Battery Capacity Testing

[Jerry 5TJ 2,323]

I test the plane’s battery capacity at each annual inspection using the test suggested by the manufacturer.

 The test is to apply a constant current load equal to the amp-hour rating.   So, a 24 volt, 12 amp-hour battery is tested at 12 amps for an hour or until it reaches the limit of 20.0 volts.  

If it teaches 20.0 volts in exactly 60 minutes it’s at 100%.   If it only takes 50 minutes to reach the limit voltage, it has a capacity of 50/60 x 100% = 83.3%.  If you have a 12 volt system the test is down to 10.0 volts.  

I always have the battery tested each annual.  The capacity is supposed to be 80% or greater.   With the two batteries in the Ovation I’d let one go to maybe 75% as long as the other was well above 80%. 

I just bought two new batteries for the P46T and tested them before installation to establish a baseline. They were at 105%.  Here are the test results: 

Question:  Do you test the battery or batteries at each annual?   Does “your” MSC do this?  

[Marauder 9,798]

I test the plane’s battery capacity at each annual inspection using the test suggested by the manufacturer.
 The test is to apply a constant current load equal to the amp-hour rating.   So, a 24 volt, 12 amp-hour battery is tested at 12 amps for an hour or until it reaches the limit of 20.0 volts.  
If it teaches 20.0 volts in exactly 60 minutes it’s at 100%.   If it only takes 50 minutes to reach the limit voltage, it has a capacity of 50/60 x 100% = 83.3%.  If you have a 12 volt system the test is down to 10.0 volts.  
I always have the battery tested each annual.  The capacity is supposed to be 80% or greater.   With the two batteries in the Ovation I’d let one go to maybe 75% as long as the other was well above 80%. 
I just bought two new batteries for the P46T and tested them before installation to establish a baseline. They were at 105%.  Here are the test results: 

Question:  Do you test the battery or batteries at each annual?   Does “your” MSC do this?  

If you want to to test your own battery capacity, what hardware do you need to provide the load?


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[DonMuncy 2,700]

40 minutes ago, Marauder said:

If you want to to test your own battery capacity, what hardware do you need to provide the load?

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It is almost impossible to discharge one at a  constant current load without a sophisticated instrument. But with 12 v halogen bulbs of known wattage and some calculation, I think you can get plenty close enough. I built one with a programmable voltage meter that records time until it reaches 10 volts and shuts off. It is pretty much overkill, but you don't have to stay with it and watch voltage and clock.

[Jerry 5TJ 2,323]

Don gets my vote for a clever & inexpensive battery Capacity test set.

I used an electronic load, a piece of test gear I bought a dozen years ago for other uses.  

 

To limit the power dissipated in the electronic load set to below 150 watts I use a resistor in series.  For 24 volt 12 ampere battery tests a 1 ohm resistor is appropriate. The resistor is dissipating 12 x 12 x 1 = 144 watts.   I used 5 “100 watt” resistors, each 5 ohms, wired in parallel and stuck them in a tub of water. 

The electronic load controls the current automatically. 

For 12 volt 25 amp-hour battery tests four or five  1.5 ohm resistors in parallel will work as well.

The voltage across the battery is monitored with a USB voltage meter.   It takes periodic readings.  The graph is nice but unnecessary— you just need to measure the time to reach the cut off voltage. 

[Marauder 9,798]

So back to the original question. Does anyone have this done during their annual or is this one of those items that a mechanic says “yeah, she cranks nice, the battery is good” kind of things?


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[DonMuncy 2,700]

I check my own once a year.

I can't believe that all AIs don't do this as a part of the annual inspection. I would think it would be a real service to the plane owner to be told "your battery capacity test shows your battery is (a) 80%, good to go, (b) 60%, a little low, but will probably be OK, (c) 40%, we really should replace it, etc." Especially since it would undoubtedly result in increased profits to the A&P. Win win.

I remember when I first bought my plane and the battery really did not crank very well. A year or so later, I replaced the battery and was astounded at how well it then cranked. I think the AI figured I knew the battery was not up to snuff. But I simply did not have enough experience to know how it should act.

[M20Doc 8,539]

9 hours ago, Marauder said:

So back to the original question. Does anyone have this done during their annual or is this one of those items that a mechanic says “yeah, she cranks nice, the battery is good” kind of things?


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We capacity test batteries in “all electric” and turbine powered airplanes at every annual, or more frequently per the maintenance schedule.  All others get tested every other year.

