Sciencemadness Discussion Board

PID Controlled Cheap 'Homemade' Hotplate

BobD1001 - 12-4-2013 at 09:59

I recently inherited a very old ceramic resistance type hot plate. Its a very good condition functioning unit, and I would like to put it to use, but unfortunately, the controls consist of the wide temperature range of ON and OFF as seen below:

So I began thinking about mounting a relatively thick Aluminum plate onto the existing surface with a thermocouple drilled deep into the side of it to get a relatively accurate reading and controlling it using a PID and Solid State Relay for the switching. Here's a link to what I'm thinking of using:

I have a full machine shop, so making/drilling the aluminum plate is no concern. I just wanted to see if anyone could find a flaw in my idea before I ordered the PID, SSR, and Thermocouple Probe.

Thank you,

Magpie - 12-4-2013 at 10:29

Hi Bob,

That's a ludicrously low cost for a PID + SSR. ;)

I use a PID to control the temperature of heating baths (water, silicone oil, molten metal, etc). By using the auto-tune feature it gives very close temperature control (1-2°C).

I think your plan will work.

ElectroWin - 12-4-2013 at 10:41

dont you want to control this based on the measured temperature of the stuff you're cooking, rather than the temperature of the aluminum plate?

BobD1001 - 12-4-2013 at 13:24

Electrowin, ill probably get an extra probe so that I can either control the plate temperature, or use the additional probe to control the temp of whatever is actually on the plate. All I would need to do is disconnect the one probe from the PID, and then connect the other. Of course I could also wire in a switch to change it from monitoring the one probe to the other.

BobD1001 - 12-4-2013 at 14:17

Well I just ordered the PID 'kit' with the SSR, K type thermocouple, and also I grabbed a big heat sink for the SSR just in case. As soon as I get it Ill update this thread and detail the building of the homemade temperature controlled hotplate so that others may be able to do the same.

[Edited on 13-4-2013 by BobD1001]

Steve_hi - 12-4-2013 at 16:04

Please let us know if you get the material and if the items are described. unbelievable price.

Good luck with your project.
Hope it works out

One Long Post.... Coming up!

BobD1001 - 11-9-2013 at 23:20

Ok, so the PID controlled Hotplate has been a pretty incredible success! Its not 100% done. Still adding the variable voltage control for the stirrer, it needs some rework to make it a bit more compact, and of course another thermocouple so that instead of just measuring plate temp, one could also control the temp of solutions or baths.

Here was the PID box as recieved from China... I was worried something might have broken, but it all was in perfect condition!

Here's the contents of the box:

I got a project box from radioshack, and cut some holes in it, then fit in the elctronics:

Here was one of the preliminary tests just making sure it all worked, and could properly monitor temp and switch the old hot plate properly:

Drilling and tapping the aluminum plate for the thermocouple:

First real life action shot! :D

I quickly determined I didn't like the old hot plate being used as my heater, so I ordered 2 400 watt ceramic heating cartridges for dirt cheap on ebay. I also have the thermocouple hole taped off here so that when drilling the heater cartridge holes no chips get stuck in there.

Perfect fit. As always. :cool:

Now for the stand: Laid out the drill points making sure not to impede upon the heating cartridge holes, and then proceeded to drill away.

Some long bolts, washers, and nuts finish the structure nicely.

Then I decided I needed an electronic stirrer as well, so I made a nice cylindrical aluminum heatsink on my lathe, centered it upon an old CPU fan, and epoxied. Next I found the center of mass of a large old hard drive Nd magnet and used high temp epoxy to fix it to the top of the heatsink. Ill get some better pictures of it up shortly.

As you can see, it works wonderfully...

More updates on the electronic stirrer control board and pictures of the cpu fan setup as well.

And as for the hotplate.... IT WORKS GREAT! The max temp programmed into the PID is at 400C which I may raise a couple hundred degrees since its a breeze to change.

violet sin - 12-9-2013 at 00:21

Rex-c 100? Sorry reading this from an iTouch. Any how I got what looks to be the same thing from eBay an the dang thing wouldn't drive the included SSR itself. Was a relay model w/ an SSR, no low voltage signal out for it. :( used a cheap LED driver through the relay terminals on PID and spent 6$ for an upgraded high temp probe from another seller. Nice stainless sheath. I also found a hot water heater control box a perfect fit for it all. Ya reprogramming the upper limits was easy. Just a few tips to offer any one trying the same thing. Guess mine wasn't a true REX C-100, but a verry affordable knockoff. The pin-out provided didn't at all match the companies online manual. Thing works fine though.

