Battery Voltage Question

[dtoelke]

I figure this is normal but I want to check since I'm still fairly new to the plane (231, 12V system).  Battery is a 1 month old Concorde.  When I turn on power I usually read 11.7-11.8 volts.  After start up/taxi this usually climbs (barely) to just above 12.  Once I apply power and take off it quickly climbs to 13.8-13.9 and stabilizes for the flight.  Drops down to the low 12s once landed and taxiing.

 

Does this sound normal?  Obviously the alternator output changes dramatically from idle to 2400-2700 rpm but I always figured it should be a bit more stable.

[carusoam]

Which voltage regulator do you have?

A couple of things come to mind...

There is a minimum rpm required before the alternator starts charging. Usually too high of an rpm to taxi with....

There may be some settings on the VR that can be adjusted. Probably a maintenance procedure to go with that...

Best regards,

-a-

[dtoelke]

Which voltage regulator do you have?

A couple of things come to mind...

There is a minimum rpm required before the alternator starts charging. Usually too high of an rpm to taxi with....

There may be some settings on the VR that can be adjusted. Probably a maintenance procedure to go with that...

Best regards,

-a-

 

I'm not sure.  Where is the voltage regulator located?

[Parker_Woodruff]

Your alternator charges at ~14V.  Your battery is a 12V battery.  When you are flying, the electronics are being run by the alternator and your battery is being charged.  At lower power settings, your alternator isn't able to hold that 14V.  Charging voltage decreases...Below a certain point, your electronics will turn back to the battery.  This is why you see a sub-12V indication before engine start.

 

TYPO EDIT: Your battery provides power at 12V.  Slightly lower indication as it discharges.

[carusoam]

Start with the first post here...

Lots of interesting details regarding the M20K charging system...

http://mooneyspace.com/topic/11591-k-model-voltage-regulator/?hl=%2Bm20k+%2Bvoltage+%2Bregulator#entry142426

Best regards,

-a-

Of course, Parker is a reliable source of Mooney knowledge. Seems what you are seeing is normal...

[Piloto]

Dtoelke

On planes equipped with alternator the charging voltage should be 14V at 1200rpm or higher at medium loads. Low voltage at low RPM usually is an indication of an open diode in the alternator.

José

[Parker_Woodruff]

Best regards,

-a-

Of course, Parker is a reliable source of Mooney knowledge. Seems what you are seeing is normal...

and fully capable of a typo...I just corrected the last line in my first post.

[Guest]

I figure this is normal but I want to check since I'm still fairly new to the plane (231, 12V system).  Battery is a 1 month old Concorde.  When I turn on power I usually read 11.7-11.8 volts.  After start up/taxi this usually climbs (barely) to just above 12.  Once I apply power and take off it quickly climbs to 13.8-13.9 and stabilizes for the flight.  Drops down to the low 12s once landed and taxiing.

 

Does this sound normal?  Obviously the alternator output changes dramatically from idle to 2400-2700 rpm but I always figured it should be a bit more stable.

Your initial battery voltage is too low, indicating either a battery problem or just simply lack of a proper charge from the alternator which I suspect.

How old is your alternator? It could have worn brushes or a slipping drive coupling.

Clarence

[Andy95W]

DtoelkeOn planes equipped with alternator the charging voltage should be 14V at 1200rpm or higher at medium loads. Low voltage at low RPM usually is an indication of an open diode in the alternator.José

Your initial battery voltage is too low, indicating either a battery problem or just simply lack of a proper charge from the alternator which I suspect.

How old is your alternator? It could have worn brushes or a slipping drive coupling.

Clarence

Agreed. If you aren't getting 13.9 volts or so at 1200 rpm or so, you probably need an alternator overhaul, or a new drive coupling like Clarence said.

Just my extra 2 cents.

[ArtVandelay]

Before you start changing expensive items like alternators, voltage regulators, get a volt meter and double check the readings, measure the voltage at the battery and compare.

What is it before you turn on the power, then turn on the power and compare to instrument panel reading.

If it was really 11.7 I would think you wouldn't be able to start the engine.

If it drops a lot when master is turned on, make sure you don't have pitot heat or some other heavy load on the system.

[pkellercfii]

Given the behavior of my 252 on the #1 alternator alone, which is the 252 analog to the single alternator on the 231, this behavior is about what I'd expect, with the exception of the high engine RPM voltage. Because of the low RPMs of the Continental gear-driven alternators, their low RPM voltage pickup is awful. It takes 1300 RPM on the engine to get 28V out of my #1 alternator alone. This said, 13.8-13.9V at high RPM does seem a bit low, and something you might want to have checked with an known accurate voltmeter. I'd suggest checking that at an engine RPM of at least 1700 RPM so that you're not mislead by the poor voltage pickup of the gear driven alternator.

