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external Battery - connected to DC-IN

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Offline whim

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Re: external Battery - connected to DC-IN
« Reply #10 on: 17 / May / 2008, 21:08:47 »
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Probably a little more, say 5Ah max because you're draining it further

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Offline vine

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Re: external Battery - connected to DC-IN
« Reply #11 on: 18 / May / 2008, 01:57:10 »
Quote from: fbonomi on 17 / May / 2008, 13:45:09
If the battery is rated 4AH for 12V, how many AH will I get after I regulate it down to 3.7?
Common sense says exaclty the same, but I have the impression I should have a better result...
You are right, exactly the same. If the camera draws 3.7V at 2A the regulator input will draw 12V at 2A from the battery then burn 8.3V at 2A that's 16.6W away. Get an appropriate heat sink.
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Offline fbonomi

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Re: external Battery - connected to DC-IN
« Reply #12 on: 18 / May / 2008, 02:35:47 »
It turns out results are quite brilliant.

With 2.5 Ah AA batteries I have never been able to go over the 1.000 shots, even with some measures to reduce power consumption (manual focus, LCD off)

With this 4 Ah battery I have got 3.200 shots over 12 hours, even with autofocus and display left on.

A few considerations on why this could happen:
- this kind of battery is made to withhold strong peak currents. The 2.5 Ah of the AA batteries are nominal, I guess that with the 1A peaks the camera requires, the 2.5 Ah of the AA batteries are purely theorical
- as whim was saying, the 12V can drop a LOT before the regulator isn't able to produce 3.7 volts

On the other hand, my AA batteries aren't brand new as this battery is.

Anyway, I am quite happy. WAAY more authonomy for my time-lapses.

It's a shame I have just put the battery to charge, and my old my car battery charger made a funny "pop".. :-(
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Offline fudgey

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Re: external Battery - connected to DC-IN
« Reply #13 on: 18 / May / 2008, 04:07:01 »
Remember not to hurt your 12 V battery by deep discharging it. The lower the current you draw from it, the higher the end voltage should be to avoid wearing it out prematurely. For 24 hour discharge you should probably recharge the battery when it reaches about 10,5 V (camera powered on). Some batteries come with a datasheet, you should read it or the manufacturer's web pages if you can find them...

Btw, a 6 volt battery might be a better fit, altough you may need a LDO regulator. In any case you'd waste a whole lot less energy i.e. less need for heatsinking the regulators and smaller size of battery versus battery life... at the moment you are wasting about 75% of the charge (which of course is completely OK if you're fine with the current setup).

A fresh NiMH cell should output the nominal charge if you continously discharge it at about C/5 (i.e 400 mA for a 2000 mAh cell) and still perform reasonably close to nominal at 2C (4 A for a 2000 mAh cell). That said, the 12 V gel battery is definitely suitable for higher discharge (but not charge) currents than the NiMH cells.
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Offline fbonomi

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Re: external Battery - connected to DC-IN
« Reply #14 on: 18 / May / 2008, 05:50:44 »
fudgey, thanks for the exact info. Batteries are the typical thing one gives for granted (just give me some elecricity!), without thinking about their "intimacies".

As per you considerations: It's an acid battery, not a gel battery, I don't know what that changes.

I know a 6v battery would be better, but my charger only charges 12v batteries and that made me select that one.

Also, the huge waste you mentioned did worry me (together with the heat dissipation), but what's an (easy and cheap) way to avoid it?

A different regulator?

I thought about a small transformer to transform the 12v in 6v before regulating it. Would that help? Would I also get more camera time?

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Offline vine

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Re: external Battery - connected to DC-IN
« Reply #15 on: 18 / May / 2008, 06:04:22 »
Quote from: fbonomi on 18 / May / 2008, 05:50:44
Also, the huge waste you mentioned did worry me (together with the heat dissipation), but what's an (easy and cheap) way to avoid it?
Using an input voltage as close to the output voltage as possible.
With a 6V battery you'd only be burning 2.3V. That makes 4.6W loss at 2A compared to 16.6W for the 12V battery.
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Offline fudgey

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Re: external Battery - connected to DC-IN
« Reply #16 on: 18 / May / 2008, 06:28:31 »
Quote from: fbonomi on 18 / May / 2008, 05:50:44
As per you considerations: It's an acid battery, not a gel battery, I don't know what that changes.

