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Functional Voltages and Current Draw on SD1000 - IXUS 70

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Offline bwh13

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Functional Voltages and Current Draw on SD1000 - IXUS 70
« on: 29 / July / 2013, 18:45:26 »
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Hi All,
I'm building a long-term, timelapse rig with and SD1000: small, robust, solar, cheap and DIY for remote applications.
The rig is in-development: using Ultimate Intervalometer v1.7; a  3.7v 6A LiPo; a 6V 2W panel.

Problem and Cause: the camera shuts down due to incoming voltage spikes greater than 5 volts (>5.0v).  Camera seems to work in 4.0+ volts range.  Have not recorded voltages for low battery shutdown yet.

Questions:
1)  Does anyone have estimates (observed or estimated) for voltage ranges (hi and lo) that this kind of camera operates within?  I'm building a LDO voltage regulator for my system and easiest solution is to use a chip that supplies 3.3v.  Does anyone have an opinion on whether this voltage is too low to power the camera?

2)  How much current draw do you estimate for this camera shooting and writing a single picture (mA / picture) ?  I'm using the script under the most power-saving settings that I can achieve.

I will post my values when I run the tests and do the math.  Thanks!
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Offline reyalp

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #1 on: 29 / July / 2013, 22:51:45 »
Quote from: bwh13 on 29 / July / 2013, 18:45:26
1)  Does anyone have estimates (observed or estimated) for voltage ranges (hi and lo) that this kind of camera operates within?  I'm building a LDO voltage regulator for my system and easiest solution is to use a chip that supplies 3.3v.  Does anyone have an opinion on whether this voltage is too low to power the camera?
The default  "min battery" is usually set to somewhere around where the camera shuts down for low battery. On sd1000, this is set to 3.5v

I have notes that another cam with a 3.7v lipo pack started blinking the "low battery" icon around 3.47, and continued to run below 3.38.

FWIW, the ACK-DC40 clone I got for my D10 puts out about 4.2v (says 4.3 on the brick) and seems to work fine.
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2)  How much current draw do you estimate for this camera shooting and writing a single picture (mA / picture) ?  I'm using the script under the most power-saving settings that I can achieve.
A few people have made measurements:
http://chdk.setepontos.com/index.php?topic=9049 Battery Intervalometer thread
http://chdk.setepontos.com/index.php?topic=3872.0 Measurements on a590 (a AA powered cam, but I'd expect current draw to be similar) the links are dead but mirrored at
https://docs.google.com/file/d/0B08pqRtyrObjbGFMZnRCOUczU0k/edit
https://docs.google.com/file/d/0B08pqRtyrObjbG90RWRfV0VodUE/edit
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Offline bwh13

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #2 on: 30 / July / 2013, 14:53:52 »
Thanks for the post and links reyalp.

I've ran a quick test on the stock NB-4L 760mA battery to get a baseline.  It seems that the camera was ready to shutdown when the battery hit 3.7v.  See my attachment which is a .jpg of a chart recording the voltage drop over the course of the test.  It shows 2 lines: Day and Night Modes.  Voltage drop (Y axis) over time (X axis).

Using the Ultimate Intervalometer script at 1 minute intervals with every power saving setting, I got about 160 pics before the camera entered 'Night Mode.'  Interesting that the battery voltage went up a bit when the camera entered 'Night Mode.'  It seemed to extend the battery for another 1.5 hours.  The script ran for about 4 hours before I accidentally hit the 'Display' button and turned on the LCD - at that point it drained what was left of the battery and it shutdown.

I added trend lines and equations to the Day and Night mode plots.  I'm going to run the test again today to see how many pics I can get with Day mode, and then run the script again in Night mode to see how long the battery lasts.

I tested the battery voltage before and after the test with a voltmeter.  Before = 4.07v and After = 3.74v.  It seems like other users are reporting lower voltages in the their cameras (which may be camera specific, I suppose.)  These batteries are a couple of years old and are probably pretty 'tired' though...  I guess I was expecting the battery to run down to 3.2 or so.

Does anyone have a good way to convert this voltage usage into mA used?  From what I understand, I would need to know either the resistance of the circuit or power.  I can't imagine that my test used all the 760 mA that the battery is rated for.

I'm hoping that the camera can run on 3.3v, because it makes the LDO voltage regulator a bit easier to build.   

Thanks for any thoughts!
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Offline waterwingz

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #3 on: 30 / July / 2013, 15:31:41 »
Quote from: bwh13 on 30 / July / 2013, 14:53:52
Does anyone have a good way to convert this voltage usage into mA used?  From what I understand, I would need to know either the resistance of the circuit or power.
Correct - google  Ohm's Law.  The formulas are  I= V/R  or I=sqrt(P/R)

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I can't imagine that my test used all the 760 mA that the battery is rated for.
Just for reference,  your battery is rated as 760mAH - the H is important.   It means the battery, when it was new, would put out 760 mA of current for one hour.   Or 1520 mA of current for 30 minutes. Or 380 mA of current for 2 hours. 
« Last Edit: 30 / July / 2013, 15:55:34 by waterwingz »
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Offline reyalp

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #4 on: 30 / July / 2013, 16:38:21 »
Quote from: bwh13 on 30 / July / 2013, 14:53:52
I've ran a quick test on the stock NB-4L 760mA battery to get a baseline.  It seems that the camera was ready to shutdown when the battery hit 3.7v. 
This seems odd, since the nominal voltage of a LiON battery should be ~3.7 volts. It will be a bit higher fresh off the charger, but I'd expect it to sag to 3.7ish pretty quickly.

