Interesting math

[Skylane81E]

Working on a plane that is drawing down a G243 battery between flights and found that amps pulled by the clock are sufficient to drain the battery in 3 weeks using the published capacity.

Just thought I'd share.

 

[Let'sgoflying!]

what is the math on that? is it an older mechanical clock with electric motor or a chipped clock?

 

[gismo]

what is the math on that? is it an older mechanical clock with electric motor or a chipped clock?

That's a good question. The earliest electric clocks in cars used a motor to wind up the mainspring whenever it got unwound to a certain point. Those clocks would pull a fair amount of current for a brief period followed by a longer interval of zero current draw. Ideally Duncan measured the current over a long enough period to determine the consistency of the reading.

Duncan, most electronic aviation clocks draw just a few milliamps on the keep alive input. Did you measure the clock's current by inserting a meter in series with the battery connection? Are you certain that the clock was the only load?

What did you see for current? The Gill G243 has a 1C rating of 10AH but the capacity is probably close to double that over a multi week discharge. 5 ma would consume 2AH in three weeks of use. That might be noticeable but just barely. If your "interesting math" indicated total discharge based on the 1C rating (10AH) in thee weeks you must have seen close to 20ma which is a lot for a clock but even then I'd expect you to lose less than half the battery's charge in 3 weeks due to the higher capacity with a low current discharge.

 

[Skylane81E]

20mA is indeed what I measured, (both inline with the clock and total master off draw) and over an extended time it never varied more than a milliamp. I will grant the charge rate is much less than that the capacity is rated at, but it's all the data I have.

I've been trying to find the normal rate for the clock, as well as the other problem causing it to die in 11days. Looking like the alternator may not have been fully charging the battery allowing the clock to polish it off.

 

[gismo]

20mA is indeed what I measured, (both inline with the clock and total master off draw) and over an extended time it never varied more than a milliamp. I will grant the charge rate is much less than that the capacity is rated at, but it's all the data I have.

I've been trying to find the normal rate for the clock, as well as the other problem causing it to die in 11days. Looking like the alternator may not have been fully charging the battery allowing the clock to polish it off.

Chances are the clock is defective. A common ESD induced failure symptom is higher than normal current draw due to damage of the ESD protection. What's the make/model?

 

[Skylane81E]

It's a Mitchell, don't have the model number.

Did replace the alternator, and it will charge at taxi speed now, should help some. I'll look into the clock draw.

 

[Tom-D]

Working on a plane that is drawing down a G243 battery between flights and found that amps pulled by the clock are sufficient to drain the battery in 3 weeks using the published capacity.

Just thought I'd share.

Pop the clock circuit breaker while in storage. we have a 150 that will do the same thing, so we keep a battery minder on it.