Sciencemadness Discussion Board - Heating Mantle Controllers

Heating Mantle Controllers

Dr.Bob - 4-2-2012 at 19:50

As I mentioned elsewhere, it is critical to use a power controller of some sort with a heating mantle (or an oil bath or similar items as well). Using one of these without a controller is like only having a stove burner that only does HIGH heat. If you put a small pan on it, with very little in it, it will overheat. Since heating mantles are designed to be able to handle any task, they can put out far more heat than needed for most lab tasks.

For instance, heating water to boiling takes an enormous amount of heat, but warming ethyl ether to a gentle reflux may take only 10% of the heat for boiling water. So if you plus a mantle directly into a 110 outlet with ether in a flask on it, it will shortly get red hot, most likely set the ether on fire, (I've seen it happen) and the mantle will overheat and melt the insulation, and potentially destroy the mantle.

I have seen someone (with a PdD, yet) boil a flask dry and melt the flask into the mantle because they plugged the mantle directly into 110 and went home for the night. It was only luck that it didn't start a fire, no ether in or near the red hot mass.

So what makes a heating mantle power controller? One type is a variable transformer (Variacs, powerstats, etc) which allow you to control the voltage to the mantle. which will regulate the amperage by lowering the voltage. This allows you to run the mantle at say 30 Volts for ether and 80 for ethanol distillation. When you start, the variac might be put to 50 (for example) and then adjusted higher or lower depending on the temperature change. Once the solvent is boiling, the voltage can usually be lower.ed. But Variacs are heavy, expensive, and tend to fail (corrode) if exposed to acids. They also require manual adjustment in most cases.

The other solution is a (switching) power controller, which turns the power on and then off for short times (at a very fast rate), such as to create a lower average power use, The example of this would be a light dimmer switch or most stoves. Some use a thermostat and self-regulate, most simple systems just allow the user to pick a power percentage (0-100%) like a light dimmer. Glas-col sells a simple power controller for about $100 that is essentially a very nice light dimmer switch.

Fancy controllers may use combinations of voltage and power controller, or even allow the use of a thermocouple to auto adjust the power, but these tend to be very expensive if for science equipment. My favorite example is JKem Scientific, who makes some great controllers, but they cost about $800+

One example of a simple heating mantle controller is a simple light dimmer switch, hooked in series with the mantle via a cord and electric box. Designs for this are available on the web, one example is listed below- but I don't have access to it.
http://adsabs.harvard.edu/abs/1995JChEd..72..733P

I am hopeful that someone who has built one would post there design and some photos. It should be possible to build a simple one for $10. As well, I was told that a simple plug in light dimmer worked OK, as well. Please give your findings, product suggestions, and comments here.

Bob

[Edited on 5-2-2012 by Dr.Bob]

smaerd - 4-2-2012 at 21:40

Is this the paper you were looking for? I have a little dimmer-switch version by glas-col but as you said they corrode over time. I'd also be interested in seeing someone else document a build for the future.

Sorry to not have much to else add.

An inexpensive alternative to commercial variable transformers
J Chem education
Craig A. Ogle
(lost the DOI/etc sorry)

Attachment: An Alternative to Variable Transformers.pdf (496kB)
This file has been downloaded 1093 times

Arthur Dent - 5-2-2012 at 05:52

I am hoping to acquire in a short while a heating mantle for my 250 ml RBFs. The two inexpensive alternatives to control the unit are either a plain light dimmer controller (heavy duty 1KW or 2KW) or my antique "variac" which I would describe more as a multi-tap transformer with a selector switch that goes from 65 to 140v.

The dimmer controller way is elegant, compact, and would involve minimal expenses... the "variac" way would be free but this ol' thing is bulky and heavy as hell, and has a limited selection of settings, some of which (above input voltage) would make the whole thing dangerous.

So I think I'll go with heavy duty dimmers made by Leviton since they have a capacity of 600 to 1500 watt, which should be more than enough to control a small mantle such as the one I am seeking. The fun part will be to "build" some sort of enclosure to put the mantle and the dimmer together.

