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  1. #1
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    Feb 2010
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    Build a ganged switch set for power settings?

    I've got the typical pot on the front of the power supply with six pin connector, and I'd like to build a switch box, preferably ganged, so that I can just select a power setting by switch.

    It's a 50K pot right now, though I don't use the full range of the pot due to my laser being 100W and the power supply max output is 130W. But when doing jobs where I run two passes, one to engrave and then another to actually cut, having to aim the laser head at the home position and dial in the power setting means extra steps but more so, variance in what it may or may not be.

    My setup is with DeskNC and not raster (variable) power at the moment.

    My idea is put 10-15 switches with predefined resistor values, or micro pots that I can dial in each one where I want it, and then just label the switch.

  2. #2
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    Quote Originally Posted by tdiaz View Post
    I've got the typical pot on the front of the power supply with six pin connector, and I'd like to build a switch box, preferably ganged, so that I can just select a power setting by switch.

    It's a 50K pot right now, though I don't use the full range of the pot due to my laser being 100W and the power supply max output is 130W. But when doing jobs where I run two passes, one to engrave and then another to actually cut, having to aim the laser head at the home position and dial in the power setting means extra steps but more so, variance in what it may or may not be.

    My setup is with DeskNC and not raster (variable) power at the moment.

    My idea is put 10-15 switches with predefined resistor values, or micro pots that I can dial in each one where I want it, and then just label the switch.

    I like that idea.

    However, what would happen if you selected a switch, and the resistor had burned out? (I don't know the answer)

    I'd consider finding the smallest usable resistor value and putting that in line always. Then let the switches put the other needed resistors in parallel with this resistor.

    Tom

  3. #3
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    Your machine may be a different configuration, but on mine the circuit required both sides of the pot wiper. Open circuit on the pot wiper is off, and actually how the laser on/off switch is wired.

    I added a rotary switch with the wiper connection to the switch common and 2 resistors equal to the pot going from the switch to the inputs, so the total between inputs is always 50K.

    It worked great except I found I still needed some fine control when engraving so replaced the switch with a new 10-turn pot that had a 'digital' readout.

    I considered using both, the switch for range selection and a pot for fine tuning but it isn't too difficult to dial in the power when you can see the setting. It sure beats counting turns.

    Zax.

  4. #4
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    The Power Supply is labeled TH and TL, the pot is hooked between TH and Ground with the wiper going to IN.

    Even a digital readout of setting would be fine in my book, I just want a way to get to a setting that I know, without having to enable the beam and look at the mA reading.

    I need to draw this circuit better than the scratch paper I have here. But this is the power supply with the current interface on it:
    http://twitpic.com/2igo65

  5. #5
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    I've come across a box with 8 ganged switches in it, they have three rails and power to light them.

    What I'm considering doing is putting an independent pot on each of the switches, and hooking that up to where the pot goes - with one of the switches having the same pot now, available via the front panel. That way I can make a bunch of presets and have access to the power directly.

    If my understanding of the circuit is correct, the least resistance is the most power. At 46.7K I get 1mA and at 12K I get 22mA. The power supply is more capable than the tube, so my thought is to do the pots with some resistors inline that no matter what I do, I always have 12K so it can never run full bore.

    I was told not to go above 25mA, I'm fine with 22mA as a stopping point.

    I gather this is using the 5V DC and simply relaying power settings to the rest of the power supply, so I don't need to have huge pots as heat bleed shouldn't be an issue?

    This is the switch gang I've decided to use.
    http://twitpic.com/2iw3l7 - a bonus would be to get the lights to work, too.

    Adding the water pump and trigger jacks to the back, I can use one of the other switches as a manual trigger, and the other as a disabler so I can run the gantry without activating the laser.

  6. #6
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    Your plan sounds reasonable and should improve the machine operation.

    I am surprised that the input is current based, I suspect it is actually a voltage drop across the resistor and resulting input voltage which is really the control but I could be wrong.

    Have you considered changing to a software based power control system?

    It wouldn't be too difficult.

    Zax.

  7. #7
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    Software, such as??

    My controller box doesn't have the ability that I'm aware of. It's an Axxis something, with Gecko drives.

    I have figured out I can change velocity during the job, but it requires me to edit the GCode myself as best I can tell, DesKAM 2000 does not allow me to do that when converting the DXF to GCode.

    Right now, what I've got to work with is DeskNC DOS, and the Axxis 2.0 controller via LPT. Software power setting would be nice as it would mean I can do raster... and single passes on all jobs, as opposed to doing dual passes now.

    If there were a pause command in GCode then I could stack the two jobs in the same file and have it do the lower power setting, wait for me to change the power and do the rest.

  8. #8
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    Quote Originally Posted by tdiaz View Post
    Software, such as??

    My controller box doesn't have the ability that I'm aware of. It's an Axxis something, with Gecko drives.

    I have figured out I can change velocity during the job, but it requires me to edit the GCode myself as best I can tell, DesKAM 2000 does not allow me to do that when converting the DXF to GCode.

    Right now, what I've got to work with is DeskNC DOS, and the Axxis 2.0 controller via LPT. Software power setting would be nice as it would mean I can do raster... and single passes on all jobs, as opposed to doing dual passes now.

    If there were a pause command in GCode then I could stack the two jobs in the same file and have it do the lower power setting, wait for me to change the power and do the rest.
    Sounds like you're using EMC2, with the Axxis user interface. EMC certainly has the capability to do all this, if you add it to your controller box.

    Editing Gcode is easy. If you're going to work with cnc, you owe it to yourself to learn at least some basic Gcode.

    And there certainly is a pause command in Gcode, as well as a Dwell command, (G04) which is a pause for a specified number of seconds.

    The emc2 can turn the spindle motor on and off using the M3, M4, M5, and the S command to set spindle speed. If you build a software/hardware controller for your machine, use M3 and M5 to turn power on and off, and use the S command to set "spindle speed", but use it to select the power setting you want.

    I'm not a Mach expert, but feel sure that Mach 3 would let you do the same things without difficulty.

    Tom

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