Clarence

Edited May 19, 2018 by M20Doc

[Yetti 3,718]

At least charging them several times a year is a good idea

[Robert C. 300]

My AP tests my batteries at every annual and discuses with me whether or not he thinks it's time to replace based on % capacity remaining.

Robert

[RobertGary1 1,216]

On 5/19/2018 at 6:18 AM, Marauder said:

So back to the original question. Does anyone have this done during their annual or is this one of those items that a mechanic says “yeah, she cranks nice, the battery is good” kind of things?


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You have to pull the battery out of the plane at annual to inspect the battery box. At that time I test it using a battery testing tool..

https://www.amazon.com/gp/product/B01LZ4SLI1/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I know that the specific gravity for aircraft batteries isn't the same as automotive batteries but in decades of using automotive testers are chargers I've never found the difference to be worth 5 times the price for the aviation version of the tool.

-Robert

[jetdriven 4,422]

Does that device put a constant 30a current draw from the battery to establish the capacity test ?

[RobertGary1 1,216]

13 hours ago, jetdriven said:

Does that device put a constant 30a current draw from the battery to establish the capacity test ?

The modern testers use a variety of algorithms to test various battery conditions including a pretty deadon CCA reading. I know what you're talking about though, I have one of the old school static testers where you push the button and it pulls either 80 or 100 amps. I haven't used the old school one in awhile though because the new style are pretty dead on and detect more battery conditions. They also let you know about battery wear sooner than we used to get with the static voltage reading under load. About 5-10 years ago you noticed that all the auto parts store switched over.

 

-Robert

[Jerry 5TJ 2,323]

14 hours ago, jetdriven said:

Does that device put a constant 30a current draw from the battery to establish the capacity test ?

If so, not for long:  It would catch fire with 350+ watts dissipated in that small plastic housing.  It appears you enter the CCA rating from a 12V auto battery and it makes a measurement based on an expected voltage drop.

It is possible that a quick load test could give a battery capacity measurement.   BUT, if you look at the curve of V versus time the trace actually rises for a few minutes as the internal resistance heats up the battery:

 

So if the tester just looked at the first few dozen seconds it would show no decrease at all. 

Two problems may come up using this in testing an aircraft battery

1. You have to guess a CCA rating as they are not provided with our batteries.
2. Only 12V batteries can be tested.

It would be great if someone could provide a "calibration" of this type device to correlate its readings with the % reading used by aircraft battery vendors.  

 

[N201MKTurbo 5,364]

When I was retired back in 10, I designed a capacity tester that used current chopping to control the current and nichrome wrapped on mica as the disapating elements. It used inexpensive switching MOSFETs. I never built the prototype, but I did extensive spice modeling of it. My goal was to build one that would work with any aircraft battery up to 250AH. The design would be scalable to higher current. It had an app that would run on a PC and a USB. connection. The MPU and fan would be powered by the DUT and its current draw would be accounted for. I was shooting for a price of < $500.

I saw comparable devices come on the market, so I got a real job. Now I'm typing this wearing a bunny suit in the worlds largest IC maker's fab.

[RobertGary1 1,216]

5 hours ago, Jerry 5TJ said:

I

Two problems may come up using this in testing an aircraft battery

1. You have to guess a CCA rating as they are not provided with our batteries.
2. Only 12V batteries can be tested.

It would be great if someone could provide a "calibration" of this type device to correlate its readings with the % reading used by aircraft battery vendors.  

 

The newer testers use a few different algorithms to determine battery health. In my experience they are far superior at finding issues earlier than the old constant draw testers. Most automotive shops have moved to the more sophisticated testers. They also provide an estimated percent of battery life available, which is helpful and they know the difference between an undercharged battery and one with low capacitance. 

-Robert

Edited May 22, 2018 by RobertGary1

[Jerry 5TJ 2,323]

26 minutes ago, RobertGary1 said:

The newer testers use a few different algorithms to determine battery health. In my experience they are far superior at finding issues earlier than the old constant draw testers. Most automotive shops have moved to the more sophisticated testers. They also provide an estimated percent of battery life available, which is helpful and they know the difference between an undercharged battery and one with low capacitance. 

-Robert

Sounds great.  I’m going to get one of them.  

Now, any idea of how to compare the “new style” test set’s reading of % capacity to the capacity % defined in aviation use?

And, what to use for 24 volt battery testing?  

