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Battery load test shortens battery life - really?

I am load testing a Concorde RG24-15 right now. It is specced at 13.6Ah and according to the instructions (still the same URL as Jesse’s 2013 post above it should be discharged at a constant current of 13.6A

Now, how many battery testers are constant current sinks? Obviously it’s easy to make one but I just don’t see the crude testers I have seen having this inside.

(The above will work with 12V or 24V batteries.)

Yet, the result of this usually-crude test is used to potentially consign a €800+ battery into the dustbin.

And that’s before you get to the battery re-conditioning chargers which can partially restore a battery, which most aircraft owners know nothing about.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Now, how many battery testers are constant current sinks? Obviously it’s easy to make one but I just don’t see the crude testers I have seen having this inside.

That is the whole point. You either build yourself as you will do, and we have done, or you use a commercial electronic load, or you buy a tester from a manufacturer, I think Gill sells one for example.

These crude testers, do some sort of testing, though are not very reliable or good for your battery.

JP-Avionics
EHMZ

good for your battery

What would be no good for the battery?

A lot of people are avoiding load testing because they are told it is no good for the battery, but as I posted further back this has to be nonsense because at 1C you are loading the battery very lightly and probably a lot more lightly than happens in the plane except when the alternator is charging it.

If somebody is testing batteries at 10C (136A for the above battery) which is more or less the starter motor current, that would be really bad.

The real problem I see is that probably a lot of batteries are being scrapped needlessly, due to crappy testers.

Administrator
Shoreham EGKA, United Kingdom

Is there something relevant to this question there, Neil? I must have missed it.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

What would be no good for the battery?

You are loading it extensive, which is not the normal work regime of the battery. It can give a high current for a few seconds (which is not to interesting) and I can do 1C for an hour. This is interesting, as you will discharge your battery in this regime when your alternator fails. Remember that this test is constant current, AND you have to stop it at 10 Volt or 20Volt depending on the battery. This prevent damage to the batttery. This is why it takes hours, the battery should be fully charged before starting the test. Test it (for an hour) and afterwards you have to recharge it before reinstallation (important) this takes als hours.

The crude high load testers don’t respect the 10 / 20 Volt limit and generally discharge as the said 10C or so.

Peter wrote:

If somebody is testing batteries at 10C (136A for the above battery) which is more or less the starter motor current, that would be really bad.

Agreed that this in’t good practice, and not relevent. 10C will be nowhere near starter motor current. Startermotor current will be much higher, especially on light weight starters, as they draw far more current then the heavy weight starters.

JP-Avionics
EHMZ

10C will be nowhere near starter motor current. Startermotor current will be much higher, especially on light weight starters, as they draw far more current then the heavy weight starters.

It depends on the starter motor. From e.g. here

The 10C current for a RG24-15 is 136A and as you can see that covers the 149NL/EC starter.

Skytec used to erroneously list the 149/NL as suitable for 24V aircraft (it has/had a 12/24 jumper) but it had a high failure rate whereby the stator would slip relative to the rest of it and rip off the internal wiring. Then they introduced the 149/NL/EC for 24V aircraft which “solves” the problem by running at 1/2 the speed But the current is 1/2 also which is probably a good thing.

In comparison the original old Lycoming heavy starter draws about 80A, but lots of people have problems especially on warm/hot starts.

Administrator
Shoreham EGKA, United Kingdom

I have just been doing a load test on my Concorde RG24-15 battery, which is 5 years old.

First I charged it from a 28.0V source. Eventually, after a day or so, the current draw was just 15mA. Then I discharged it into a 2.7 ohm power resistor

An an average current of 9A it lasted over 1:45 which is not bad at all (13.6Ah battery). Then I recharged it with the “special conditioning charger” from CTEK (model MXT4.0) and the discharge result is amazingly the same in terms of capacity, although the voltage was slightly higher along the way (so, with a resistive load, there was a net very small increase in the capacity).

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Is there something relevant to this question there, Neil? I must have missed it.

Yes, it’s the sections on the differences between high current (“Starter”) batteries and Deep Discharge types. It is apparent that the Starter types have a very short life in terms od deep discharge cycles (as low as 15 cycles), so in capacity testing by deep discharge you are using up a significant portion of the life. The article also explains why a deep discharge is bad for the thin plate high current types.

Darley Moor, Gamston (UK)

Peter wrote:

It depends on the starter motor.
Peter wrote:
In comparison the original old Lycoming heavy starter draws about 80A, but lots of people have problems especially on warm/hot starts.

This is incorrect information Peter, and now where near real life.

The data you refer to is test data, so with a 22 Volt it should draw 85-125 Amp and reach 140 RPM.

The heavy weight MHB-4016 does 35 Amp at no load and about 260 Amp under heavy load.

JP-Avionics
EHMZ
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