Robert

watson.fawkes - 5-2-2012 at 08:32

Quote: Originally posted by Dr.Bob

I am hopeful that someone who has built one would post there design and some photos. It should be possible to build a simple one for $10. As well, I was told that a simple plug in light dimmer worked OK, as well.

Someone has recently done this, in another thread on furnace construction; there are a few photos. The modification was to an off-the-shelf dimmer control for better heat dissipation; there were no changes to the circuit. The triac inside the dimmer was in a package that allowed easy remounting on a heat sink system originally for a CPU. Because dimmers are mounted in wall, where there's no good method for heat rejection, it's necessary to derate the triac for a higher operating temperature. So the triac device in this dimmer was rated for 25A, even though at 1000W service it would only ever draw maybe 10A. Getting the triac out of the original enclosure and into one where it can get adequate cooling allows the device to live up to its full potential. It's a good and practical modification.

If packaging one of these up for lab use, use a vented metal enclosure for mechanical robustness. Also, it would be good to have an ammeter for knowing the actual current flow, rather than relying on just the slider position. Analog panel meters are only around $10. All this increases the cost, of course, but the total should still be less than $50, perhaps a little more if you really don't have an old heat sink lying around.

entropy51 - 5-2-2012 at 09:20

Quote: Originally posted by Dr.Bob

The controller I built was simplicity itself. The dimmer was just off the shelf at the hardware store, it was intended to be mounted in a wall junction box like a switch and is rated at 600 watts. I mounted it in a little aluminum chasis box from Radio Shack. One line of a heavy duty extension cord was cut and wired to the two dimmer terminals. The other line of the extension cord was left intact so that the dimmer is in series with whatever load is plugged into it.

I haven't used it in a while because I discovered that Variacs could be picked up cheap at hamfests and they give somewhat finer control than the light dimmer I have. But it does work for controlling a mantle.

Funkerman23 - 5-2-2012 at 11:50

as a Antique electronics restorer myself Variacs can definitely be bought cheaper at hamfests as well as Electronics surplus stores and from certain sites that cater to the Tube electronics community. the cheapest I know of , aside from some Chinese variacs( which work well but beware of cheap cases and iffy sockets..I usually just wire in new ones ) are the case-less coil assemblies. IF you make your own cases you must fuse the output side of it( the part you plug the mantle into). Fuses: fast blow is better but ordinary ones work as well. Do not use slow-blow types as this means it will take longer to shut off. The important thing here being you would want the fuse to blow if the current exceeds what it would be operating at the mantles intended maximum temperature. for this group I'd recommend looking up Surplus Sales of Nebraska on Google if you feel up to wiring your own.. U2U me, or reply here, if anyone here would like a schematic or plans on building their own variac box.

Quote: Originally posted by entropy51

Quote: Originally posted by Dr.Bob

[Edited on 6-2-2012 by Funkerman23]

Dr.Bob - 5-2-2012 at 14:18

Someone asked me about heating mantles verses oil baths, so I am including part of the note I sent them. I hope this is useful.

As for heating mantles, they have good and bad points. They are much neater than oil baths, don't spill or catch fire (it is quite hard to set an oil bath on fire, but can be done, just look at people deep frying turkeys...), and they are efficient for larger flasks. For smaller ones, they are not as big an advantage. Mostly they are much neater in a hood than oil baths, as oil spills easily from them, especially when you have several in a hood. They are easy to regulate with a variac or power and/or temp controller.

Oil baths are cheaper, and easy to use with a variety of temperature regulation and heat sources, whether manual or automatic. Did I mention that they are less expensive, in most cases.

A smaller flask can be used in a larger mantle, and sometimes, with the fabric mantles, a larger flask can be used in a smaller mantle. The 1000 and 500 ml mantles tend to be flat enough that a one size larger flasks can be used in them. If you want to use a much smaller flask in a larger mantle, you can create a sand bath in it, and just put the flask in the sand. We use that to heat vials and tubes in mantles often. DON'T try to use anything but sand, and you CAN use a piece of heavy alumnium foil to keep the sand from touching the mantle, if you keep the temperatures down. Oil will not work! (No, I haven't heard of anyone trying this, but I have seen people try to use other materials instead of sand). Many salts melt at low temperatures...

