Non-powered "spindles"

jhllt67
Posts: 47
Joined: Fri May 04, 2012 1:57 am

Re: Non-powered "spindles"

Post by jhllt67 » Thu May 10, 2012 10:50 pm

I designed the driver based off of the many constant current power supply schematics out there. The reason there are so many resistors it to deal with the power dissipation that is required which is much higher than most other drivers due to the high current draw of this diode (almost 2 amps).

http://www.ti.com/lit/ds/symlink/lm338.pdf
If you scroll down in the data sheet you will see an example they call "Precision current limiter" which is basically what mine is. Unfortunately you cant get a pot with a low enough resistance and a high enough power rating to work by itself so I had to put many other resistors in series and parallel to meet the requirements (if you're curious the formula for the resistance you need for a certain current is in the datasheet, R = 1.2/I).

As far as the pot on the adjust pin I think that would make a constant voltage source, which is not what you want for a laser diode because they can "runaway" (as they warm up they draw more current which heats them more etc.) so you need way to limit the max current.

Here is one of the videos I watched as I was trying to make this driver.
http://www.youtube.com/watch?v=2UDVLeCqZl0

Keep in mind that I'm pretty new to electronics and still learning so I would be happy to hear any suggestions for a more elegant solution.

jhllt67
Posts: 47
Joined: Fri May 04, 2012 1:57 am

Re: Non-powered "spindles"

Post by jhllt67 » Thu May 10, 2012 10:56 pm

Also about your mosfet circuit, that is pretty much exactly what I am working on. I have all of the power regulation on the positive leg and the mosfet on the ground.

I did run into a small glitch where I tried to mount the fet to the same heat sink as my voltage regulator, which shorted the cases together and stopped it from working. Should be easily solved with an isolated mosfet.
JCPhlux wrote:What if you put a switch on the z axis like an end stop to turn the laser on and off. raise the laser and it is off lower it and it turns on.
I really like this idea, so simple. You can use standard gcode and you wont have to mess around with grbl to get a signal pin.

scholzie
Posts: 3
Joined: Wed Jan 30, 2013 5:12 pm

Re: Non-powered "spindles"

Post by scholzie » Fri Feb 22, 2013 11:22 pm

jhllt67 wrote:Hey guys, just wanted point out this laser:
http://www.ebay.com/itm/1-5-2W-445nm-Bl ... 27bb33a762

Its a little more expensive than most of the others but as far as I know its the most powerful laser diode you can get (over 2 watts optical).

I built a simple constant current driver circuit and mounted it and was really surprised how well it works. It is a little touchy on the focus but I can cut anything up 1/16" plywood no sweat.
It can also cut 1/8" ply but it takes multiple passes and chars the edges pretty bad. I'm thinking an air-assist should help out.

The whole setup was less than $100.
Have you tried it on craft foam? Something like EPS (expanded polystyrene) or depron in the 6mm range? This is a typical craft foam in the RC community. It would be interesting to know if this works on thicker pieces of lighter wood, like 1/4" to 1/2" balsa. That is much less dense than birch ply, but may catch fire or have some orthogonality issues. Would be great to see some tests before making the investment.

Really cool project so far.

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