Alternate power for small laser...

[mr2gobyby]

I have one of those small "laser pointers" that is powered by 3 of those small button cell batteries. I want to convert it so that it's powered by an "AA" battery. I'm not very knowledgable about what I'd need to put together to make sure I don't fry the laser or whether the "AA" battery is even enough to power it.

Currently, power is supplied by 3 AG-13 PLE batteries in series. I don't know how much power/voltage/amperage the laser is capable of handling or how much it requires.
I need it to be compact and to be able to pick up the parts required at Radio Shack.

I've built small electronic projects before, with the aid of a parts list and schematic, so if you have any ideas or can help I'd appreciate it.

 

[things]

Just buy a 2 AA battery holder, and hook it up to the laser! It works well, i have done it numerous times. Positive to the spring, negative to the case.

 

[audioguru]

The 3 button battery cells are tiny so they have enough internal resistance to limit the current.

2 AA cells are much larger so they have a very low internal resistance.
You must limit the current with a series resistor or if the laser diode's voltage is slightly low and the AA cells are new then the laser diode will blow up.

 

[things]

The laser already has a limiting circuit in it. Well unless they have changed since then, but all my ones have.

 

[audioguru]

The laser already has a limiting circuit in it. Well unless they have changed since then, but all my ones have.

The current limiting for the laser diode is designed to be used in series with the high internal resistance of 3 tiny button battery cells.
You are using cells with a much lower internal resistance and you are using a much lower battery voltage.
Your circuit has many unknowns. You are lucky that it works.

My son had a keychain flashlight. It used 4 tiny button battery cells and a white LED (similar to a laser diode). It was very bright until the LED burned out. It had no current-limiting except the internal resistance of the battery.

 

[things]

hmm i have done it with multiple lasers, even green ones, although the greens are regulated much better. Although if you want simple, just do what i did, it works perfectly fine, and its still going strong even today! Yes i realise the internal resistance of the batts and their effects, but every time i have done this to those little lasers, it has worked, even hooking them up to a big C cell 3V battery pack.

 

[HarveyH42]

Could you use the 'Joule-Thief' circuit to drive a laser pointer off a single AA? The laser is slightly higher current.

 

[audioguru]

I think a Joule Thief provides only a few mA (5mA?) to an LED.
A Laser diode needs 20ma to 50mA.

A FAQ article on the web talks about cheap laser diodes and how they blow up and about good laser diodes that have a light intensity monitoring circuit to limit their power:
https://www.repairfaq.org/sam/laserdio.htm#diodlm2

 

[Helder Ferreira]

If you strip a Duracell 9 volt battery you will find it's conposed of 6 thin and long cells. They are about half the diameter of an AAA cell. You can use 3 to get the 4,5v needed.

 

[HarveyH42]

Six button cells cost about the same as the 9v battery, and you don't have to tear anything a part.

 

[audioguru]

A new 9V alkaline and Ni-MH battery has six skinny AAAA cells. They have hardly any capacity but tiny button cells are worse.