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Electrical issues

warren.huisman

By warren.huisman
in Modern Mooney Discussion

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warren.huisman Collaborator

warren.huisman

Posted
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Have had a couple of instances where I had electrical anomalies. First instance was over voltage warning during climb. I had already entered IMC so I kept climbing- the issue “corrected “ it self after 10-15 seconds. Second instance was also during climb in IMC where the voltage was dropping out to 11-12 volts.
Both time the TKS pumps were on. When I was getting low voltage, the amp meter was indicating about 40 amps as almost all electrical devices were on. The issue was corrected after we popped out on top and started shedding electrical loads. Also had a humming in the headset during this time as well.
I am wondering if I have a voltage regulator issue or an alternator issue? Potentially I could have a slipping belt but I don’t think that explains why I had a over voltage condition. Thoughts?
 
 
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Yetti Grand Master

Yetti

Posted
Posted (edited)

The condition is when pulling lots of amps.   Easy thing is check the belt tension.   Check the ground strap to the engine.  Check the battery terminals.  Everything about terminals should be shiny bright.   Stainless detail brushes are fantastic for making things shiny bright.  Ones that brush is contaminated around the battery it should not be used on other parts of the plane.    Check the B+ wire off the alternator, the big one. Test the alternator.

Edited by Yetti
Runway37 Explorer

Runway37

Posted
Posted (edited)

Sometimes humming can be caused by bad/old electrolytic capacitors. I dont know if there are any capacitors in the vr or elsewhere in your charging system, but with a hum, that's where I'd look if it was anything ham radioish.

A supporter even though it doesn't show as such

Edited by Runway37
Yetti Grand Master

Yetti

Posted
Posted

There is a big ole filter next to the VR on the older models.  Oh and those guessing if your belt is tight enough.   You should not be.  It is a walk around item. 

Marauder Grand Master

Marauder

Posted
Posted
Sometimes humming can be caused by bad/old electrolytic capacitors. I dont know if there are any capacitors in the vr or elsewhere in your charging system, but with a hum, that's where I'd look if it was anything ham radioish.
A supporter even though it doesn't show as such


There is an Rf filter on my plane. I know of one plane where this failed and caused the humming. Not sure it is related to the other anomalies he is seeing.


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warren.huisman Collaborator

warren.huisman

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Posted

The humming noise was gone as well as the low voltage indication as soon as I started shedding electrical loads. Pitot heat, TKS pump, etc. Is this consistent with a bad filter?


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carusoam Grand Master

carusoam

Posted
Posted

It’s a sign the noise filter isn’t working...

But is there an electric challenge that is causing the problem..?

Could be the angle of the climb causing something to change...

 

If you can...

Get noise...

Turn stuff off, one at a time... or in groups to narrow things down... if that helps...

 

Anything with a motor in it is suspect for making noise... lots of noise available when the motor is on... grounding and shielding are typical solutions...

 

An example... you find the TKS pumps are working fine... you hear noise in the headsets... switch the TKS system off for a few seconds... the noise goes away... pumps back on... noise comes back...  write down the squawk for when you are on the ground.... Expect to be looking for a ground wire that is no longer attached the way you want it to be... could be Engine, air frame, or TKS system...

Things to cause over voltage one day and low voltage the next.... that is really unsettling? The VR is struggling to keep up with something... either internally or externally...

Thinking about the effects of a loose belt... one day it is working fine, the next day the alternator can’t keep up... causing a low voltage sign... the VR calls for max volts... if the belt stops slipping there will be a real leap in volts... this could occur when the belt seems tight, but doesn’t meet the tightness spec...

Could be that field wire challenge..... a loose field wire makes the VR look wonky...

Does your JPI collect voltage data?   You might be able to narrow down the challenge by posting voltage vs. time...

PP thoughts about trouble shooting, not a mechanic...

Best regards,

-a-

skykrawler Proficient

skykrawler

Posted
Posted

Unless you have an instrument that tells you the total current load......the stock ammeter just shows the rate of current between the battery and the alternator.  So if your ammeter showed 40 amps then your battery was charging furiously.   If the alternator is not putting out then the ammeter will show negative current (needle deflects left) and you are running off the battery.

If there is resistance in the regulator sense circuit (field wire mentioned in previous post, which goes through the master switch) then the system may try to charge the battery unnecessarily (needle to the right).  This may also be implied by the over voltage indication.....the regulator thinks the voltage is low so it jacks up the alternator output.

The nominal case is the alternator has capacity to carry all loads you turn on and the needle only momentarily deflects.  Pitot heat is probably the highest load (aside from starter) when it is first turned on (> 16 amps) until it heats up, resistance increases and the current goes down.

 

Runway37 Explorer

Runway37

Posted
Posted

When checking connections and wires, really look closely for anything that may be causing a partial short or open. When playing with radios I often use magnification. Troubleshooting for an "intermittant" can also involve gently tapping on components and connections while looking for symptoms. I dont know how you could safely (without damaging any systems or sensitive instrumentation) do this, but I would consider doing the above while listening for a hum and looking for a voltage drop.

People smarter than I should correct me if any of this is inadvisable, I mostly wanted to convey that it's easy to just glance at a connection and sign it off, but I've been fooled a number of times by not being suspicious of every component in a system I'm troubleshooting.

Good luck, these things are irritating, but you've got quite a few "good" symptoms pointing to the problem.

A supporter even though it doesn't show as such :o

Shadrach Grand Master

Shadrach

Posted
Posted
On 2/17/2019 at 10:29 AM, Yetti said:

There is a big ole filter next to the VR on the older models.  Oh and those guessing if your belt is tight enough.   You should not be.  It is a walk around item. 

A walk around will only tell if the belt is very loose. Perhaps some hands are more calibrated than others but I don’t trust mine. One really needs to put a torque wrench on the pulley and verify it slips in the proper range for a new or used belt. 

Yetti Grand Master

Yetti

Posted
Posted (edited)
12 hours ago, Shadrach said:

A walk around will only tell if the belt is very loose. Perhaps some hands are more calibrated than others but I don’t trust mine. One really needs to put a torque wrench on the pulley and verify it slips in the proper range for a new or used belt. 

Most people are pretty good at feeling what 10 lbs of pressure and a 1/4" of deflection looks like.

Edited by Yetti
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