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  #1  
Old 09-18-2022, 07:58 PM
Triumph1974 Triumph1974 is offline
 
Join Date: Feb 2008
Location: Richmond VA
Posts: 115
Default Suspect Plane Power Voltage Regulator on the Way Out??

Noticed something odd this week. Normally the voltage output is 14.4, but did a several hr. cross country flight this week and started noticing voltage drops on the Skyview display. Did some inflight testing and voltage output would go down to as low as 13.9 volts at times as additional items where turned on (nav, strobe, wig wag landing lights etc), voltage output would go back up to the 14.4 as I reduced the electrical load. So needless to say I did the remaining trip with min. electrical loads.

I am thinking that the Plane Power voltage regulator may need to be replaced, it has 400 Hobbs, or 305 tach time.... Any other potential items that I should look at?

I have the blast tube going to the internal regulator..... Any additional ideas on how to get more life out of these alternators?

Thanks,
Paul

Standard RV7A
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  #2  
Old 09-18-2022, 08:03 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 8,544
Default

Check your field line (which does double duty as a sense line), connections, CB, for any loose/oxidized connections.
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  #3  
Old 09-18-2022, 10:27 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,443
Default

Also check for loose belt and check the brushes.
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RV-12 Flying
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  #4  
Old 09-19-2022, 07:12 AM
Freemasm Freemasm is online now
 
Join Date: Nov 2017
Location: Orlando
Posts: 900
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Wouldn't a bad battery cell cause a similar behavior, i.e. electrical demand exceeding supply? An amp meter/current measurement would be a nice data point here. Without such, if the previous suggestions check out then a battery capacity check should be considered, IMO.

Of course, battery type is no longer a given any more.
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  #5  
Old 09-19-2022, 08:14 AM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by Freemasm View Post
Wouldn't a bad battery cell cause a similar behavior, i.e. electrical demand exceeding supply?
No. The battery is floating above 13 volts and not adding energy. It is a sign of the ALTERNATOR not meeting electrical demand OR not properly managing th voltage level.

Larry
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  #6  
Old 09-19-2022, 08:17 AM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by BobTurner View Post
Check your field line (which does double duty as a sense line), connections, CB, for any loose/oxidized connections.
Generally, resistance on the voltage sense circuit results in higher than normal Alt output voltage, not lower. The resistance lowers the voltage that the regulator sees on it's sense input and in response does its job by increasing the output voltage on the B lead. I have had this problem on my ship and it was a loose terminal on the CB.

Larry
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Last edited by lr172 : 09-19-2022 at 08:20 AM.
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  #7  
Old 09-19-2022, 08:32 AM
Freemasm Freemasm is online now
 
Join Date: Nov 2017
Location: Orlando
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Quote:
Originally Posted by lr172 View Post
No. The battery is floating above 13 volts and not adding energy. It is a sign of the ALTERNATOR not meeting electrical demand OR not properly managing th voltage level.

Larry
Help me understand Larry. Forgive me as Iím ME not EE. A bad cell tends to make heat versus excite electrons in its electrolyte. Itís worse than just losing its 2.2 volts of potential; itís a black hole for wattage and subsequent unrecoverable potential work. Makes it very easy to exceed the alt output when combined with other loads. Yes itís anecdote but I had a bad battery kill an alt (also ruined some
Paint when the top of the battery separated and put acid all over stuff.

Iíll state again, current measurement would be a good data point. Now that the clamp-ons for DC are affordable, itís pretty easy and cheap now.
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  #8  
Old 09-27-2022, 08:17 PM
Triumph1974 Triumph1974 is offline
 
Join Date: Feb 2008
Location: Richmond VA
Posts: 115
Default Status update

Thanks everyone for the comments.

I checked the alternator plug....pulled out with less resistance than ideal....crimped the terminals a littlw, sprayed the connections with electrical connection cleaner, and made sure the main voltage wire at the alternator was tight..

Did a test flight and voltage was back at the normal 14.4 volts and rock steady through various electrical loads.

Thanks!
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  #9  
Old 09-28-2022, 08:01 AM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,727
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Quote:
Originally Posted by Freemasm View Post
Help me understand Larry. Forgive me as I’m ME not EE. A bad cell tends to make heat versus excite electrons in its electrolyte. It’s worse than just losing its 2.2 volts of potential; it’s a black hole for wattage and subsequent unrecoverable potential work. Makes it very easy to exceed the alt output when combined with other loads. Yes it’s anecdote but I had a bad battery kill an alt (also ruined some
Paint when the top of the battery separated and put acid all over stuff.

I’ll state again, current measurement would be a good data point. Now that the clamp-ons for DC are affordable, it’s pretty easy and cheap now.
Your description kind of explains everything. A bad cell in a battery will consume very large amounts of energy from the alternator, often trashing them in the process as you saw (they won't run very long at full capacity, which is why we size them to run at 75% capacity or less). When the alternator starts to approach it's capacity (remember that capacity is different for each RPM level), it can no longer maintain the voltage that the VR is trying to achieve (14.2 in this case). Bad cells usually present with system voltages substantially lower than the target voltage due to the bad cell taking the Alt all the way to capacity. In that case, the Alt wouldn't be able to make 13.9 volts. The more current an Alt is asked to produce, the lower it's voltage output will be or at least will be once the cross over point drops below the target voltage (they produce quite a bit more than 14 volts at low loads, which is why the VR rapidly starts and stops the field current). You can think of the old points based VR's as a pre cursor to modern PWM. The output will drop to around 10 volts or less at full capacity (typically more than rated capacity).

Therefore, a system voltage of 13.9 pretty much excludes a diagnosis of a bad cell in a battery.

Larry
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Last edited by lr172 : 09-28-2022 at 08:17 AM.
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