Voltage problem, need suggestions

[Paul K]

VPX experts out there. Is it possible the VPX unit is having a bad day! Is there anything in it that could cause this issue?

Just fishing as I am stumped for the time being!

[Mich48041]

As other have said, a charged battery should have a voltage of about 13. Put a charger on the battery and charge it up. Take the charger off and wait a few hours, then measure the battery voltage to see if is about 13. Just because a battery is new does not necessarily mean that it is good. It probably is, but should be checked to make sure that it holds a charge.
The charger can be left connected to the battery during testing to keep it from running down. Take some more voltage readings. But this time put the red meter lead on battery positive and the use the black meter lead to measure the voltage on the POSITIVE terminals of various components. So you will be measuring the voltage drop on wires from end to end. A voltage drop of 1/2 volt or more is cause for concern. Make the measurements with a heavy load so that problems will show up better. Include the "B" terminals of the alternators in this test.
Another thing to try is to disconnect one of the alternators from the master contactor to see if that fixes the problem. If not, disconnect the other alternator to see what happens. I am thinking that maybe a bad alternator or some other device could be dragging the voltage down. Is any device warmer than it should be? Does the VP-X get warm?
If the master contactor is the problem, then there will be a voltage drop across it. It is unlikely though if the engine starts OK. Let us know what the voltage drops are between the positive battery terminal and the positive side of various loads.

[Mich48041]

With master on, battery side 12.38.
Test at VPX terminal with load 11.38

If the above tests were made within a few minutes of each other, then there is definitely a bad connection. What about the crimps of terminals on the ends of wires? Pull very hard to see if a terminal will come off. Or better yet, measure the voltage drop across the crimps.

[Paul K]

Just an update, I think the real problem has been identified. It was screaming at me all along, I just didn't see it! It was a "runaway flap" warning. What does that have to do with any of this?

First let me warn you about cheep big box voltage meters. Please check them againat a known standard to see if they are accurate. Mine was about a half volt low acrost the board. In the trash it goes! No big loss, it only cost about $8.00 many years ago. So, all of the voltage readings were low but the differences in voltage readings between two ends of a wire or relay were fairly accurate but the low voltage readings were keeping me sidetracked.

Back to the runaway flap warning, I realized it was another new issue I hadn't seen already and attributed somehow to the low voltage. Funny thing is, the flap motor wasn't runnung and the switches were in the normal or non movement position. Also, the flaps functioned absolutely normal after the VPX was reset. That alone caused me to send off an email to their service department and within about 10 minutes, my phone was ringing with Chad Jenson on the line. Didn't take long for Chad to tell me he was sending the return forms via email for the return of my unit. I guess I'm the second one to fail like this and it sounds like an easy fix.

One other indicator that the cockpit readings were wrong is that the more times I powered everything up, the crazier the readings got. At one of the power ups, one buss read 12.6, another read 9.2, and the third read 2.1 volts. Absolutely not possible.

Chad assured me I would have it back in plenty of time to reinstall it and perform lots of test before OshKosh. Even said he would let me use his personal unit if necessary to get to OshKosh! Kodos to Chad and Aerotronics.

[BillL]

Happy to hear you got to the bottom of your problem, Paul. Now you can shave your head so all the hair can grow back evenly

Anyone who can sort through a vacuum resin infusion for making a plenum (as you have shown) can solve any problem. It has taken me months to get this one stupid VARTM part to come out right.

[Paul K]

Good news, bad news! Chad called today and let me know the issue is one of the circuit boards melted! Sodder actually melted and ran off. They don't know why but think high voltage or something like that. No, I have never been hit by lightning and the only nights out of the hangar have been at OshKosh and a few overnight trips. Never fly anywhere near Lightning!

Anyway, that's the good news. Ths bad news is that they don't have the parts to repair it in time for my trip to OshKosh but they do have a loaner that might get to me by Friday. If and this is a big if, I get the loaner before Friday, I hope to still make it to OshKosh early in the week. Not what I was hoping for but might be the best I can do. Hate to scrub it this year but ****, I'm stuck!

[912ry]

I've been having a low voltage problem lately. Sometimes while starting, the engine would barely turn over, other times it would work ok. While running the system voltage would be around 13.1~13.4 volts. I checked the troubleshooting page from Plane Power and went to the hangar ready for a diagnostics session. Getting started I decided to give all the big connections an inspection. The cable below connects the engine to the firewall. When I pulled on it the connection was snug, but it moved a little. Another tug and the wire came out. You can see the wire has been blackened due to the electricity trying to flow through it. Fortunately this wire is plenty long, so I was able to cut it back and crimp a new connector on. Problem solved!
RY is ~2 1/2 years old with 235 hours.






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[BillL]

Originally Posted by 912ry

I've been having a low voltage problem lately. Sometimes while starting, the engine would barely turn over, other times it would work ok. While running the system voltage would be around 13.1~13.4 volts. I checked the troubleshooting page from Plane Power and went to the hangar ready for a diagnostics session. Getting started I decided to give all the big connections an inspection. The cable below connects the engine to the firewall. When I pulled on it the connection was snug, but it moved a little. Another tug and the wire came out. You can see the wire has been blackened due to the electricity trying to flow through it. Fortunately this wire is plenty long, so I was able to cut it back and crimp a new connector on. Problem solved!
RY is ~2 1/2 years old with 235 hours.

Was this a Vans part or "home built"? Vans had some weak joints a few years back. The pull test on a #2 connector is about 550 pounds. That's right, 550. This should be kept in mind when checking in the plane- the pull force for a good joint is substantial.

[tkracmer]

I had the same problem with the engine to firewall ground cable from Van's. I cleaned and soldered mine and have had no further problems.

[az_gila]

Originally Posted by tkracmer

I had the same problem with the engine to firewall ground cable from Van's. I cleaned and soldered mine and have had no further problems.

Good "how-to" courtesy of Aeroelectric Bob here -

http://www.aeroelectric.com/articles/big_term.pdf