kenofken
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Heating mantle question
Since I've done most of my work with flat-bottomed gear, I've always worked with hot plates, but on a lark I decided to buy a heating mantle. Found
myself a glascol TM570 on Ebay. I took at look at the company literature, and I was dismayed to learn that, apparently, one needs some sort of
additional control unit and thermocoupler or something? Does anyone know about this and any low-cost workarounds or used gear? I really don't want to
plow another $300 into this to complete the setup.
I'm mostly a biologist, but I've sort of fallen in love with organic synthesis through some very hard-won knowledge over a couple courses, and I
wanted to move up from that dinky micro-gear they use to a proper 24/40 setup. This mantle fits a 500 ml round bottom I believe. I was naive enough to
figure it was self-contained like a hot plate stirrer, with maybe a rheostat for heat control and then you'd monitor it by thermometer.
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bob800
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To properly control your mantle, you need to buy a variac transformer. These are usually expensive when new, so not exactly a low-cost workaround.
A cheaper route would be to use an ordinary lamp dimmer. You won't have much control over temperature, but it's much cheaper. Here another thread on this.
Quote: Originally posted by kenofken  | | I was naive enough to figure it was self-contained like a hot plate stirrer, with maybe a rheostat for heat control and then you'd monitor it by
thermometer. |
Some mantles do have a built in rheostat, but are quite expensive. You could buy a cheap $40 chinese version, though I don't know how long it would last. I have seen videos with these mantles being used, and they seem to work.
You could also use an air bath, oil bath, water bath, or sand bath on an ordinary hotplate to heat round bottom flasks. There are many threads on
this, so check the search function!
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chemrox
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I have five variacs for sale: $75 + shipping
They are the familiar American ones that last forever
[Edited on 2-4-2011 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Contrabasso
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A lamp dimmer capable of driving 300+watts will suit your needs for manual temperature control. For auto control you will need something better, and
could use a thermocouple probe into the liquid or vapour according to the reaction needs.
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food
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| Quote: Originally posted by bob800 | To properly control your mantle, you need to buy a variac transformer. These are usually expensive when new, so not exactly a low-cost workaround.
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fwiw I've had a Chinese variac now for about fifteen years or so with no complaints. It's not an item that I have in constant use, but as I say it's
been problem free.
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kenofken
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What does anyone think of this as an alternative? It's a router controller. Somebody in an older thread mentioned it, and it looks like it might be
less dodgy than a homemade setup with a light dimmer (of course looks can be deceiving)!
http://www.harborfreight.com/router-speed-control-43060.html
On this note, how does one determine the required amp rating for a variac relative to the mantle you're using? Most variacs I've seen seem to be 10
amp rated, some 5 and some 15. Apparenlty my mantle, which I haven't received yet, is rated at 270 watts, which seems like I could get away with a
relatively low amp device.
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peach
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Power = Current x Voltage
Or, "Power equals ivy watts" as we were taught to remember it. 
Assuming you're in the US, or one of the other 110V countries, that's;
270 = Current x 110
Which, rearranged, is;
270 / 110 = Current
= 2.45 amps
And about half that if you're in a 230V country. That formula doesn't hold true for a lot of AC electronics, but a purely resistive element doesn't
have a lot of inductance or capacitance to skew it. Once you add either of those, it gets more complicated and not only does the formula not work so
easily, the dimmer may not like it either.
You don't need to worry about the currents if it says the power rating somewhere on the pack. A lot of the dimmers I've seen are rated to 250W because
the most they have on the front is two dials, for controlling two bulbs. When 100W bulbs were still being produced, that'd be 200W with 50W spare.
100W incandescents are now out of production in Europe.
One neat possible option with the dimmer would be to unsolder the variable resistor and replace it with a thermistor or thermocouple so the dimmer
adjusts it's power output based on temperature as opposed to dial position alone; closed loop feedback.
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mr.crow
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I use a 600W wall dimmer for a 2L mantle. The 2L mantle kicks ass. Its a purely resistive load so it should be OK. Just mount it in an electrical box
with a receptacle.
If you want to take apart the dimmer you can put a heat-sink on the triac. The tab will be connected directly to line voltage so watch out.
Double, double toil and trouble; Fire burn, and caldron bubble
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Lambda-Eyde
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Somewhat related: What would happen if I were to use a 110 V heating mantle with 230 voltage and a compatible dimmer? I don't see what could go wrong
since it is, as you said, a purely resistive load?
This just in: 95,5 % of the world population lives outside the USA
You should really listen to ABBAPlease drop by our IRC channel: #sciencemadness @ irc.efnet.org
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mr.crow
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Well as long as you keep the power level at 50% or below. The problem is the dial on the dimmer isn't really quantitative, it might not even be
linear.
A really dumb way to do it would be to use a high current diode to cut off half the AC wave.
Double, double toil and trouble; Fire burn, and caldron bubble
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