External battery pack questions

[u_rebelscum]

I'm looking for a universal external battery pack for digital cameras.

I just started trying my hand at timelapse & motion detection photography.  I'm using chdk to add these features to a basic canon camera (an A470 ATM).  It uses two AA batteries, nice and cheap, and rechargeable, but not the best in constant use time.  I have an AC/DC power converter, which is great if there's a power plug somewhere near.  So I want a large battery pack so I can do a full day timelapse away for the power plug.

I need ~3.0-3.3 v @ 1.5-2.0 amp power source ATM, but might upgrade the camera at some point, which is why I'd like a universal. 
I've seen many 5v USB device-charger battery packs and external laptop battery packs, but not many universal battery packs that can do ~3.15 @ 1.5 amp (canon's official ACDC adapter) or 3.0 @ 2.0 amp (the cheaper adapter I have).  the places I've googled don't have enough info for me to go on.

Anyone have any recomendations?  I'm open to ready to use packs, or BYO / modify packs.

Thanks

[protokatie]

Car battery with a power inverter, using your AC/DC adapter. You might be able to just use a cheap 12 volt deepcycle motorboat battery as well.

This is the only tried and true thing I can think of, esp since the car battery + inverter combo will work for pretty much any thing you need AC or DC power for. (also, if you keep a charged car battery around you will have a free jump, and those 12 to 120 volt inverters come in handy in so many instances.) Think future backup lighting for your house if the power goes out (or for that matter powering the blower on a wall based propane heater, as they use a simple standard plug).


Sorry to go long winded on that, but I figure if you are going to buy anything that acts as an external/portable power supply, might as well get something that is component replaceable as well as multifunctional.

[u_rebelscum]

Hmm, I tried a UPS (since I have it all ready and it's a battery + inverter), and it didn't work.   I think the AC/DC converter I have isn't liking the "simulated sine wave" the UPS is outputing; IOW, my converter isn't putting out its rated 3 volts with the non-"true sine wave" AC the UPS is outputing.

And AFAIK all car converters I've seen do simulated sine waves, also.  So I'm pretty sure they won't work. either.  Maybe if I got the canon brand AC/DC adapter it might work, as it's rated at higher output (3.15 V), so it has more room to drop (assuming my guess is right).  But it costs 4x what I paid for my current one (and almost half the cost of the camera), and I'm not possitive it will work.


I do like the car battery idea, though.  How efficent is going DC->AC->DC?  IOW, can't I do a 12V DC to 3V DC direct convertion?  (I don't think a resister is the most power efficent way though, right?)  And what about a smaller (and lighter) motercycle battery as an alternative to the full size car battery?

Maybe I'll try getting a cheap DC/AC inverter anyway, and see if my adapter works.  (Hmm, car cigarette inverter so I can time lapse driving places without carrying any extra batteries....)

[DrumAnBass]

Hmm interesting, the timelapse sounds cool! Can't help you much other than to say that Bescor makes nice 12v battery packs for video cameras; I wonder if these can be adapted for your use? http://www.bescor.com/

[protokatie]

@rebel

I have never experienced a problem with powering a DC device (via a transformer/rectifier/capacitor combo) with an inverter. Did you test the output voltage with a multimeter? (Related note, and not to make you feel stupid, but did you make sure the thing was plugged into the battery backup plugs and not the surge suppressor only plugs?) [Yes I have done that, dumb me]. AFAIK the "simulated sineoidal waves" are generated digitally now, and use a DSP like chip to do it, so it would be a stair-step immitation of a sine wave. Considering the resolution and Hz of this, there would be a very small change in the amount of inductive energy that would transfer through the AC/DC converter.

As per efficiency of DC-AC-DC, well, it isn't very efficient, but with a good car/motorcycle battery it will give you the time you need. Make sure to get a deep cycle one tho, as the "quick start" types use a metal foam for surface area, but are not meant for longevity as the solid plate batteries are.

[u_rebelscum]

@protokatie,
I did some more testing on the UPS, and none of the battery plugs worked for my camera.  The funny thing was that none of them worked when the UPS was plugged into the wall, too.  (The surge side worked fine when plugged in.)  The UPS is an APC brand UPS, and is able to power a computer for minutes fine.


I'm asking pure sine vs modified sine wave because some stuff requires pure sine (x10), when most intverters output modified sine (or even worse, plain square wave).

I haven't tried other UPS or bought an inverter, yet.  Nor tested the voltage on the UPS; I'm very curious on what's happening with that UPS. 

Are what you talking about any different from the normal modified sine wave inverters?  Any good links?  I've found stuff that cost <$10 to multiple hundreds of dollars.


@DrumAnBass
12V batery packs with shoulder cary cases & cigarette outlets.  If the car inverter works, these would be the easy and clean way to carry around the battery, for sure.  I little more expensive, but not an ugly hack by me (that might fall apart at the wrong timie).  I'll definately look into these.  Thanks.

[protokatie]

If you are willing to do a little experiment, buy a decent sized capacitor and put it across the lines (make sure to get the polarity right) on the DC end of your cameras power supply. I am wondering if the AC to DC converter might not have a big enough cap in it to smooth out the pulsed DC the rectifier generates. If this is the case, then the camera would be the thing insensitive to the DC produced during the AC/DC conversion. I would really like to see what voltages you get off of the UPS, as well, if you have access to an occilloscope I wonder what the waveform looks like on on the UPS output as well as on the DC the converter is giving off.

As per waveform from inverters, one thing to keep in mind is that the greater load they are under, the less accurate the sine wave is. I havent looked into an inverter for a long time, so maybe a google search would be useful in finding models that output very stable voltages as well as a good sinewave.