Battery losing charge problem

[Wojciech Kacprzyński]

Hi guys, 

For some time now I've been struggling with a problem with my electrical system. I own a 1977 M20J. It all started 8 months ago. All of the sudden after annual, my battery started to lose its charge in a matter of days. Literally after 3 days of staying in hangar, it would be so depleted that it wouldn't start anymore. After some troubleshooting we determined that the battery was old and thus it was losing its charge. I replaced it and everything worked great for some time. The longest lasted without flying was 2 months and it still had 12v precisely. A few weeks ago the problem started all over again. It started to lose power to a point where after two weeks it wasn't able to start-up, then one week, then 3 days and now it's hard to start it normally after 8hrs... It can be relevant that 2 weeks ago my alternator stopped working mid flight and was allegedly repaired by a mechanic in a foreign country. Nothing I did with the breakers or anything did anything mid flight. We checked the battery once again but it turned out to be perfectly formed and not missing any electrolyte from any of the cells. Do you guys have any idea what could be wrong? Has anyone encountered a similar problem in the past? Any suggestions? 

Best regards, 

Wojciech Kacprzyński,

A fellow Mooney owner

[Marauder]

Hi guys, 
For some time now I've been struggling with a problem with my electrical system. I own a 1977 M20J. It all started 8 months ago. All of the sudden after annual, my battery started to lose its charge in a matter of days. Literally after 3 days of staying in hangar, it would be so depleted that it wouldn't start anymore. After some troubleshooting we determined that the battery was old and thus it was losing its charge. I replaced it and everything worked great for some time. The longest lasted without flying was 2 months and it still had 12v precisely. A few weeks ago the problem started all over again. It started to lose power to a point where after two weeks it wasn't able to start-up, then one week, then 3 days and now it's hard to start it normally after 8hrs... It can be relevant that 2 weeks ago my alternator stopped working mid flight and was allegedly repaired by a mechanic in a foreign country. Nothing I did with the breakers or anything did anything mid flight. We checked the battery once again but it turned out to be perfectly formed and not missing any electrolyte from any of the cells. Do you guys have any idea what could be wrong? Has anyone encountered a similar problem in the past? Any suggestions? 
Best regards, 
Wojciech Kacprzyński,
A fellow Mooney owner

Are you certain your alternator has been charging the entire time? You did not mention what kind of voltage you were seeing in flight. I would pick up at a minimum one of those cigar lighter voltage meters and make sure you are consistently seeing at a nominal 13.8 volts.



As for the draining while sitting. I know some devices draw a small amount of current to keep memory. Maybe you have something drawing power with the master off.

In my Mooney, if you accidentally leave the overhead light on, it’ll drain my battery over time.


Sent from my iPhone using Tapatalk Pro

[Fly Boomer]

5 hours ago, Wojciech Kacprzyński said:

We checked the battery once again but it turned out to be perfectly formed and not missing any electrolyte from any of the cells.

While it's not a substitute for a capacity check, measuring the OCV (Open Circuit Voltage) is a pretty good proxy for battery condition.  If the OCV goes down day by day or week by week then there is probably a small load on the battery with the master off.  If the battery is good and it won't start, then something downstream is at fault:  ground or other connection, solenoid, starter, etc.

[shawnd]

I would recommend checking the voltage regulator while you are investigating this. With a busted VR, your alternator field circuit isn't going to be powered and therefore no output from the alternator. Also, ensure you are not drawing power when the master is turned off.

There's alternator/vr troubleshooting guides you can use:
- Hartzell: https://hartzell.aero/wp-content/uploads/2015/10/Alternator-Trouble-Flowchart.pdf.
- Plane Power: https://planepower.aero/aircraft-alternator-support/troubleshooting/

 

[Bolter]

How old and what brand is the replacement battery?  With recent alternator failure, if the battery was run down sufficiently, it may not recover.  The proximity in time between battery issue and alternator is probably not a coincidence.

