Old alarm battery for LPC-815 with LM317?

[Kandrix]

Hey all,

I've recently managed to change battery in alarm and i got this pretty nice, kinda year or two years old battery

It outputs ~13.25V when fully charged. I have made very simple DIY laser

Specs written at image above. I'm just thinking if using this battery (with aligator clips, and just at home, because 4AAs aren't very durable in this little thing) is safe for my non heatsinked driver (LM317T with 3.0 Ohm resistor) and non heatsinked Aixiz module. I'm talking about run max 2-3mins with time for cooling everytime. Or i do have old DIY Pentium 4 Air cooler, remade to cool me in those summer days, I can point it onto module... Thx for any kind of responses

 

[Cel]

It's a nice build, but if everyone could stop posting over-sized pictures on the forum, that would be great.

 

[Cyparagon]

Your driver is now 20% efficient, the heat generation in the regulator has tripled, the weight has quadrupled, and your run-time has not improved at all.

 

[Kandrix]

Oh, sorry for oversized pictrures... I hoped the forum can resize it into iframe... But anyways, I tried connecting it together, laser was stable, but heat... Aixiz module was 100% fine, but driver got pretty hot in just like 30 seconds. So i tried to add another resistor between the battery + and conection to the power switch in laser. I found pretty big, nearly 0.5 inch long and 0.20 inch wide one, which had 150 ohms. I tried to put it all together again, laser was working fine, but i think that 150ohms is kinda 3 times more I'd like to add. Laser was nicely stable, nicely cold, but output power was ... maybe 50-100mw. Not much enough even to light match in focal point. (I also tried to use graphit from old pencil, it worked with not so much heat in laser, but this "resistor" get brutally hot and smoking in like 15 seconds, so this try failed so hard.) So I'll try to find some 20-50ohm resistor, i hope it will be some ceramic one, that could do it better. Also I'd like to find some passive cooler for my LM317t driver, anybody has any idea about anything, which could be electrically isolated from the back side of driver, but still keep cooling? Thx for any responses

 

[Jamez99]

Thank you for this great news and your article very Great pics are too good it is very amazing It just seems like it'll look even better in person; all those curves.



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http://en.wikipedia.org/wiki/Carnegie_Mellon_University

 

[Leodahsan]

@Kandrix
The heat generated is by waste, excess voltage on your driver.
The LM317 dumps extra voltage into heat. Your diode uses around 3v, so for 13.25V (full charge) 380mA output, thats

13.25 - 3v * 0.38A = Nice 3,895W of heat. [(Vin - Vout) * Iout]

The minimum "extra" voltage the LM317 needs is around 3v. You can test that using a variable voltage source as supply, and find the regulation point (should be 6v~7v depending on laser diode Vf, IIRC the LPC-815 uses around 3.6V at 400mA).

If you use the lowest possible voltage, you will have around 1,14W of heat, around 70% less heat on your driver. For higher efficiency, use a pre-regulator on your driver, such as a Buck driver. Those are available @ th e bay for around $3 each. They lower your 13v to 6v with a high (>85%) efficiency, making your runtime very higher (don't make me calculate).

Oh, and on your "quick specs" pic, its 380mA output, not 380mA @ 1.25v. Its 380mA on any voltage up to 10V, because laser drivers are constant current.
A proper label would be "@380mA Constant Current"