Electrical issue.....please help

[bnicolette]

So.........we got the engine back on my airplane. Took it out for the run-up and everything was beautiful except the volt meter was right about on the 0 mark and the moment we would load it up with some draw items, it would go below (left) of zero. The JPI was showing about 13 volts right after start and then as we loaded it up it would drop down to about 12 volts and even below momentarily.

I have a plane power alternator that was installed just a couple months ago and has about 25 hours on it.

What we have done since finding the issue:

Installed a new Zeftronics regulator

Installed a new Concorde battery (R35AXC)

We checked the wiring to the alternator of course and everything is correct. The system was working just fine before we removed the engine.

I have only been there intermittently while the mechanic was working on it.

What are some things that you guys would suggest for troubleshooting?

[KSMooniac]

Zeftronics has detailed troubleshooting instructions on their site (or at least used to) that tell you explicitly where to measure with a multimeter, and what you should see. I would start there... good luck! I have the exact same components on my plane now after my alternator puked a couple years ago.

[larryb]

An alternator is a simple device. Assuming the unit is functional, if there is current through the field winding there will be output. So the first thing I would measure is field resistance to ground. It should be 3 to 5 ohms. If it is high, the brushes or alternator are bad. If it is 0, then there is a short to ground. The field is fed by the voltage regulator. The regulator adjusts the alterantor output by modulating the field current.

Next I'd measure voltage at the field terminal. Master switch on, engine off. It should be near battery. If you get no voltage, you have trouble in the wiring or voltage regulator.

In the original alternator there are 2 field terminals. One is tied to GND through a jumper, the other is connected to the voltage regulator. When I say "field terminal" above I'm talking about the one connected to the voltage regulator.

While you're at it, check the voltage at the battery terminal of the alternator. You should see battery voltage there.

Larry

[Marauder]

If all what above checks out, I would make sure your belt isn't slipping. I had a problem with my gear popping the breaker on extension. Went through all of the normal "electron" testing stuff only to find out when the alternator was loaded up, the belt issue came into play. Don't ask me to explain it, nor think I am nuts... I spent a lot of money to rebuild an alternator, replace the circuit breaker, the voltage regulator, re-working the gear, blah, blah, blah -- to find out that, for some unknown reason, replacing the belt fixed it...

[carusoam]

Zeftronics also has some onboard LEDs to help with trouble shooting...

Check your wires' continuity. Be careful when being near moving machine parts...

Best regards,

-a-

[Steve65E-NC]

I think that gage you are calling a Voltmeter is actually an Amp Meter and behaving appropriately. The only thing that I heard wrong was the JPI going down to 12 volts with load. However, my JPI always shows about .5volt below the battery terminal. So, even that may be ok. Are you sure that you even have a problem.

[laytonl]

My guess is a loose belt, loose connection in the field circuit, or a bad diode in the alternator. I would check in that order.

After checking belt tension, the next thing to do is check field voltage at the alternator with the master on and engine off. It should be about 1-1.5 volts less than the battery voltage.

Good luck and let us know what you find.

Lee

[bnicolette]

I think that gage you are calling a Voltmeter is actually an Amp Meter and behaving appropriately. The only thing that I heard wrong was the JPI going down to 12 volts with load. However, my JPI always shows about .5volt below the battery terminal. So, even that may be ok. Are you sure that you even have a problem.

Steve thanks for that...yes I meant the amp meter. My JPI always was at 14v right after the engine start and then would stay continuously between 13.8 and 13.7 volts for the remainder of the flight. I don't ever remember seeing the amp meter stay below (left) of the zero mark. Also I never had the low voltage light on the annunciator blinking at me during idle before.

Funny the only thing that changed since we took the engine off was we installed a new belt as we couldn't find when the last one was done and since the prop was off, we decided to put a new one on. Not that it couldn't be slipping. It is certainly tight though.

The green light on the Zeftronics regulator is on steady when running the engine or with the master switch on.

The resistance was 3.? between the terminals on the alternator. IIRC Don't ask me which terminals, I just know that that check was normal.

The voltage off of the field wire (coming from the regulator) when the master switch is on (engine not running) is right around battery voltage.

The mechanic was thinking that perhaps since he had the wires pulled back during the engine removal that perhaps the field wire (coming from the regulator) could be the culprit and not making a good connection. But then why would it read okay when the plane is just sitting there?

The hours are ticking up as he troubleshoots this!!

[laytonl]

You are on the right track. Based on your tests, I suspect the field wire as you mechanic suggested. Put the voltmeter back on the alternator field connection and wiggle, pull, and tug on the field wire and see if the voltage drops. Lee

[N601RX]

It sounds like voltage is getting to the field. The other end of the field winding must be grounded to complete the circuit. On my alternator their is a short wire that does this. Make sure that whatever it grounded to isn't painted over.

