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Battery pack for Digital camera,

Iain

Jun 23, 2012
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Joined
Jun 23, 2012
Messages
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Hello folks,

I would like to design a battery pack for my camera as it uses a lot of power, circa 10W/hr, and I get though a lot of AA batteries

so would like to make a rechargeable 150 watt pack, that can run the camera using a coiled power cable that uses a 1.4 inch power jack

Time constraint: needs to be done within a month
Cost constraint: £100/$150<
Camera: Fuji S7000
Power required: 5V at 2A regulated DC
Camera batteries: 4xAA batteries

Pack: 6v x 22.5A (4x10AA) or 7.4v x 20.1A (2x5) NCR 18650

Problem:
I have looked at batteries and its hard to find one that is at the right current and ampage that I need, however I am struggling to find a 2 amp voltage regulator that will cover the required ampage, and would like to ask for some help

1, will this need a charge protection circuit to protect the batteries in the camera? - voltage regulation should do the job im thinking?
2, will it need a protection circuit for the battery pack as its custom? - i am guessing this is a must,
3, how to reduce current and volts though voltage regulation without wasting it as excessive heat through resistors - diodes?
4, as the pack will be around 1.5x4 (6v) in series, to get the current I need it will be several amps (5x2250)11.25A
or 3.7x2(7.4v x 3.35x5A) 16.75A
will a simple voltage regulator do the job?
5, just better to buy a lot of batteries?

idea was to use two 7608 type 5 volt voltage regulator in parallel with smoothing cap on the output side and possibly an electrolytic smoothing cap in the intake side but I dont think this will be this simple


thanks

Iain
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
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Jan 21, 2010
Messages
25,510
I think that one problem is that you confuse power and energy, and then capacity and current.

It seems that the camera has a 5V 2A maximum requirement.

At full power that means it requires 10 watts of power (which is a rate, so adding "per hour" is meaningless at best).

Firstly, that 10W is likely to be a maximum, but if you assume it's an average then anything which meets this will likely deliver better performance (longer time between recharges) than you calculate.

The next issue is that batteries often have a specified capacity (mAh or Ah) as well as maximum currents (A or multiples of "C" -- which is the capacity)

For simplicity you ned a battery which delivers 5 V or more over its discharge cycle. A 7.2V lithium battery serves that purpose.

Next, divide the capacity by your required current to get an estimate of time to discharge. For example if you need 2A (or 2000mA) and your battery has a capacity of 1250mAh then the time to discharge is about 2500 / 2000 = 1.25 hours. These capacity ratings are often based on a 20 hour discharge, so if you get a result less than 20 hours the actual life will be a little less.

Finally you may require a voltage regulator to reduce the voltage to 5v.

Applying all of that, you want a 5v or higher source with a rated capacity of 2000 mAh or more.

Two batteries in parallel will double the capacity in mAh, two in series will not.

Some regulators (switchmode) can change these assumptions a little, but they add some complexity too.

Finding a battery pack with a USB output an rated at 2Ah or more (technically 10Wh or more) would be the easiest solution. Beware because some of these state their capacity in deliberately misleading ways.
 
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