Battery capacity checks

[dkkim73]

Hello All, 

I'm now somewhat used to my plane and in the great open desert of "what maintenance do I really need to do next?". 

At the annual-as-prebuy, the factory did not have the ability to do battery capacity checks. I had some intermittent cranky cranking on one battery a few weeks ago (could be anything really) and otherwise no real problems. Batteries above 24V at switches-on but not far. Alternating as taught between 1 and 2 for successive flights (unless learning how not to do hot starts

So... is it more advisable or cost-effective to have shops do a capacity test, or should I buy a capacity tester and cowperson up? 

David

[larryb]

If you are just a little bit technically inclined it's easy to check with these automated testers. Lots cheaper than having a shop do it. And less down-time as well. 

Larry

 

https://www.ebay.com/itm/355674571930?itmmeta=01J4WT16D7M504FM71EDBVAPG6&hash=item52cfdb449a:g:R5AAAOSwstJmLxnD&itmprp=enc%3AAQAJAAAA0HkqbIbAmrTTVqu5wWCYxR5enELks7HQT2w14pWPKFbjmWVwq7bfAvPD0sM3ZUaHulAeM8w%2BAUQ0QuQiFtU74aiwM0xznsinxaZ22DA4P8kkJqJaAI4s2dW%2BQq%2BaUUfgpsVyYl6SsXLz3vBNYQDKcEeR07KoWJz1hXVkJGGL4TpOoSEW78fBvRonefaaTSqrlsyDwsCm2%2BRFQSwUXHjdH4%2F6qkJgqH%2BHEuoQGmIDgpy%2FMwjsefg7YQ8wmzFGB1wcFo%2Fy3rTyjCAmLkqLxLB%2BJnQ%3D|tkp%3ABFBM2uaEmqdk

[Will.iam]

Or the totally free route turn on everything electrically you would want working if you had an alternator failure and needed to get down to land. Then start a timer see when things stop working. If it’s past an hour good to go put the battery back on the battery charger. If not then replace the battery. 

[EricJ]

If you buy a capacity tester (and there are lots of reasonably-priced options), get a copy of the Component Maintenance Manual (or equivalent) for your batteries.   There will likely be a procedure in there on how to check capacity and what to do if it doesn't pass (Concorde manuals have this).    There are rehab cycles that can be done to try to restore capacity if it is too low, which does require additional equipment.   

[PT20J]

If you do your own capacity tests, in addition to the load you also need a good charger because the test will deeply discharge the battery and you will want to immediately recharge it. Concorde recommends charging at a constant potential with a charger capable of putting out a high current (up to 8xC1).

[Jerry 5TJ]

1 hour ago, PT20J said:

Concorde recommends charging at a constant potential with a charger capable of putting out a high current (up to 8xC1).

So a 35 amp-hour battery would be charged at 280 amperes?  Seems pretty high to me. 

[jetdriven]

You discharge it the C1 rate which for an RG35 is about 33A…..it  should last for 80% of an hour. Then you charge it back up at 10% of the C1 rating for 18 hours, let it rest for a few hours, and then you can capacity test it again. It’s all in the Concorde RG series component maintenance manual

[Utah20Gflyer]

Are our aircraft batteries deep cycle or starting batteries?  I was under the impression they were starting batteries.  Seems to me the battery test people are talking about is abusive to a starting battery.  I don’t know this for sure but I’ve heard that a starting battery will be damaged by complete discharges and repeated  complete discharges will likely be fatal (5-6).
 

When I was a tire and Battery tech at sears at 18 years old we tested starting batteries by putting a high amp load on them and watching the battery voltage.   A good battery would drop in voltage slightly and then slowly drop.  A bad battery would drop a lot in voltage immediately down to 9 or 10 volts.  This test took 30 seconds to do.  If I were to test my battery this is the type of test I would do.  It approximates the use case for the battery and doesn’t abuse it.  
 

If you want any to regularly test amp hour capacity then I would recommend getting a Lithium Ion battery.  They can be fully discharged 1000+ times without any appreciable effect.  

[PT20J]

19 minutes ago, Jerry 5TJ said:

So a 35 amp-hour battery would be charged at 280 amperes?  Seems pretty high to me. 

The battery will draw whatever current it can during the constant potential charge. The idea is that the battery should be the limiting factor, not the charger. Obviously it’s not going to draw 280 A for any length of time and most chargers won’t put out that much. The idea is just that you should use a hefty charger to charge it as fast as possible. 

[Jerry 5TJ]

 I read that section 8 as recommending “0.2 x C1” which for 35 amp-hour battery is ~ 7 amperes.  

[Fly Boomer]

59 minutes ago, jetdriven said:

charge it back up at 10% of the C1

That sounds more like a "trickle" charge?  At 3.3 amps?

[Fly Boomer]

16 minutes ago, Jerry 5TJ said:

 I read that section 8 as recommending “0.2 x C1” which for 35 amp-hour battery is ~ 7 amperes.  

