Air Filters

[steve-o]

So, I'm putting on a show, and the green DPSS laser cuts off from over-temp about 2 hours into the show. I have a sealed optical deck, which I believe is getting too hot inside. The green module that's in the RGB (a 500mw 532nm Lasever) has a fan that blows surrounding air on to the heatsink of the laser head.
So I'm thinking, a little fresh cool air from the outside of the enclosure may not be a bad idea, but I don't want to suck dust, pollen and bugs into the optical deck. (I do mainly outdoor shows)
Keeping a positive pressure inside the cabinet is a good thing, but keeping the air extremely clean is a must-do too. Any recommendations for a good air filter anyone?
Thanx in advance,
Steve-o

[The_Doctor]

Go for volume rather than a film, because if there's smoke or fog or cooking fumes or anything else sticky in the air it will clog a thin filter fast, and you'll have heat trouble again. One way is to get the cheapest sleeping bag you can find with that hollow-fibre polyester in it. Damn good stuff, you can put it in speakers for sound damping, wrap laser tubes in it for ideal packaging in the mail, etc. A new sleeping bag with colours no-one wants to buy at the end of summer (not long now!) will make it cheaper than rolls of wholesale padding. I use it in the air intake for a fan cooled 1U rack computer, and I also use it in a dehumidifier intake. To renew it, best to pull off the dirtiest of a few layers of it, then add a clean layer on top of the cleanest side. You can control the density by how much you squeeze into the space made for it. The cheapest way to add a filter like this to an existing design might be to pack the stuff into an old fan frame, get a new fan guard, and some long bolts to replace whatever holds the existing fan in place. A bit more thought will be wise, to make the filter accessible without upsetting the fan or losing nuts amongst the innards when you replace the filter padding. The stuff will also help to silence the fan.

EDIT:
One other thing: Some kind of coarse polymer mesh sheet should be placed on the outer side of the padding layer, to prevent bugs from trying to live in the padding. How coarse that mesh should be will depend on the bugs, but best go as coarse as you can get away with.

[steve-o]

Thanks Doc, I appreciate the info. I was kind of thinking also of a pro-grade laboratory clean-room type of filter made for a small chamber if there is such a thing, and if they're not too awfully expensive ..

As far as bugs living in the filter, the laser is only exposed to the outside environment for a few hours (not a permanent installation) and the filter will be removed and cleaned or replaced for every show. I only do a few shows per year too. Not a whole lot.

[The_Doctor]

I'm not sure. They might be, given that it's dealing with two contradictory needs (air in, nothing else in).

There may be another way: Two heatsinks, back to back on one thin wall, and a small fan for the internal one. The outer heatsink might not need one if there is any breeze. This would dramatically improve thermal coupling from case inside to outside, while allowing it to be fully sealed.

Edit:
I think cleanroom filters use electrostatic charges. Overkill in this case probably.. That polyester stuff is great, and if you're changing a filter for every show this is likely the best bang per buck. There are knurled nuts you can fit a fan guard with. Just undo those, pull out the pad, wipe the sides of the fan frame, stuff more in.. You could spend a lot making it work better or easier.

[Photonbeam]

A HEPA filter for a vacuum cleaner would provide clean filtered air but maybe not enough volume.

[steve-o]

All good ideas! Thanks guys !

[White-Light]

Doesn't Rob Stanwax sell these?

I'm sure I've seen them in his shop both as a full kit with holder and as separate pads.

[steve-o]

Thx WL ! I'll check out Rob's site It's been a little while since I've been there ..

[norty303]

I use a variety of filters, none of which stop particles completely.
If you are going to pass air through your optical deck, arrange inlet and outlet ports so that the air flow doesn't pass over your optics or laser output windows. Keep these around the edges in the dead air.
Best option is to keep the space sealed and improve the thermal transfer to the outside of the sealed space.
Incidentally, you don't need to have a completely sealed deck, so long as the air inside is dead air, so you shouldn't get any/much transport of particles.
In fact, a few small 'vents' may even help the air stay cooler than with a fully sealed deck.

[MIIKKKLLLL]

Hi Steve-O,


I had the similar problem 2 years ago with the same green laser head.

In fact, the over-temp was set to 28-29°C and this temperature was quickly reached in summer .


To solve that, you need to open the driver cover by removing the 2 screws on the top.

Then you have 4 potentiometers. You need to turn the closest potentiometer from the power supply cables.

Turn ANTI-CLOCKWISE, 2 complete turns will be enough (1 turn = +- 3°C).


A good way to check if the head is near the over-temp limit is to turn the potentimeter clockwise (don't forget to count how many turns you do ) and take a look at the upper green led. Once it turn red, the driver is in "security mode". You know now how close the temperature of the head is (ex : 3 turns = 9-10°C from the temp limit).
Then you have to turn back the pot, and cut power to reset the driver.

Attachment 39416



It's easy and keep dust away!