Help wiring True Green Laser 5mW

[Chronicdiving]

Hey guys...building a spyrograph and need to wire up my True Green Laser Pen 5mW to power...I have the pen and cannot seem to get it working on my PSU...I've got a 5v line coming out which i've resisted down(58ohm) to 3V which is what the pen requires(2xAAA) but it won't turn on when i connect the positive to the back end and the negative to the spring...i notice that when i turn on the laser my ohmmeter reads a current draw but there are no results...I check it afterwards with the batteries and it's still working...does anyone know what i'm overlooking? Thanks!


-Ray-

 

[cexshun]

Check the current across the wires of the PSU? Is this a PSU salvaged from a PC?

 

[Chronicdiving]

yes it is...it's 5v coming out, resists down to 3 and when i wire everything up and press the button on the laser i see a current pull but no laser

 

[cexshun]

PSUs are designed to run with a load on a 5v rail. When I converted my PSU to charge R/C batteries, I had to put a 25W 2ohm resistor on a 5v rail in order to bring the operating voltages up. Although I was using the 12v rail. Not sure if it makes a difference on the 5v rails.

 

[ElektroFreak]

How much current is it drawing at 3V? Normally a 5mW green will draw between 250-300mA when working correctly. Readings other than this may indicate a blown pump diode..

 

[Chronicdiving]

I have an arduino running off it and the fans for the spyrograph so it's definetly working since everything else is pulling current so i don't think it's that there's no load...i did have that problem with another supply once though...and i take the point offline and put the batteries back in everytime i test it and each time the batteries light it up again...so that proves it's not damaged since the batteries work...it has something to do with not connecting correctly but i don't understand what's different about this one since i've hooked up lasers before with no issue


i tried puting in something that was the length of the batteries and then attaching the wire to each end hoping that might make a stronger connection but that didn't work...i've cut a hole in the back so it's easier to get to and secure the wires

 

[phoenix77]

Are you sure your wires to the + & - hookups aren't shorting out someplace ?

 

[Chronicdiving]

yes the wire is full insulated and alligator clips are used to make connections so they have a rubber sleeve over them

 

[goamarty]

Probably the crude reduction with the series resistor is the problem. It gives you only 34mA for 3V. If it is a computer supply then you could use the 3.3V rail (batteries have a little more than 1.5V when they are fresh), or use the 5V with 3 dropping diodes. The most safe solution would be a 3V regulator, for example a LM317 with resistors.

 

[rog8811]

I have had success with using a piece of bamboo as a battery replacer, might be worth trying to be sure of a good connection.

Solder the neg wire to the screw and the pos wire to the brass washer.

Regards rog8811

 

[rog8811]

Found a "how to" for the above.

Regards rog8811

 

[Chronicdiving]

I ended up figuring it out but thanks! I tried a variation of that