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DonMuncy

Battery capacity testing

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DonMuncy    1,322

I keep my aircraft battery on a Battery Minder full time. After a trip to the Mooney Summit a couple of years ago, when I got ready for the flight home, the battery would not start the engine. I found out that battery voltage is almost meaningless as an indication of how your battery is going to perform.

Last year at the MAPA homecoming, a representative for Concorde told us that capacity tests were supposed to be done on our planes at annual, and that our planes were not airworthy when the capacity dropped to 85%.

I decided to take it on as a project, and ultimately wound up with a testing device, which, although not perfect, appears to be fairly accurate at measuring the capacity.

My testing indicates that if you go by Concorde's numbers, you may be buying a battery a lot more often, but capacity checking seems to be a very helpful exercise. If it drops down below about 50%, you should seriously consider replacement.

 

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carusoam    3,906

Don, you're the most technical and hands-on lawyer I know..! :)

Can you give a hint what a capacity tester looks like, how it works?

I know mine get tested at annual.  It's been a long time since I looked on that far wall...

Best regards,

-a-

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DonMuncy    1,322
30 minutes ago, carusoam said:

Don, you're the most technical and hands-on lawyer I know..! :)

Can you give a hint what a capacity tester looks like, how it works?

I know mine get tested at annual.  It's been a long time since I looked on that far wall...

Best regards,

-a-

The tester is basically a 6.25 amp load made up of the unit's own draw and two 12v halogen bulbs which are activated by a programmable electronic voltmeter. That activation also starts a clock through a relay. When the amperage drain pulls the battery down to 10 v, it shuts off the bulbs and clock. Starting with a fully charged battery, you and hook the clips on it (either in or out of the plane). When you come back the clock will tell you how long it took. You could do the same thing without the gadgetry if you were willing to watch a clock and a voltmeter for the length of time it takes. By dividing the amp hours of the battery by 6.25, you can calculate how long it should take and calculate the % capacity.

SAM_1669.JPG

SAM_1667.JPG

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cliffy    703

With one alternator and one battery what is your "out" if the alt. gives up the ghost in flight, at night, or in IMC ? Your battery! How long will your battery work for you if it has to do all the work? In the Boeings I flew we were told if we went DC power only we'd have 30 mins. Do you think your battery is as good as the ones we had? How long will it take you to get on the ground? Do you think there might be some urgency in the issue? When you go out to start your plane and the battery won't crank it over, how much "capacity" do you think it had on your LAST flight if you needed it? Was your last flight at night? Was it IMC? Just something to think about.

Don has brought up a very timely subject here and it serves good to think about it. You gotta remember that starting actually uses very little of the batteries capacity. If it didn't start your airplane this time, it didn't have much the last time you flew. Have you ever jump stated your airplane and then gone right to flying? How much capacity do you think it had for the next hour as it charged? How much capacity did it lose by being drained to nothing and refilled? It will always lose some capacity by doing that.  

Just something to think about as you read Don's thread. He has a good point to be made. 

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Piloto    1,285

Voltage reading after one week with no charge is a good indication of the battery ability to hold charge. If it is above 12V you have a good battery. Below 12V it is time to get a new battery. But my best capacity test is cranking the engine after two weeks shutdown and no charging. Charging voltage is a also important. The Concorde will charge to maximum capacity when charged at 14.2 Volts.

José

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DonMuncy    1,322
58 minutes ago, cliffy said:

With one alternator and one battery what is your "out" if the alt. gives up the ghost in flight, at night, or in IMC ? Your battery! How long will your battery work for you if it has to do all the work? In the Boeings I flew we were told if we went DC power only we'd have 30 mins. Do you think your battery is as good as the ones we had? How long will it take you to get on the ground? Do you think there might be some urgency in the issue? When you go out to start your plane and the battery won't crank it over, how much "capacity" do you think it had on your LAST flight if you needed it? Was your last flight at night? Was it IMC? Just something to think about.