I really like the cartridge element idea, looks sweet ;). Nice craftsmanship

bfesser - 12-9-2013 at 06:42

I've been waiting for this thread to resurface so I could post this:
<a href="" target="_blank">DIY PID Controlled Soldering Hotplate</a> (

BobD1001 - 12-9-2013 at 08:08

violet sin, I know that there was a lot of confusion on which ones will actually switch the SSR.... I suppose some unscrupulous some eBay sellers just include an SSR with their cheaper model to make customers think it will work. Here's a picture of the box label on my PID:

The important thing to see if the "V" at the end of the model name, it means that there is a voltage output which will switch an SSR. However in your situation, with the cheaper relay controlled types, if you find the input leads for the relay, you can solder in a wire on each the + and -, which can the directly switch an SSR.

bfesser, I did come across that page when designing my hotplate, some helpful information!

violet sin - 12-9-2013 at 13:02

Ya mine was designated "Rex-c100 fk02 m-an" and just had an SSR included :(. Even though I asked prior to purchasing. But the 3 diode driver i got puts out 12-18v 300ma and runs a couple light indicators + 12v cooling fans from a dead computer. Just take the needed 20ma from one LED and loop through the relay terminals. So it's not a big waste of space/money. 3.50 shipping included from china off eBay. I work a LOT away from home (3.5hr drive gone for weeks at a time, actually get to go home today, yay) so stuff usually just waiting for me when I get home :) otherwise think the shipping time would piss me off, 3+ weeks. Again nice work.

Think the seller was " easebon" on eBay. Deff gotta read the serial #'s before buying even if you ask them.
-Violet Sin-

I also read about unsoldering the relay to use its 12v signal to switch, and am proficient in soldering, but chose to take a more creative attack. The power on indicator lights n pair of <1w fans were handy.

[Edited on 12-9-2013 by violet sin]

[Edited on 12-9-2013 by violet sin]

BobD1001 - 22-10-2013 at 17:53

Well I just uploaded a video on my youtube channel showing the workings of the hotplate and newly implemented PWM stirrer controller. Check it out, and let me know what you think.

Still some refining and finishing is needed, but it really turned out better than expected! Sorry for the slight shakiness, couldn't find my tripod.

<iframe sandbox width="400" height="315" src="//" frameborder="0" allowfullscreen></iframe>

[Edited on 23-10-2013 by BobD1001]

Dariusrussell - 23-10-2013 at 02:39

If you haven't already done this, one thing would be to use the program button on the SSR. It should be somewhere on there or in the chinglish instructions. Once you do that set it like normal and leave it for a few hours (4ish) and it should do a much better job with keeping in range.

bismuthate - 23-10-2013 at 03:17

That's amazing. How much did it cost to make and how long did it take?
P.S. this reminds me of when I made a centrifuge out of Legos.

BobD1001 - 23-10-2013 at 03:29

It ran me about $65 total, as I had quite a few of the parts already laying around, and it wouldn't have been much more if buying everything new if one knew where to look.

Organikum - 15-11-2013 at 11:00

REX-C100, I have some of these, for 12$ inclusive shiping a bargain and they do a pretty good job on standard setting already.

I got the kind with relais though, just removed this and drive a SSR with the 12V for the relais - this works flawless.

Some thermocouples are just not good I found out, if there is a problem its always on contacts or thermocouple.
There is a hiden setting to change the input from thermocouple type K to PTC 100, this changes also the reading to 10th of degrees Celsius, say not 000°C but 000,0°C and it can be set as such. Just if someday a more detailed regulation is wanted. The PTC has also a smaller risk of misreadings for any reasons, more robust and professional and they got pretty cheap too nowdays, I prefer them.

If you want a fast heating up and a better regulation its possible to use a second relais connected to the alarm output. Alarm set to low so the relais opens and serves full power to the heating element up to a certain temperature, then the PID takes over and regulates only the last 20% - thats in many situations a good thing as the REX has no "ramp" feature.
A other variation which makes even more sense is to have two heating coils, one to heat up by relais and one to hold and fine-regulate by SSR - the second much less powerful then the first of course. In this configuration a heatsink on the SSR gets virtually obsolete, no need to stress the part too much and even if it should burn out - having 150W full on is a big difference to having 1500W blasting, what can get unpleasant rather fast.

Great work!
Split pole motors (from microwave fans for example) are better for stirrers IMHO , more powerful and they couple so very well to the stirbar. IKA uses them too and they are free (s.o.)

I wish I had and could work a lathe too, oh yes! I am jealous lol


[Edited on 15-11-2013 by Organikum]

violet sin - 16-11-2013 at 03:26

Nice, I like your alarm for coarse tuning and SSR for fine tuning. Great idea

Cattmy - 25-12-2013 at 13:46

Hi there!

I just recieved the last part for my Hotplate, and I just finished the machining. Now, I have the M*AN controler and was wondering how I can wire it up. I saw you wrote something on this before, but I dont understand. Can you please explain?

Thanks in advance!

Cattmy - 26-12-2013 at 09:56

I found a method on Youtube.

<iframe sandbox width="560" height="315" src="//" frameborder="0" allowfullscreen></iframe>

Its a really easy way of making a M*AN control an SSR.

Thanks, and Merry Christmas!

[Edited on 26-12-2013 by Cattmy]