There is more info on this topic in other threads, and even more in the old CPA forums, but most of it boils down to this: Tom Carr recommended removing the alt restart battery pack and placard in the system inop with a logbook entry. His theory is that pressing that button releases unregulated current from the alternators into the system and if a diode is failed, could start an electrical fire or explode the batteries. My airplane was missing the battery pack on delivery, and I’ve chosen to just placard it inop and move on.

I’ve run the overvolt test and it went fine, and twice I’ve turned off an ALT and back on with no issues (all as ground tests). I mitigate the risk of not having the battery pack by limiting my flight in Hard IFR.

-LJ

Hi Ed, I have had a couple of High Volt events also, the checklist restored alternator power … for a while. The fix was two new voltage regulators and replacing all the diodes on the electrical panel circuit board on the front firewall.

I took me probably six to eight months for my name to come up on the wait list for a hangar. Since I needed one of the 48 ft. hangars, it took a little longer for one of those to come open. I expect you’re in that same boat. Once they let you know your name has come up and you get moved, it’ll be great having you here!

Rick

Tim, I’m a nerd and do all the tests, I can’t do the ALT restart as the system was removed at some point in the past and was not documented. The button is on the panel and with the panel upgrade this coming year, the restart kit is going back in. Years ago, while flying patrol in the 337, I actually used the button to restart the electrical system where other attempts failed.

I do the electrical system ops test on every flight after both engines are started, before the radio master switch is turned on. It looks at some very important stuff and takes seconds once you have done it a couple of times. The test actually caught one of the warning lights being out, one flight it was good, the next not. Individual lights are not replaced, the unit is pulled out and a new one is put in.

Thanks for all the info Rick...

Alot of interesting information here, have been reading and absorbing very interesting stuff.

I did find in the maintenance manual that the purpose of the restart switch is for when the alternators drop out due to high electrical load such as use of flaps motor (see attached photo of page out of maintenance manual for my E model). Apparently the older systems (voltage regulators) would drop offline with heavy load. Maybe we don't experience/expect that as much now with more modern electricals, lower draw avionics, better charging gear.

I can not find in my manual any specs on maintenance of the system.

Now I am probably going to do something I will regret as I am sure there is someone more knowledgeable than me. But I will stick my neck out here.

Thinking about the original problem, there is a low voltage at the field connection of the alternator when the restart button is pushed, 0.3v and 0.6V. Something in the back of my head, that I may have read a long time ago, says it doesn't take much juice to restart an automotive style alternator field. Witness the battery pack of 2 D cells (3V) or 4 C cells (6V). That said: thinking back to college physics, decades ago (gulp), V (volts)=I(current) x R(resistance). So we have a circuit with 4 cells and a resistor with 12 ohms. Best I can find, looks like healthy "C" cells are capable of 1 amp a piece unbridled. So that means when the button is pressed 4 amps max can come out of the box. Suppose the cells are at least a little dated. Maybe assume 0.5 amps max output a piece, or 2 amps when the button is pushed with a somewhat dated contents in the battery box. The voltage drop across a resistor will be subject to the V=IR rule. So assuming 2 amps of current and 12 ohms of resistor, 2 x 12 = 24 volts drop across the resistor. Subtract 24 volts resistor drop from the 4 "C" cells voltage of 4x1.5 = 6 volts and an output of 0.3 to 0.6 volts at the alternator field starts to sound pretty good. This gets to MSHAC's question of what should the voltage at the alternator field terminal be when that switch is pushed. And maybe the answer is pretty low.

Also, the issue to excite the alternator may not be so much voltage from the restart circuit, but current. Current, movement of electrons, creates the field that the armature spins in to generate electricity. When the button is pushed, it's not so much how much voltage is in the field but how much current is going through it. Again, V=IR or V/R=I. We have 6 volts of "C" cells and 12 ohms of resistor: 6 divided by 12 = 0.5 or 1/2 amp. My reading, 1/10 of an amp is enough to excite an automotive style alternator.

I will not be offended if I get quickly dispatched on my discussion by anyone more knowledgeable. Just sticking it out there. Maybe the voltage stats detected are the norm.

Perhaps the next test is not a voltage test of various wiring junctures but an ammeter test of the alternator restart circuit. See how much or if any current flowing through when button pressed. Also, another next step might be a test of the system switches per the procedure outlined by others here to see how the system works. Or was dysfunction on a test what started the dive into probing the circuit?

see attached

wslade2, thank you for lending some mental energy to this circuit. Your thought process seems sound.

1. Monday, I'll check the amperage load while the circuit is energized. Maybe it's not volts that are needed to restart an alternator, ... maybe it's amps?

2. The switch in the restart system is good. To eliminate the switch as a culprit, I have even bypassed the switch during testing, but to no avail.

The two diodes in the system, as well as the resistor, all check within specifications. The alternator switches are good. The voltage regulators are good. The entire electrical system works great ... except for this Alternator Restart circuit.

Is it to be expected that voltage should drop to zero when the dry-cell batteries are connected to the alternator's field terminal? Or, is there something wrong inside the seemingly good alternator/s?

