# Hot plate circuit

I want to teach myself how to build a DC temperature controlled circuit, and use a thermo-probe for a closed-loop feedback to dial-in a specific temperature.

For the hot plate, I have the bottom surface of a coffee machine. A metal top, on the bottom looks like ceramic coated, with two leads sticking out where the A/C wires used to go.

I am measuring 9 ohms of resistance between the two leads.

I know how to drive mosfet with a PWM signal. I was going to hook that up to the coffee-plate. Since it's pretty much a short circuit, I suspect that's probably not a good idea. What circuit or device should I use to connect from my pulse signal to drive a 12-volt DC power into this hot-plate?

12volt/9ohm=1.33Amp

Not a problem for a logic level power mosfet. leo..

Wawa:
12volt/9ohm=1.33Amp

Not a problem for a logic level power mosfet.
leo…

What temperature do you wish to achieve ?

Probably 150 (C), possibly up to 200 (C) I hope. At 300, I think my solder joints would melt.

Coffee maker hotplates are generally designed to operate at 110 or 240 V ac.

12V at 9 ohms has no chance of achieving that sort of temperature. Do you mean the drive requirement for an SCR. ?or similar.

DocStein99: Probably 150 (C), possibly up to 200 (C) I hope. At 300, I think my solder joints would melt.

Weeeeeell https://youtu.be/hPwc2fDhuM4?t=3m31s

Boardburner2: Coffee maker hotplates are generally designed to operate at 110 or 240 V ac.

12V at 9 ohms has no chance of achieving that sort of temperature. Do you mean the drive requirement for an SCR. ?or similar.

I didn't know what an SCR was, until I looked it up just now. I wasn't planning to use A/C current if that's possible. I don't need to use this coffee plate, it's just some trash I had around that I could use without buying something specific.

Set your temperature goal a bit lower. If powered by 12V, the hot plate should make a fine hand warmer.

Hi, Is there a nameplate on this device? Voltage/Current?

Did this plate boil water in some container??

HI,

jremmington was correct. At full power, your would generate ~16 watts (E^2/R = 144/9 = 16 watts)

Think of an incandescent 15w bulb. That about the heat would will be able to generate at full power.

JR

Ok well, I guess it’s probably not going to get too hot. I just want to test and start with something, but I was uncertain about run power through the mosfet to it. I realize now, it’s about the same thing as an incandescent bulb so it’s enough to get me started.

I also have this nichrome wire, someone asked me to build them a foam cutting tool - I will test out on that too.

You'll want to measure (hopefully) temperatures above 200F.

Take a look HERE about using Thermocouples with Arduino to measure temperatures up to 1500F or so.

With some thermocouple wire, you can make your own Thermocouples. See How Here

Nichrome wire works beautifully on expanded polystyrene foam...

And you can make your own thermocouples - but it takes oxy-acetylene to do the job.

Allan

it takes oxy-acetylene to do the job.

..or a 12V Car Battery

There's a whole bunch of things, like making a bag-sealer for my foods to freeze in. A heated jig for bending thin plastics to make an enclosure box. Maybe a molded concrete/rubber top for the steps and walkway for the front of my house, so I can hit a switch then smile while I watch the snow melt away as I enjoy hot coffee while watching the neighbor's do back-breaking snow shoveling on their walkways.

From what I learned about the termocouple's, is two different material metal wires, welded at the point - as shown in the picture "terryking228" post. That is definitely interesting. These pre-made temperature probes seem to be cheap enough for me to buy a few to try them.

terryking228: ..or a 12V Car Battery

Have you actually managed to get that to work ? I have tried numerous times without success.

terryking228: ..or a 12V Car Battery

There are video's where people just use car batteries attached to jumper cables and a stick welder, to do dirty quick farm equipment repairs. I see video's some people tie the batteries into IRF3205 mosfets, to do small pulse welding.

Boardburner2: http://www.ebay.co.uk/itm/152445814581 Have you actually managed to get that to work ? I have tried numerous times without success.

This is an air solenoid. Not sure what it has to do with a hot-plate circuit on this thread. Ironically, I actually have got this air solenoid to work. I have 8 of them into a manifold, driven my tip 120's to trigger musical sequenced air horns. It's definitely one of the must fun projects I've done, that everyone loves. Unfortunately, I do not live on a farm, where I can test 90+ decibals of horns for hours without driving the people around me mad crazy. I don't know what to do with the project, since I have to tune the horns for frequencies.

I edited the post. Copy paste error./ Crosspost.