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CHDK voltage meter, 4x AA NiMH batteries?

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Offline glutto

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CHDK voltage meter, 4x AA NiMH batteries?
« on: 26 / May / 2008, 18:18:43 »
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Hello,

I just picked up my first decent digital camera a few days ago, a Canon S5 IS,  and nearly immediately stuck CHDK onto it, Allbest build 51.  In just a few days I've explored the basics of CHDK and attempted to rewrite some scripts with no previous UBasic experience.  So far I really enjoy using it!

I've been using 4x 2000mAh NiMH rechargables with the camera and it seems to work great.  Great, except that the camera seems to chew through them at a quick pace.  I haven't really taken that many photos with it each session.  I don't use the flash that often.  The large LCD is disabled. 

I've heard that CHDK doesn't add any extra load to the camera, so I immediately ruled that out.  I then thought perhaps my batteries were lacking or malfunctioning.  That didn't seem likely.  I then noticed that the CHDK battery icon uses battery voltage to gauge the remaining charge, with default values of MAX=5500mV and MIN=4700mV.

From what I've noticed my batteries seem to stick around 4.7V to 4.8 volts, which is what I would expect from four 1.2V NiMH batteries.

My questions are:
Do these max and min values reflect the voltages of alkaline batteries with 1.5V each?
Will these values work with NiMH batteries at 1.2V?
If not, what should they be changed to?

Much thanks in advance!
« Last Edit: 26 / May / 2008, 18:40:39 by glutto »
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Offline DataGhost

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #1 on: 26 / May / 2008, 19:11:24 »
The values are different for every type of battery. I calibrated them (the defaults you see) on Sanyo Eneloop NiMH-hybrid-whatever batteries (low discharge) and the leave the charger at a nice 5.6-5.8V. When using them they drop to about 5V where they stay and when they drop below 4.950 it won't be very long until they're empty (batteries don't have a linear discharge curve). At about 4.600V, the camera would show the low battery icon and shut itself down not long after that, so I set CHDK to use 4.700V so I'd have a safe margin. You should adjust them for your batteries, that's what the configuration option is for. Just look at the value when they're fresh out of the charger, a couple of hours later (without using them) and when they're about to die. Those are the values you're looking for.

As for the rapid battery discharge: maybe your batteries just need to 'get used to being used' if they're new, else you could try setting the brightness lower. I don't think the EVF uses significantly less power than the big LCD, they're both LCD screens with PWM-controlled backlight. Lower backlight = lower power usage = more battery life :)
It could also be that your batteries are indeed malfunctioning. If you have a charger like the Voltcraft IPC-1L (or any other charger with the required functionality), you can let the charger discharge the batteries and figure out what capacity remains.
And as in the FAQ... you're probably using it more, so the batteries drain faster :p
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Offline glutto

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #2 on: 26 / May / 2008, 19:57:20 »
I suppose I'll have to experiment, then.  Oh, darn!  :D

From what I've gathered, 4.8V for four AA NiMH in series is about right for something like 85% of the lifespan of each charge.  When the voltage suddenly drops below 4.8V they're near empty.  I'll just keep an eye on the meter and create the values accordingly.

So it's likely there was no rapid battery discharge, just the default MIN and MAX values doing their job.

I'll meddle around with it and post results in a few days (or weeks).

Much thanks!
« Last Edit: 27 / May / 2008, 14:31:53 by glutto »
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Offline GrAnd

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #3 on: 29 / May / 2008, 13:19:51 »
A month ago I bought fresh 4x Sanyo 2700mAh AA NiMH batteries. After the first discharge-charge cycle their capacity were only 900-1100mAh (I have LaCrosse BC-900 charger which allows to measure parameters of batteries). So, I put batteries to the charger again and activated the refresh procedure (continues charge-discharge cycles while the capacity of batteries will increase). Then, only after 5-6 days (8-10 cycles, I think), I had got 2700-2800 mAh on each battery.

BTW. If you use fast (1-2h) chargers you will never get 100% charged batteries (80-85% max).
« Last Edit: 29 / May / 2008, 13:28:22 by GrAnd »
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Offline glutto

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #4 on: 03 / June / 2008, 22:45:30 »
I recently pulled about 505 shots during a time-lapse session using the mentioned 2000mAh NiMH batteries.  I used PC software so the LCD's were shut off, and no flash was used either.

At the very least, it's a decent guideline for future reference.

I use a Rayovac PS3 charger which slow-charges the batteries over 14 hours, according to the Rayovac website.
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Offline jojo99

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #5 on: 08 / June / 2008, 22:39:27 »
I am a newbie to CHDK and I DO NOT understand the battery settings in CHDK.

Canon says that nominal voltage is 1.2v DC.  But they don't give any range info.