"at least 0.2xC1".  More is better.  "as high as possible" up to 8xC1.

[jetdriven]

14 minutes ago, Fly Boomer said:

That sounds more like a "trickle" charge?  At 3.3 amps?

It’s a recovery charge and like I said, read the manual and follow that.

[Will.iam]

1 hour ago, Utah20Gflyer said:

Are our aircraft batteries deep cycle or starting batteries?  I was under the impression they were starting batteries.  Seems to me the battery test people are talking about is abusive to a starting battery.  I don’t know this for sure but I’ve heard that a starting battery will be damaged by complete discharges and repeated  complete discharges will likely be fatal (5-6).
 

When I was a tire and Battery tech at sears at 18 years old we tested starting batteries by putting a high amp load on them and watching the battery voltage.   A good battery would drop in voltage slightly and then slowly drop.  A bad battery would drop a lot in voltage immediately down to 9 or 10 volts.  This test took 30 seconds to do.  If I were to test my battery this is the type of test I would do.  It approximates the use case for the battery and doesn’t abuse it.  
 

If you want any to regularly test amp hour capacity then I would recommend getting a Lithium Ion battery.  They can be fully discharged 1000+ times without any appreciable effect.  

Airplane battery is both a starting battery and a backup source of electrical power to use to get down safely if the alternator fails in flight. Unfortunately some people believe that if the battery is able to start the engine that it is also good backup power supply for your electrical loads. The reality is that the start is so short that even an old battery that’s lost alot of capacity will still get the engine started but when the alternator fails will not keep the other electric load for very long and in short order will leave you completely electric out. That is what the capacity load test is for. To verify the battery can sustain the load for at least 1 hour. 

[PT20J]

1 hour ago, Jerry 5TJ said:

 I read that section 8 as recommending “0.2 x C1” which for 35 amp-hour battery is ~ 7 amperes.  

I think it is clear from the text that 0.2xC1 is the minimum. More is better and the battery can take as much to 8xC1. I discussed this with a Concorde rep and he said that unlike older lead acid batteries that needed to be charged slowly, the Concorde batteries should be charged as quickly as possible at whatever current the battery will take.

[Will.iam]

15 minutes ago, PT20J said:

I think it is clear from the text that 0.2xC1 is the minimum. More is better and the battery can take as much to 8xC1. I discussed this with a Concorde rep and he said that unlike older lead acid batteries that needed to be charged slowly, the Concorde batteries should be charged as quickly as possible at whatever current the battery will take.

So would the battery minder tender designed for concord be enough current charge or does it need to be a dedicated charger for that since a standard 120 wall outlet circuit breaker tops out at 20amps at best with most standard outlets being 15amps.  I. E. Get a special charger that uses 240 outlet instead to get the high amps needed in the initial start of the charge?

[MikeOH]

I bought an electronic load and did the capacity test myself per the Concorde MM.  I then used my battery minder to recharge; no issues, but not certain what it was charging at.  Remember, you are NOT necessarily limited to 15A charge just because it's a 120V 15A circuit as the battery charger is converting that to 12/24DC and can supply more current depending upon its design.  Power from 120V 15A circuit is 1800 Watts, in theory (100% efficient) a charger could produce near 150 Amps at 12V.

[Fly Boomer]

2 hours ago, jetdriven said:

It’s a recovery charge and like I said, read the manual and follow that.

Right you are.  I need to re-read from the top.  I thought we were talking about the constant potential charge following a capacity test.  And to be clear, my comment was only related to Concorde--I have no idea what other brands require.

[PT20J]

1 hour ago, Will.iam said:

So would the battery minder tender designed for concord be enough current charge or does it need to be a dedicated charger for that since a standard 120 wall outlet circuit breaker tops out at 20amps at best with most standard outlets being 15amps.  I. E. Get a special charger that uses 240 outlet instead to get the high amps needed in the initial start of the charge?

As an example, a Concorde 24V RG-24-15 is rated at 13.6 AH, so the C1 current is 13.6 A. The minimum charging current is 0.2 x C1 or 2.72 A. The 24 V BatteryMINDer is rated at 4 A, so it exceeds the minimum. It is just not optimum. Does it materially affect battery life? Probably not if you are only doing this once a year.

[PT20J]

3 hours ago, Utah20Gflyer said:

Are our aircraft batteries deep cycle or starting batteries?  I was under the impression they were starting batteries.  Seems to me the battery test people are talking about is abusive to a starting battery.  I don’t know this for sure but I’ve heard that a starting battery will be damaged by complete discharges and repeated  complete discharges will likely be fatal (5-6).
 

When I was a tire and Battery tech at sears at 18 years old we tested starting batteries by putting a high amp load on them and watching the battery voltage.   A good battery would drop in voltage slightly and then slowly drop.  A bad battery would drop a lot in voltage immediately down to 9 or 10 volts.  This test took 30 seconds to do.  If I were to test my battery this is the type of test I would do.  It approximates the use case for the battery and doesn’t abuse it.  
 

