Minimum voltage input to power supply to get laser to fire?

[naPS]

On my 40W laser and power supply that I purchased from lovehappyshopping I have to turn the 0 - 5 volt signal to somewhere in the .75 - .8 volt range to get the laser to fire. Anything below that, and when I hit the fire button, it won't even mark paper. Is this fairly common? I'm thinking it's not, as I see a lot of folks using settings on their DSP / RE of 10% power for doing raster work, which would correspond to about .5 volts. That wouldn't even fire my laser.

[r691175002]

That is normal. The percent values used in software are duty cycle and have no relation to the analog signal.

[naPS]

So is there something to adjust the voltage in the software? Right now using the Mach3 engraving plugin, I use the pot to set the voltage, and then the plugin cycles the laser depending on how dark the particular pixel is, which is what I imagine the software is doing when it's duty-cycling as well.

[r691175002]

As far as I am aware no controllers change the voltage that limits laser power. There was talk of using a digital to analog converter on the retinaengrave but I don't know if that has happened yet.

Your statement is correct:
"...the plugin cycles the laser depending on how dark the particular pixel is, which is what I imagine the software is doing when it's duty-cycling as well."

Currently controllers just use PWM ( http://en.wikipedia.org/wiki/Pulse-width_modulation ) on the TTL line. There are virtually no advantages to controlling the voltage - As you have discovered the voltage to laser power relationship is non-linear and would possibly change with temperature.

The only place where analog control of the laser would have an advantage is if you are moving faster than the frequency of the PWM (or switching time of the laser).

Any requirement to play with the potentimeter is mainly a limitation of your controller. Both the retina and DSP allow engrave and vector cut power to be adjusted so the potentiometer is redundant (useful only for very very low power since switching time can make 0.1-1% slightly more powerful than intended).

[LeonS]

One could put a low resistance trimmer potentiometer between ground and the "bottom of the power adjust pot. The trimmer pot would allow one to raise the minimum voltage provided by the power adjustment pot above 0 volts. This would not change the non-linearity of the actual power to voltage relationship.

It really doesn't make much difference if two passes at 20% doesn't equal one pass at 40%. The only thing that is important that 40% power (or any other value) is able to be dialed in accurately whenever needed.

I am using the DSP to control power with PWM and it doesn't start firing until you get to 12 or 13%. The PWM signal is smoothed out into a dc voltage inside the power supply and I think exhibits the same non-linearity you are experiencing using analog input.

Regards,
Leon