Been awhile since I’ve posted a dispatch. Not for lack of wanting or a lack of time or projects though. My PRU has been taking prolonged bench naps.
A few weeks ago two things occurred that conspired to put him to sleep. First we had a heatwave here in CT. That’s relative - low 90s F temps qualify as a heatwave here. That resulted in pretty consistent 80F temps in my basement where the GF lives. A few years ago the basement would have acted as a great heat or cool sink because it’s a poured concrete foundation nearly all underground. We got tired of it being cold in the winter so we finished it off which included wall insulation but not a/c. So it no longer gets cold in the winter. Or the summer.
Now we don’t spend much time there - well not the family anyway. I use it for my laser. And the laundry is down here and my wife’s food supply - if Armageddon comes you know where you’ll find months of food… especially if you like cookies and other baked goods - there must be 100 bags of chocolate chips and M&Ms alone.
There is a dehumidifier down there though and it’s generally fairly pleasant with a sub-40% relative humidity which makes a 78 or 80 degree temp pretty comfortable.
This year though we have a GF who wants temps less than that. At the same time the basement was headed to 80 or more because it was 90+ outside, the mothership sent an update to shut the GF down in high temp scenarios. In concept this is a good thing - tube life and reliable operation is hampered the higher the temps. I have the Redsail set to shutdown at 30C as recommended by their tech team. I’ve had it do that once in the past couple of years and I knew it was coming based on the results I was seeing. That’s about 86F. 80F is about 26-27F. 78F is about 24.5 and the GF’s temp controls don’t seem to like anything that high. So even though the basement is fine for humans, it’s sleep-inducing for the GF.
Well, we’ll just wait for it to cool back down in the basement. Yeah. Been hot and stayed hot for the better part of a month. Besides, what about using a GF at a summer fair or festival or even a MakerFaire? It can be hot and they’re often outside around here. Planning to do a local one in the fall when it might be 50F or 100F all depending on the weather gods.
Seemed like a good reason to experiment with ancillary cooling (adding a/c to the basement would require getting a portable unit with another exhaust to poke out the little windows I have on one wall and $500). Ancillary cooling off just the air entering the GF would be handy for the basement but also for those travel events where we’re under a tent and hot.
Heat in the Basic is dealt with by running the coolant through a heat exchanger and relying on the incoming air that is used to supply the exhaust to cool the heat exchanger. The air enters under the right side below the glowy button. Above the intake is a black perforated metal plate that is the visible portion of the heat exchanger.
It’s about 10" long and 4" wide with an upswept curve as it nears the side of the case. Pretty neat design but it’s not going to cool hot tube coolant below 78F when the incoming air is 80F. (Note - I don’t know the upper limit is 78F but that’s the highest temp I recall it working with.)
Thermal management has been a topic of interest of mine (I designed a super-efficient wood fired pizza oven that can cook bread in it 12 hours after making pizza without any added heat). So I decide I’ll cool that incoming air.
Shouldn’t be hard. The vents are directly below the area of the heat exchanger.
No Glowforges were tipped on their back for that photo. Rather I lay down underneath it and pulled the corner off the cart it’s on.
Not a huge area so I figured I’d just have to direct a flow of cooled air under the GF from the right side. I scrounged a plastic container from the recycling, grabbed a couple of PC gaming cooling fans and two blue ice blocks from the freezer. (I didn’t want to put anything in the GF as a) it’s not mine and b) I promised not to modify it in any way and c) I didn’t want condensation or other issues that might arise if I simply dropped one or two of those blocks on the heat exchanger)
Here’s what GF Chiller V1 looked like - plastic box with 2 fans screwed into the back pushing air from the room into the box across the ice and out a slot I cut in the front of the box.
Pushed up against the side of the GF I measured a 10F reduction in air temp from ambient to the flow coming out of the slot. Nice chilly 70F air being sucked into the GF.
Fired it up, yellow alert. Leave it on to circulate the cooled air & coolant. Turn it off. (yellow temp alerts won’t reset without a power cycle) Restart. No go Charlie.
Okay, maybe I need to chill more air because the intake is longer than the slot in my chiller box. My guess is the rest of the air was overwhelming my cooling supply.
Chiller V2 will be a tray that slides under the GF, has a short back wall (it’s only about 3/8" off the tabletop so the tray needs to be shallow) a wider longer section on the outside of the GF with high walls and a top to mount the fans.
Something like this.
The short slot in the base is to allow it to slide alongside the support rail under the GF. And no I didn’t cut that part out with the Redsail - I forgot to account for it so had to either re-laser or use a utility knife. It’s a testament of sorts to the Redsail that it was faster & easier to use the utility knife.
Yes, that’s PG Draftboard. Yes it cuts fine on a Redsail but darned if I could find PG settings on the big red beast And I taped it instead of gluing (or making a nice finger joint box - just hacking something together and if it works we’ll make a nice one out of contoured acrylic, PG of course )
More chilled air came out of this one. Had a full 10" of length instead of the wimpy slot.
Laid the fans on top instead of screwing them on - again proof-of-concept here (and yeah forgot to add the screw holes for the fans). Casey swings again and it’s another strike.
Perhaps the small fans don’t provide enough air. Take off the top. Grab a desk fan - one of those 15" things with 3 speeds and big blades. Direct it down over the ice blocks and under the GF.
And Casey strikes out. No lack of yellow alerts. But a profound lack of tube cooling. In retrospect we need a ton more cooling mass to offset the heat generated by the tube when the coolant transfer fluid is air. There’s a reason the Redsail has a commercial chiller piping cooled water through the tube. Or the K40 has a 5 gallon bucket of water that often needs to be supplemented with ice (although that lives in the garage where it often gets to be 95F+).
What we really need is a Peltier cooler or two mounted on the heat exchanger. They can create a temp differential of 30-40 degrees F with enough power and appropriate heat sinking. I’ve got on on the bench in fact, but that would require a mod to the GF because I’d need to attach it to the heat exchanger and get 12VDC in there which ain’t happening with not-my-forever-GF. It’s not gonna happen with my forever-GF either because that on is a Pro And because the Pro has its own Peltier.
So standing in the aisle at Lowes looking at a/c units, two things happen. Similar to the two that started this story (it’s almost done, I promise, and there will be llamas). First Dan posts a note about changing the temperature threshold used by the GF to decide when to shut itself down (technically it doesn’t shut off, it just stops with the whole pew-pew-pew thing). They’re raising the temp threshold so warmer than chilly office temps will work. Not sure how much warmer but higher. The second is the heat goes away. With a vengance. It went from 83F yesterday to 61F today. Gonna be in the 50s tonight.
Yesterday I did a quick test - 78F ambient air temp and two small jobs and no temp alerts. Is that the new limit? Don’t know because today the basement is 66F (opened up the hatchway door and pulled in some air to cool it down).
But, I did my first project on the GF in weeks. I’ve done a couple on the Redsail but it wasn’t the same. Felt like I was using a stone hammer and flint chisel. Tonight I tossed off a quick little project for my wife.
Yes, that’s Drama the Draftboard Llama. I like Proofgrade. Just let it pick the settings, just needed to change one cut to a score and hit Print. 36:42 later Drama was done.
My wife is using him to hold a wrap of needlepoint floss. The mouth is cut out with a slot to leave the end in so it doesn’t get lost or tangled.
A little large so I fired off Drama Jr (25% smaller) and 24 minutes later Junior popped out of the GF. Cool. A barnyard of floss animals will follow but these two have broken the dry spell