Electric heat regulation?

brain · Linguist Extraordinaire

Hawe somebody a shematic about electric hot plate regulator? regulation of temperature? [220-230 V] ? Smile

bio · Working Bee

There is a link in the other thread on heating bath method I posted look there.

http://www.littelfuse.com/cgi-bin/r.cgi/know_file_detail.html?LFSESSION=kwuoltYTqE&FilebaseID=901

Also many here.

http://www.discovercircuits.com/list.htm

Elementary · Wed May 11, 2005 4:34 pm

Some of the higher wattage lamp dimmers work fine as heat controllers

Just check that the rating of the dimmer is greater than the heating element

IndoleAmine · Dreamreader Deluxe

- Thats what I was thinking about too recently...

So lets say, a 230V~/50Hz dimmer rated at 400W would suffice for regulating a 250W heating mantle? Then put a bit cooking oil inside a RBF, place thermometer inside, and heat while regulating the power, taking notes on how much percent heating power cause which temp. after a reasonable time (20 minutes?), or how do you "calibrate" the controller?

Elementary · Mon May 16, 2005 7:50 pm

This circuit will control up to 750w at 230vac

http://www.geocities.com/tomzi.geo/dimmer/dimmer.htm

I know that maplin electronics (UK) sell a nice vellerman kit that allows DC control, this would give you the option of thermostatic control using a thermocouple and a simple op-amp circuit.

brain · Linguist Extraordinaire

thanks Elementary !! Very Happy

bio · Working Bee

............. put a bit cooking oil inside a RBF, place thermometer inside, and heat while regulating the power, taking notes on how much percent heating power cause which temp. after a reasonable time (20 minutes?), ......

This would work OK for the same size setup under similar ambient conditions.

.......... how do you "calibrate" the controller?..................

Take a look at the littel fuse link above. In that application note there is a chart giving percent power versus voltage for a full wave triac controlled circuit. Set the voltage with the dial to say every 10% power increment with a load connected. Mark the dial and now you have the percentage power delivered (watts) to any load within the rating of the device. It is NOT linear and the symetrical firing circuit is recommended using about 20% minimum power when choosing the resisitors (conduction angle). This way the adjustment is spread over about 3/4 of the dial. Cheap dimmers drop out at low load and if calibrating as described only about half of the dial range is usable but it does work adequately. For the same reason do not use a heater bigger than needed or controllability suffers. Manual control of the oil bath is within 1-2 degrees if done properly.

Guest · Tue Jun 14, 2005 2:26 pm

Just getting my head around this one, what would be the best type of heating wire to use for this, just plain simple nichrome wire, whose wattage is less than the specified wattage of the dimmer, is that right, or are we talking an actual hotplate element, with the correct wattage rating,?

Thanks Elementary, a very informative post.
After viewing Brainfert DIY mantle, this is a must do for anyone wanting build there own.
I am very humbled by the resources of our members, and the collective work done here.

Well Done

syn

bio · Working Bee

.....................just plain simple nichrome wire, whose wattage is less than the specified wattage of the dimmer, is that right, or are we talking an actual hotplate element, with the correct wattage rating,?.....................

Either one or any other resistance device (halogen lamp etc) within the wattage rating of the device.

I use an immersion heater 300w which will heat a 3L flask oil bath to 220 deg no problem and is also fine with a 250ml very small bath. Try doing that with a hotplate and see how much wattage it will take while mostly heating the room and you!

If you want to make your own coil from NiCr just remember to keep the wire temp design below around 450deg.

bio · Working Bee

............I know that maplin electronics (UK) sell a nice vellerman kit that allows DC control, this would give you the option of thermostatic control using a thermocouple and a simple op-amp circuit...........................

Elementaryl Triac drivers Motorola MOC series are 4pin $2 parts from Radio Shack etc. that allow you to drive the circuit you posted (triac phase controller). It replaces the diac BR100 and is an optical isolator 5KV. So all you have to do is drive the LED inside with any circuit you like and control AC directly. The 555 or 556 timer makes a good controller if you want to do PWM (pulse width modulation) or just use a thermostat of any design with a DC output for the LED.

This greatly simplifies the circuit by eliminating most of the parts otherwise required.
_________________

Guest · Wed Jun 15, 2005 1:30 pm

That's a great tip Bio,

A Immersion Heater, clever thinking, and simple, another great Idea.

How much did that cost you?

fogged · Thu Jun 16, 2005 3:56 am

Hey all... Now, these may seem like stupid questions to some of you, but it seems as if it could be important so I'll ask anyway! I've done electronics work before (including with mains supplied stuff) but it's always been from kits so I've never thought about any of this stuff in a practical sense.

For the circuit above, what are the specifics of the components? For example, what wattage of resistor should be used, the voltage of the capacitors, and anything else I've overlooked? Also, it seems that the triac listed (T0609MJ) is unavailable to me - could this be replaced with an alternative triac?

Likewise, for the circuit at http://www.geocities.com/brainfevert/heatstir.html, the same questions (except for the replacement - this triac is available!). Although I think 3000W is a little powerful for my taste in a heating mantle, so intend to scale it down to around 600W max (just to confirm, this simply means that i increase the resistance of the load, in this case the heating coil, correct? Perhaps even take advantage of this and add a fan in series to provide better cooling for the triac...)

Advice would be appreciated; I intend to build the mantle at the above page, see what I can do to improve the design, and I'll be more than happy to share the results - perhaps even come up with a useful PCB design, at which point it becomes neat and simple for anyone else who wants to try at it!

bio · Working Bee

..................For the circuit above, what are the specifics of the components?...............

Take a look at the link I posted in the other thread on a similar subject. It is a design manual for triac phase control. Resistors 1/2 watt, capacitors voltage rating should be well above the peak voltage of the source, the inductor is for RFI and may be omitted.

Choose a triac at least twice the RMS circuit voltage with load no more than 70% of the current rating. Sensitive gate devices require higher resistor ratings than standard triacs due to lower gate current (2ma versus 25ma).

...........I think 3000W is a little powerful for my taste in a heating mantle, so intend to scale it down to around 600W max ........

Yes, waay too much and would be very difficult to control. 600w is fine for up to about 3L unless doing high temp inorganic work. Check the ratings of commercial mantles as a guideline.

.............add a fan in series......................

Fan has to be paralleled and is not required normally. The heat sink only needs to be sized to the forward voltage of the device (about 2V) so not much wattage is dissipated. Phase control is a switching technique and doesn't "throttle" the power so the voltage across the device is relatively constant regardless of current.

Synthetika the setup was quite costly. $2.20 for the 300w aluminum clad coiled immersion heater , $4.50 for the 600W dimmer and $5.50 for the six pack of beer it took to plug it in! Get a triac ceiling fan controller as they have less hysteresis and a trim pot on the face. I modify my own el cheapos although they work OK right out of the box.