Probably nothing much, other than the obvious i.e. that you need to be careful about keeping it in upright position.

Quote from: fbonomi on 18 / May / 2008, 05:50:44
Also, the huge waste you mentioned did worry me (together with the heat dissipation), but what's an (easy and cheap) way to avoid it?

A different regulator?

I thought about a small transformer to transform the 12v in 6v before regulating it. Would that help? Would I also get more camera time?

Transformers need alternating current to work, you have DC. A different regulator indeed, you need some sort of a switching power supply. No biggie, but you aren't going to find one that's both as cheap as your LM317 and as easy to use. Switching power supplies can be quite tricky to design from the scratch, and complete modules tend to be a bit expensive in low volumes. If you're up for it, using something like National Semiconductor's simple switchers could be the most cost efficient choice for you, but I wouldn't recommend trying this unless you know your way around an oscilloscope.

AFAIK, the Canon power supply is 3,15 VDC, 1.5A for the a570is and probably all other dual-AA-cell models.

I have a 12V in, 4A @ 3V car adapter for my NiMH charger. Something like that would probably be good, but you'd have to know the output is clean (I'm not saying 3V is enough for the camera, I'm only guessing it probably is since the camera uses batteries down to 2 volts; I'll guess that a lower than 3,15 V supply may make the camera draw current from the batteries first until their voltage drops a bit).

The bottom line is that the easiest solution for you to improve the efficiency of your setup may very well be to find an inexpensive 6 volt Pb battery charger.

edit: Just to remind, your camera has a different input voltage than mine and it's probably for a reason. ;)
« Last Edit: 18 / May / 2008, 06:32:48 by fudgey »
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Offline fbonomi

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Re: external Battery - connected to DC-IN
« Reply #17 on: 18 / May / 2008, 06:34:39 »
Quote from: fudgey on 18 / May / 2008, 06:28:31
Transformers need alternating current to work, you have DC.
Doh! I knew that, but I completely forgot :-)

Better keep myself to programming. I can play a little bit with digital electronics, but as soon as we get into analog, I am lost :-)

Quote
The bottom line is that the easiest solution for you to improve the efficiency of your setup may very well be to find an inexpensive 6 volt Pb battery charger.

Thanks. Especially given my dumbness :-) that's very sound advice!
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Offline jetzt

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Re: external Battery - connected to DC-IN
« Reply #18 on: 18 / May / 2008, 12:52:54 »
Well, my attempts are also only with linear regulators, but I think I have the parts for a switching one here.
But as I'm afraid of loosing my camera (I mean making it a nice to watch brick), the LM317 does the job right now.
I have 7,2V Li-ion batteries of an old (seems too old) tablet-pc.
So I'll have to invest some time again, if I have some ready to use results, I'll post again.
For a clock generation I recently bought some ics, but they didn't arrive yet. :D

For the curious ones: I also think of using a 12V Dell-Laptop battery I didn't send back. (It has (80 WH and is only one year old. Should do it for some shots!  ;))
« Last Edit: 18 / May / 2008, 12:55:21 by jetzt »
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Offline brainwash

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Re: external Battery - connected to DC-IN
« Reply #19 on: 26 / May / 2008, 09:00:47 »
UPS batteries are mostly deep-cycle with a relatively low peak-current, automotive ones are designed to support large crank currents but not deep-cycle.
UPS batteries also come in 6v flavours I think.
You should really think about using a Buck supply (google for buck voltage regulator). I think cameras using 2 AA batteries have a buck-boost voltage converter right after them. You do not need the boost part since you are doing step-down conversion. These regulators ca be bought completely assembled for less then five dollars.
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