What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Another alternator problem

Veetail88

Well Known Member
I have a problem that may or may not have anything to do with my 60 amp Plane Power alternator.

Closing in on 600 hours on the unit, I've pretty much always had an intermittent problem with the field circuit breaker popping. Resetting it always works. Sometimes for 20 minutes, sometimes for 50 hours. As such, I haven't been able to track down the problem.

Having researched the problem some, I've changed the connector plug end with no change.

But that's not what I'm writing about, I don't think.

On a trip out east over the last couple of days, the breaker popped. I reset it, and a little while later, it popped again. When I reset it, I noticed that the amperage indicator started rapidly climbing. By the time it got up to 50 amps I pulled the breaker. Tried it again with the same result.

Fortunately, I have a backup B&C SD-8 dynamo on board and it did it's job, happily churning out it's 8 amps or less as needed. Buss voltage hung in at 13.8 so my mission didn't even experience a hiccup.

Not being any kind of electrical expert I'm stumped. I understand voltage runaway but that's not what happens. If amperage is a product of what is demanded, how can the system indicate a high draw from the main alternator but not from the backup when the main is offline?

The output from the main alternator is measured by a shunt, whereas a hall effect transducer measures the output from the SD-8. Both are wired into an AFS 4500.

I considered that maybe something in the system is drawing big amperage and that maybe I'm not seeing the indication from the SD-8 because 8 amps is all it can give, but with a little load shedding I get the amp draw down to 6. Switching the main alternator on in that condition still sees the indication go through the roof.

Could it be a problem with the EFIS? Maybe a messed up shunt assembly? The latter seems impossible as it's such a simple thing.

Thoughts? I've included the schematic below. It's based on a Bob Nuckolls' design.

2le2mmo.jpg
 
Last edited:
I have zero expertise to even begin to offer any explanation but..... It seems to me that if you had any component trying to draw that much current it would be toast. In my mind I keep going back to a thought of some type of intermittent short to ground or a bad connection somewhere before the buss.

The experts will chime in soon. Threads like this are interesting and educational. Sorry you're having an issue.
 
What kind of battery do you have?

The EarthX Li ion batteries will pull a TON of current on initial charge, if you had run on th battery for a few minutes before resetting that may have been the battery taking a charge.

After start mine will pull 40-50A+ for a short period.
 
Agreed, the ETX batteries can accept pretty much whatever the alternator can deliver when the voltage is a bit low - but if you're running a standard battery then the problem is likely with your voltage sensing wire, or ground. The alternator is thinking your voltage is too low and is ramping up the field current - that causes the high output current on the B lead, and the high field current is tripping the field breaker.
 
What kind of battery do you have?

The EarthX Li ion batteries will pull a TON of current on initial charge, if you had run on th battery for a few minutes before resetting that may have been the battery taking a charge.

After start mine will pull 40-50A+ for a short period.

Interesting thought. I do have an EarthX Etx900. It's difficult to remember every detail of when I did what, so I suppose it's possible the battery was down when I started the alternator. I'll shoot out to the hanger later on, drag it out of the hanger and see what happens.
 
You do need 'one issue at a time'. :)

Recheck current draw after making sure the bat is fully charged.

But since you've been having long term issues with the 'field' breaker popping, I'd be taking a long hard look at the alternator.

Note that I put 'field' in quotes; has Plane Power ever shared the internal schematic for their alternators? Without an internal schematic, we have no way to know whether the 'field' terminal really does remove power from the field, or is just a control terminal that tells the internal regulator to shut down the field. Either way, frequent trips indicate:1. defective breaker 2. intermittent short to ground of the field wiring/connectors somewhere downstream of the breaker 3. Assuming the alt has OV protection, then OV condition, or false detection of OV condition, causing the crowbar to trip the breaker 4. intermittent internal short to ground or intermittent failure mode of the regulator.

For excessive current on only the PP alt, easiest 1st: check the B-lead from the alt for worn insulation.
2nd, if you have an efis/engine monitor, check history for short term voltage excursions to over the OV trip point (field breaker faults).

Last, my money is on an intermittent, failing alternator 3 or 4).

I would agree that the 40-50A readings could easily be the E.X. battery, if it's in a discharged state when the main alt comes on line.

