Low Voltage - Battery or Alternator

[MICKEY]

I am looking at replacing my battery.  I am showing about 13.6-13.7 V during flight.  I have no other issues.  The Aircraft starts just fine and have never had any other electrical issues.  Seems like the alternator is doing its job.   Thoughts?  If a battery.. Which specific battery to get?

 

Eric

[Ragsf15e]

30 minutes ago, MICKEY said:

I am looking at replacing my battery.  I am showing about 13.6-13.7 V during flight.  I have no other issues.  The Aircraft starts just fine and have never had any other electrical issues.  Seems like the alternator is doing its job.   Thoughts?  If a battery.. Which specific battery to get?

 

Eric

So we’ve got this other thread going with the exact same problem although my voltage is more like 13.2 consistently.  I replaced the battery because it was old and failing capacity check.  Replaced the alternator at annual and neither thing worked.  I have a data recorder on the engine and i can see it has been a slow voltage decline for a year or two.  It could be the voltage regulator or something else.

I wouldn’t recommend starting to replace things until you troubleshoot.  There’s a zeftronics VR troubleshooting guide and a Planepower alternator guide reference in the other thread.

[1964-M20E]

Changing your battery will not do anything.

You can check your alternator belt to make sure it is tight enough a slipping belt could cause lower volts and wear you belt out faster.

You can adjust the voltage regulator to get it closer to 14.0V.  I typically see 13.7 to 14.1 volts on mine generally after running for 15 to 20 minutes it will settle down at 13.9 to 14V.

[Ragsf15e]

35 minutes ago, MICKEY said:

I am looking at replacing my battery.  I am showing about 13.6-13.7 V during flight.  I have no other issues.  The Aircraft starts just fine and have never had any other electrical issues.  Seems like the alternator is doing its job.   Thoughts?  If a battery.. Which specific battery to get?

 

Eric

To answer your initial question... I don’t think the battery will cause you to indicate low voltage during cruise if the VR and Alternator are working properly.

[jaylw314]

37 minutes ago, MICKEY said:

I am looking at replacing my battery.  I am showing about 13.6-13.7 V during flight.  I have no other issues.  The Aircraft starts just fine and have never had any other electrical issues.  Seems like the alternator is doing its job.   Thoughts?  If a battery.. Which specific battery to get?

 

Eric

• Your voltage during flight is your regulator voltage, it tells you nothing about the battery (and it sounds a little on the low side for normal weather).
• Your voltage on the ground with the alternator off might tell you something about your battery, but you'd need to know the exact load for it to be informative.
• Your voltage with the battery unloaded will not tell you what its total capacity is, but it will tell you what percentage of that capacity is charged.

The only way to truly determine the battery capacity is to do a capacity test--charge until it's at 100%, discharge it until it's at 50% charge and record the total current.  If you have a 40 Ah battery, it should take 20 Ah to discharge it to 50%.  If it only takes 10 Ah, that means your battery has lost half its capacity.

Edited May 6, 2019 by jaylw314

[Ragsf15e]

Just now, 1964-M20E said:

Changing your battery will not do anything.

You can check your alternator belt to make sure it is tight enough a slipping belt could cause lower volts and wear you belt out faster.

You can adjust the voltage regulator to get it closer to 14.0V.  I typically see 13.7 to 14.1 volts on mine generally after running for 15 to 20 minutes it will settle down at 13.9 to 14V.

Some VR are not adjustable, what kind do you have?

i have a Zeftronics r15300 digital one and its not adjustable.

[1964-M20E]

I'm not sure which is in mine but i do know the plane power regulators are adjustable.

 

 

[EricJ]

As others have said, when the alternator is turning sufficiently the voltage is driven by the alternator and regulator and should be significantly above the battery voltage.   You should see ~12-12.5 volts (maybe a bit more) with the engine off and >13.5 volts when the engine is running.    Low voltage, above ~12.5V, when the engine is running has nothing to do with the battery.

[Ross Taylor]

Hi @mickey,

Are you getting the battery/system voltage off a JPI, by any chance?  Or, where are you measuring that?  I only ask because I heard Mike Busch explain how the JPIs indicate voltage a bit lower than actual... but I may be very wrong and dreamt that.  We have a JPI EDM-700 and ours reads about 13.5-13.6.

Ross

[jaylw314]

18 minutes ago, Ross Taylor said:

Hi @mickey,

Are you getting the battery/system voltage off a JPI, by any chance?  Or, where are you measuring that?  I only ask because I heard Mike Busch explain how the JPIs indicate voltage a bit lower than actual... but I may be very wrong and dreamt that.  We have a JPI EDM-700 and ours reads about 13.5-13.6.

