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Converting 5.7v DC plug pack to charge 3v DC camera

I have a Nokia mobile phone and a Kodak EasyShare Z700 camera which I travel with frequently.  I want to use the Nokia plug pack to charge both the mobile phone and the camera.  How can I adapt the plug pack to do this?  Is it simply a matter of putting a resistor in series when charging the camera to drop the voltage to 3V?  If so, what value resistor do I need?
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akb
Asked:
akb
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1 Solution
 
mysticaldanCommented:
Try here if you are of a technical bend.
http://www.powerdesigners.com/InfoWeb/design_center/articles/DC-DC/converter.shtm

Normally you would have to put capacitors and resistors unless current requirements are same for both. Its not just the voltage you need to keep in mind but the current also. It would be a lot easier to just carry the charger seperately since if you damamge the camera with the wrong charger you might void its warranty. Its not worth it to save the hassle really.

As you would see from here http://www.maxim-ic.com/appnotes.cfm/appnote_number/998 its not just the resistor involved even though simple physics might lead you to believe that.

Dan
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Gary CaseRetiredCommented:
Mr. Ohm (of Ohm's law fame) doesn't let you use a simple resistor to do what you want for two reasons:  (a)  the load in your camera is a reactive (not pure resistive) load; and (b) the current changes as the state of the charge changes -- so even if it was a purely resistive load the value of the voltage-dropping resistor you'd need in the circuit will change.  

I used to travel with one of these:  http://www.youdoitelectronics.com/id529_philmore_48_1088.htm

As long as the current capacity is enough (1000ma) and the voltages are what you need it works very well.   Much better than jury-rigging something to drop the voltage from your adapter.   Note that the 600ma version (if that's enough current) accepts any worldwide input voltage.
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ridCommented:
Assuming the camera takes DC input, you can actually use a resistor, but you'd have to adjust its value every time, since the camera may not take the same current during the whole charge cycle. To do the adjustment properly, you need a voltmeter (or other voltage indicating device) to monitor camera input and allow for the adjustment.

I am certain that a very small voltage regulator can be found at an electronics store, which could provide a drop from 5.7 to 3 V DC. It'll need some cooling, probably, like a small aluminium plate. I think I'd go for that solution.
/RID
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Gary CaseRetiredCommented:
I'm sure you could build a simple regulator as well -- an LM series regulator IC, small pot, and a capacitor will do it ==> but by the time you've built that little gadget, why not just take along the 2nd charger?

I like the single, adjustable voltage charger concept :-)
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akbAuthor Commented:
I don't have a charger for the camera.  The camera charges when it is on the docking station which is too big to take with me.

I like the idea of using a regulator so I will try that before I award the points.  I'm not even sure if that will work as I can't find any specs on how many mA's the camera draws.  The Nokia charger is 800mA.
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burrcmCommented:
There are plenty of multi voltage power supplies out there. A multi voltage charger must exist?

Chris B
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ttterkCommented:
Don't bother with the "charger" for the Kodak EasyShare Z700. It doesn't charge the battery. Check the user manual (http://www.kodak.com/global/plugins/acrobat/en/service/manuals/urg00342/Z700_GLB_en.pdf) at page 62, where it sez, "Kodak 3-volt AC adapter—powers your camera." and also sez, "IMPORTANT: Do not use the AC adapter included with the Kodak EasyShare camera dock
or printer dock to power your camera."

The only way to charge the battery in the camera is to put it in the dock. The input port will only power the camera; it isn't connected to the battery and won't charge it.

I learned this after my EasyShare (7590) camera died while I was in a butterfly sanctuary when I thought I'd been faithfully charging it on our trip. I ended up buying a spare battery and a battery charger and its transformer (cool--now I have three (3) more little rectangular thingies to carry around!). Actually, it's not that bad. I keep a charged battery in my camera case, and between the one in the camera and the other one, I've taken over 300 pictures in a day without running out of power. Of course, then I have to charge them both up that night, but having that many shots to choose from makes beautiful memories easier to select.

Now as for only carrying one transformer, I can only wish you luck. The (no brand) LIon Charger (Model #CH-3200CL) I acquired at Wolf Camera uses a 12VDC 600mA transformer, and I think it'll take more than a resistor to get the Nokia charger to supply this. If you insist on carrying only one transformer, I'd look into one of the multi-output versions with the multiple tips, polarity changing capability, and at least 1000 mA capacity to power all your toys. Then, each evening, you'll need to power up the laptop to run a scheduling optimization routine so everything gets its fair crack at the power supply! Personally, I just started using my old shaving kit to store all my little square boxes, wireless mouse, spare cables & other stuff that's hard to find at 10pm in a strange town.
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mysticaldanCommented:
In Theory if ur camera requires x voltage and y current then getting a travel multi variance adapter shud be okay. The problem with these modern cameras is that the amount of current given to the battery changes as it gets charged which means that if ur self made or bought charger with variable adjuster keeps giving it a constant voltage then ur killing the battery in no time. My suggestion is to either get a spare battery as ttterk above says or take the mobile station with you. No easy way arnd this. Either get a camera thats more EasyUse or you would need to stand the inconvinience, sorry.

Dan
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ridCommented:
Charging batteries is a science in itself and not to be taken too lightly. NiCd and NiMH batteries are usually charged with a constant current for a defined amount of time in the more unsophisticated chargers. They all assume the batteries are empty and then they do the "current times hours" arithmetic to fill the cells with 1.4 times the nominal mAh rating. More advanced chargers measure temp variations and the small voltage drop that occurs at full charge of a NiCd/NiMH cell and these can handle partially discharged cells much better. Fitting either variety of charger inside a camera is perhaps not a very useful solution, so the charger circuitry will probably reside in the cradle for your unit. Li-ion batteries also require a charger that keeps track of battery voltage and the amount of mAh that go into the cells - so the same idea applies if such cells are used. Lead-acid cells can be charged with constant voltage power supplies, but I haven't heard of such batteries being used in modern equipment for a while now.
/RID
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akbAuthor Commented:
Thank you all so much for your help with this.  I had no idea that the batteries wouldn't charge in the camera without the docking station.  What a stupid design!  I'll go buy myself a charger for the Ni-MH batteries.  Looks like I'll be carrying two sets of chargers after all.  BTW, after doing some more research I have discovered that I can build a small circuit with 2 or 3 components including a small regulator (thanks Rid) to run the camera from my Nokia charger, but I won't bother as that won't charge my batteries.
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ttterkCommented:
Glad to help, and even gladder someone else doesn't end up missing a photo opp due to a dead battery!
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