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Author Topic: 12v dc to 7.2v dc - help needed  (Read 8657 times)

Para Monkey

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12v dc to 7.2v dc - help needed
« on: July 25, 2011, 11:49:38 AM »

Been a long long time since I've posted here, in fact I'm not so certain anyone even looks here anymore... but from what i recall there was a rather intelligent audience so I thought I'd give this a shot here :).

What I'm trying to do is simple (I hope). I want to take a 12v 7ah battery and run it into my dslr camera for extended life.

I have a canon t2i/550d, and it takes 7.2v 2000mah batteries. I'm not sure how much juice the camera is actually rated to take, but the last thing I'd like to do with this experiment is blow up a $700 camera.

My thought is to use an LM317T to regulate the voltage. Based on my simple calculations, with R1 at 240ohm, I'd need R2 @ exactly 1142ohm to yield 7.2v. My options are 1100 or 1200ohm resistors, rounding up will drop the voltage slightly.

Seems simple in theory, but wanted to field it here to see if anyone can shoot holes in it. I'd like to try with the 1200ohm resistor to avoid overpowered, but am I going to over heat the LM317t or any other part of the circuit by dropping 12v to 7.2?
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YucA

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Re: 12v dc to 7.2v dc - help needed
« Reply #1 on: August 30, 2011, 02:35:24 PM »

Something like that should work, but if you don't have the battery yet I'd recommend to look into a Lipo or Lifepo4 pack. It would suck to fry your camera due to a failure in the regulator system.

With the proper configuration of cells you can get one to be 7.4v @ whatever amperage you want (obviously, more MAH = more cells / larger pack). You will save a ton of space and weight compared to an SLA or AGM battery. Granted you will need a charger/balancer for the lipo/life packs but they will last much longer.

To give you an idea, check here:

http://www.batteryspace.com/7.4V-5.5-Ah---10-Ah-Battery-Modules.aspx

They sell chargers too.

Hobbyking.com is a good source for cheap Lipo/life packs.
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