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Batteries capacity measure

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Offline c_joerg

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Batteries capacity measure
« on: 01 / August / 2016, 07:17:29 »
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Hello,
I have a couple of NB-10L batteries. Is there any way with CHDK to measure the capacity? For time-lapse I want to know, which is my best Akku. It’s not necessary to know the absolute value of the capacity, but would be interesting. The easiest way would be if I could measure the batteries current like the batteries voltage but I think that’s not possible or?

Another idea is, to measure the current with my external power supply in playback mode with a fixed picture. Then I would start a script in playback mode which logs the voltage over time. After the run I could nearly calculate the Batteries capacity.

Does anybody else has another solution?

Great Joerg
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Offline waterwingz

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Re: Batteries capacity measure
« Reply #1 on: 01 / August / 2016, 08:07:35 »
Quote from: c_joerg on 01 / August / 2016, 07:17:29
I have a couple of NB-10L batteries. Is there any way with CHDK to measure the capacity? For time-lapse I want to know, which is my best Akku. It’s not necessary to know the absolute value of the capacity, but would be interesting. The easiest way would be if I could measure the batteries current like the batteries voltage but I think that’s not possible or?

Another idea is, to measure the current with my external power supply in playback mode with a fixed picture. Then I would start a script in playback mode which logs the voltage over time. After the run I could nearly calculate the Batteries capacity.
Measuring current draw does not tell you anything about a battery's capacity. Current draw is determined by what the camera needs and it will actually appear to go up as the battery voltage droops !

The only thing you can do is measure the time to a fixed voltage droop as the capacity nears exhaustion.  The battery with the longest time has the most holding capacity.
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Offline c_joerg

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Re: Batteries capacity measure
« Reply #2 on: 01 / August / 2016, 08:41:27 »
Quote from: waterwingz on 01 / August / 2016, 08:07:35
Measuring current draw does not tell you anything about a battery's capacity.

Why not?
May be the cam needs in playback mode 500mA und the cam run 2h then the capacity would be around 1000mAh.
I would think that the current in playback mode is nearly constant (may be +-10%). If I do one measurement with external power supply, this might be correct enough.
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Offline waterwingz

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Re: Batteries capacity measure
« Reply #3 on: 01 / August / 2016, 09:19:41 »
Correct.   I'll clarify my previous statement.   Measuring current draw tells you nothing much about a battery's capacity.  Measuring the time that a battery can draw a set amount of current does. 
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Offline c_joerg

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Re: Batteries capacity measure
« Reply #4 on: 05 / December / 2016, 03:50:12 »
I would like to share the results of my measurements.

How did I perform the measurement:
- Camera in playback mode (gray image)
- Display brightness on 2/5
- Measurement of current via DC coupler (mean value)
- Measurement of the time in the playback mode via a script.
- capacity = current (mean value) * time

Interestingly, all the spare batteries (except for HAMA) had no temperature sensor.

NB-10L
Canon I  (920mAh, 3-4years old)  => 910mAh
Canon II (920mAh,3-4years old)  => 860mAh
Canon III (920mAh, 3-4years old)  => 908mAh
Hama (820mAh, 1-2years old)  =>  836 mAh
Baxxtar (950mAh, 1-2years old)  =>  972mAh
2 * No Name died  in less than 2 years capacity < 100mAh

NB-5L
Canon (1120mAh, 4years old)  => 990mAh
No Name I (1200mAh, 5month old) => 680mAh
No Name II (1200mAh, 5month old) => 700mAh


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Offline jmac698

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Re: Batteries capacity measure
« Reply #5 on: 28 / January / 2017, 00:01:33 »
Thanks for posting your results. I was aware that off-brand batteries would have less capacity, but I just needed something that works for now.  I noticed something, my universal charger says it's NiCD, not Li-Ion.  Another test I could run, is compare the voltage dischage curve.  Luckily I have this plotted from the old battery.
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