[bnicolette]

It sounds like voltage is getting to the field. The other end of the field winding must be grounded to complete the circuit. On my alternator their is a short wire that does this. Make sure that whatever it grounded to isn't painted over.

Are you referring to the shielding? The field wire that comes up to the alternator is shielded and the shielding is grounded.

Thanks everybody for your help. It's been since September since I've flown my plane. Just when I thought it was time to get back in the air after getting the engine back on, we ran into this. Very discouraging!

[N601RX]

No. There should be a short wire that goes from a terminal on the alternator back to ground. I'm not familiar with plane power, but this is the way most alternators are set up.

[N601RX]

One other very important thing. There should be a heavy braided ground strap from your engine case to the firewall. Make sure this is in place and there is no paint under it.

[bnicolette]

One other very important thing. There should be a heavy braided ground strap from your engine case to the firewall. Make sure this is in place and there is no paint under it.

I think this is the one you are referring to? Is this setup okay?

[N601RX]

Yes that's it. Without it the engine will ground throught the prop and mixture cable and will basically melt them.

[N601RX]

Here is the wiring diagram. With the master on if you are getting close to battery voltage on F1 and F2 is grounded the alternator should produce output when spinning. If not its bad. I have saw F2 grounded a couple of different ways before. Some are just grounded to a point close to the alternator, and some run the ground back to the ground point on the regulator, which is also grounded to the firewall.

http://www.plane-power.com/images/Installation_Packages/SINGLE_ENGINE_WIRING.pdf

[Lionudakis]

You can have near battery voltage at the alternator field terminal sitting static, but find it drops quickly in operation, it does require a small amount of current that it might be starved of while in operation. I have piggy backed a wire on each point (field, ground, and batt terminal's at alt and battery for voltage drop) and zip tie them back into plane for 'in operation testing' with a meter, something You can't do very safe with a prop spinning. It can save some serious time just seeing what's going on in each department while operating and probably find the missing electrons quickly, could be as simple as a near break in a wire that's got insulation around it hiding it, carries voltage, but not amperage very well. I've ran many a wire on the outside of a regional jet to troubleshoot head scratcher's. Good luck

[duke]

MAKE SURE YOU TEST THE FIELD VOLTAGE IN CIRCUIT AS A HIGH RESISTANCE WILL STILL SHOW BATT VOLTAGE WITH AN OPEN CCT

[bnicolette]

MAKE SURE YOU TEST THE FIELD VOLTAGE IN CIRCUIT AS A HIGH RESISTANCE WILL STILL SHOW BATT VOLTAGE WITH AN OPEN CCT

Duke

Can you explain what you mean by check it in circuit.

[wishboneash]

Duke

Can you explain what you mean by check it in circuit.

I think he means to check it under load. The only way to that would be to add an auxiliary wire that can be safely brought out of the engine area and voltage measured while the engine is running. Suggested in a post above.

[Alan Fox]

If the jpi is reading over 12.8 volts you are charging , If the ampmeter is not working , check the two inline fuses at the shunt..... If the JPI voltage is over 13 and dropping with load , it is probably a loose belt.... Also check the ground wire at the engine mount bolt , it is a braided cable, although if this was forgottrn it probably wont start...

[bnicolette]

Thanks for all the input. I will let you know how the mechanic makes out on Monday. Fingers crossed that he finds the culprit.

Found a really good article for folks like me that don't know anything about the electrical system and how it functions. If nothing else, I'm getting a good understanding on the electrical system on my airplane. Certainly an area where I was lacking!

http://www.nflite.com/ChargingSystem.html

[carusoam]

I'm betting on the slipping belt solution. Any takers?

It is a little more challenging to get right compared to current automotive technology. They don't squeal noticebly like slipping auto belts.

Best regards,

-a-

[bnicolette]

I'm betting on the slipping belt solution. Any takers?

It is a little more challenging to get right compared to current automotive technology. They don't squeal noticebly like slipping auto belts.

Best regards,

-a-

I sure as heck hope to be able to let everybody know Monday morning (Not afternoon) what the shop finds!!! I also sure hope that he doesn't have to pull the prop back off. What a pain in the butt that design is twisting each one of those prop bolts a little at a time. And then trying to safety wire with the thicker wire and the safety wire holes are never in the alignment that you want them to be! Ughhhhh.

[Marauder]

And until we officially find out, some Buschism on the topic: http://www.eaavideo.org/video.aspx?v=1549006054001

I love the guy but if I am at all the least bit tired when when I begin watching one of these, Zzzzzzzzz