 

--Paul Keller

'89 K

[dtoelke]

Battery is brand new.  Can't remember the exact open circuit voltage but it was well within the appropriate bounds for the battery.  It drops to 11.7-11.8 (reading from the JPI unit) when the master is flipped on w/the rotating beacon running.

[ArtVandelay]

You need to open up the battery compartment and put a good digital voltmeter on it, it should read about 12.8 when idle. Pull the CB for the turn coordinator and the beacon, turn master on, it should not drop more than 0.1v, it's only powering the relay I would expect, the plane should be silent (radio avionics master is still off), if it drops to much more than that, you need to find what's drawing the power, as I said I suspect the voltage the JPI is seeing is not the true battery voltage, bad connection to power or to ground could cause it.

[carusoam]

Consider the voltage drop across the solenoid while looking at possibilities...

Old or dirty solenoids are known to add some voltage drop...

Best regards,

-a-

[ArtVandelay]

Consider the voltage drop across the solenoid while looking at possibilities...

Old or dirty solenoids are known to add some voltage drop...

Best regards,

-a-

I would think that would effect his starts.?

[carusoam]

TJ,

Below 12V probably does effect the strength and speed of the starter...

It's been a few years since I had 12V aviation experience. And my memory has left the building...

Asking my son, his CAR battery is reading 12.5V after sitting overnight.

I believe the well charged Concorde battery should be near 12.5V as well.

Of course, this is directly reading at the battery with a portable Fluke meter...

The way batteries store energy is directly related to the voltage. A low voltage reading because the battery is weak will be different than a low voltage because of additional resistance in the line....

In other words...a low voltage reading like this, and the starter still working...leads me to want to look in additional places for the cause of the low V reading...

Is the battery being charged fully? Probably is with the given alternator readings...

Does it hold it's voltage overnight, for a couple of days, all month?

At 11.5V (direct read on battery) 95% of the useful charge is mostly gone...? (Nice way of saying I don't know exactly, but it is not linear from 0 to 12V...)

My kind of questions,

-a-

[ArtVandelay]

I thought Concorde were AGMs? AGM have higher resting voltage.

Voltage is ultimately effected by several factors including temperature, rest time since charge, and amount of drain.

You son's car battery actually has a drain on it: clock, alarm, key receiver....assuming it was below 72F, both account for a lower readings then book.

A plane battery should be idle, no load with master off unless somebody added a keep alive your clock, or you leave the cabin light on, both are hot wired

If it's fully charged, the charging voltage will drop to about 13.2-13.5

This normally should happen with 30 minutes of flight.

My plane has an ammeter, does OP, by pulling CBs he can verify he doesn't have a load on the system.

[Marauder]

I thought Concorde were AGMs? AGM have higher resting voltage.

Voltage is ultimately effected by several factors including temperature, rest time since charge, and amount of drain.

You son's car battery actually has a drain on it: clock, alarm, key receiver....assuming it was below 72F, both account for a lower readings then book.

A plane battery should be idle, no load with master off unless somebody added a keep alive your clock, or you leave the cabin light on, both are hot wired

If it's fully charged, the charging voltage will drop to about 13.2-13.5

This normally should happen with 30 minutes of flight.

My plane has an ammeter, does OP, by pulling CBs he can verify he doesn't have a load on the system.

Concorde sells both AGM and standard lead cell batteries.

Sent from my iPad using Tapatalk

[dtoelke]

You need to open up the battery compartment and put a good digital voltmeter on it, it should read about 12.8 when idle. Pull the CB for the turn coordinator and the beacon, turn master on, it should not drop more than 0.1v, it's only powering the relay I would expect, the plane should be silent (radio avionics master is still off), if it drops to much more than that, you need to find what's drawing the power, as I said I suspect the voltage the JPI is seeing is not the true battery voltage, bad connection to power or to ground could cause it.

 

Checked this when I first got the battery (same behavior then), and the idle voltage was right around 12.8.  Nothing has changed since.

[ArtVandelay]

Checked this when I first got the battery (same behavior then), and the idle voltage was right around 12.8. Nothing has changed since.

So if the voltage at the battery is 12.8, power up the master, radio stack, re measure the battery voltage and compare with JPI, the JPI should be same or maybe .1 volts less. If it's more than .1 check the voltage at the radio switch, both sides, this will narrow down where the bad connection is.

[Zwaustin]

I have a fresh concorde batt and I show 13.8 typically on the JPI EDM 700 in normal power setting...