Instructables

A TEMPERATURE CONTROLLED LABORATORY HEATER

A TEMPERATURE CONTROLLED LABORATORY HEATER

 

The device described is an electrically heated air bath with adjustable power input and temperature regulation via a PID digital temperature controller. It is suitable for use as a heater for chemical apparatus, such as that used in distillation and reflux operations.  An air bath is the preferred means of heating distillations flasks, because its superior uniformity of heating avoids local overheating and charring effects, which are commonly experienced with electric heating mantles. The digital temperature control is optional; the heater can be used with the energy regulator alone if the user is present to monitor the operation and manually control the temperature as necessary.

 

Parts Required ( Prices taken from eBay listings ) 

BASIC HEATER

1 Aluminium saucepan, approx 150 mm diameter with lid § $ 2.00

1 empty tin can, 100 mm diameter x 150 mm high $ 0.00

Fibreglass Electrical Heating tape, 25 mm x 1 metre, 220 V 100W $ 3.00

1 x IEC panel mount sockets with screw terminals $ 2.50

Glass wool insulation ( salvaged )*

1 x ABS plastic enclosure 70 mm x 40 mm x 25 mm $ 2.00

1 x ABS plastic enclosure 120 mm x 75 mm x 60 mm $ 9.80

1 x IEC Power Cord $ 2.75

1 x SCR Power Controller 220 V 2000 W $ 7.50

250 mm Copper braid ( salvaged from old coaxial cable )

2 x Cable Clamps & Terminal Strips $ 1.00

Assorted screws & nuts $ 2.00

( Sub-Total ) ($ 32.55 )

DIGITAL TEMPERATURE CONTROL

Type K Thermocouple probe 400 oC $ 1.00

Digital PID Temperature controller 220 V $ 13.00

1 x ABS plastic enclosure 120 mm x 75 mm x 60 mm $ 9.80

1 x 220 V Extension cord, 1 m $ 4.00

2 x Cable Clamps & Terminal Strips $ 1.00

 

( Total ) ( $ 61.35 )

§ from a second hand shop

* found in old electric ovens or ceiling insulation batts.

 
As can be seen, the most expensive items are the plastic boxes for the electronics. If you can use boxes you already have or make your own, you can save nearly 1/3 of the cost.

 

 

 
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corradini5 months ago
A few thoughts:

(a) I wouldn't run the condenser coolant tubing in front of the heater; you're risking melting the tubing, and spillage on the heater. (I assume you know this; just mentioning for the kids at home.) I like to run the coolant from under the bench and behind when possible so any 'disconnection event' will point spillage *backwards* (DAMHIKT).

(b) and btw, a plastic insulated camping ('Coleman' in the US) cooler works great as a coolant reservoir, w/ water/ice/CaCl2 (sold as closet dampness remover) bath).

(c) ELCB is a great (i.e. mandatory) idea; in the U.S. you'd want a GFCI (Ground Fault Circuit Interruptor) - same thing in Americanese. And our closest equivalent to 'mains' is probably 'wall power'. (I'll not translate 'aluminium', which is actually a far better spelling.)

(d) A PID is initially more hassle -- figuring out how to wire it up can be a PITA, and you really should spend some time learning programming and esp. 'self-learning mode' -- than a simple 'turn the knob until it gets to the right temp' control, but it's WELL worth it; you'll never go back. (Oh, definitely wire it to/through an SCR (w/ heat sink!), and have THAT switch the actual 'mains' power, don't use the internal relay - trust me.)

