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Author: Subject: Use a dimmer to control heating mantle
shifty
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[*] posted on 18-3-2008 at 10:50
Use a dimmer to control heating mantle


Used heating mantles can be picked up for very cheap these days, so I've become interested in how to regulate the power for these in a cheap way. (Commercial regulators are ~US$140+)

Reading old posts, there are several mentions of using ordinary house hold dimmer switches for these, as long as their wattage is rated high enough and you adequately protect the connections from heat and condensation/spillover. Unfortunately, there are no diagrams or pictures to help the electronically-challenged.

Does anyone have any further advice you could give on how to build one? Is it really as simple as dropping an adequately-rated household dimmer switch inline between the wall outlet and the heating mantle? After sealing up the connections with hot glue and plenty of tape, you're done?

Regards,
S
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arevelacao
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[*] posted on 18-3-2008 at 11:08


An electric shower temperature controller (+6000W) it can be an excellent reference to you dimmer. Replace the Triac and the dissipation system. Search for projects and patents in the net.

[Edited on 18-3-2008 by arevelacao]
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Nicodem
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[*] posted on 18-3-2008 at 11:18


Quote:
Originally posted by shifty
Is it really as simple as dropping an adequately-rated household dimmer switch inline between the wall outlet and the heating mantle?

Yes. There is really nothing else to it other than you already mentioned.
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dann2
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[*] posted on 18-3-2008 at 14:29


Hello,

A variable voltage transformer (obviously!!). Not very cheap though.

Dann2
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bio2
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[*] posted on 19-3-2008 at 20:55


A ceiling fan controller is also a phase controlled triac same as an incandescent dimmer.

These can be used also and have the advantage that they are more stable at low
settings (no dropout) and have a minimum voltage (speed in the case of a fan)
potentiometer. This offers some range adjustment which allows better linearity
of the dial.

A cheapo dimmer will become unstable at less than 25% setting and the first 180 degrees of dial movement only changes the voltage a little.

[Edited on by bio2]
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chemrox
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[*] posted on 19-3-2008 at 23:17


I have a few variacs I'm selling for $50/ea. I understand "router controllers" from Harbor Freight work well .. or as well as can be expected.. they don't burn up or so I'm told.



"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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S.C. Wack
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[*] posted on 20-3-2008 at 01:23


For distillation, especially fractional, fine temperature control is desirable. This is more difficult with a dimmer.

Having a few homemade dimmer controls, mantles, and "real" controls, I'd suggest buying a Powerstat, Staco, Variac, or at least a solid state controller made for this sort of thing, instead of using a dimmer. Really. If you think that I'm wrong after comparing them, you can always sell it.

In the attached picture, we have a pair of such dimmers. The one on the left plugs into a wall socket directly, and is hanging by the wall plug for the one on the right, which has a cord for the wall outlet. In the backround is the crapsmanship wall of shame.

[Edited on 20-3-2008 by S.C. Wack]

crapsmanship.jpg - 25kB
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shadow
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[*] posted on 21-3-2008 at 23:03


Is a variac output AC or DC?


On another note, I went through the dimmer exercise last year when I wanted to reduce voltage to a metal grinder for more control, and the dimmer switch was perfect.
I think I'll hook it up to my hotplate.
In a perfect world, a temp sensing device (thermocouple)would relay the temperature of your distillate to your computer that would adjust the voltage going to your heating device.

[Edited on 21-3-2008 by shadow]

[Edited on 21-3-2008 by shadow]
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bio2
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[*] posted on 22-3-2008 at 12:12


@ S.C. Wack

Some time ago I posted a circuit that linearizes and
provides full wave symmetrical control for a domestic
grade dimmer. It's in one of the older "dimmer" threads.

This gives fine control, no dropout and a linear dial setting which is easily calibrated in watts ( RMS power).

Quite simple as only 4 diodes and 2 resistors need to be
added and is the same concept used on the commercial
triac type mantle controllers.

For even finer control the control pot range is easily changed by paralleling the appropriate resistor. This will
allow manual setting to 1-2 volts.

For the ultimate fine control from 0-100% a multi-turn pot could be used but hardly necessary IMHO. About 30V RMS
is already only a couple percent power in a phase controlled circuit.

A snubber circuit could also be added but is hardly needed with a resistive load and the modern triacs have built
in snubbing suitable for even inductive loads.

........I understand "router controllers" from Harbor Freight work well .. or as well as can be expected.. .......

WTF is that? Routers draw a very small DC current.
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Magpie
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[*] posted on 22-3-2008 at 14:48


For the best control of AC power for resistive heating I would think an "autotransformer" type controller would be the ultimate as it just changes the output voltage without changing the waveform (sine wave). I have a 360w autotransformer for my smaller mantles and a Staco autotransformer good for up to 1000w. Variac is also a well-known brand for these autotransformers.

Next best would be a solid state dimmer using triac thyristor circuitry. This just chops out part of each sine wave. So this chopping is happening evenly 120 times a second (@ 60 Hz) and thereby should provide a very smooth application of power. A 2000w dimmer is what I built for my upcoming tube furnace.

The worst would be an "on-off" delivery of full power, usually regulated by a thermostat. I have one of these, regulated by a thermocouple/PID controller, but don't use it much.

[Edited on 22-3-2008 by Magpie]
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bio2
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[*] posted on 23-3-2008 at 10:40


The wave form really doesn't matter for accurate resistive power control just the "chopped" wave can produce some annoying buzzing in the heating element especially at low settings. RFI is also produced but many dimmers have a ferrite toroidal or rod inductor to filter this out.

The full wave symmetrical phase control circuit I posted in the other thread resets the circuit at every zero crossing so largely eliminates the "noise" and gives a repeatable wave form not subject to the normal random turn on.

A half wave symmetrical (2 diodes) circuit is adequate for resistive control but the
full wave version operates "smoother" and "quieter".

Variacs are very nice to use just they cost an arm and a leg for a new one.
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YT2095
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[*] posted on 3-4-2008 at 07:34


have a look at this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&i...

it May be of some use to one of you guys here?




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