Low Voltage Troubleshooting?

[Ragsf15e]

2 hours ago, ArtVandelay said:

He is only showing 3 amps. Sounds like VR issue. I had this problem and fixed it with a new VR.


Tom

I tend to think (or maybe hope) you’re right. However, I’d really like to check out the VR before replacing it.  Unsure how to do that, but learning quickly!

[Paul_Havelka]

Did you ever put your volt meter on the battery itself? Also, just because the alternator is relatively new, that doesn’t mean it can’t be bad.


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[carusoam]

1) Study up on what VR you have... manufacturer and model number... This will tell you what the voltage out should be...

2) Get help for measuring voltage... if you decide to run wires to the VR to see what is happening there...  you will be plenty busy being PIC...

3) Study the graph for your VR... in your application.... it will have a graph of V vs engine rpm...  yes, voltage will vary some with engine rpm... at idle, it will barely charge the battery or slightly discharge depending on what else is running....

4) Suspect everything... the further downstream you go, tiny wires, and dirty connections, and heavy loads, will cause variations in readings...

5) Some VRs are not adjustable... they either work or don’t work right... 

6) As for how Mooneys are wired... the cigarette lighter plug depends on the model... most are wired from the bus to ground with a CB in the way to protect it...  Early LBs leave this source un-switched... it is hot with 24V at all times... later LBs got 12V step down transformers to keep portable devices from getting fried accidentally....

PP thoughts only, good luck with your search...

Best regards,

-a-

[N231BN]

Also, inspect the field wire from the VR to the ALT. Look for frayed connections at either terminal or a partial break along the wire. This will limit the field current available which will limit the ALT's output.

[cliffy]

Let's go back to basics folks

The alternator puts out a voltage that is regulated by the VR. The VR "samples" the voltage it sees and adjusts what it sees to a predetermined figure (usually somewhere between 13.9 -14.2  or -.3

What you want to know is what the alternator is actually putting on the main buss and at the battery terminals when it is running. The only way in most cases to do this is to actually test it with a good volt meter (hand held) at those points. So, before you get your panties all wound up find out what is actually going on by taking (or have someone take) a volt meter to the battery (while the engine is running at more than idle, with master on and radios on) and put the tester leads to the battery posts and see what the actual battery is seeing for voltage. If you need basic testing instructions they usually come with a volt meter, Red lead to positive post, black lead to negative post on the battery. Write down what you find. Do this also with the engine shut down and all power turned off in the airplane. 

Next you'll have to gain access to the main buss in the airplane where all the circuit breakers are connected to) and test the voltage there also. Writhe that down also and then get back to us here. All the plug in voltmeters are nice but they won't tell you what the battery sees or the buss is actually seeing as they sample somewhere else in the voltage line. 

Just as a point of reference, most automobile alternators (with the built in VRs) actually run a "sense wire" from the alternator all the way to the instrument panel inside the car to sample the actual voltage at the "main buss" in the car so the alternator voltage can be adjusted to show what they want at the buss. There is always some voltage drop throughout the system as the electricity passes through different connectors and devices. 

PP has a complete trouble shooting procedure on their website It is designed for mechanics but it is very informative Here's the link-     https://planepower.aero/wp-content/uploads/2018/02/Troubleshooting-Single-Engine-Externally-Regulated-Alternators.pdf

 

 

 

[cliffy]

Forgot to add- When you check the battery voltage without the engine running or a battery charger hooked to it make sure that you turn on the Master switch and a landing light for about 30 seconds then turn them and everything else off to check the no load, no charging voltage. This removes the "surface charge" voltage  that the battery  will show if it has just been charging. It now will show a true battery voltage. 

[Ragsf15e]

On 5/3/2019 at 6:50 AM, N231BN said:

Also, inspect the field wire from the VR to the ALT. Look for frayed connections at either terminal or a partial break along the wire. This will limit the field current available which will limit the ALT's output.