Charlie
 
Thanks for the help guys. I ran out to the airport, hauled the 8 out and started it with the alternator offline. After the EFIS booted, I energized the field and sure enough, the amp draw went up to 60, the max of the unit. In a half a minute or so, the number came down but bumped around between 12 and 28 amps. The longer I ran it the more it settled down. I normally see 14.4 volts though and it didn't come up to that, but I only ran it for a short while.

I agree though, I would like to figure out what has been making the field circuit pop.
 
I had the same symptoms. Replaced the alternator under warranty due to an intermittent stator wiring. Has been OK for a few years now.

Unfortunately, it took its toll on the Odyssey battery which died prematurely recently.
 
Voltage staying low, yet high indicated AMP Draw

If the alternator was really putting out 60 AMPS the voltage would also be rising sharply unless there was some type of short. Looking at your schematic a short is unlikely since the SD-8 was functioning fine. I would check the shunt, if that is starting to open the voltage across it would rise indicating an erroneous high amperage on the EFS.
 
Windings

Had the same problem as Vern, if one of the stator lines break the result is somewhat unpredictable. I think it's possible this also causes a noisy DC bus, one so dirty that the EFIS may not be able to give you an accurate current or voltage reading.
I was able to shine a flashlight into the back end on my PP and actually see the broken winding.
 
If the alternator was really putting out 60 AMPS the voltage would also be rising sharply unless there was some type of short. Looking at your schematic a short is unlikely since the SD-8 was functioning fine. I would check the shunt, if that is starting to open the voltage across it would rise indicating an erroneous high amperage on the EFS.

Lithium chemistry batteries can suck a *lot* of amps if they are significantly discharged. Their 'source impedance' is very low, which is why they can output such massive current into a starter without voltage drop, unlike a lead-acid. But the flip side is that they present a very low 'load impedance' (bordering on looking like a short to the unwashed) when being charged. That's one of my pet peeves about E.X. They put this elaborate set of smarts in the battery; why not include a charge regulator instead of telling the purchaser to limit their alternator capacity?
 
This from Earthx's site.

"Why do you use the alternator output to size your batteries in cars or airplanes? Starting the engine (cranking amps) is only one part of what the batteries does. Your battery is also part of the charging system and the current from the alternator goes through the battery. You must use a lithium battery that is designed to handle the current from the alternator or you can damage it, cause premature failure or possible even cell rupture. In the lithium world (LiFePo4) the maximum current rate is 5C x true amp hour (not equivalent rating). As an example, the ETX900 is a true 16Ah battery. The max charge rate then is 80A (5C x 16AH = 80A)."​

And,

"I just installed my EarthX battery in my aircraft and started the engine and my charging amps was really high, is this normal?
Yes, this is normal. A lithium battery can and will accept a much higher charging current than an equal size lead acid battery. If your battery is not fully charged, your alternator can potentially output a current equal to or slightly above the alternator?s rating for a few minutes to top the battery off. Your fuse, breaker, or current limiting device should be sized approximately 20% above the alternator rating. Example, if you have a 40 amp alternator, use a fuse, breaker, current limiter set to 48 amps (or 50amps)."​

So given the above, the 60 amps I saw today when energizing the alternator field makes sense as my alternator is indeed a 60 amp model. And as I do have the EXT900, my alternator is not oversized. Guess I won't worry about it.
 
What size is your field breaker? Maybe it's getting weak and needs to be replaced?
 
Take the alternator to an auto parts store and have it checked. I suspect it's the built-in regulator. Or, if you can borrow an alternator, try that.

-Marc
 
High current

Of all the problems that are possible in an electrical system, I worry most about high current faults. These have the potential to cause serious problems if not attended too. I was in a spam can and the alt cb popped. Pushed it back in and kept going. Turns out the alternator had an internal short. Didnt know how lucky I was until I got the note from the mechanic.
 
They put this elaborate set of smarts in the battery; why not include a charge regulator instead of telling the purchaser to limit their alternator capacity?

Absolutely Charlie, that would be fundamental to a clean sheet system designed around a lithium chemistry. A regulator with active amperage management, not just a fixed voltage. Or a completely separate path to charge the battery though the fancy battery system using an actively controlled DC-DC inverter. It would maintain cell balance and sense internal temperatures.