So whatever you can make work is fine. I have used oil baths on a hot plate, but you will need to watch them carefully, and not go too high on the heat. They are slow to reach a consistent temperature. Sand is even slower to reach equilibrium. But it works well if you are careful.

So oil baths are practical in colleges and low budget labs, mantles are neater but more expensive, used mostly in industrial labs.

entropy51 - 5-2-2012 at 14:57

Quote: Originally posted by Dr.Bob

DON'T try to use anything but sand, and you CAN use a piece of heavy alumnium foil to keep the sand from touching the mantle, if you keep the temperatures down. Oil will not work! (No, I haven't heard of anyone trying this, but I have seen people try to use other materials instead of sand). Many salts melt at low temperatures...

Oil and salts are not good, but some people use small copper shot, which seems quite reasonable since the thermal conductivity of copper is much better than that of sand.

I find it useful to have a thermometer in the sand.

I line my mantles with aluminum foil when I use them for sand baths and it seems to work well, but I usually stay below about 150 C.

Dr.Bob - 8-1-2018 at 08:33

Bump. I'm trying to keep this visible, as people have posted a number of questions regarding heating mantles and this helps describe the issues of needing some sort of controller. I will try to consolidate the previous posts here soon to help with that.

JJay - 8-1-2018 at 08:36

Quote: Originally posted by Dr.Bob

Bump. I'm trying to keep this visible, as people have posted a number of questions regarding heating mantles and this helps describe the issues of needing some sort of controller. I will try to consolidate the previous posts here soon to help with that.

My first post: https://www.sciencemadness.org/whisper/viewthread.php?tid=63...

I still use this device as a heating mantle controller.

Gurt - 8-1-2018 at 09:11

An AC fan motor speed control works well, just wire it into a box, and have the controlled wire feed an outlet in a separate box. Dimmer switches are ok, but I feel they don't have the best precision for low heat. With a dimmer there is often a point where you lose low temp control, being left with just "on" or "off." One other advantage to fan controllers in my mind, is that they can handle a higher wattage (usually) and some can even be fused.

highpower48 - 8-1-2018 at 09:13

EBay sellers have a
2000W AC Motor Speed Control Controller Adjustable Voltage Regulator 50-220V which works great for a heating mantle controller oust of the ones I have bought is $1.52. These are a simple pmw controller, have not mentioned any dealers by name but a simple search will yield a dozen or more.

Specifications:

This controller uses novel bi-directional high-power SCR. It can be very convenient adjust the current up to 25A, and solve the over current problem of the heating wire resistance is too small in the case of cooling causing good.
The output voltage is adjusted anywhere between 50V-220V for use with electrical appliances. It can use to such as electric stove, water heater tune thermal, lighting dimmer, small motor speed, electric iron thermostat, and achieve dimming, thermostats, pressure regulator effect.

100% brand new and high quality.
Input supply voltage: 110V ~ 250V AC
The output voltage:50V-250V(Output voltage <= Input supply voltage)
The maximum output power: 2000W
The maximum output current :25A
The voltage regulating range:50V-250V AC(Output voltage <= Input supply voltage)

semiconductive - 22-1-2018 at 18:09

Quote: Originally posted by Dr.Bob

The other solution is a (switching) power controller, which turns the power on and then off for short times (at a very fast rate), such as to create a lower average power use, The example of this would be a light dimmer switch or most stoves. Some use a thermostat and self-regulate, most simple systems just allow the user to pick a power percentage (0-100%) like a light dimmer. Glas-col sells a simple power controller for about $100 that is essentially a very nice light dimmer switch.

