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10-15 AMPs w/ potentiometer.

So, as a chemist I thought it would be fun to save some $ by making my own hot plate & magnetic stirrer.

I am using Thermoelectric cooling device (TEC) to heat my stirrer, and a small DC motor to stir.

Here's the problem - if you've ever taken highschool chemistry you will know that a hot plate with a stirrer has a potentiometer for Temp & Stirring speed - I'd like to do the same!

Problem:

the TEC takes anywhere from 5-20 amps in operation @ 12 volts DC. Adding a potetiometer to this in parallel is out of the question - I can't fine a potentiometer that can handle greater than 2 watts. ( i may just be looking in the wrong place)...

So.. all in all I'm looking for nearly 140-170 watts of power for my heating plate. (The motor will be using much less, almost negligble to the heating plate)

So, if I can't put a potentiometer in series for power regulation, how can I get my temperature to vary? If this is going to require a circuit board, I may need some help with a design :)

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lemonie7 years ago
You want to be switching the heat on and off with a thermostatic control, or doing something like by controlling current by time rather than continuous flow.

L
GreenD (author)  lemonie7 years ago
Oh, so I want a ... mmm timing device?

So... nooby knowledge is telling me: get sometype of timing device, have it connected to a power mosfet? 

So On...Off cycles?

Ugh! this is more work than I had hoped for :\
Jayefuu GreenD7 years ago
Look up PWM - Pulse Width Modultation. It varies the on/off ratio of current to your device and is commonly used in temperature control of TECs.
Jayefuu Jayefuu7 years ago
(I'll draw you a diagram later if you like, I'm off to play with my TEC for my project now,)
GreenD (author)  Jayefuu7 years ago
You should get back to me on this!! I'm still interested.
GreenD (author)  Jayefuu7 years ago
That would be awesome! thanks. I'll do some research
lemonie GreenD7 years ago
How does your cooker / stove work? Mine clicks on and off except at full power, I believe it's a bimetallic device. Perhaps you could find one of those - they're current based.
See here - just your sort of area I think:
www.coleparmer.com/techinfo/techinfo.asp

L
GreenD (author)  lemonie7 years ago
I haven't made it yet, its from scratch...

If you look online a magnetic stirrer with a hotplate with both speed of motor and temp° variability is well over 300$.

If you buy the parts and design it yourself, you can save atleast 100$.

I just am having trouble controlling the current that would theoretically be going through the device. Here is the instructable that gave me the idea.

https://www.instructables.com/id/Magnetic-Stirrer-w-Hotplate-for-30/
lemonie GreenD7 years ago
Too weedy, you'd struggle to make a cup of tea with that. What are you planning to use for heat?

L
gmoon7 years ago
Try searching for rheostat, rather than potentiometer.

Even so, your rheostat should be rated at ~240 watts (20 * 12), which won't be cheap.

An alternative way: use a power MOSFET.