Large Warm Darkroom Trays

koraks

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Kino said:
VIVOSUN Durable Waterproof Seedling Heat Mat
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Keep in mind that these are IP67 rated; this may (will) not be sufficient for an application where it's likely that significant amounts of water slosh around.

YMMV of course, but something to keep in mind.
 

koraks

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cowanw said:
Thermal glass beads might be better than a water bath, whatever heater you use.
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Do you think so? I have some doubts.... Wouldn't heat transfer from a typical heating element to the glass beads be substantially reduced compared to water? Firstly because the thermal contact is quite poor (they're round after all, so the contact surface is minimal), secondly because convection is limited to the air moving between the beads, which will be virtually insignificant.

Have you tried it, and did it work well?
 

cowanw

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Firstly there is no evaporative loss of heat as with water and secondly these are used in optical shops and ENT clinics to heat tools and spectacles. Glass is a great insulator and so retains its heat. Heat transfer to start a cold system may be longer than water but so?
Leaving an aqueous solution intact for so long would invite bacterial/fungal contamination. Glass beads are dry and easily sterilized.
So, maybe the pig warmers covered in a glass bead tray and the solution bath tray set in the glass bead tray.
Yes it works well. Aluminum beads are commonly used as well but glass is a better insulator and so would be a more stable source of heat.
 

koraks

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cowanw said:
Heat transfer to start a cold system may be longer than water but so?
Click to expand...

My point is that the method of heating must be compatible with these beads.
Suspend a generic AC heating element into it and it'll burn out. It should work fine with the heat mats underneath a tray.
 

mshchem

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One other great trick is keep a microwave handy in the darkroom. I've been using one for 20+ years. Scoop up a quart of your cold water in an old Kodak plastic 1L beaker, warm it up to 120°F. Do this a couple times and you're ready to go.

I warm color solutions this way, I can be ready to go in 10 minutes.
 

Mal Paso

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A 1000 Watt stainless immersion heating unit for $15 on amazon has better efficiency than a microwave.
 
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Carnie Bob

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Thanks for all the suggestions, I am going with the pig warmer idea with stainless steel tray thin gage on bottom. If this does not work I will
use an aquarium heating device laid in the tray with a mesh over top so the prints do not hit the elements.
I will post my results when completed and thoughts on how it works.
 

MattKing

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You might get the best results from combining more than one of the approaches.
Although only one should have any automatic temperature control built in!
 

DREW WILEY

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How much splash over the rim, Bob? If it doesn't get messy under your main tray, you could use several old adjustable temp Salton hot trays, like people used to use for keeping TV dinner trays warm. Used ones are pretty cheap. The top surface is glass.

I wouldn't use a recirculating thermoregulator for actual chemical solutions, just surrounding water jacket water.
The problem with the big ones like you potentially need is that they might not work lower than 75F.
I have a 2000W one - a serious darkroom commercial unit - and it's a headache, but will keep water temps within 1/10th deg F! Take Mal's Amazon price and multiply it by 100 times as much. But I don't use mine anymore, so if you are looking for a deal on one, just message me.

Immersion heaters don't work well in big tanks unless you also have a recirculating pump. Either way, you need to start out with a water temp not too far off from your target point. Failure to do so will prematurely wear out the unit, or worse.
 
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Mal Paso

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I built a water tempered E6 line using Kreonite parts. A recirculating pump took water from one end, pumped it through a temperature controlled heater and returned it to the opposite end.

With your size I would use Water Heater Elements $12-$24 dollars each for 4500 watts at 240, 2250 watts at 120. A single stage fractional horse power recirculating pump would be fine. I recommend Auber Instruments for a temperature controller. Universal 1/16 DIN PID Temperature Controller They do a good job supplying decent equipment and have technical support. There is a lot of junk on the market and some of the amazon PIDs are counterfeit, I bought one, that's how I know. You will need a Solid State Relay and a thermocouple to complete the controller. Should be under $100 with shipping. Omron PIDs start about $400, Auber has very fair prices. You should be able to hold the temperature within a degree or two.

I have Auber controllers running a 450,000 BTU Hot Tub and 800F lead melters. There are different thermocouples for almost any application. I have no affiliation with Auber but have bought from them for about 15 years now.

You can download the instruction manual from the page above and see if it suits you.
 
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