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I have got an old camera that runs on 7.2V (2 cell li-ion). I only have a 4 cell li-ion battery. Is it possible to divide the voltage without using a DC-AC converter and a transformer?

I have looked up "Voltage divider", but this will not work as I don't know the resistance of the camera, which probably isn't constant either.

Is it possible to do this?

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  • \$\begingroup\$ The reason why I need this old camera to work, is because I need to transfer some old Video8-cassettes to the computer before they diminish. \$\endgroup\$ – Friend of Kim Jul 5 '14 at 16:37
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The term you are looking for is "Voltage Regulator".

A voltage regulator takes a higher input voltage and scales it down to a lower voltage.

There are two main types of voltage regulator:

  • Linear

These act like an automatic variable resistor keeping the output voltage constant regardless of current draw. They are very simple to use, very cheap, but also inefficient.

  • Switching

(Also known as "Buck" regulators) These use PWM to chop the DC voltage into a waveform that represents a percentage of the incoming voltage. The output is then filtered and smoothed. They are much harder to work with than a linear regulator, but they are much much more efficient.

Ideally for a battery source you want to work with a switching regulator as your battery will last longer. You can buy pre-built adjustable switching regulators quite cheap off eBay.

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  • \$\begingroup\$ I've got many Video8 cassettes (old analog 8mm tape) that I want to transfer to the computer. This is why I need the camera to work. I don't need it for more than the time it takes to transfer the video to the computer. Do you think the linear voltage regulator is good enough (home made)? \$\endgroup\$ – Friend of Kim Jul 5 '14 at 16:46
  • \$\begingroup\$ 27 3/8. The answer is as meaningful as the question. How long are the tapes? What rating is the battery? What is the power consumption of the camera? I would suggest a mains power supply (wall wart, 9V) if you wanted to use a linear regulator. You'd need to check the required amperage as well, as a linear regulator can get VERY hot. \$\endgroup\$ – Majenko Jul 5 '14 at 16:49
  • \$\begingroup\$ The original battery is 7.2V and 0.5Ah, meaning it draws approximately 0.25A (it lasted a couple of hours). \$\endgroup\$ – Friend of Kim Jul 5 '14 at 16:53
  • \$\begingroup\$ Then an LM317T plus the right resistors and capacitors would do the job. Still best to use a wall wart than mess around with batteries - you're not worrying about how much time you have left then. \$\endgroup\$ – Majenko Jul 5 '14 at 16:54
  • \$\begingroup\$ Your answer is very good, and answers the question posed perfectly. I believe this is important for future users. But instead of waiting three weeks for a voltage regulator to arrive (eBay), do you think five 1.5V batteries might work? As a li-ion battery can reach 4.2V per cell, meaning 8.4V. \$\endgroup\$ – Friend of Kim Jul 5 '14 at 16:55

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