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I am planning to make a battery pack, by using rechargable batteries, that i can use to power my DC-coupler for my DSLR camera.

(Ref. Image) enter image description here

On my original camera battery it says 7.4V 1.2A but i was measuring 8.03V.

So I was searching for a voltage regulator with 7.4V output, but I couldn't find one in my local electronics store. Thats why I want to use an adjustable voltage regulator with as less dropout voltage as possible, so i can use 9V batteries or a couple of AA batteries ( that adds together to 9V ). I know that i need keep the unbalance that occurs when putting batteries parallel to add the current, in mind. But thats another problem for later

So my question is: How can I get to 7.4V by using batteries and a circuit that regulates the voltagr down from 9V ? Should I use adjustable voltage regulators ? And if so, how do I need to use them / build the circuit to power it with batteries ?

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  • \$\begingroup\$ the adapter in the picture says 8.4V, and 2A output. \$\endgroup\$
    – KyranF
    Nov 1, 2014 at 22:54

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First question: Well, yes, but probably not the way you think. That is, making a 12 volt battery and tapping off a lower point in the chain is a very bad idea, particularly if you want to use rechargeables. As you pull current out of the pack, the lower cells will discharge faster than the upper cells, since they are providing current to two loads, while the upper cells only power one. If you draw too much total current, you will wind up reverse biasing the lower cells, and this is technically known as A Bad Thing. As in, you may permanently damage the lower cells. What can be done is to have a single string of cells with common in the middle, providing (for instance) +12 and -6 volts. But this is not what you want.

Second question is easy : No. See, for instance http://www.techlib.com/reference/batteries.html for "normal" battery currents.

Since you want to power lights with this thing, you will need serious batteries. High-capacity LiPos are the current choice. NiCads and NIMH are the runners-up.

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  • \$\begingroup\$ Thanks for that answer. But isnt it possible to get up to maybe 12V by using 10 x 1.2 rechargable AA batteries and than use a voltage regulator that drops it to 8.4V ONLY ? So i will forget about the multiple outputs of the battery pack and restrict myself to 8.4V only. \$\endgroup\$
    – Ace
    Jul 3, 2014 at 21:00
  • \$\begingroup\$ I've edited my question \$\endgroup\$
    – Ace
    Jul 3, 2014 at 21:12
  • \$\begingroup\$ Yes, you can do that. You'll be at the limit of what you can get from NIMH AA cells, and you'll get about an hour running time (and they'll get warm, too). As for regulators, you can find the data sheet for the LM317, and you can parallel them, but be aware that you'll need a pretty good heat sink, since (12 - 8.4 volts) x 2 amps = 7.2 watts. And you'll have to make sure the heat sink airflow doesn't get blocked. A field-grade battery/regulator would be a pretty ambitious first electronics project. \$\endgroup\$ Jul 3, 2014 at 22:45
  • \$\begingroup\$ Okay, now i have researched a little bit and updated the values in my question. Now i get to about 2W that is ok i think. Also its not my first electronics project, i just had no projects before using voltage regulators and batteries :) \$\endgroup\$
    – Ace
    Jul 4, 2014 at 11:26
  • \$\begingroup\$ I assume you're planning on using fewer than 10 cells to keep the voltage across the regulator, and so the power dissipated, low. With batteries this is not a great idea if you want maximum operational duration, since the battery voltage will vary with temperature and state of charge. Plus, "regular" (non-LDO) regulators will need a minimum of 2 to 2.5 volts to operate. If this is so when the battery is nearly discharges, the voltage will be a good deal higher when the battery is full, and I don't see how you're going to keep your power at 2 watts. \$\endgroup\$ Jul 4, 2014 at 13:06

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