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Voltage Question?

Flyingbeard

Active Member
Hi All of you Electrical Guys,

I have an RV-8 with a B&C BC460H 60 amp alternator controlled by a B&C LR3C-14 voltage regulator. All has been normal for the last 185 hours, but yesterday day I had a low voltage warning on start up. The voltage read 12 volts at first and slowly increased to above 12.6 volts and the warning went away. Almost like it needed to warm up. Is it possible the regulator needs adjustment due to winter operations.

Thanks in advance, for any ideas where to look and what to trouble shoot.


Mark
 
First thing we need to know is where are we reading the voltage from.

If the voltage is reading from your main bus (most likely), then I would check your alternator for output. If the alternator is working properly, you would get a reading of around 14.3 volts or so depending on the adjustment on your regulator. A reading of 12.6 volts would indicate that only your battery is powering your main bus. Less likely, your regulator may be the culprit but I would look at the alternator first.

You didn't mention if you have an ammeter. If you do, what's it reading and is it connected to measure the amps out of the alternator or the battery?
 
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What is your battery no load terminal voltage? You can just use engine off buss voltage as an indication as well if getting to the battery terminals is too hard.

Carl
 
Got called to work

Hi Carl and Pat,

First off, thanks for the quick reply! I just got called in to fly a trip for work and I will out of town for a few days. I will check the alternator out put and note the ammeter meter reading as soon as I can. I am also running two earthX ETX 680C batteries and will note there voltage also.
 
BC alternator and regulator is very reliable.
First thing I would check the alternator belt for slipage.
Next thing, page 10, check the wire F on the back of the alternator.
It is subjected to vibration.

https://bandc.com/wp-content/uploads/2018/05/lr3c_technical_manual_revC.pdf#page=6

Good Luck
Beat me to this. Before you get too deep into the troubleshooting try these first. Especially the loose belt. It can show on the volt meter as low voltage. Tightening the belt could be all that is needed.
 
A little more information

I had the day off between trips this week, so quick trip to the hangar today.

Pulled the engine cowling off and inspected the alternator, the belt was tight and shows no signs of slipping. Voltage right from the alternator is 14.0 volts. Each of the EarthX ETX680C batteries voltage was 12.5 & 12.6 volts.

I ran the engine at 1090 RPM for a few minutes, system Volts read 12.2 and had a draw of 20 amps slowing decreasing to 12 to 11 amps.

No low voltage warnings today. it was unusually warm for December temp in the mid 50s.

For now, the plan is to watch and fly.:eek:
 
SNIP…

I ran the engine at 1090 RPM for a few minutes, system Volts read 12.2 and had a draw of 20 amps slowing decreasing to 12 to 11 amps.

No low voltage warnings today. it was unusually warm for December temp in the mid 50s.

For now, the plan is to watch and fly.:eek:

No - absolutely not ready to fly.

Forget your low voltage warning - that can be set at any value. Your data that voltage never got above 12.2 volts says you have a problem. Normal bus voltage for you should be around 14vdc.

The current draw seems normal, so perhaps you just have a voltage instrument error.

You need to find out where you are measuring voltage. If you can’t do that, do the same engine run with a multi meter connected to the main buss (the one that is fed from the battery that is on the operating alternator). This will tell truth, from that you can figure out what is going on.

One other data point missing, what is your battery terminal voltage, no load (as in the master(s) off)?

Carl
 
Thanks Carl

Thanks Carl!

I am currently working this weekend and will be looking into next week.

I will post what I find.

Mark
 
Update!

Merry Christmas Everyone!

While traveling for work, I called B&C Specialty and spoke with Nathan, he directed me to check the voltage the Alt, Batteries, and other places on the voltage regulator. The alternator and voltage regulator were operating normally.

Then I called Rob Hickman who built my Advanced Panel for help trouble shooting. We talked about my system and how it uses an ACM (advanced control module) Red Box and that I should check the voltage at the input power red terminal and the black ground.