Fancy controllers may use combinations of voltage and power controller, or even allow the use of a thermocouple to auto adjust the power, but these tend to be very expensive if for science equipment. My favorite example is JKem Scientific, who makes some great controllers, but they cost about $800+

I have a design for a kiln controller that is capable of 1 to 1150C temperature regulation, without a probe; but it does depend on the heating element material. eg: It's designed for Kanthal only. (With silicon carbide, tungsten, or other heating materials it could go to 2500C or more.) By measuring power absorption and heating element changes, it can crudely determine if the element is getting hotter or cooler to better than 1%. It's more precise than a simple voltage controller which simply gives a user 0 to 100% of line voltage; You may not realize it, but line voltages often vary by a few percent throughout the day. Since power goes as voltage squared over resistance ... that can lead to significant temperature changes at a fixed voltage on to off time as both the line voltage and the heating element change with time and temperature.

$800 is a high price for an amateur controller...!

But the low cost controller I designed is not a simple amateur project to build. (I'm a BSEE, so electronics is my life.)
The current embodiment is not ready for production runs, as I'm still doing experiments on replacing Kanthal heating elements with graphite/silica electrodes and replacing expensive refractory bricks in commercial kilns that I have with gypsum-hybrid cements; but within two years, I will have a fully production ready controller. I'm curious as to amateur needs:

Right now, I have a green four digit LED display which will show 0.1 Celsius precision up to 999.9C or 1Celsius for 1000C and above. It also lets the user program time, heating ramp profiles degrees/minute, idle time and shutoff. It's more intelligent than a microwave controller.

It's purpose was for firing ceramics in a kiln with a thermal profile and crude heating element regulation (better than 1% of full temperature range) ... but it would be trivial to modify it for use as a magnetic stirrer or heating mantle controller. It's like a dual loop controller, which regulates power delivered to the heating element real time to crudely set the element temperature, and allowing fine control from a thermal probe. In that way, it can prevent accidents when the probe is set on the table or falls out of the solution bath; because the temperature may not be precise ... but it will still maintain the bottom of the flask within 10Celsius or so.

I expect that the controller cost would be less than $100 including a thermocouple jack.
I have already planned on adding it to my chineese 85-2 magnetic stirrer to replace the controller ... but I need to find or make a better hot plate (110V rated) before I bother. That's a summer project for 2018.

[Edited on 23-1-2018 by semiconductive]

A (somewhat) related lab heating material find...

Bert - 22-1-2018 at 21:24

Re: oil baths/sand baths/other solid heat transfer media...

I have found a source for (relatively) cheap Aluminum pellets for a "shot bath". On eBay, $50.00 delivered for 10 lb. of approximately 1/8" pellets. This has an apparent volume of around a gallon. A commercial, chemistry supply oriented source of such media wanted $60.00/1000ml plus shipping for similar material.

https://m.ebay.com/itm/Recycled-Aluminum-Pellets-Hobbyist-Je...

https://www.amazon.com/gp/aw/d/B074HDZMQS/ref=mp_s_a_1_1?ie=...

These little discs are the hydraulic press hole punch waste from a factory building wheel chair ramps and related equipment. I took around 6 lb. of the as delivered material and ran it in a half filled ball mill (rock polisher!) for 12 hours with water and a few ml of a neutral cleaner concentrate which I normally use in the same equipment with stainless steel pellets to clean reloading brass. This nicely removed the sharp edges from the pellets and cleaned off the light coating of cutting oil used to keep the punch press dies working well, which would have burned off in use with some nasty smells.

I am going to try this stuff out for a few operations sometimes conducted with an oil or sand bath, such as nitric acid synthesis from sulfuric acid and a nitrate salt.

Sidmadra - 23-1-2018 at 17:21

For controlling heating mantles I've always used this Variac controller that I bought for $20 at a hydroponics store many years ago. It's never failed me. I'm sure these controllers can be gotten very cheaply on amazon these days.

JJay - 23-1-2018 at 17:44

I just got a 2000 watt oven dimmer that I'm going to use for fine tuning with my PID controller. I'm going to destroy at least one and probably two extension cords in the process.

happyfooddance - 23-1-2018 at 17:53

https://m.harborfreight.com/router-speed-control-43060.html?...

Up to 15 amps for $20, not bad if it works

PirateDocBrown - 25-1-2018 at 16:28

Just happens I found this bad boy at University surplus today, for $36. 1kW, tests OK, just needs some cleaning up.