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Update/advice: full custom 2w 462nm build

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I posted a while ago asking about drivers, and more recently about beam dispersion. So far I've been out of my element, but we're into the mechanical design so it's my time to ask a few questions but also show off a bit.

This is my design for the host. As shown, it will be 11.5" long and 2" around the heatsink.


Cutaway with callouts of components:


Key features:
  • Adjustable power by rotary encoder rather than potentiometer, ensures that laser is always at safe levels when powered on
  • Encoder knob has integrated LED which will be programmed to change from green to red based on power output
  • Encoder knob also has a pushbutton which will be programmed to jump straight to minimum power
  • Power indicator LEDs on the main power switch, the firing switch, and power knob
  • High power interlock allows operation without key from 0-50mw (should I set the limit elsewhere?), 0-2000mw with key
  • Thermal isolator (black) separates heatsinking components from handle and electronics

To do:
  • Finalize electronics mounts
  • Recess power knob a few mm if there's space?
  • Battery tray for positioning and easy removal

I have a few questions about it, and wanted some pro input.

1. Is the heatsink total ridiculous overkill? I was originally planning to use the fan to force air through the host past the aluminum fins, but I happened to have a hunk of brass tube available so I threw it on there as a thermal mass and because it's pretty. Should I ditch the fan? the brass? both? I don't have specific plans to upgrade diodes, but the driver board is rated up to 8A with proper heat sinking.

2. Should I be concerned about the focus head floating on the laser's own focus threads? I would have a hell of a time getting fine focusing threads into those 1.75" bores, but I'm a bit worried what a drop on its nose would do to the laser housing.

3. What are your general thoughts on a software-limited interlock? I want to be able to remove the key and not worry about letting people handle it without glasses, but still have the ability to access the full power of the laser when it's appropriate. The lock is rated to handle the full system power, but I'd prefer to do it the other way.
 

paul1598419

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First of all, the 3s Lipo is a very bad idea as these have an inductance factor that in powering down cause spikes from 20 to 30 volts p-p. This has killed many drivers by others using these battery packs. You would be much better off using two single cells like 18650s or 26650s. If your current demand isn't over 2 amps you might get by with a couple of high drain 18350s. I would use a 1.8 amp X-Drive from DTR's site as your driver. You wouldn't need to heat sink the driver if you do, but it is never a bad idea to heat sink it even if it isn't necessary.
 

Lifetime17

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Hi,
Great start one thing change that brass 10oz. sink to copper ..

Rich:)
 
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First of all, the 3s Lipo is a very bad idea as these have an inductance factor that in powering down cause spikes from 20 to 30 volts p-p. This has killed many drivers by others using these battery packs. You would be much better off using two single cells like 18650s or 26650s.
A couple questions-
Is this inherent to the 3s batteries somehow? I have a hard time understanding why it should be different than just using 3 18650's in series. I've picked this battery because I already have it lying around and it's got discharge capacity to spare (a 20C battery from a dead quadcopter), but if cheap 18650s are going to protect my components I'll get those instead.

Why do you say 2 cells and not 3? I'm sure you have a reason, but I don't see it. Electronics aren't my strong suit, but I've been assuming that between the arduino, the fan, the diode, and the driver board I'll be more comfortable running at 11.1v with voltage regulators than at 7.4v.
 

paul1598419

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Well, the 11.1 voltage spec when fully charged is more like 12.6 volts. The inductance that causes these spikes is there and to the best of my knowledge has been measured. Why it is there, I don't know as this is not something that I have used in the past. I wouldn't recommend "cheap" 18650s like in ultrafire or other off branded Chinese knockoffs that boast a 5000mAh capacity. I would recommend Panasonics, which is the brand I use most. You can get a real 3400 mAh Panasonic with a low internal resistance. I use www.liionwholesale.com. They have the best prices I have seen for brand new batteries that check out to be exactly what they claim to be.

I recommended two batteries as it is sufficient and three makes the host unwieldy and much longer than it needs to be. But, if you would rather use three batteries I see no other reason to not do it that way.

I see they are having a clearance sale, so I bought 5 18650s. Got 2 3500 mAh 10 amp drain LG and 3 2500 mAh Efest for $31.88 total including priority shipping.
 
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