3. Yes, all this started when the checklist specified test failed to restart the alternator/s. The checklist specifies in the event the alternators do not restart, reduce the electrical load, and try again. I attempted that, without success.

Thanks again,

I'll report back Monday evening ...

Rick

Also, be sure to check the ground. Will have to have a good ground to make a complete circuit especially if it’s low amps. I expect the negative side of the battery box to be secured to a ground somewhere. Also attention to the ground for the engine (which becomes the ground for the alternator).

Will do, thanks again.

So, today I tried to do an amperage test to see what the current draw is when the dry cell batteries are supplying power to one alternator. I know I'm not proficient in the use of a multimeter ... I had no success. I even resorted to YouTube to see how to measure an amperage load, and I followed those instructions, but to no avail. I'll attempt that again tomorrow.

I checked the grounding circuit and there was no resistance at all between the ring terminal on the negative battery cable and the airframe anywhere I measured it, even at the alternators.

Tomorrow is another day...

Rick

Ammeter should be hooked in “series”. one probe of the meter hooked to one end of wire and other probe hooked to the other end. Just think of it like cutting the wire and putting the meter in the line, like two leads of a light socket. If you’re able to select, start high on the amperage and work down. I don’t buy very expensive meters and most of those have a 10 amp capacity. It’ll say on the meter. They usually use a fuse and if apply too much current they’ll blow the fuse and end reading zero. If zero reading, check fuse in meter in case it’s blown. You should get some kind of reading. If not back to testing every connection and solder joint

wslade2, thank you again. That is how I thought the multi-meter should be hooked up to read amperage. That's how I thought I'd done it successfully in the past, and YouTube verified that. What I didn't check is the fuse in the multi-meter. Perhaps I can get to that tomorrow, as I'd still like to know.

Well, today I had some level of success. After doing three different iterations of an under-load test at each junction in the restart system, (for some unknown reason), the system started showing voltage at the field terminals. I don't know why, which is frustrating, because the problem could return anytime.

The decisive test will be to run the engines and perform the Alternator Restart Test to see if the 1.75-ish volts at each alternator are enough to excite the fields and restore power to a cold electrical system.

Rick

With wiring issues, sometimes you just have to keep going over it. A little detail can be the problem.

Today there was a measure of success.

We ran the engines and performed a pseudo test of the Alternator Restart system. It worked!

The entire system has not been reinstalled yet from the testing, so I just used dry cell batteries to excite the rear alternator and it fired off with 1.5v. Once the rear alternator restarted, the front came up as well. The next step is to reinstall the system and do another test. Since testing has shown I will have 1.75-ish volts at each alternator's field terminal when the system is installed, I'm hoping I'll be good to go.

I did see it would NOT restart with ANY load on the system though. Since an alternator's field has about a 3.5 amp load, I think it would be advisable to only try to restart one alternator, then turn on the other alternator.

There will be more testing to follow.

So, I have:

• Changed from the original two D-Cell batteries to the currently specified four C-Cell batteries,
• Replaced the Alternator Restart switch,
• Replaced the resistor,
• Replaced the two diodes,
• Reinstalled, and tested the system.

I now have 2.2 volts on the field terminals of the voltage regulator's Molex connectors.

Either alternator will now consistently restart when:
1. The electrical system is unloaded, "and"
2. Only one alternator switch is turned on.

My experience has yielded the Alternator Restart system will not restart both alternators at the same time, nor will it restart if there is anything but the most minimal load on the bus when the restart system is activated. I was able to restart an alternator, with one led taxi light switch turned on, but with nothing additional.

Both the "Alternator Restart Test" checklist, as well as the "Total Loss of Electrical Power" checklist, indicate the electrical load should be reduced, and specify both alternator switches should be turned ON when trying to restore power. So, if you really must use this system, contemplate turning only one alternator ON, as you follow the checklist.

Once one alternator is restarted, and power is being resupplied to the General Bus, there will be power to the remaining alternator's field terminal, so when the remaining alternator's switch is turned on, it will come online also.

Has anyone been able to restart more than one alternator at a time, and/or restart with any kind of a load on the electrical system?

Can anyone explain what the purpose of the resistor is in the line from the dry-cell batteries to the Alternator Restart switch? It sure seems counter-productive as it lowers the voltage at the field terminals of the voltage regulator's Molex connectors.

Rick

Rick, as I study the system, it makes no sense to me why the resistor is in the circuit. If its voltage that makes the alternator restart, and more voltage is better (at least up to the alternator's rated voltage), why would we want to reduce the voltage in the circuit with a resistor???

It would be like putting a resistor in a circuit with a light bulb - the light bulb would be dimmer due to lower voltage.

A resistor may be used to prevent voltage spikes, but again, in a DC circuit with small batteries like this one, I just don't see the need.

You could simply put an alligator clip test lead on either side of the resistor to bypass it, and then test your voltage at the field when pressing the restart button. You should see an increase.

If you do this test, please let us know your findings.