[Jerry 5TJ 2,323]

Update

I capacity tested the old batteries. 

Those tests are 371 and 372.  Same test conditions as new pair. 

One was about 30%, the better one around 60%.  

The two curves with “A” suffix are from tests starting right after disconnecting the charger: That’s more like unplugging the Battery Miinder just before starting the engine.  

 

 

[DXB 2,053]

Am reading and reviving this thread. I want to get a battery capacity tester for my 4+ year old Concorde RG-35A battery before the winter.  Are these low cost automotive battery testers that use a 30 second load test to measure CCA an adequate tool for this purpose?  I'm not too sharp when comes to stuff that has to do with electrons.  

https://www.amazon.com/VIDENT-Analyzer-100-1100-Automotive-Passenger/dp/B07ZT49LX7/ref=sr_1_14_sspa?dchild=1&keywords=12V+battery+capacity+tester&qid=1596330246&s=automotive&sr=1-14-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyOVVHMlpMWTIyMUdCJmVuY3J5cHRlZElkPUEwNTIwMjc4QlBNVjRXVzBUSVdUJmVuY3J5cHRlZEFkSWQ9QTA5ODgxMTU1VVRUWE9IRlM1T0Qmd2lkZ2V0TmFtZT1zcF9tdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

[carusoam 12,069]

Dev,

That sure looks interesting...

The actual capacity test we use in aviation is a pretty heavy load for a long period of time... to ensure real capacity data...

I Would like to see a Mechanic actually use one before I would spend the money... 

See if @Jerry 5TJ and @M20Doc have seen something like this battery capacity tester...
 

It might give enough insight for you and me... even if it is not the official required capacity test...

Having a good quality battery, in a one battery ship... is pretty important... for flying in IMC.

PP thoughts Only, not a mechanic...

Best regards,

-a-

[wishboneash 263]

I had been skeptical about conductance testing and found this site - 

https://marinehowto.com/are-battery-conductance-testers-worth-it/

They seem to be OK for predicting CCA but not that good for A-h capacity estimation. Perhaps more research & development is needed.

[PT20J 2,313]

The problem with the capacity test is that it takes time and automotive shops want to move stuff through quickly so they need a quick and dirty test to find really bad batteries. I have a 5 year old battery in my Subaru airport car that sits a lot between uses and the shop where I recently had it serviced tested it with some 2 minute tester and said that it has 60% of it's life left. Do I believe that? Surrrrrrrrrrrrrre. Car batteries always last 12 years, right?

Skip

[M20Doc 8,539]

We use a Concorde battery capacity tester in the shop.  It takes a bit of time to properly charge, capacity test then recharge the battery to determine airworthiness.

Clarence

[DXB 2,053]

7 hours ago, wishboneash said:

I had been skeptical about conductance testing and found this site - 

https://marinehowto.com/are-battery-conductance-testers-worth-it/

They seem to be OK for predicting CCA but not that good for A-h capacity estimation. Perhaps more research & development is needed.

Thanks - that's the info I was looking for!   Pretty disappointing -  CCA seems like is a miserable estimate of Ah capacity per the direct testing in the article. CCA does not seem to drop even when there are very significant decreases in Ah capacity.   As @PT20J says, these testers seem just good enough for car batteries, where you just want not to get stranded when it won't start.  In planes you also want the battery to last a long time after the alternator / generator croaks.   I suppose any significant measureable loss in CCA might make one replace the aircraft battery, but I'm still not sure how bad Ah capacity has to get before one sees a drop in CCA.

I might have to figure out how to test Ah capacity for myself properly, or just start replacing batteries at a conservative time interval.  Having never been to @Clarence's shop, I seriously doubt anyone has ever done a proper Ah capacity test on my battery at annual. It's too bad - I really do think it's a safety of flight issue that should be addressed at every annual.  

[DXB 2,053]

Also I found this post, where someone did a bunch of direct CCA vs. Ah capacity measurements on different types of car batteries. It appears that there is a somewhat linear correlation but it is not a tight one.  It would be interesting to see similar test curves for aircraft batteries, which I suspect are designed differently in regards to providing continuous vs. surge power.

https://www.mathscinotes.com/2016/12/relationship-between-battery-cold-cranking-amps-versus-capacity/

[RobertGary1 1,216]

I use a modern tester. Put in the rated cca and it gives a print out of various parameters and if the cca is still good. The cca of an airplane battery is amazingly low compared to a car battery. 
 

-Robert