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Switching high amperage heating elements
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| endlesscycles |
Posted on 07/28/2010 10:29
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1/2 Pounder
Posts: 239
Joined: 11.04.09
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I'm trying to figure out how to attenuate a high amperage heating element. Router speed controllers work fine for ten or fewer amps, but I'm interested in twenty to a hundred amps, 240 volts. I'm imagining a dial adjustment knob that controls a SSR. I've read very little about infinite heat adjusters, but suspect they are limited adjustment. Any ideas what device exists to fit my needs?
-Marshall Hance
Asheville, NC |
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| endlesscycles |
Posted on 07/28/2010 11:02
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1/2 Pounder
Posts: 239
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Found this http://www.patioc...ntrol.html
Still interested on other options.
-Marshall Hance
Asheville, NC |
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| milowebailey |
Posted on 07/28/2010 11:55
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1/2 Pounder
Posts: 113
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100 amps 240 volt is no amateur device....
You can use a Triac for up to 25 amps, but 100 amps.... frightens me just to think about that. |
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| endlesscycles |
Posted on 07/28/2010 12:05
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1/2 Pounder
Posts: 239
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I'll be recruiting a pro to wire it right. Looking forward to switching to electric.
-Marshall Hance
Asheville, NC |
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| Dan |
Posted on 07/28/2010 12:41
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1 1/2 Pounder
Posts: 979
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I'd like to know, too. I have 4 15kw ovens at work and they need 40 amp, 4-pole relays to control the heaters. I found some high amp 3-pole SSR, but nothing big enough.
One way to control electric heaters is to use a percentage timer running a relay or SSR. The timer turns on the heat for a certain percentage of time (0-100% via a pot). If the timer cycle is 10s or less, the result is continuous heater control. |
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| bvwelch |
Posted on 07/28/2010 15:12
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1 1/2 Pounder
Posts: 892
Joined: 27.12.07
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This is scary stuff - I doubt if I would try to build such a beast myself - PCB layout, big/fat traces, heat-sinking, opto-isolation, all of these will be important.
Philips/nxp makes the BTA140 series for up to 25 amps. Note that the 'tab' is HOT, so you must insulate it from the heat-sink. These can be driven with a MOC3041 opto-isolator.
This is about the limit that I've seen. The controller could be as simple as a 555 or as fancy as an Arduino.
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| bvwelch |
Posted on 07/28/2010 15:37
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1 1/2 Pounder
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Just a thought - any chance you could use multiple 20/25 amp heater elements? |
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| allenb |
Posted on 07/28/2010 15:45
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Administrator
Posts: 293
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I would suggest the Watlow Din-a-mite series SCR which uses phase angle or burst fire which is less prone to surging the rest of your power grid. They'll do up to 100 amps.
http://www.watlow...cr0805.pdf
The Dinamite can be configured for a 4-20 milliamp input and there are plans out there showing how to make your own 4-20 current source with a 12vdc wall wart, a couple of resistors and simple rotary potentiometer.
This is not the cheapest way to go but is probably one of the simplest and safest.
Allen
Edited by allenb on 07/28/2010 15:52
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana |
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| endlesscycles |
Posted on 07/28/2010 17:19
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1/2 Pounder
Posts: 239
Joined: 11.04.09
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This percentage timer thing sounds exactly what I need. Amps should be managed by the ssr, ideally.
-Marshall Hance
Asheville, NC |
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| endlesscycles |
Posted on 07/28/2010 21:34
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Posts: 239
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How do adjustment dials on electric stove tops work? Those eight inch coils draw some power!
-Marshall Hance
Asheville, NC |
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| endlesscycles |
Posted on 07/28/2010 21:43
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bvwelch wrote:
Just a thought - any chance you could use multiple 20/25 amp heater elements?
That's not a bad thought. I like the simplicity of one heat element, but several switched and one controlled might be just fine.
-Marshall Hance
Asheville, NC |
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| seedlings |
Posted on 07/29/2010 07:24
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Super Admin
Posts: 3056
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The dial adjustment knob can be an easy timer circuit - even salvage the circuitry from your speed control. You can find high amperage SSRs, but the key will be keeping that baby COOL to get optimum performance.
Could you trigger 2 50A SSRs, one on each leg of the 220?
CHAD
"You know, I think that horse is getting deader." |
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| endlesscycles |
Posted on 07/29/2010 08:22
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seedlings wrote:
The dial adjustment knob can be an easy timer circuit - even salvage the circuitry from your speed control. You can find high amperage SSRs, but the key will be keeping that baby COOL to get optimum performance.
Could you trigger 2 50A SSRs, one on each leg of the 220?
