Alternator Failure

Took my 9A up to do to work on some of the test flight time.

I was flying along working on getting comfortable with the AP, when the entire electrical system went dead.

Just as I was starting to try and figure out what the problem was, everything started rebooting.

After the screens came back up, the VPX gave me an overvoltage error and said it had shut down the Alternator field.

I talked with Chad, and he confirmed that the VPX behaved as designed in an overvoltage situation. It should shut down, and then come back up with the alternator field disabled, so that is good.

Here are my questions:

1 - I have less than nine hours on the plane. How likely is it that the alternator really did go bad? It is a plane power. I took it to the local auto parts store, and they tried to run a test on it, but couldn't figure out how to hook up the alt field lead. However, he did run the voltage test and it failed. I'll call plane power in the morning, but how reliable is that test without the alt field enabled?

2 - I have an IBBS backup battery that has the main screen, engine monitor and one ADAHRS wired directly to it. Why would they all reboot as well? This one really concerns me since I hope to use this as an IFR airplane eventually.

Thanks!

-Dan

It is most likely that your voltage regulator went bad, not the alternator. Some alternators have an internal/built-in voltage regulator and some use an external. If your alternator is set up for an external regulator, it will not produce any voltage or current without a field hooked to a voltage source. If it is an internally regulated, the regulator must be in good health to pass the voltage test and your symptoms indicate that it is shot (i.e. should have produced an over-voltage condition).

The fact that your VPX drives an Alternator field, tells me that your setup is likely externally regulated. Most internally regulated alternators do not have a field connection. The PP may be an exception.

2) I would expect that the VPX would kill the power feed to the instruments listed during an over-voltage condition and should not affect operation on BB. Is the battery backup internal or external to the unit? In the case of the latter, I would suspect that it may not be wired up properly. Depending upon how high the voltage got, I suppose it is possible those units shut down on their own to protect themselves. I don't have experience with any those specific units.

Good luck,

Larry

Talk about the law of unintended consequences.

I guess we know not to put all of our eggs in the VPX basket, especially if IFR.

To answer your question #1, you can't test the alternator without connecting the field. PP are usually internally regulated, with over voltage protection built in.

BTW, I think this might require NTSB reporting if I remember correctly. I believe the criteria was loss of greater than 50% of your instrumentation on an EFIS equipped aircraft.

Paige

I have the PP 60A alternator. It is internally regulated. The field wire is buss voltage (and power) for the field . The internal regulator "regulates" the amount of that "power" that goes to the field, not the VPX. My PP also has an internal over voltage limiter. The VPX only provides amp sensing and shuts off the field if the voltage goes too high - a redundancy for that function with the PP.

If the sense/field wire does not provide buss (also battery) voltage back to the alternator, then 1. it does not know what the buss voltage is, and 2. it has no power for the field to generate output. If, the voltage back to the field is low,lets say 1.0 volts below buss, then the regulator thinks it's output is 1 volt low and will increase output by +1 volt. This increases the output to 15.0 volts instead of 14.0 volts.

1. You should know what alternator you have, and how it works
2. Connect the field line to the B+ (and 12v to start the process) on the test stand to generate the test. The person testing did not understand the equipment.
3. Look for a loose connection somewhere from the plug on the alternator back to the buss for the field wire.
4. I believe the VPX will do what you want, but don't trust some black box to read your mind and hope it will do what you expect. Know how it works.

dweyant said:

2 - I have an IBBS backup battery that has the main screen, engine monitor and one ADAHRS wired directly to it. Why would they all reboot as well? This one really concerns me since I hope to use this as an IFR airplane eventually.

Click to expand...

What avionics package are you using? You may need to take that one up with the manufacturer.

Since I'm not flying I can't talk from experience but from what I read in the vpx manual, an alternator over voltage should shut down the alt field and give the warning. Seems like the main battery should have stayed on and continued to supply power. Maybe the vpx shut off the battery as well for protection and then powered it back on when safe? I know there are several ways to hook up the ibbs. You may want to make sure it is wired correctly.

PaigeHoffart said:

Talk about the law of unintended consequences.

I guess we know not to put all of our eggs in the VPX basket, especially if IFR.

Paige

Click to expand...