It wouldn't be surprising if there was variation between individual cameras, but there has to be a calibrated value somewhere for the firmware to know when the battery is actually low. I would have expected the battery voltage function to return the calibrated value, but perhaps it doesn't.

The voltage will sag a bit under load, so when the logging is done relative to the power-hungry activities like shooting could affect the logged results.

FWIW, measuring the NB-6L from my D10 with a multimeter (no load) gives 3.76v, while in camera playback mode gives 3.73
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Offline bwh13

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #5 on: 30 / July / 2013, 17:10:05 »
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Just for reference,  your battery is rated as 760mAH - the H is important.   It means the battery, when it was new, would put out 760 mA of current for one hour.   Or 1520 mA of current for 30 minutes. Or 380 mA of current for 2 hours. 
Of course!  I've looked right at it 100 times.  This helps to be reminded of that.

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This seems odd, since the nominal voltage of a LiON battery should be ~3.7 volts. It will be a bit higher fresh off the charger, but I'd expect it to sag to 3.7ish pretty quickly.
That's what I thought too.  When I accidentally hit the 'Display' button, the OSD battery voltmeter read ~3.2volts -> which I can see because it's powering the LCD.  But I didn't expect the ending voltage to be 3.7 with the voltmeter.

Like I said, the battery that I ran it on was old (4+ years of good use).  I'm running the Day mode test on a different, 760aH NB-4L battery right now.  2+ hours at 1 minute intervals and it's still plugging away.  More on that when it's done.
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Offline bwh13

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #6 on: 31 / July / 2013, 17:26:11 »
Hi All,
I've finished up test #2 where I ran the Ultimate Intervalometer script to low voltage shutdown.  The battery was an NB-4L 3.7v 760Ah battery.

I started at noon and it took pictures until 7pm at 1 minute intervals.  At 7 the camera entered 'Night Mode' and did not take shots, but wrote a line to a .log file.  The camera shut down at 11pm.

The attached graph is a plot of volts per unit time (or picture - the same in this test).  Results show that battery voltage showing a fairly steady drop of ~~0.1v per hour of shooting (60 shots).  Around 3.8ish volts the decline looks to be ~~ 0.2 volts per hour.

Most interesting is the precipitous drop of voltage that last hour of 'Night Mode' where the loss is 0.35 volts per hour.

I'm guessing the battery was pretty well depleted, because the lens didn't retract when the camera shut down.

Not sure if this is a function of my 'tired old' batteries or if this is a common phenomena.  The decline started very soon after the battery dropped below 3.7v.  I wonder if it was a battery with more AmpHours if the decline would have been less dramatic...

As far as Waterwingz' script goes, the 'Night Mode' is clearly saving battery life.  From the beginning of 'Night Mode' the battery drops only a little more than 0.1 volt over 3 hours.  Good to know!
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Offline ahull

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #7 on: 31 / July / 2013, 18:12:19 »
The "precipitous drop" is due to the battery protection IC. These LiPo batteries are actually "smart" in the sense that they contain circuitry to ensure safe charging and discharging. 

For more details, take a look here at the recent tear-down I did of a similar NB-4L to the one you are using.

A battery with "more amper hours" would have a longer discharge curve, but a similar cutoff, but be aware that not all clone batteries actually live up to heir claimed capacity. To be sure of a significantly longer running period, you will need to use an external battery or mains adaptor, as realistically even the best battery of this physical size is unlikely to even reach 1500 mAh (regardless of the wild claims of the supplier, stating 1400mAh or even 2000mAh in your advert is not the same as actually supplying a battery of this genuine capacity).

I assume your battery is probably close to its stated capacity of 760 mAh, so probably it would be unrealistic to find a battery with a capacity to do any more than double the ability of the one are using.
« Last Edit: 01 / August / 2013, 04:33:38 by ahull »
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Offline bwh13

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Re: Functional Voltages and Current Draw on SD1000 - IXUS 70
« Reply #8 on: 04 / August / 2013, 19:18:43 »
I did check out your tear-down and thanks for explaining the voltage drop.

I ran the Ultimate Intervalometer v1.7 script again yesterday, but this time I made sure that it would drain the battery in 'Day Mode' only (i.e. taking pictures.)

I plotted this latest test alongside my previous test, where the script went into 'Night Mode.'  I think the results are pretty interesting (see attached graph.)

In the graphic: the green line is the latest test (Day Mode only), the blue and red lines are the previous data (Day and Night Mode in one test.)  Here are the 3 things that I notice:

1- Night Mode uses less battery power (the obvious, I know), but how much more?  Night Mode allowed Test#2 to continue for another 45 minutes before the low voltage shutdown. 

2- Night Mode allowed the battery to drain to a lower voltage - 3.2v versus 3.3v.  Whether or not this is significant...

3- The shape of the discharge profile is pretty much the same shape for Day and Night modes, but the Night Mode is extended a bit along the X axis.

So, how many mA does the script use per picture?  Follow my logic and math and tell me if I'm missing something big (or small.)

Battery: 760 mAh
Test #3: 10 hours of shooting pictures (603 minutes)
1 picture / minute

76 mA / hour * 1 hour / 60 pictures = 1.26mA / picture

I was very surprised that the NB-4L battery could last for 10 hours at 1 shot / minute.  Go Canon batteries!  Ultimately, I was wondering how long and how many shots I could get with my 6000mAh battery  - the point of these tests.  If I make the assumption that the battery behaves as well as the Canon, then we are in business.  Anyone care to share a thought or opinion?
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