CHAD
I like the idea of multiple circuits with just one attenuated circuit. Two or three total would do the trick.
How does the speed controller work? How would it be able to act as a timer / SSR controller?
I plan to keep things cool by placing all circuits in the air inlet before the heaters. That will be effectively overkill.
-Marshall Hance
Asheville, NC |
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| qajariaq |
Posted on 07/29/2010 09:48
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Posts: 135
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Household electric ranges usually have adjustment via an infinite switch:
http://en.wikipedia.org/wiki/Infinite_switch
The highest wattage range element that I can find (with a quick search) is 2100W, so at 240V that's only 8.75 amps...
endlesscycles wrote:
How do adjustment dials on electric stove tops work? Those eight inch coils draw some power! |
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| seedlings |
Posted on 07/29/2010 10:08
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Super Admin
Posts: 3056
Joined: 27.06.07
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The voltage output that controls the triac should be able to trigger an SSR. Don't quote me on that, but it should work. Pull up the datasheet for whatever triac chip is in your speed control, and see what power it requires for on-off. SSR, I think, only needs 5V.
You can also make a timer circuit yourself, Bill has a post around here with a DIY SSR...
Warning Use At Your Own Risk
Warning Use At Your Own Risk
Substitute a SSR for the triac.
CHAD
"You know, I think that horse is getting deader." |
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| scarter11 |
Posted on 07/29/2010 10:44
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Posts: 27
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Sorry for the stupid question, but what is an SSR?
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| Dan |
Posted on 07/29/2010 10:46
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1 1/2 Pounder
Posts: 979
Joined: 24.10.05
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Here's the percentage timer I use in my sample roaster. The timer and SSR are combined. This is their 120V-15A unit with 5 second cycle time. The wiring schematic is printed on the top of the unit! In operation, the potentiometer knob works just like the knob on a gas range.
http://precisiont...|1004|1058
SSR = Solid State Relay
Edited by Dan on 07/29/2010 10:46 |
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| bvwelch |
Posted on 07/29/2010 13:43
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1 1/2 Pounder
Posts: 892
Joined: 27.12.07
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If you've got enough room in the budget, those ready-made solutions like Dan and Allen suggested sure look a whole lot simpler and safer to me.
SSR generally refers to a ready-made unit. Inside the unit, you'll find a circuit similar to the one shown above - it might be using a Triac, a SCR (silicon-controlled-rectifier), or other similar 'solid-state' device. The idea is that it doesn't have a mechanical relay.
Dan's version includes something like the '555 timer chip inside as well.
-bill
Edited by bvwelch on 07/29/2010 13:48 |
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| endlesscycles |
Posted on 07/29/2010 17:11
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Posts: 239
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I'm more interested in the getting the project done than learning along the way! However, I'm happy to realize that I don't need or even want to attenuate the entire amperage, as I never cut power by half when roasting; greater control in the adjusted range is far better. I'll probably do the same with the blowers. One VC is on/off, the other gets the router speed controller. That combo gives full controlled range from 0-100%, anyways!
Thanks as always, y'all!
-Marshall Hance
Asheville, NC |
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| allenb |
Posted on 07/29/2010 19:02
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Posts: 293
Joined: 23.02.10
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While I'm no expert with these devices, I'll try to provide some clarity.
An SSR (solid state relay) which a lot of us use with our PID controllers instead of a mechanical relay typically takes a 3 to 32 volt dc input from the PID controller to latch it in the on state. If the settings on your controller is a one second time base the SSR will be on for a certain portion of the one second interval then off during the remaining portion. While the SSR is latched, it is conducting AC current. The SSR is just an electronic version of a mechanical relay with no other bells/whistles.
SCR's (silicone controlled rectifier) conduct DC current but when companies utilize them in multiples along with phase angle firing electronics, you get AC in either a full sine wave (full power) or a proportionally chopped waveform for power levels lower than 100%.
With these "packaged" SCR power controllers, all you have to supply is either a 0-10 volt or 4-20 milliamp variable input to the unit either from a simple home built variable output rig with rotary dial or from your PID temperature controller.
Something to consider when heating an air stream with resistive wire heaters is anything more than a 1 second time base causes too much of a swing in temperature (for me at least). With non-moving air, much longer time bases work fine.
For a roaster drawing 100 amps of current you could and probably should (as mentioned in a previous post) use multiple heating elements with a couple of SSR's being controlled by a single controller. If your minimum power level is 50% then you can manually switch half the load and control the other half via SSR with either PID controller or manually with a proportional-duty cycle input with rotary dial similar to the one Dan is using. After looking at the high prices of the SCR power controllers it makes more sense to go with SSR's and break up the elements.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana |
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thanks for your patience and support!
