# Thread: Calculating mw output from current draw

1. ## Calculating mw output from current draw

I have a green laser that is drawing 600ma from a 4.2v li-ion. Is there a way of calculating the mw output knowing the current draw? I know there are other factors to consider such as the driver efficiency but I would just like to know a in the ball park figure. I have searched for a figure but could find nothing. This laser will burn thin black plastic if given a few seconds. So I 'am trying to figure out what ball park this is in. I can guess by what others say it takes to burn something. But that too depends on alot of variables such as how well its focused. I would still like to know the equation for figuring the power out if one exist.

2. ## Re: Calculating mw output from current draw

Ballpark? W = I * V. So 600mA * 4.2V = 2520mW

Edit: given that the cell is more likely to be around 3.?-3.7V than 4.2, it'd be somewhere between 2000 and 2200mW.

I guess the circuit must use up most of that power, seeing as the laser would be only a tiny fraction of that in output. They must be very inefficient...

3. ## Re: Calculating mw output from current draw

This is only a 250mw china rated green laser. I know it doesn't put out no were near 250mw. Just trying to find out if there is a way to figure out a ball park figure with just current draw. If somenone knows what a china circuit efficiency for a green 200mw laser usually is then I could probably get close.

4. ## Re: Calculating mw output from current draw

You could get close with a straight diode, but with anything frequency doubled your going to have to take into account the loss in the crystals. You might have a 30-45mw laser. Green is not as bad as 473 which is done with crystals also but it is less efficient than the green.

5. ## Re: Calculating mw output from current draw

You could get close with a straight diode, but with anything frequency doubled your going to have to take into account the loss in the crystals. You might have a 30-45mw laser. Green is not as bad as 473 which is done with crystals also but it is less efficient than the green.

6. ## Re: Calculating mw output from current draw

A pretty efficient DPSS frequency doubled system may have efficiency around 18%, according to Sam's Laser FAQ. Of course, this number varies wildly depending on things like crystal alignment, pump focus, types of lenses used, quality of optics used, etc.

Laser power meter is the best way, really.

7. ## Re: Calculating mw output from current draw

Originally Posted by bshanahan14rulz
A pretty efficient DPSS frequency doubled system may have efficiency around 18%, according to Sam's Laser FAQ. Of course, this number varies wildly depending on things like crystal alignment, pump focus, types of lenses used, quality of optics used, etc.

Laser power meter is the best way, really.
Thanks for all your responses. I see now that there are to many variables to even make a close guess. The laser will burn black electrical tape slowly. A LPM would be the way to go. I just dont play with lasers enough to justify buying one.

8. ## Re: Calculating mw output from current draw

You might consider joining one of the laser forums and asking a reputable, close-by member to meter your lasers for you.

From my experiences with handheld single-mode 532nm DPSS-FD lasers, I can only say that your laser is somewhere between 20mW and 140mW.

Also, since it hasn't been mentioned in this thread yet, not all of the optical power from a DPSS-FD laser will be in the given wavelength. Often, the IR filter will be omitted to cut costs. This means you may have 532nm visible light being emitted from the aperture, but you may also have 808nm near-IR and 1064nm IR being emitted as well. So you may have a green laser that is measured at 30mW, but maybe 5mW of it is actually 532nm.

9. ## Re: Calculating mw output from current draw

Depending on quality, most of your higher powered chinesse green DPSS lasers, use a 1w IR diode and after xtal loss u end up with aprox 150mw of green... if no IR filter, you'll also get around 500mw of IR out the front as well. this is bad. that IR will register on a laser power meter and give a false reading. using a remote controls IR pass filter, you can see whether or not you have IR leakage by looking thru most dig cams. if filter is in place infront of pointer, you can see a blue glow on the cams viewfinder. this means there is no IR filter on the pointer, making it much more dangerous. if no glow is found you can then use a laser power meter to test tru lasers power in the green spectrum.
ether way, be very cautious with these lasers, eye damage can occur very easily even without your looking into beam. reflection and refraction of beam and damage can happen without you even knowing till hrs or even days later.

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