Regarding voltage regulators as @shawnd brings up, I say if you have the original one in place, go get modern one just as a preventive maintenance item.  The old one will fail, why wait for it to damage other things in the process?  Easy to replace, and about $600 for the part.  (https://zeftronics.com/shop/r15300/)

[Wojciech Kacprzyński]

On 8/8/2022 at 7:01 AM, Fly Boomer said:

While it's not a substitute for a capacity check, measuring the OCV (Open Circuit Voltage) is a pretty good proxy for battery condition.  If the OCV goes down day by day or week by week then there is probably a small load on the battery with the master off.  If the battery is good and it won't start, then something downstream is at fault:  ground or other connection, solenoid, starter, etc.

Its not like its not giving power at all, just the longer it sits the less its got. After 3 days it barely has enough to spin the prop 3-4 times which is often not enough.

[Wojciech Kacprzyński]

4 hours ago, shawnd said:

I would recommend checking the voltage regulator while you are investigating this. With a busted VR, your alternator field circuit isn't going to be powered and therefore no output from the alternator. Also, ensure you are not drawing power when the master is turned off.

There's alternator/vr troubleshooting guides you can use:
- Hartzell: https://hartzell.aero/wp-content/uploads/2015/10/Alternator-Trouble-Flowchart.pdf.
- Plane Power: https://planepower.aero/aircraft-alternator-support/troubleshooting/

 

Thanks I will check the VR, althrough, when the engine is running it shows that the battery is recharging. I tried to check with master off if the power drains somewhere but on battery it doesnt show even an miliamper of drain.

[Wojciech Kacprzyński]

3 hours ago, Bolter said:

How old and what brand is the replacement battery?  With recent alternator failure, if the battery was run down sufficiently, it may not recover.  The proximity in time between battery issue and alternator is probably not a coincidence.

Regarding voltage regulators as @shawnd brings up, I say if you have the original one in place, go get modern one just as a preventive maintenance item.  The old one will fail, why wait for it to damage other things in the process?  Easy to replace, and about $600 for the part.  (https://zeftronics.com/shop/r15300/)

The replacement battery was brand new from GLL (G35), so its only 8mths old. After the troubleshooting I will try replecing the alternator, thanks

[Shadrach]

2 hours ago, Wojciech Kacprzyński said:

The replacement battery was brand new from GLL (G35), so its only 8mths old. After the troubleshooting I will try replecing the alternator, thanks

Should be easy to verify the system is charging. I have had lousy experiences with G35s.

[GeeBee]

Sounds like a short on the hot bus. Charge the battery fully. Place a sensitive ammeter at the battery post. If there is a significant draw with the master switch off, you need to hunt down the culprit draining the battery. Pull all breakers and remove all fuses. Add them back one at a time while checking the ammeter. When you see it jump up, you know the problem circuit. One time for me on a Cessna, it was a reading light in the cabin shorting.  

[Wojciech Kacprzyński]

24 minutes ago, Shadrach said:

Should be easy to verify the system is charging. I have had lousy experiences with G35s.

yeah it is, thats for sure, the alt was repaired after that and i havent noticed any problems yet. I will try replacing the VR. What do you mean by lousy experiences? I would like to hear about it.

[Wojciech Kacprzyński]

9 minutes ago, GeeBee said:

Sounds like a short on the hot bus. Charge the battery fully. Place a sensitive ammeter at the battery post. If there is a significant draw with the master switch off, you need to hunt down the culprit draining the battery. Pull all breakers and remove all fuses. Add them back one at a time while checking the ammeter. When you see it jump up, you know the problem circuit. One time for me on a Cessna, it was a reading light in the cabin shorting.  

okay, will do that tomorrow and post back if anything comes up, thank you

[Shadrach]

7 hours ago, Wojciech Kacprzyński said:

yeah it is, thats for sure, the alt was repaired after that and i havent noticed any problems yet. I will try replacing the VR. What do you mean by lousy experiences? I would like to hear about it.

in my experience their capacity deteriorates quickly. I think I had just one that lasted more than 3 years. They would be fine for dispatch because I keep my batteries on a tender.   More than once after sitting for a few days at my destinations, I’d need a jump to get home. Perhaps they have improved, but it’s been nearly 10 years since I’ve run one. I switched to a Concord AGM battery. I don’t remember the cost delta between the two then, but I think it’s less now even though both are significantly more expensive than they were just a few years ago. Gil also makes an AGM battery which may be as good as a Concord.

