Miny Cascade : Budget Dual 1/2hp

[tiborrr]

Just a thought Adam: Maybe time to change the layout of your cascades? Putting the HX parallel to the fan/condensor assembly would most likely widen the footprint of the cascade but you would avoid the airflow over the HX (even though it's insulated - every plastic is porous). Maybe cut the last bend on the condensor and splitting it into a 1st stage condensor & 2nd stage discharge gas/oil cooler? You would gain quite a lot in term of footprint.

Also - as you know - these rotaries aren't meant to run in vacuum (they're MBP), they need sufficient back pressure in order to cool them down. The 9600btu/h compressor on the auto-cascade I've built doesn't even get hot even after extended overclocking session, it's just fairly warm. High pressure ratios also put stress on the compressor. You should check the power draw of your compressors if you think they're running too hot. Maybe your start/run capacitors is not correct for this compressor?

All in all - waiting on the subzero digits!

[n00b 0f l337]

Little issue with airflow, moving up to a 13W motor on the fan almost makes the unit want to take flight. The airflow gets well directed, but once you see the outside of the case on you'll see its got 2" of clearance all the way around.
I wouldn't want to split the condenser though, these small ones help quite a bit. We're not pulling much in terms of power actually, sub 300-400W at most according to the kill-a-watt. So 25uf is right for these. Right now I'm definitely undercharged though, and being in vacuum doesn't help their temperatures.

[n00b 0f l337]

Just saw -95C unloaded. The more I charge the lower my unloaded, total reversal, but I think the first stage is just too cold.. At 200W it was starting to crash though (150W @ -84C) so need to add more to first stage, which I am waiting for it all to cool/warm up depending on what it needs to do .

Current temperatures across the board at 150W so far.

Stage 1 Discharge: 66C
Stage 1 Suction: -55C
Stage 2 Discharge: 54C
Stage 2 Desuperheater bottom: 28C
Stage 2 HX outlet: -51C
Stage 2 Evaporator: -84C

Rotarys are hot to the touch obviously, but with 90-110C being their upper range I am really not worried. Many get spooked when it's hot enough to burn your hand, but you get a burning sensation at about 45C on metal, after all 110F(+-) is quite hot. But rotarys will run well into the "I just cooked an egg on the .......... " territory.
Since I think I am out of R290 I will stop by airgas tomorrow to pickup my order.

Guess I'll get on the electrical side of things then.

[wdrzal]

Guess I'll get on the electrical side of things then.

Don't forget to ground that metal case & verify a ground path with a ohm meter.

[n00b 0f l337]

Will do, both sets of plugs will have their ground wire wired to the case at separate screws or a grounding bar, and compressors to that.
Will verify as well, good point.

[runmc]

How did this one turn out Adam? It was going so well!!

[n00b 0f l337]

Currently enjoying its home at Columbia University's Laser lab after a retune for there load specs.

She did 250W@ -81C, but they ultimately needed to only hold 40W, so she got R1150 and runs -105C ~ -110C @ 50W with extended captube to 12' of .031".

Just has an 8020 frame since they passed on needing any casing, and last time I saw it they got some acrylic panels for it on their laser cutter.

[mytekcontrols]

Too bad it didn't get skinned with aluminum. Based on what you were doing with the framing and base pan, I bet it would've looked real sweet.

Can you get any pictures of what it looks like now with the plastic panels?

[n00b 0f l337]

I'll drop them an email

[sdumper]

250-300W is not enough nowadays. Aim for 350+ albeit with higher temperatures. This cascade should pull 350W @ -75°C w/o issues on R-1150 and TEV on 1st stage.

Is 350 really the norm these days? Seems like a lot of heat.