Finally, (e) every lab worker, no matter the budget, learns that aluminium (!) foil is as indispensable as duct tape and super-glue are at home -- but BE CAREFUL what/where it touches. It *probably* won't conduct enough to short out YOUR 'circulation pump', but it can fry plenty of other things. Easy to get casual with it, but remember that it's basically a big sheet of WIRE. >;-)
kymyst (author)  corradini5 months ago
Thanks for the input
(a) Yes, That is good advice The hoses weren't long enough to run around the back when I set up the photo. They weren't actually touching the heater but would have got rather warm after a while.
(b) I have a couple of 3 litre wide necked Dewar flasks which I use for ice baths.
(c) Thanks, I had never heard of the term GFCI. It's always hard to know how to translate Australian into American.
(d) The PID is definitely worth the extra $ 12. Setting it up was very easy, even with the rather weirdly translated tech data sheet. The SCR is still essential, as you say.
(e) The alfoil is there to reduce heat losses through the top of the flask and the Vigreux column. It's difficult to maintain the column temperature without it. The circulation pump is 2 metres away on the end of the water supply hose.
corradini6 months ago
Where on earth did you get a 1m 100w heating tape for $3 (never mind which currency that $ is! >:-) I use that kind of thing a LOT, and if I could buy 'em for $3 -- AUS, US, whatever -- it'd make me quite happy...
kymyst (author)  corradini6 months ago
I bought it from eBay, item 281135728130 from China. The store name is popularstar2013. They are still selling them at that price ( US $ 3.00 )
corradini kymyst6 months ago
Good lord - I just checked -- WOW. That's a screamingly good price (similar deals on longer ones, too). Just wish they had a bit more info, like max temp -- did yours come with ANY literature, or model/mfg, anything? (I'm going to e-mail them, too...) This could have a HUGE effect on my startup, thanks!
kymyst (author)  corradini5 months ago
No, there was no information supplied. I have run this heater at 280 degrees Celsius with no ill effects. At a guess I think the tapes would be OK up to 400 degrees C, but probably the only way to find their upper temperature limit would be to test one to destruction. Most commercially made heating mantles are rated at 450 degrees C maximum, but they could have thicker resistance wires than these cheap tapes ?. Generally these tapes deteriorate faster through oxidation when operated at high temperatures for long periods. The lower the temperature the longer they will last. But at least they are cheap to replace.
corradini kymyst5 months ago
Generally these seem fairly standard, looking at McMaster & Omega (both resellers). Wattage generally a function of length (actually lxw), with the 480°C ones (1" wide) being about 50w/ft, the 760°C ones being 155w/ft. (Obviously amps vary linearly too as voltage is constant.) They're MUCH more expensive from either - Omega's (760°C), 1.22m is $89, the 480°C one is $50. (5 weeks lead time on most lengths, so they're no doubt getting them from China.) McMaster carries only the high-temp version, closest version is about $50 (they're usually cheaper than Omega, and again this is the high-temp). SO - my GUESS is that, at that price, it's a 480°C (900°F) heater. They're also the 'double-insulated' type, from the photo, which would tend to confirm that. I think that to get up to the higher temp, they have to be a dual-element, and of course would pull higher amps (right?), so the wattage rating, correlated to a commercial heater, should give you max temp. I think? >;-)

I've used one (from Omega, single-insulated, 480-rated) at 250-300 (intermittent peaks up to ~350), inside an outer Pyrex tube, for ages w/ no burnout, although probably in an N2 environment for part of that, now that I think about it. I've also been using one of the double-insulated ones (single- are light brown with a back-and-forth sewn 'S' pattern; double- are snow-white fiberglass flat sheathing) for a little while, in air, no outer insulation/tubing, no troubles - I don't think much air gets into the inner insulation, but I do hear the same thing about deterioration at higher temps.

Thanks for the info! I like your stuff, btw. When I was starting up my company (actually in my garage!), I had to improv EVERYTHING, from Home Depot, drug store, aquarium store (!), Target, Goodwill, you name it. A few eBay things, but mostly lots of crafty repurposing and looking at, sigh, 'illicit' sites. (Oh, yeah, 'tobacco accessory' stores have lots of good stuff, esp. scales, heating, and pyrex. >;-) Fortunately I got funded and could buy 'real' stuff (2,000° lab furnace was nice), but I still kept the 'scrounge-and-repurpose' mentality. (I.e., using a $13 coffee-grinder from Rite-Aid instead of a $200 lab ball mill for catalysts; a Rival 'dorm-room hot-pot' for a water bath, Goodwill toaster coils for heaters, Pyrex measuring cup 'beakers', etc.) My investors LOVE that stuff -- and I can podge together something from my scrap-bin NOW, not pay for overnight or wait 3-5 for UPS... ;-) Plus, Freecycle and Craigslist are beautiful -- I have a fantastic full 4'w lab fume hood I think I paid $50 for, temp-controlled heating stir plate for $20, massive vacuum pump (free), full-size freezer (free), old gas chromatograph w/ columns (free (!)), etc. And huge parts of our pilot plant - which we raised $1.2mm with - were still podged together from Home Depot plumbing, etc., parts... (It's just fun, innit? >;-)
Cheers, Andrew
kymyst (author)  corradini5 months ago
That is all good information Andrew. I agree with your assessment of the heating tapes, they are probably the 480 degree type, which is quite adequate for organic chemistry work. I'm glad I could put you on to a less expensive source. It's probably the same situation with most lab equipment suppliers, they have an enormous mark-up which they can get away with because most of their customers are government funded in some way. When I was working in labs we built a lot of our own apparatus including weatherometers, environmental cabinets, and sundry test devices, which is where I developed the same scrounge and re-purpose attitude as yourself.

rsmith796 months ago
What is the controller used for if you are regulating the temperature with the SCR?
kymyst (author)  rsmith796 months ago
As stated in the introduction, the PID temperature controller is optional. The temperature can be regulated with the SCR if the user is present to monitor the operation and make adjustments as necessary. With the PID controller it can be set to the required temperature and it will be automatically maintained. This is useful if you need to carry out reflux operations overnight, etc, and also provides a safeguard against overheating. It is a convenience, not a necessity.
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