Ross

That might be, but other factors are probably more important, since most people have a significant current load when the Master switch is turned on.  If the voltage measuring instrument is on the radio master, even more so.  You can pull a bunch of circuit breakers to try to compensate, but IIRC even the master solenoid takes 1 amp or more to run.  I suspect an instrument measuring the voltage bus will always be a little lower than the open voltage if you took a voltmeter to the battery terminals.

[ArtVandelay]

Some VR are not adjustable, what kind do you have?
i have a Zeftronics r15300 digital one and its not adjustable.

Not true, it has an internal pot that you adjust, but you should use electronic cleaner first, since it being dirty could be the problem.


Tom

[Ragsf15e]

1 minute ago, ArtVandelay said:

Not true, it has an internal pot that you adjust, but you should use electronic cleaner first, since it being dirty could be the problem.


Tom

I don’t think so.  At least not the r15300 adjustable in the field... however, I’m madly looking it up because that would be great.

My IA also said it wasn’t adjustable... but I’ll still look it up.

[Ragsf15e]

27 minutes ago, ArtVandelay said:

Not true, it has an internal pot that you adjust, but you should use electronic cleaner first, since it being dirty could be the problem.


Tom

http://zeftronics.info/documents/PIT/R15300(B)-PIT.pdf

pretty sure these don’t have the adjustment or it’s not accessible in the field.  Above is the installation and troubleshooting and nothing is mentioned about adjusting voltage-even in the troubleshooting portion.

[ArtVandelay]

-PIT.pdf'>http://zeftronics.info/documents/PIT/R15300(-PIT.pdf
pretty sure these don’t have the adjustment or it’s not accessible in the field.  Above is the installation and troubleshooting and nothing is mentioned about adjusting voltage-even in the troubleshooting portion.

My hangar fairy did it, But I still replaced with new and my old one is now in spare parts inventory because in my experience once a pot starts get dirty, the electronic cleaner is only a temporary fix.


Tom

[Ross Taylor]

4 hours ago, jaylw314 said:

That might be, but other factors are probably more important, since most people have a significant current load when the Master switch is turned on.  If the voltage measuring instrument is on the radio master, even more so.  You can pull a bunch of circuit breakers to try to compensate, but IIRC even the master solenoid takes 1 amp or more to run.  I suspect an instrument measuring the voltage bus will always be a little lower than the open voltage if you took a voltmeter to the battery terminals.

Nicely put.  Like Schrodinger's cat, maybe? You can't measure the voltage with a meter powered by the master or avionics bus without impacting the voltage measurement. (Huge apologies to Scrodinger, for both butchering his thought experiment and for not knowing how to type an umlaut on my phone.)

[Ragsf15e]

2 hours ago, ArtVandelay said:

My hangar fairy did it, But I still replaced with new and my old one is now in spare parts inventory because in my experience once a pot starts get dirty, the electronic cleaner is only a temporary fix.


Tom

Gotcha, thanks.

[carusoam]

Holy Cow!  The return of Schrodinger’s Cat... 

Do not lift the lid of Schrodinger’s trunk...it could be an ugly mess in there.

DanB recently reported a cat on his cylinder... then reported the cat to be OK...    that would be one hot cat!  Probably a typo...

 

So...

1) Voltage at the Voltage regulator is usually a couple of volts or three higher than what is expected at the battery... depending on 12V or 24V application... 

2) in cruise the voltage you see is typically controlled by the VR...

3) on the ground without the engine running, the voltage reading is from the Battery...

4) Voltage readings didn’t really become important until digital engine monitors became popular...

5) There is lots of voltage losses going from the battery, to the instrument panel, to a JPI, and back to ground.... it is possible to be reading a slightly lower number than actual... So get a good feeling for what normal numbers are for your ship... a high number for charging... a low number for when the alternator is not on... and a really low number when things start to flash and stop working....

6) The cool thing about a zeftronics VR.... It is digitally controlled, it usually works or doesn’t... it can send a light to the IP indicating it is not working...  it is 10X better than the sticks, stones and springs of the original VR...

7) Often the alternator belt is responsible for slipping...  check the belt tightness following the procedure... it is really tight and requires a tool to get to the usual tightness...

PP thoughts only, my C got a zeftronics when the original took a vacation... adjusting the original one cooked the generator as well... melting all the solder off of a few wires...

Best regards,

-a-