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Help troubleshooting a Plane Power Alternator

UnPossible

UnPossible

Well Known Member
Hey - I am having issues with my Plane Power alternator, and I'm not sure where to start trouble shooting.

When I start the plane the alternator comes on line, voltage on the main bus is 14+ and everything appears to be working fine.

However, as soon as I go full power for take off, I am getting an alternator short alarm from my VP-X system. I have tried to reset the alternator in the air (under relatively high power) and it trips off as soon as it resets. Once I am on the ground and back at low power, I can reset the alternator and it doesn't trip.

Nothing has changed in my electrical system. My alternator is 6 years old with about 275 hours. If the alternator is bad, I'll replace it, but I just want to avoid spending $500 on a new alternator that doesn't solve the problem.

So electrical experts.... what is the best way to trouble shoot this issue to figure out what is going on?
 
Step one is to look at or replace the connector at the alternator. Numerous VAF'ers have posted problems with this connector on the PP alternators and have had to replace the pins. It is unclear to me if this could cause your problem, but is definately a good place to start.

Larry
 
UnPossible said:
Hey - I am having issues with my Plane Power alternator, and I'm not sure where to start trouble shooting.

When I start the plane the alternator comes on line, voltage on the main bus is 14+ and everything appears to be working fine.

However, as soon as I go full power for take off, I am getting an alternator short alarm from my VP-X system.
Click to expand...

What is an "alternator short alarm? What exactly is your VPX trying to tell you?
 
Overcurrent on the Alternator field lead.

The PP has a built in crowbar OV device that could be shorting the field lead.
 
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I don't recall the exact wording of the error message, but was something like "alternator short circuit detected". I know for sure the word "short" was in the message. In the G3X data log, it's just reported as ALT Fault

FYI - I looked at the data log to see if there was anything goofy going on with the main bus voltage, and once I started the engine, the main bus voltage bounced around between 14.4 and 14.6 volts during taxi and run-up. Once I went to 2700 rpm, the alternator tripped, and voltage dropped to 12.8V.
 
Brantel said:
Overcurrent on the Alternator B lead.

The PP has a built in crowbar OV device that could be shorting the B lead.
Click to expand...

A crowbar typically shorts the alt field when it senses an over voltage condition. I don't know of any crowbars that measure current. It definately does not short the B lead, though the B lead my see the short as the B lead is often tied to the voltage sense input of the VR (which is what the crowbar shorts), unless the PP has a separate voltage sense input, which I suspect it does. I am unfamiliar with the PPs .

EDIT: On second thought, I can't imagine a crowbar design that would sink the VR feed to ground if it was tied to the B lead, so am guessing there is a discrete VR sense input on the PP, called Alt Fld, with it's own CB and this circuit is what would see the short if the crowbar activated.

I do agree though that a tripping crowbar is good guess given the symptoms (assuming the short was detected on the Alt Fld circuit.

Larry
 
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lr172 said:
A crowbar typically shorts the alt field when it senses an over voltage condition. I don't know of any crowbars that measure current. It definately does not short the B lead, though the B lead my see the short as the B lead is often tied to the voltage sense input of the VR (which is what the crowbar shorts), unless the PP has a separate voltage sense input, which I suspect it does. I am unfamiliar with the PPs .

EDIT: On second thought, I can't imagine a crowbar design that would sink the VR feed to ground if it was tied to the B lead, so am guessing there is a discrete VR sense input on the PP, called Alt Fld, with it's own CB.

I do agree though that a tripping crowbar is good guess given the symptoms.

Larry
Click to expand...

I mistyped. The field or control lead is what I meant to refer to not the B lead. Thanks for the correction.

The PP is an internally regulated alt with a single control lead. The VP-X monitors the current in this lead. Similar to a field circuit breaker that is traditionally used.
 
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One more data point, I went back and looked at the data log on a long flight in July and the main bus voltage bounced between 14.4 and 14.6 V the entire flight... which is the exact same numbers I saw from the flight when the alternator faulted.
 
UnPossible said:
One more data point, I went back and looked at the data log on a long flight in July and the main bus voltage bounced between 14.4 and 14.6 V the entire flight... which is the exact same numbers I saw from the flight when the alternator faulted.
Click to expand...

Verify the amp setting on the VP-X alternator circuit.

What was the current being measured by the VP-X on the alt circuit?
 
Brantel said:
Verify the amp setting on the VP-X alternator circuit.

What was the current being measured by the VP-X on the alt circuit?
Click to expand...



Interesting... it was bouncing around between 16-19 amps.... but 4 or 5 seconds after I went to 2700 rpm, there was one reading of 66 Amps and then it tripped. What would the amps to jump so high with increased rpm?
 
UnPossible said:
Interesting... it was bouncing around between 16-19 amps.... but 4 or 5 seconds after I went to 2700 rpm, there was one reading of 66 Amps and then it tripped. What would the amps to jump so high with increased rpm?
Click to expand...

A failing connection on the alt fld connector pin could cause the VR to think the volts are low. It's job is to keep throwing more current at the buss until the volts come back up.

As I mentioned, start with the connector, as it is a known weak point on the PP and a possible cause for these symptoms.

The RPM component could be anecdotal and the connector is not failing until the RPMs come up.

Larry
 
UnPossible said:
Interesting... it was bouncing around between 16-19 amps.... but 4 or 5 seconds after I went to 2700 rpm, there was one reading of 66 Amps and then it tripped. What would the amps to jump so high with increased rpm?
Click to expand...

To clarify I was asking about the alt field circuit not the B lead current. Typically the field is less than 5 amps.....
 