I have 4 sets of MAHA PowerEX 2700mAH batteries to play with.

DHCK uses the terminology mV and a 4 digit number like 4800.  Since my camera uses 4 batteries, am I then to assume that normal voltage would then be 1.2v * 4 = 4800mV?  Is 4800mV minus some factor (say 100) then the lower limit I should set in Battery MIN voltage?

I just did a Refresh/Analyse cycle on a set of batteries using a MAHA C-9000 charger.  I am using new batteries that have only been used 1 time before (I did a break-in cycle with them before the first use).  At completion of the Refresh/Analyze cycle, I have the following results:
Battery 1 = 2510 mAh/1.43v
Battery 2 = 2496 mAh/1.42v
Battery 3 = 2524 mAh/1.42v
Battery 4 = 2504 mAh/1.43v

If I take the 4 volt numbers above and add them together, I would get 5700.

So, I tried setting the battery range in CHDK to:
Max=5700, Min=4700

But doing this with these 100% charged batteries, gave me a 80% on the battery icon!

So I tried lowering the max value to 5450.  Now the battery icon shows 100%?  Further experimenting, it seems there may be some relationship with the delta between the min & max battery values. 

What is CHDK reading and why do numbers I set change what CHDK shows in the battery icon.  Why can't CHDK just read the absolute power left?  Isn't that what Canon does when it finally shows its low battery icon?
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Offline GrAnd

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #6 on: 09 / June / 2008, 02:41:25 »
Quote from: jojo99 on 08 / June / 2008, 22:39:27
What is CHDK reading and why do numbers I set change what CHDK shows in the battery icon.  Why can't CHDK just read the absolute power left?  Isn't that what Canon does when it finally shows its low battery icon?

CHDK reads the current voltage of the battery set, nothing more.
But do not forget that discharge curve of NiMH batteries is not linear. It looks as
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Offline jojo99

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #7 on: 09 / June / 2008, 05:10:24 »
Quote from: GrAnd on 09 / June / 2008, 02:41:25
Quote from: jojo99 on 08 / June / 2008, 22:39:27
What is CHDK reading and why do numbers I set change what CHDK shows in the battery icon.  Why can't CHDK just read the absolute power left?  Isn't that what Canon does when it finally shows its low battery icon?

CHDK reads the current voltage of the battery set, nothing more.
But do not forget that discharge curve of NiMH batteries is not linear.

The graph is nice (how did you get this?) but it doesn't seem to answer my questions.

You say CHDK is reading the current voltage, of the battery set.  How is it doing the % calculation?

I'm guessing that it takes the difference between the Max and Min numbers to represent the range from 0-100%.  If the current voltage falls somewhere in this range, the % remaining can be calculated.

Now when I put these newly charged batteries in, the MAHA charger showed me that there was a total of 5700mV.  But using this figure caused CHDK to show only 80% capacity.  Which would seem to mean that the Canon camera is reading less voltage from the batteries than the MAHA charger was showing.  Changing to 5450mV brought the battery indicator up to 100%. 

So what happened to the missing 250mV?  Could this be a Canon calibration problem?  Or a CHDK problem?  How to tell?

If Canon just shows less, then I think I should lower the Min number by 250mV to compensate.

Also, each set of batteries will be slightly different.  So I will need to do new calculations whenever I switch sets.  For instance I am charging a battery set now that is showing 1.46v  across the board at this point in the cycle.  That would be 5840mV total (minus 250mV? = 5600mV).  So on inserting these batteries, I would have to make a modification to the battery numbers again.

This is sure complex!
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Offline scharfis_brain

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #8 on: 09 / June / 2008, 05:15:53 »
the camera measures the voltage of the batteries under load.
and the charger probably measures the voltage without load.
this may explain the difference well.
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Offline DataGhost

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Re: CHDK voltage meter, 4x AA NiMH batteries?
« Reply #9 on: 09 / June / 2008, 05:26:21 »
You could also just relax a bit and just forget about those few millivolts. The battery indicator is meant as a guideline, it can never be accurate because of the graph GrAnd showed. Just calibrate the graph at something which works for you and then don't adjust it again unless you switch to another brand or type of batteries. On my S5IS, I see that the voltage drops quite fast to 5.2V and then gently slides down to 5.1V, where it stays for a while. As soon as it drops below 5V, I know it can't be long anymore. I set the CHDK battery meter to show 0% at 4.7V, as the Canon firmware shows the battery indicator around 4.6V and shuts off shortly after that. I guess the Canon indicator measures the voltage drop and if it's large enough it tells the user the batteries are empty. Because of the amount of different batteries that can be used in the cameras, it's near-impossible to implement a battery indicator which works across the entire range, so I guess that's why Canon chose not to do that.
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