I purposely did not post in this thread until we had a better idea of what happened. After a couple of days of working with Dan, he did find a loose wire on his master switch. Subsequent flying has resulted in no failures of the electrical system as a whole, alternator, VPX, or IBBS.

More flying will be done to be sure, but the VPX and IBBS are working just fine.

cjensen said:

I purposely did not post in this thread until we had a better idea of what happened. After a couple of days of working with Dan, he did find a loose wire on his master switch. Subsequent flying has resulted in no failures of the electrical system as a whole, alternator, VPX, or IBBS.

More flying will be done to be sure, but the VPX and IBBS are working just fine.

Click to expand...

Facts and data are always better than speculation - - Chad, the OP said the EFIS rebooted, and he has an IBBS. Any words of wisdom for us on how to wire that IBBS to avoid blank screens from a single point failure (like this) at a critical moment?

Disclosure: I don't have the VPX, but think the issue is more basic than this product.

BillL said:

Any words of wisdom for us on how to wire that IBBS to avoid blank screens from a single point failure (like this) at a critical moment?

Click to expand...

Page 46 of the VPX manual

BillL said:

Facts and data are always better than speculation - - Chad, the OP said the EFIS rebooted, and he has an IBBS. Any words of wisdom for us on how to wire that IBBS to avoid blank screens from a single point failure (like this) at a critical moment?

Disclosure: I don't have the VPX, but think the issue is more basic than this product.

Click to expand...

Bill,

First, Chad was absolutely great in helping me get this very bizarre issue resolved. It took us about two days and about 20 e-mails to get it sorted out, but without his help it would have been a lot worse.

Turns out I had two (mostly) unrelated issues.

First - I had a loose wire at the master switch. Just loose enough it turns out to occasionally while in flight (vibration) to cause the master solenoid to drop off and back on. That caused a lot of unusual behavior. Including causing both the A and B bank on the VPX to "fail". Something that Chad said while theoretically possible, was highly unlikely.

Second - I had, it turns out not configured the VPX properly for the IBBS battery. I'll take most of the blame for this one, but I did point out to Chad that the VPX manual could use some tweaking to make the why's of setting up the backup methods clearer. Because I had not set them up correctly when the VPX went down, the IBBS never got notification that there was a problem, so it didn't kick in.

I also had the pleasure of finding a really cool shop in the next small town over. They rebuild alternators, and have since 1940. They tested my plane power alternator and when we found it was fine refused to let me pay them for anything. Everything in the shop looked like it was WWII surplus.

After we figured out the loose wire issue yesterday, I made the firmware changes to the VPX and went out and flew. I put about 1.5 hours on the plane and the VPX did exactly what it was supposed to do. I also tested (on the ground) pulling power to the VPX and the IBBS battery is now kicking in properly with no avionics reboot.

-Dan

Mark Dickens said:

Page 46 of the VPX manual

Click to expand...

There are two things you need to do.

One you need to wire it properly (the manual shows you how to do that).

Also, you need to make sure you configure the VPX so that it know what you have done. That is the step I had not done properly.

-Dan

And if anyone has the newer IBBS system, I have instructions for that that haven't made it to the install manual yet. Next manual update will have them included.

Excellent Dan! Good you have this all squared away now. I did not realize that the VPX handled the IBBS switching too. Mine operates differently. Thanks for the explanation - it will surely help others to ensure a safe airplane.

My IBBS backup system scared the **** out of me a couple weeks ago. I was wiring up my panel and finally got to the forest of grounding tabs. I spent about an hour stripping, crimping, and pushing them on the tabs. I went in for dinner and when I came out, both of my G3X screens were on and flashing "message".

As I looked down at my empty battery tray I had no idea what was going on. Then I realized by finally grounding the tabs, I had energized the IBBS system.

I can attest that the IBBS battery can sit in a box, then mounted on the sub panel for several months and still have power enough to power 2 10" screens and scare one builder!

I guess I need to use more inline quotes so people can't take my comments out of context...

dweyant said:

I talked with Chad, and he confirmed that the VPX behaved as designed in an overvoltage situation. It should shut down, and then come back up with the alternator field disabled

Click to expand...

Chad can you confirm that the above statement in the original post is inaccurate?


Paige

Sorry I missed this Paige...the VPX will shut off if the set voltage limit is exceeded and it will shut off the primary alternator field so when powered back up the OV condition is isolated.