Correct me if I am wrong, but I don't think the G3X reports the amp draw of that circuit....

I pulled the connector and the pins in the connector and on the alternator all look clean and straight. Is there anything in the connector I should be looking for specifically?
 
The G3X will show the individual current on each circuit. One of them should be your alternator field.
 
I've been doing some transition training in the past two weeks in an older (early 90's build) RV-6.

Airplane does not have a voltmeter, except for one in the 396.

Long story short, confirmed overvoltage sometimes reaching 20V. Noticed first with some flickering of panel lights.

When we stopped on the ground to troubleshoot, at runup RPM it was reading 14-15V. In the air it was between 17-20V.

Pulled the cowl, reseated connectors, and checked wiring. Nothing amiss. So yesterday I pulled the alternator. The original one has been on the airplane since new as far as I can tell, and it is a ND 14684N for a Suzuki Samurai. Brand new replacement on order, cost $58.00. We could have got a rebuilt unit locally for $150.

25 years on an inexpensive alternator is pretty good for service life.
 
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UnPossible said:
Correct me if I am wrong, but I don't think the G3X reports the amp draw of that circuit....

I pulled the connector and the pins in the connector and on the alternator all look clean and straight. Is there anything in the connector I should be looking for specifically?
Click to expand...

You are looking for a bad crimp on the pin or frayed wires at the crimp. Hit it again with your crimper or add some solder. If you solder it, you'll need some strain relief.

My thoughts:

If you are sure the crimp is good, check the wires from the alternator back to the firewall. If good, I would suggest having the alternator tested locally or look for a replacement.

Larry
 
rocketbob said:
I've been doing some transition training in the past two weeks in an older (early 90's build) RV-6.

Airplane does not have a voltmeter, except for one in the 396.

Long story short, confirmed overvoltage sometimes reaching 20V. Noticed first with some flickering of panel lights.

When we stopped on the ground to troubleshoot, at runup RPM it was reading 14-15V. In the air it was between 17-20V.

Pulled the cowl, reseated connectors, and checked wiring. Nothing amiss. So yesterday I pulled the alternator. The original one has been on the airplane since new as far as I can tell, and it is a ND 14684N for a Suzuki Samurai. Brand new replacement on order, cost $58.00. We could have got a rebuilt unit locally for $150.

25 years on an inexpensive alternator is pretty good for service life.
Click to expand...

I have 600 trouble free hours on my 14158, externally regulated alternator - cost = $35 + VR.
 
lr172 said:
You are looking for a bad crimp on the pin or frayed wires at the crimp. Hit it again with your crimper or add some solder. If you solder it, you'll need some strain relief.

My thoughts:

If you are sure the crimp is good, check the wires from the alternator back to the firewall. If good, I would suggest having the alternator tested locally or look for a replacement.

Larry
Click to expand...

Next dumb question..... I have never removed pins from this type of connector. Is there some sort of trick or tool that is needed?
 
UnPossible said:
Next dumb question..... I have never removed pins from this type of connector. Is there some sort of trick or tool that is needed?
Click to expand...

Yes, a pin extractor. Though you can sometimes get them out with a small piece of thin metal. I don't know the PP's and therefore the connector used, so you'll need to do research on pin extraction. Google is your friend.

The pins have a small tang sticking out of the pin. When you push the pin into the connector, the tang locks the pin in. You need to get the extractor in on the other side to push the tang in as you pull the pin out. If the wire breaks when you pull, as I suspect it will if that was the problem, you need something like a small drill bit to push it out.

Larry
 
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UnPossible said:
So electrical experts.... what is the best way to trouble shoot this issue to figure out what is going on?
Click to expand...

The best way I know of is to try a replacement Alt and see if the problem is cured.

I had my field CB keep tripping on my PP Alt. I tried a replacement CB and checked the connections. Replaced the Alt and problem solved! If you were closer I would loan you my old unit to try. I loaned it to another guy who used it to make a 1000 nm flight home so I know it works in cruise flight.

Other than that, take it to your local Auto parts shop for testing, but it may or may not show a problem on the bench.

-Marc
 
My experience

I have had some recurring issues with the Plane Power installed on my -8. I have had the pin in the connector fatigue and break ( I now fill the back of the connector with RTV to support the wires). More importantly since my experience with the second problem was similar to what you are currently experiencing is the fit between the bearing that supports the aft end of the armature and the rear housing was not good and allowed the outer bearing race to spin in the housing. The initial symptom was intermittent failure only in flight and once the housing had worn enough it allowed the armature to contact the windings and shorted the internal regulator creating a total failure. My suggestion is to remove the drive belt from the pulley and check for any play in the alternator shaft. The issue with the bearing to housing fit has happened to me on two separate Plane Power alternators even though the drive belt was tensioned per the Plane Power recommended procedure.
 
I am fortunate that some of the folks that developed the Plane Power alternator live near by. I was able to get a hold of a couple of them and they came over this afternoon. They checked all the pins in the connector, etc and everything looks good.

We swapped the internal regulator out of another PP alternator and...... same problem. At startup, everything works fine, bus is at 14.4 volts and charging, but once I increase the rpm above 2,000 rpm I got the same alternator short message.

At this point it doesn't appear to be an alternator issue. I am going to call the folks at VP-X in the morning and see what suggestions they may have for trouble-shooting.
 
I had a PP Alt trip every time I took off recently. Changed the master solenoid, no help. Changes the PP brush and VR assembly, no help. Changed the $4.95 battery master switch, Tada!
 
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