If you want any to regularly test amp hour capacity then I would recommend getting a Lithium Ion battery.  They can be fully discharged 1000+ times without any appreciable effect.  

Depends on the battery. Flooded cell lead acid batteries don't like deep discharge. AGM batteries are more tolerant. According to Concorde, capacity testing once a year with prompt recharging does not appreciably affect the life of the battery. https://batteryuniversity.com/article/bu-201a-absorbent-glass-mat-agm

[jetdriven]

3 hours ago, Will.iam said:

So would the battery minder tender designed for concord be enough current charge or does it need to be a dedicated charger for that since a standard 120 wall outlet circuit breaker tops out at 20amps at best with most standard outlets being 15amps.  I. E. Get a special charger that uses 240 outlet instead to get the high amps needed in the initial start of the charge?

No, the battery minder is not gonna be adequate for the constant current recovery charge. You need a power supply that will put a steady 3.5 A into it and up to about 16.5V for 18 hours. These automatic chargers taper down the amps as the voltage comes up and then they stop and go to a float cycle. You purposely overcharge it for a reason. But however, on Amazon, there are several power supplies that you can use to constant current charge it with.  I’ve also seen the recovery charge take these things from 50% up to 75 or even 90% capacity in the re-test.  Maybe it just reforms the lead on the plates but it’s something that pretty much nobody does but it’s really important.

we use this at the shop. https://a.co/d/3I3JzYY

[PT20J]

There are three charge regimes described in the Concorde Maintenance Manual (which would shorten this thread if everyone would download it and read it  - CB note: it’s free)

1. Constant Potential Charge - normal charge mode. Used after the capacity test. It’s the way airplane charges the battery after you start the engine. 

2. Conditioning charge - used to attempt to recover a battery that fails the capacity test.

3. Recovery charge - used on an essentially dead battery to attempt to recover it with the least long term damage.

[Pinecone]

I cannot cut and paste, but the Conditioning Charge (used if it fails the capacity check, they say to charge at 1/10 C for 16 hours.  The let it cool for 8 hours or until within 18 degrees of ambient

The charger needs to be capable of 17 volts for 12 volt batteries and 34 volts for 24 volt batteries.

Most chargers will not do this, so you may need an adjustable power supply.

But you only need 1/10C or 2.5 amps for a 25 amp/hour battery.

Due to the voltages, this should NOT be done in the aircraft as you could damage aircraft systems

[PT20J]

Normal charging is a constant potential (voltage) charge -- The charging voltage is constant and the battery takes whatever current it takes (up to the limit of the charger). This requires a constant voltage power supply per table 101/102 in the MM.

Conditioning charge is a constant current charge  -- The charging current is constant and the battery voltage goes to whatever it goes to (the supply must be capable of supplying current at a high enough voltage). This requires a constant current power supply per table 101/102 in the MM.

 

[Vance Harral]

On an anecdotal side-note about battery capacity...

This weekend, one of my airplane partners had an alternator failure in our airplane - exactly the contingent situation being discussed here.  This occurred in IMC, though fortunately he was only a few minutes from home, with a healthy battery and a dual G5 setup that has it's own backups.  Anyway... we've done capacity checks on our battery using the "turn on the stuff in the airplane in the hangar" method, and being a bit of an electrical engineering nerd, I even know what the voltage vs. remaining capacity curve looks like for our Concorde RG-35A battery, driving an "emergency" electrical load.  The interesting thing is that when the alternator failed - which my partner was alerted to immediately via the bus voltage annunciator - he observed an indicated battery voltage of 11.7V.  That's abnormally low for a healthy battery, even taking into account the IR drop between the battery terminals and the voltage gauge.  It's much lower than we ever saw on that gauge in our capacity test.  Once he got on the ground and shut down, the indicated voltage immediately went back to 12.3.  Voltage at the actual battery terminals was slightly higher, of course; but the point is that battery voltage with the engine running was lower than with it stopped.

The cause of the failure turned out to be simple: just a broken field wire at the alternator.  But his observations suggest that a spinning alternator with a broken field wire actually puts an additional electrical load on the battery, beyond the "turn on all the switches" load one might use in a practical capacity test.  I can see how that might be the case, because the alternator output wire to which the battery is connected, would at that point also be connected to an un-energized rotating electro-magnetic system.  I confess I haven't dug out my electromechanical machines textbooks to verify that idea, though.  Anyone know if this is actually the case?

If the hypothesis is correct, then in the event of electrical failure, it might be a good idea to pull the main alternator breaker (not the field breaker) to disconnect that parasitic load.  That assumes you can pull the breaker, though.  The main alternator breaker in our airplane is of a type that cannot be manually pulled, for whatever reason.