This does not help the OP, though.
 
Last edited:
What about swapping out the battery with something like an odyssey to see if your current draws come back to "normal?" I know the battery is different size but you could rig up something just to hold it for an engine run.
I don't know anything about the EX batteries but man that kind of current flow would make me nervous.
 
Last edited:
Why the sudden increase in current in flight

I can understand having the high current on startup, but the OP stated it happened in flight when the battery should already be charged or close to it. Also he states the current continued to increase which is counter to how a battery charges. The current should start high, then decrease. The OP also states that the SD-8 worked as expected indicating the battery and wiring are ok. He did say the voltage was lower on the SD-8 so if the Earth X has a failing cell the higher voltage from the main alternator maybe causing the good cells into an over charge state. I believe the Earth X has a fault light so that can easily be checked. As suggested swapping out the battery would be very helpful in tracking down the issue.
 
Maybe this will answer some questions. I think the discussion is good and I appreciate everyone?s input.

There are two questions. #1. Why does the alternator trip the field breaker. #2. Is the EarthX battery performing correctly or not and is it dangerous to keep flying it.

For sure, the EarthX has nothing to do with the field breaker tripping. I?ve had this issue long before I put in the EarthX. I ran a PC 680 for three years prior and had the same problem. Nothing about that changed when I added the EarthX. I will say that I?m reticent to go back to a PC 680 as the EarthX is such a superior product in terms of performance. The PC 680 at times struggled with turning the motor whereas the EarthX spins the prop with gusto! I could **** near taxi with it. Then there?s the weight. If I could buy that kind of weight savings for myself, I?d be svelte. I?m not.

Regarding the high amperage draw when the alternator comes online, there are things I cannot confirm one way or the other. During my normal start procedure, I usually crank the motor over while the EFIS is still booting so I would never have looked or noticed if there was a high current draw as it takes a while before the screen lights up. Even then it has not been my habit to immediately check the amp draw. It will be now.

It seems that the more the battery is depleted, the higher the current draw would be, but I know about as much about that technology as I do about brain surgery. No one calls me doctor. The exact words from their FAQs however states that if the battery ?is not fully charged? that it will draw as much as it can until topped off, specifically stating it will go to the limit of the alternator. Maybe that?s a problem with their design or not, but that is what appears to be happening and is in keeping with what they think is ok, by default.

I cannot say for sure that when the breaker first tripped the other day, that I noticed it very quickly or not. It may have been a few minutes. Don?t know. In that condition, with everything turned on, the SD-8 wouldn?t be able to keep up and the battery might have been down a little. As well, the SD-8 doesn?t produce the same voltage of the big alternator, or so it seems as in order to see that, I need to have things powered on, which is drawing current. But that raises the question of ?what is fully charged? and ?will the battery draw big amps for a few moments even if it is down just a tiny bit??

It may also be possible that there is some minor issue with this particular battery, although it holds a charge extremely well and has cranking power out the wazoo! I?ve not rigged an annunciator light to the lead from the battery, but I will now.

The bigger issue for the moment remains tracking down the field circuit breaker problem. A great friend has a spare alternator on the shelf that is a direct swap, so I think I?ll bolt it in and see if the problem continues.
 
Also he states the current continued to increase which is counter to how a battery charges. The current should start high, then decrease. The OP also states that the SD-8 worked as expected indicating the battery and wiring are ok.

Regarding this, when in flight and upon resetting the field breaker, the amperage indication did start to climb, but very quickly. Kind of like when you first plug a multi tester into an electrical outlet. Seems like the instrument takes a few tenths of a second figuring out what the value is. Also, I would think that when the demand from the battery reaches the alternator, that the alternator would take a short bit of time to ramp up to meet the demand. In flight, I pulled the breaker immediately and didn’t give the battery a chance to take any charge. On the ground yesterday, with infinitely more courage as I was “on the ground”, I let it climb to the high reading. Within moments the reading did start on its way down.
 
Last edited:
It seems the most prudent approach now is just what you are planning to do...
alt swap and see what you get.
 
Back
Top