[DonMuncy]

After a good charge (flight or charger), disconnect a battery cable. After 3 or 4 days reconnect and try to start it again. If no start, replace the battery. If it starts fine, go to the other possibilities.

[Fly Boomer]

9 minutes ago, DonMuncy said:

After a good charge (flight or charger), disconnect a battery cable. After 3 or 4 days reconnect and try to start it again. If no start, replace the battery. If it starts fine, go to the other possibilities.

^^^This is really good!

[Bolter]

6 hours ago, Wojciech Kacprzyński said:

yeah it is, thats for sure, the alt was repaired after that and i havent noticed any problems yet. I will try replacing the VR. What do you mean by lousy experiences? I would like to hear about it.

I also avoid Gill as Concorde lasts much longer in my Mooney.  This includes the latest (as of 2016) Gill sealed battery type.   It was worn out in 2 years  Enough that I could hear the starter turning slower.  I went back to Concorde.  At 5 years, I could not detect any loss in performance, and most of its life it was on the ramp, so no maintenance charger option. 

[Shadrach]

1 hour ago, Bolter said:

I also avoid Gill as Concorde lasts much longer in my Mooney.  This includes the latest (as of 2016) Gill sealed battery type.   It was worn out in 2 years  Enough that I could hear the starter turning slower.  I went back to Concorde.  At 5 years, I could not detect any loss in performance, and most of its life it was on the ramp, so no maintenance charger option. 

I keep saying I’m going to replace my Concorde on age. I will eventually because it is not really deteriorating. I keep it on a tender most of the time, but leave it off for a week or so just to see what the OCV is after a week of sitting. Still holds strong after 8 years.

[Wojciech Kacprzyński]

10 hours ago, GeeBee said:

Sounds like a short on the hot bus. Charge the battery fully. Place a sensitive ammeter at the battery post. If there is a significant draw with the master switch off, you need to hunt down the culprit draining the battery. Pull all breakers and remove all fuses. Add them back one at a time while checking the ammeter. When you see it jump up, you know the problem circuit. One time for me on a Cessna, it was a reading light in the cabin shorting.  

Did that just now. With master off, no drainage at all, but when i pull every CB out, there is a 0.63A of drainage and when pushing them in one at a time, alt field would drain around 2.9A. Is that normal? I disconected the battery at 12.55V and will be at the airport in 3 days to see if it stays roughly the same.

[GeeBee]

Was the field switch off when you pushed in the breaker and were drawing 2.9 amps?

[Wojciech Kacprzyński]

1 hour ago, GeeBee said:

Was the field switch off when you pushed in the breaker and were drawing 2.9 amps?

I dont dormally ha ve a switch to tur it off.

[Ragsf15e]

1 hour ago, Wojciech Kacprzyński said:

I dont dormally ha ve a switch to tur it off.

I’m no EE, but if your master solenoid is working, then the only draw can come from anything attached to the hot terminal on it (or hot wired to your battery). With your master off, the solenoid shouldn’t allow power to the main bus.  That should be obvious.  After that, you’ll need to check anything on the hot terminal or hot wired to the battery.  There’s a light in the cabin/baggage that is on the hot terminal that has got many people.  Maybe @PT20J could help?

[Ragsf15e]

1 hour ago, Wojciech Kacprzyński said:

I dont dormally ha ve a switch to tur it off.

The older ones (not sure if this includes yours) have the field wire switched with the master switch (the master is single throw, dual pole). So it provides neg to the madter solenoid and connects the field wire.  Cessna and others provided those split switches we’ve all seen.  I doubt this has anything to do with his issue unless his master solenoid isn’t shutting off.

[GeeBee]

I am not familiar how the J is wired but 2.9 amps through the field circuit with the master switch off is not normal. That will deplete your battery. That is 72 amp hours per day.

[Shadrach]

35 minutes ago, GeeBee said:

I am not familiar how the J is wired but 2.9 amps through the field circuit with the master switch off is not normal. That will deplete your battery. That is 72 amp hours per day.

Doing a rough calculation, the battery would be dead inside of four hours.

[David Lloyd]

.63A is way too much for any keep alive circuit or clock. It’s probably enough to pull in a relay.