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16 volts and a LM7805? Answered

I was wondering I'm making a very tiny project with that requires 5v. I'm using these little 3v batteries (CR2016). If I use like 6 of those and a 5v regulator, approximately how fast will they drain? Is that not a good way to lower the voltage? 

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steveastroukBest Answer (author)2013-03-13

How long is a piece of string ? It all depends on the load you are supplying. What's it for ? It might not need regulating even.

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HavocRC (author)steveastrouk2013-03-13

A laser. I was just wondering if the 5v regulator itself would be pulling a lot much current to work it, not the actual load. I'm sorry, I should have clarified that.

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steveastrouk (author)HavocRC2013-03-13

The regulator consumes very little to run itself, a few microamps typically. Why would you want 6 batteries, and not just two ?

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HavocRC (author)steveastrouk2013-03-13

CR2016 are very tiny, thin batteries. I figured if I used a bunch of those, with a regulator, it would give me more battery life then just two or three?

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steveastrouk (author)HavocRC2013-03-13

Not connected in series, they will give you a very hot regulator and the same battery life. I really don't recommend connecting them in parallel if you can help it.

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HavocRC (author)steveastrouk2013-03-13

Ok well it's a 5v laser. It has a SMT resistor that is say "910" on that. That's supposed to be 91 ohms. Using ohm's law, I calculated that there should be roughly 55 mA going through them. If I increased the voltage to 7.4v (two 3.7 volt rechargeable batteries) then using logic, I should increase the resistor to 136 ohms, or in more practical terms, 150?

Thanks!

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steveastrouk (author)HavocRC2013-03-13

The logic sounds OK. Lasers are pretty sensitive, so its important to err on the side of caution, as you have

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HavocRC (author)steveastrouk2013-03-13

Ok, I think I'll probably just settle with that. I've already burned out 2 of them :D
One more question : )
Should I replace the resistor or should I use a few diodes to drop the voltage? Which is better? I'm assuming the reistor.

Thanks!

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steveastrouk (author)HavocRC2013-03-13

It has an action nearer that of a voltage regulator than a resistor.

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HavocRC (author)steveastrouk2013-03-13

Wait- 6 batteries with a regulator vrs 3 batteries without will give me the same battery life?

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steveastrouk (author)HavocRC2013-03-13

Yup, arranged in series. In parallel, if it works, you'd get 3 x more for 3 x more batteries,

You need 2 x 3V - actually I'd probably just use a series diode to control the voltage = 1 unit of battery life

Putting 6 in series gives us more than 12V to WASTE, to deliver the current the laser needs, and we need a proper regulator.

Put 2 in series, with 2 in series, parallel connected, with 2 in series parallel connected, will, if the batteries are ALL new to start with SHOULD/MAY give you 3 x 1 unit of battery life.

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ubdussamad (author)2013-03-13

use only two of the and put a 7805 and it will drain after a long duration

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