjusted for float voltage, if necessary. The wiring is different because the over voltage relay is internal, but it isn't significant.

That solved it with no further issues.

https://www.aircraftspruce.com/pages/el/alternators_0planepoweralternators/planePowerSAL2.php

PA 18 with the InterAv STC is on the AML.

P.S.: The InterAv regulator was mounted on the firewall below and to the right of the muffler. The replacement was moved inside the cabin to eliminate the possibility that radiated heat was causing the problem.

Also add a good ground wire from engine/alternator to airframe if there is none


Sent from my iPhone using SuperCub.Org

Plane-Power is ALWAYS the answer to an Interav problem.

If you stay with the Interav system, have the alternator bench checked. Without being there to troubleshoot it, I'd have to agree that bad brushes sound like the most likely cause. If the alternator bench checks good, check for voltage at the field terminal on the back of the alternator. With the system 'on' and the engine not turning, the voltage should be near battery voltage.
With the system 'on' and the engine running, that voltage should be a couple of volts or less. Anything else and the reg or wiring is bad.

Web

Keep those helpful hints coming. There is a wealth of information in this group! I'll be starting to record some numbers either tonight (10/21) or tomorrow, beginning with the battery's current draw (taxi and landing lights on w/engine off). Battery draw with engine off is 12.68. After that a close look at the alternator to see if it can be removed without taking off the prop (looks like the prop will have to come off, and I'll likely have to hire a mechanic for this). Before prop removal I'll pull the OVR breaker to see if this makes a difference. Will do this with engine running. If not, off comes the alternator to be bench checked and following your orders. I really appreciate all of your help! Thanks.
Phil

Quite a few years ago when I was in Kodiak with a 1979 Super Cub I had to replace the brushes in the interav alternator. An old guy at the Marine electrical shop on Lily Lake knew all about those Ford alternators and had a set of brushes for me. Can't remember the whole procedure, seems to me there was a toothpick involved. I was able to replace the brushes without taking the prop and nose Bowl off. That was with the old guys instructions he was pretty cool.

The alternator can be removed without pulling the prop. Prop needs to come off if replacing the belt, though.

Web

I’ll go straight from “not recommended” directly to “HELL NO”. There is a very good reason that an o/v relay is installed in the first place.

It appears that you are conflating draw (current) with voltage. In the absence of a working charging system, current increases with load and voltage drops.

I’ll say this with no malice or intent to insult whatsoever, but when you consider bypassing safety equipment, the consequences can be quite serious. This might be the time to step back a bit and enlist the assistance of someone with a bit more experience.

suupercub said:

Today I ran some numbers as you requested. With engine off, the battery draw was 12.68. Then with taxi light 12.06, and landing light 11.98. I pulled the OVR circuit breaker and started the acft. With the electrical components on but leaving landing lights off, the ammeter was indicating normal. However when I deployed the landing/taxi lights, the ammeter immediately went into discharge. I did this over again to determine that the OVR was malfunctioning. My question: Is it safe to fly with the OVR disabled? I rarely use the landing lights anyway, but looks like I'll have to order a new OVR to make the system complete. Would appreciate your thoughts on this. Thanks.

Click to expand...

No offense taken. Will order a new OVR tomorrow. Thanks.

suupercub said:

Today I ran some numbers as you requested. With engine off, the battery draw was 12.68. Then with taxi light 12.06, and landing light 11.98. I pulled the OVR circuit breaker and started the acft. With the electrical components on but leaving landing lights off, the ammeter was indicating normal. However when I deployed the landing/taxi lights, the ammeter immediately went into discharge. I did this over again to determine that the OVR was malfunctioning. My question: Is it safe to fly with the OVR disabled? I rarely use the landing lights anyway, but looks like I'll have to order a new OVR to make the system complete. Would appreciate your thoughts on this. Thanks.

Click to expand...

Hang on a second. The over voltage relay is just that; a relay. In this system a sensor in the unit looks for high voltage. When voltage exceeds a certain limit, the relay opens the field circuit, stopping the charging system from operating. When you pulled the circuit breaker, the relay opened the field circuit shutting the alternator system off. You were just running on battery power. I'm curious about the ammeter reading 'normal'. Was it just reading '0'?

Start your engine. Make sure your alternator field (over voltage) breaker and output breaker are both set (pushed in) See what your buss voltage is, with a digital volt meter. If you can't reach the bus to clip on the positive voltmeter lead, see if you can put it into a lighter socket. Turn on all electrical loads and see if your buss voltage drops. It should stay around 13.8 volts. Make sure the battery is charged up from the engine start and the idle rpm is above 1000 rpm.

If you pull your over voltage breaker, it just shuts off your charging system. As long as you minimize the electrical load (don't turn on anything not needed for flight) and you understand that the battery will not be recharged as you are flying, your perfectly safe to fly.

And as stated in moneyburner's post you have rolled voltage readings and current readings together. It's quicker to troubleshoot a charging system using voltage readings but the 'load' on a charging system is actually current measured in amps. If you have an ammeter in the battery lead (old school, as in original generator systems), it will ALWAYS read discharge if the electrical system is on and the engine is off. If it goes into discharge when the engine is running above idle, it's indicating that the alternator is not able to supply power and some of that power is coming out of the battery.

Web

wireweinie said:

If you pull your over voltage breaker, it just shuts off your charging system. As long as you minimize the electrical load (don't turn on anything not needed for flight) and you understand that the battery will not be recharged as you are flying, your perfectly safe to fly.

Web

Click to expand...

I thought he meant to by-pass the O/V relay; that wouldn’t be safe. I didn’t read it hard enough.

This is the O/V reset procedure.