When I got home, I checked the red power terminal and noticed some wires on it were a little loose. On closer inspection, I noticed evidence of sparking and heating from the loose wires. Removed the nut from the terminal and cleaned and inspected the wires. Replaced the Nylock nut and torqued the nut correctly.

On run up and test flight, system voltage is now a steady 14.1 volts. I am not sure, but the terminal nut must of been loose since installed and 180 hours of flight and turbulence must of combined to loosen up the eyelets to spark and create voltage fluctuations.

My thanks to Nathan and Rob! They helped me sort thought this issue.
 
Best Advice

Merry Christmas Everyone!

While traveling for work, I called B&C Specialty and spoke with Nathan, he directed me to check the voltage the Alt, Batteries, and other places on the voltage regulator. The alternator and voltage regulator were operating normally.

Then I called Rob Hickman who built my Advanced Panel for help trouble shooting. We talked about my system and how it uses an ACM (advanced control module) Red Box and that I should check the voltage at the input power red terminal and the black ground.

When I got home, I checked the red power terminal and noticed some wires on it were a little loose. On closer inspection, I noticed evidence of sparking and heating from the loose wires. Removed the nut from the terminal and cleaned and inspected the wires. Replaced the Nylock nut and torqued the nut correctly.

On run up and test flight, system voltage is now a steady 14.1 volts. I am not sure, but the terminal nut must of been loose since installed and 180 hours of flight and turbulence must of combined to loosen up the eyelets to spark and create voltage fluctuations.

My thanks to Nathan and Rob! They helped me sort thought this issue.

So the best advice you got was from the poster who said, "not OK," He may have saved your bacon. Time to send VAF an annual donation.
 
Thank You!

Thanks again Carl, Pat and the others who posted. Flew 4.8 hours on day after Christmas and the electric system is back to normal!:)
 
This is very helpful. I have had similar issues. On a recent flight my voltage was decreasing down to 12.2. I got very nervous and started to divert when it instantly went back up to 13+. But I’ve never seen it anywhere near 14V. I have a Plane Power 60A alternator (#99-1012).

I’ll remove the cowl and have a look at this tomorrow, but any suggestions on where to focus my efforts is appreciated.

I have a VP-X Pro and here are the readings I was describing:
IMG_7920-L.jpg


And then it returned to normal:
IMG_7921-L.jpg
 
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Also, my airplane (RV-7 w/ IO375) now has 220hrs and I found this picture from one of the first ground runs (<1hr), so it DID work at one time. Any suggestions are greatly appreciated!

IMG_2430-L.jpg
 
Also, my airplane (RV-7 w/ IO375) now has 220hrs and I found this picture from one of the first ground runs (<1hr), so it DID work at one time. Any suggestions are greatly appreciated!

IMG_2430-L.jpg

As many have mentioned, including me, check the belt tension first. That is the simplest to start.
 
As others have mentioned, if it has been going down over a long period of time then check the belt tension first. If it dropped all of a sudden then check the regulator adjustment.

:cool:
 
So I checked the alternator belt tension and it was a little loose. I tightened it to specs, run-up looked okay with 10A+ going to the battery and 13-14V showing on VPX. Departed and it instantly showed 0.2A charge going to battery, battery voltage dropped to below 12.2V, and I RTB’ed. Parked, put a Voltameter on the battery and it reads 12.75 without the engine running. What is going on!?!?

I think the VPX is just not wired correctly. I’ve never had any indication of a low battery in flight, just low readings on the VPX.

Thoughts on where to start (over)?
 
Chris, intermittent electrical problems are caused by bad connections.
Take every connection apart that is related to the charging system.
Also suspect contacts inside of switches.
12.2 volts means that there is a load connected to the battery, but the battery is not being charged.
12.75 volts means that no load is connected to the battery which is not being charged.
Monitor the voltage with an independent meter while cruising.
 
i pulled the alternator, sent it in, bench test revealed a bad alternator. Plane Power sent me a new one today.

Thanks all for helping!
 
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