Don has brought up a very timely subject here and it serves good to think about it. You gotta remember that starting actually uses very little of the batteries capacity. If it didn't start your airplane this time, it didn't have much the last time you flew. Have you ever jump stated your airplane and then gone right to flying? How much capacity do you think it had for the next hour as it charged? How much capacity did it lose by being drained to nothing and refilled? It will always lose some capacity by doing that.  

Just something to think about as you read Don's thread. He has a good point to be made. 

All good points Cilffy. If flying at night, IMC, Concorde's recommendations are not bad. For day VFR, one might relax a bit. But I think it is good to know you battery's capabilities. And I am not sure all annual inspections include battery capacity testing.

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teejayevans    837
Voltage reading after one week with no charge is a good indication of the battery ability to hold charge. If it is above 12V you have a good battery. Below 12V it is time to get a new battery. But my best capacity test is cranking the engine after two weeks shutdown and no charging. Charging voltage is a also important. The Concorde will charge to maximum capacity when charged at 14.2 Volts.
José

I assume you are taking these voltage readings with a load on the battery (master on, nav lights on), otherwise the voltage is not a good indicator of battery condition. I've seen batteries unable to supply enough charge to turn over, but still show 12v at rest. I also had my battery cold start the engine with no problem and after an hour flight completely die on a hot start.

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tigers2007    141

I use the Solar BA9 and it gives the CCA via a capacitance test. The instructions say to use this after charging - so you know the full capacity.

http://www.cloreautomotive.com/sku.php?id=512

I have had float chargers dry out batteries before too. Always check the water level. I use Battery minder and Noco Genius brands (seven of them).


Sent from my iPhone using Tapatalk

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Piloto    1,285
7 hours ago, teejayevans said:


I assume you are taking these voltage readings with a load on the battery (master on, nav lights on), otherwise the voltage is not a good indicator of battery condition. I've seen batteries unable to supply enough charge to turn over, but still show 12v at rest. I also had my battery cold start the engine with no problem and after an hour flight completely die on a hot start.

The voltage readings are in the airplane with master on using the plane voltmeter.

You can read more details at:

http://www.concordebattery.com/otherpdf/5-0324-rg-manual.pdf

José

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DonMuncy    1,322
2 hours ago, Mark89114 said:

This project looks too much like that clock bomber kid from a year ago.......

That's where I got the idea. :) 

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Jerry 5TJ    722

Lots of ways to skin the capacity cat.

I read the battery capacity test requirement as

  • test at constant current
  • current = amp hour rating at 1 hour
  • must remain at above 1.67 volts per cell at 80% of the 1 hour interval = 48 minutes

For the RM24-11M in my Ovation (either of the two, batteries, not Ovations)

  • constant current for C1 = 11 amps
  • must remain at above (12 x 1.67 volts per cell)  20V total after 48 minutes

That's all fine, but I don't have a Constant Current load that will sink over 150 watts.  So I could test at lower than the C1 rate and extrapolate the results. 

Usual web research yields this curve of battery voltage versus time at various rates of discharge. 

Ref:  http://home.planet.nl/~dortu001/duration_discharge.png

duration_discharge 12V battery vs Cx.png

Note that this battery appears to FAIL the 80% test at C1.  (1.0C on the graph).  It should hold 10V for 48 minutes but it is headed down the waterfall at about 40 minutes.  

Noted also that the battery voltage remains relatively flat until nearly exhausted, then the terminal voltage plummets.  So those of you who test at constant Resistance rather than constant current are not far off.

Given my electronic load test set's limitations (max 150 watts), I need to test at slower than C1.  Seems to me after inspection of the curves that the 80% limit could be tested at C0.2 rate by

  • Setting CC to 11/5 = 2.20 amps
  • Measuring V terminal of 20.0V or greater for at least 80% of 240 = 192 minutes

When I do that I see that one of my batteries is at about 75% and the other about 85%.   On average, they're at 80% and I left them in for another year...

 

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