This post may have nailed it.  I’ve been through the whole electrical system with a multimeter and I think I’ve got it down to an issue with the field wire.  Here’s the problem, the 2 x cannon plugs make it almost impossible to get a voltage output from the Voltage Regulator at the Voltage Regulator.  I can’t get to the wires to check them with power on to the VR.

I did check the field wire at the alternator, and its 2V less than the input to the VR.  That’s right on the bottom of their spec range.  I measured the resistance of the field wire and it’s high, like 10 ohms.  

Heres my question, does the field wire really go through both the black plastic cannon plug and the big metal one in the picture?  Why?  Is it possible to simplify this wiring?  Is there another way it should be?

[carusoam]

For simplicity of wiring...

My 65C was probably wired directly... single wire from generator field to controller field.

10 ohms sounds kind of high for what should be a 0 ohm direct connection...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Ragsf15e]

5 minutes ago, carusoam said:

For simplicity of wiring...

My 65C was probably wired directly... single wire from generator field to controller field.

10 ohms sounds kind of high for what should be a 0 ohm direct connection...

PP thoughts only, not a mechanic...

Best regards,

-a-

Yep, I agree with both.  Mine is a 68F, it seems that a direct field wire from VR to Alt would be fine, but no such luck.  The bigger metal cannon plug looks old.  Like maybe original? And yes, 10 ohms is definitely high.  I want to tear into those cannon plugs, but I think I’ve hit my limit, maybe time to get my IA on this.

[N231BN]

Alternators usually have circuit protection on the field wire. It may leave the VR, go inside to the CB panel, and then head back to the ALT. I'm not sure about that, the Field CB may just power the entire VR.

[Ragsf15e]

4 hours ago, N231BN said:

Alternators usually have circuit protection on the field wire. It may leave the VR, go inside to the CB panel, and then head back to the ALT. I'm not sure about that, the Field CB may just power the entire VR.

Yep, the diagram shows the CB powering the whole VR, but you’re right, I need to see exactly where that field wire goes.  Thought this was going to be easier..,

[ArtVandelay]

Thought this was going to be easier..,

That’s funny.
Are you new to aviation maintenance?


Tom

[Ragsf15e]

2 minutes ago, ArtVandelay said:

That’s funny.
Are you new to aviation maintenance?


Tom

Well this whole low voltage troubleshooting thing makes me think I should bring beer to my IA more often when I pick it up after maintenance.

[MikeOH]

2 hours ago, Ragsf15e said:

Well this whole low voltage troubleshooting thing makes me think I should bring beer to my IA more often when I pick it up after maintenance.

Just be glad it isn't HIGH voltage troubleshooting..adds a whole 'nother dimension

[Yetti]

I have found the cannon plugs are not immune to corrosion.  Sometimes taking them apart and putting them back together makes them good for another couple years.

[N231BN]

This post may have nailed it.  I’ve been through the whole electrical system with a multimeter and I think I’ve got it down to an issue with the field wire.  Here’s the problem, the 2 x cannon plugs make it almost impossible to get a voltage output from the Voltage Regulator at the Voltage Regulator.  I can’t get to the wires to check them with power on to the VR.
I did check the field wire at the alternator, and its 2V less than the input to the VR.  That’s right on the bottom of their spec range.  I measured the resistance of the field wire and it’s high, like 10 ohms.  
Heres my question, does the field wire really go through both the black plastic cannon plug and the big metal one in the picture?  Why?  Is it possible to simplify this wiring?  Is there another way it should be?

When you checked the field wire was it disconnected at both ends? 10 ohms sounds about right for the field winding if you still had it connected to the alternator.

[Ragsf15e]

I’m happy to close this one out with a solution and a lot of learning. Oh, and an AMU or two thrown out chasing the wrong culprit.

The problem started with a low bus voltage, around 13.2, but sometimes 13.5, sometimes 12.9. Relatively variable during flight.  Looking back through engine monitor data, it has been slowly declining on average for 2 years.  Before that, it was solid at 14.0.

