My RadioShack Greenie (1st Mod)

[jmgallego]

I have a good Craftsman voltmeter, but im not sure how to measure current exactly?

I am interested in learning how to properly measure the currents on laser pointers.

Thanks!

 

[IgorT]

[quote author=troop231 link=1199645393/0#12 date=1199659076]I have a good Craftsman voltmeter, but im not sure how to measure current exactly?

I am interested in learning how to properly measure the currents on laser pointers.
[/quote]

You have to select the current measuring range on the DMM (Digital Multi Meter) and then pass the current through it.

If the batteries go in at the back, and a tailcap closes it, you can simply remove the tailcap and touch one of the DMM probes (the negative - black) to the metal of the body, and the other (the positive -red) to the battery "+" contact sticking out. Since the pointer has a pushbutton, you have to use some sort of clip to hold the button down, while you're doing this, and when you connect the DMM to the pointer the right way it will light up and the current will show up on the display.

It is best to use the highest range on the DMM (usually 20A to introduce the least resistance), and you usually have to move the red probe to another socket on the DMM, so the current can pass through it. In the voltage measuring range, no current passes through the DMM.


If it's a different style pointer, or if you have it appart, you still have to put the meter IN BETWEEN (in series) one of the circuit connections and the correct battery potential.


There are some tutorials around here, on testing circuits (Testing DDL driver thread), with pictures on how to measure the voltage and the current.

 

[Hemlock_Mike]

He says he has a volt meter - Not a DMM. That will only measure current using a shunt resistor. What is the lowest voltage range you have?

Mike

 

[IgorT]

Oh, i see.. I was actually answering the second question, not asked by the same person. No equipment was specified.

And i really wouldn't recommend using your own shunt (unless it is a VERY low resistance and a VERY low voltage range) to measure the current in a green laser, because most of them are unregulated, so the current could be drastically affected by the shunt. That's why it's necessary to use the highest possible current renge on a DMM, where the shunt is a thick metal rod. And yet it can still change the behavior of an unregulated laser.

I have noticed as much as 200mA difference between the 20A and the 2A ranges when measuring an unregulated green with a 0.5W pump. And sometimes even the 20A range would halve the brightness.

 

[jmgallego]

You have to select the current measuring range on the DMM (Digital Multi Meter) and then pass the current through it.

If the batteries go in at the back, and a tailcap closes it, you can simply remove the tailcap and touch one of the DMM probes (the negative - black) to the metal of the body, and the other (the positive -red) to the battery "+" contact sticking out. Since the pointer has a pushbutton, you have to use some sort of clip to hold the button down, while you're doing this, and when you connect the DMM to the pointer the right way it will light up and the current will show up on the display.

It is best to use the highest range on the DMM (usually 20A to introduce the least resistance), and you usually have to move the red probe to another socket on the DMM, so the current can pass through it. In the voltage measuring range, no current passes through the DMM.


If it's a different style pointer, or if you have it appart, you still have to put the meter IN BETWEEN (in series) one of the circuit connections and the correct battery potential.


There are some tutorials around here, on testing circuits (Testing DDL driver thread), with pictures on how to measure the voltage and the current.

Thanks followed your intructions and I have been able to measure the current of my pointers.  THANKS, good instructions  

 

[IgorT]

Thanks followed your intructions and I have been able to measure the current of my pointers. THANKS, good instructions

Glad to have helped!

So what current did you measure? And you may want to repeat the measurement through a lower current range, to see if the reading changes. And then repeat after the batteries are not full anymore. If it doesn't change, and the current remains constant even after the batteries are not completely full anymore, the laser is current regulated.

This means that every time you turn it on, it comes on at the same power. Unregulated lasers come on at a lower power every time you turn them on, because the batteries slowly lose voltage.