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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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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.

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.

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

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?

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.

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!

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

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!

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

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

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.

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