Mechanic suggested replacing alternator at last annual so I did.  Brushes were worn.  I trust him very much on engine/cylinders/flight controls... in the future, I’ll do much more homework with electrical issues.

No change with alternator.  Lived with it for a while but it was declining.  Tried to use Zeftronics troubleshooting guide but needed just a little more specific help as I had no experience troubleshooting electrical.  Now I do.

Talked to different mechanic.  Talked me into new voltage regulator because “that’s cheaper than paying us for a few hours of troubleshooting.”  No change in voltage.  Although now I have a spare Zeftronics VR if anyone needs one.

Decided to try my own hand.  Bought $20 voltmeter at Lowes.  Spent couple hours quality time with airplane apart.  Cowl off, battery/avionics compartment open, instrument panel cover off.  

Identified two issues... Master Switch on my airplane is a single switch, dual pole.  Not only does it Power the master relay, but it connects the alternator field wire.  It isn’t the later model split switch. My switch is getting old.  Voltage drop across it is the maximum allowable on the Zeftronics troubleshooting guide, .5 V.  There is absolutely no access to change that switch without tearing out the panel.  It’s on the list for next time the panel is apart.

The other issue was the bus voltage was good (matched battery relay) but power input to the VR was .4-.6 volts lower.  Found out the “alt field” circuit breaker was actually the power for the VR.  Tested drop across the CB... .5 volts.  New circuit breaker cost me $20 on spruce.  It was accessible from under the panel so I changed it.  Just flew it... 14volts and rock steady!

Be aware, the electrical diagrams in the maintenance manual are model and year specific.  I was surprised to see that both my field wire and my VR power wire went back behind the panel and then came back to the engine compartment.  Also, that “battery master” switch on older models also cuts off the alternator field, so could be an area for resistance.  They are cheap switches if you can get to them.

Anyone want a working alternator with worn brushes or a gently used Zeftronics VR?? 

[BaldEagle]

Just went through something similar myself.  If it's any consolation you can get a $200 core credit for your old alternator.  Thanks for sharing the details, I'm sure this will help others in the future.

[carusoam]

Nice sleuthing and writing skills, Rags!

Nicely documented.

Thanks for sharing the details.

Best regards,

-a-

[N231BN]

Did you buy yourself a beer yet? Nice work!

Now just imagine what this would have cost at a MSC.

[211º]

Thanks for the write up and conclusion. Very helpful. 

[Ragsf15e]

4 hours ago, 211º said:

Thanks for the write up and conclusion. Very helpful. 

No problem.  However, my voltage declined again about a year later and I had to start again.  This time I got help from a EE friend. We checked voltage at the alternator with the engine running, 14.0. Ok, VR is good, alternator is good. Checked voltage at the alternator noise filter connections, still 14.0.  Checked the voltage before and after the alternator circuit breaker (70amp), 14.0.  Finally checked voltage at the jumper between the “power bus” and main bus.  13.5.  Took apart the connection, cleaned it with sandpaper (it had surface corrosion), and 14.0 everywhere again!

I highly recommend checking alternator output with engine running. Just do it carefully with alligator clips from a distance.

[211º]

Such good intel - there are several "gem" threads on MS.  I'll put this one in that category - thanks for the double follow up.

[khedrei]

I will revive this "gem" of a thread to add in my own issue and maybe someone can nudge me towards a solution.

I have a 1980 231.  14V.  I have a G500Txi with the Bus voltage and the amps displayed digitally on the engine monitor strip on the right hand side.  I will try to find an example pictures but I think that because I have the voltage displayed constantly might help troubleshoot and eliminate some of the places I might need to test.  I have gone through RagsF15e's posts and some of those seem plausible.  I had the aircraft battery replaced last year.

Situation is this: after start up the voltage only goes up to about 12.2-12.5ish and the amps show a discharge of -15 and once the avionics are turned on it jumps to -25.  The factory low voltage annunciation above the radio stack flashes.  When I got to doing the run up and revved everything up it went back to normal and I showed 14V and +2 amps for the whole flight.  On the way home same thing happened right after start up.  This time even before the run up I simply shut off the master and turned it back on and the problem went away and it was fine for the whole flight.  My friend flew it a while ago and he said that happened to him and that was the first time I had heard of it happening.  He reset the master and problem was solved.  It didn't do it again until 2 months and 15+ flights later.  Now it seems reasonably consistent.

