Battery Check Anyone do it?

[N201MKTurbo]

1 hour ago, Tom said:

See the "AC Conductance" section on this website. 

From this website:

There is a notion that internal resistance is related to capacity, and this is false. The resistance of modern lead acid and lithium-ion batteries stays flat through most of the service life. Advancements in electrolyte additives are reducing internal corrosion issues that were in part responsible for the rise in resistance.

 

The only way to accurately measure the capacity of a battery is to measure it directly. You could get pretty close by interpolating the results from a smaller voltage decrease then the specified 10V terminating voltage. As you can see from Emmet's graphs, the discharge rates are pretty linear.

[DonMuncy]

1 hour ago, Tom said:

See the "AC Conductance" section on this website. 

I'm not near smart enough to understand that, but I interpret what they are saying is that the HF device is helpful in determining the health of a battery, it is not a very good indicator of the "capacity" of the battery. And for our purposes, the capacity is how long it will run our stuff in the event of an alternator failure.

 

[Mooneymite]

I have an acquaintance that has a battery tester with a load that looks like a toaster oven.  I've used it in the past, but now I'm thinking that since the point of testing your battery is to see if you can get the airplane on the ground with an alternator/generator failure....why not just leave the master switch on, turn on all the items you would need for your descent and approach in IFR and see if the voltage stays above 11.5V, or some other "acceptable voltage" after 30 minutes?

Wouldn't that be a more "realistic" battery capacity test?

I heartily agree that a fast turning starter is no assurance that the battery has the appropriate staying power.

 

Edited January 4, 2016 by Mooneymite

[Tom]

1 minute ago, N201MKTurbo said:

The only way to accurately measure the capacity of a battery is to measure it directly. You could get pretty close by interpolating the results from a smaller voltage decrease then the specified 10V terminating voltage. As you can see from Emmet's graphs, the discharge rates are pretty linear.

The question to clarify is "what do we expect or hope that the battery test can tell us?"  Here are some possible answers:
a) "I want to know that the battery will start the engine and keep the radios on for a while if the alternator fails." 
"I want to know if the battery is nearing the end of its life, even if it's still right now able to start the engine and keep the radios on for a while if the alternator fails." 
c) "I want to get a sense if my battery will start the engine and keep the radios on for a while if the alternator fails quickly, without performing a load test."

The required annual load test answers question A (though I think this is not routinely done).  This load test in theory does shorten the lifespan of the battery, except that the batter doesn't live long enough to notice...
Measuring the initial internal resistance and monitoring it over time can, without any damage to the battery, provide a means of monitoring the battery for potential problems brewing. 
Similar to the preceding sentence, measuring internal resistance while measuring the voltage while knowing the rated discharge capability provides a quick means, albeit not fully reliable, of getting a sense of the health of the battery and thus indirectly the battery's capacity to work.  This is NOT to be relied upon, but it is a quick and non-harmful test to perform on the battery between annual load testing.

*All references to "quick" above assume that the battery is not held behind a panel held on by 16 or so fasteners......
 

 

 

 

[Tom]

24 minutes ago, Mooneymite said:

Wouldn't that be a more "realistic" battery capacity test?

Mike Busch in the link that I provided above describes basically doing what you are suggesting.  You can spring $20 for a 100amp load toaster coil or just do a little math with known loads off your bus.

[Mooneymite]

4 minutes ago, Tom said:

Mike Busch in the link that I provided above describes basically doing what you are suggesting.  You can spring $20 for a 100amp load toaster coil or just do a little math with known loads off your bus.

Bush's solution is more mathematical, my proposal is more pragmatic.  My suggested test would avoid missing something on the load list.

What I do not know is:  What is an acceptable minimum voltage at the end of the test?

Obviously, if radios stop working, or the turn coordinator unwinds before the 30 minute test is up, that's unacceptable, but how low can the voltage drop and still be considered, "acceptable"?  I'm guessing somewhere near 11.5 for a 12 volt battery, but I suspect the electrical engineers on this forum can come up with a real answer.

[cnoe]

1 hour ago, Tom said: See the "AC Conductance" section on this website. 

From this website:

There is a notion that internal resistance is related to capacity, and this is false. The resistance of modern lead acid and lithium-ion batteries stays flat through most of the service life. Advancements in electrolyte additives are reducing internal corrosion issues that were in part responsible for the rise in resistance.

 

The only way to accurately measure the capacity of a battery is to measure it directly. You could get pretty close by interpolating the results from a smaller voltage decrease then the specified 10V terminating voltage. As you can see from Emmet's graphs, the discharge rates are pretty linear.

Emmet's battery looks to be in good shape but a weak battery will typically show a steep voltage curve downward plotted against time well before it reaches 10V.

It's quite simple to add an appropriate load (whether from a resistance apparatus or your high-draw equipment) and plot the voltage drop over time. The results will easily show if the battery is bad.

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[cnoe]

To clarify, I'm not talking about testing the resistance of the battery; I'm talking about using resistors to impart a load on the battery.

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[cliffy]

That's a cool website I gotta take time to really read it  Thanks!

[cliffy]

The battery manf and the FAA also recommend that the battery make 80% capacity to pass the test. To really know what that is you need to do the load test as specified by the manf. 

Again the only reason I bring it up is that your life may depend on it if you fly IFR.

Question #2  Have you ever had a dead battery and jump started the airplane and then gone flying to charge it? Did you at the same time go IMC? How much use would that battery have been if you needed it? 

 

[carusoam]

The nice thing about the standardized test is...

it's results are go/no go.  The results can be used to describe how your equipment should work in real life.  Because that is what the real life guys have tested against and described the successful battery with the standardized test.

changing the test up to not go the full distance may not show how strong the downward curve has become over time.  This downward curve appears to change with age.

batteries appear to be linear in this case. Until they are no longer linear like at the end of their lives.  Real life is not linear.

testing the battery capacity using real electronic loads is a good idea, sort of.  It is a great test, but it could be hazardous to the health of your equipment.  Some electronics don't protect themselves very well against variations in voltage.

Saving a battery at the cost of the avionics would be really annoying.

I'm only a PP, not an electrical engineer or mechanic.

Best regards,

-a-

[jetdriven]

I like the earlier suggestion.  Turn on all the radios and the lights.  wait 30 minutes. If the engine cranks up, you are good for another year. 

[Guest]

In an all glass/ all electric airplane battery capacity testing is more important. Concord make a very nice capacity tester for their own batteries.

On the same subject line, how many do the battery test for their Aspen or electric standby gyro if it has its own external battery?

Clarence