I will try it again tomorrow on the ground and see if it does it again.  Resetting the Alt field CB doesn't seem to do anything.  The master was able to solve the problem at least twice now and the other time it simply went away during the run up.  Has me wondering if its an issue with the second pole on the master switch turning on the alternator field (as mentioned above), or possibly a bad voltage regulator.  The VR is under the copilots left knee under the panel and easy to access, though the harness/connections would make it tough to check any voltage there.  The other option mentioned above is the jumper between the power bus and the main bus....  where would I find this connection?  Is that at the battery near the aux power outlet?  The are no obvious signs of frayed or damaged wires but the fact that this started off as very intermittent and has gotten progressively worse has me leaning towards a bad VR.  The wire that looks to go to the VR from the alternator does seem to have a small bit of oil on it (as does the general area like a small mist) but otherwise the connections are all fine and there is no obvious damage.

Any input is appreciated.

Kevin

Edited September 21, 2021 by khedrei
spelling

[Ragsf15e]

1 hour ago, khedrei said:

I will revive this "gem" of a thread to add in my own issue and maybe someone can nudge me towards a solution.

I have a 1980 231.  14V.  I have a G500Txi with the Bus voltage and the amps displayed digitally on the engine monitor strip on the right hand side.  I will try to find an example pictures but I think that because I have the voltage displayed constantly might help troubleshoot and eliminate some of the places I might need to test.  I have gone through RagsF15e's posts and some of those seem plausible.  I had the aircraft battery replaced last year.

Situation is this: after start up the voltage only goes up to about 12.2-12.5ish and the amps show a discharge of -15 and once the avionics are turned on it jumps to -25.  The factory low voltage annunciation above the radio stack flashes.  When I got to doing the run up and revved everything up it went back to normal and I showed 14V and +2 amps for the whole flight.  On the way home same thing happened right after start up.  This time even before the run up I simply shut off the master and turned it back on and the problem went away and it was fine for the whole flight.  My friend flew it a while ago and he said that happened to him and that was the first time I had heard of it happening.  He reset the master and problem was solved.  It didn't do it again until 2 months and 15+ flights later.  Now it seems reasonably consistent.

I will try it again tomorrow on the ground and see if it does it again.  Resetting the Alt field CB doesn't seem to do anything.  The master was able to solve the problem at least twice now and the other time it simply went away during the run up.  Has me wondering if its an issue with the second pole on the master switch turning on the alternator field (as mentioned above), or possibly a bad voltage regulator.  The VR is under the copilots left knee under the panel and easy to access, though the harness/connections would make it tough to check any voltage there.  The other option mentioned above is the jumper between the power bus and the main bus....  where would I find this connection?  Is that at the battery near the aux power outlet?  The are no obvious signs of frayed or damaged wires but the fact that this started off as very intermittent and has gotten progressively worse has me leaning towards a bad VR.  The wire that looks to go to the VR from the alternator does seem to have a small bit of oil on it (as does the general area like a small mist) but otherwise the connections are all fine and there is no obvious damage.

Any input is appreciated.

Kevin

Ouch, intermittent ones are tough.  Probably no way to troubleshoot it when it’s working normal.

The jumper that caused my issues is in my panel CBs copilot side.  There are 3 bus bars there.  Jumpers between them.  The mx manual for my 68 calls them power bus, aux bus and something else.  Someone else added an avionics bus at some point.

If you have the problem and can check the field wire into the alternator (you can check this without the engine running, but you won’t know if the problem is occurring or not).  It should be 1-2v below bus.

If you can force the problem and check alternator output and field wire input that would speak volumes.

Theres a reasonable troubleshooting guide on Zeftronics website.

Good luck!