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10-15 AMPs w/ potentiometer. Answered

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 :)

Discussions

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

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 :\

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.

(I'll draw you a diagram later if you like, I'm off to play with my TEC for my project now,)

You should get back to me on this!! I'm still interested.

That would be awesome! thanks. I'll do some research

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

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/

Too weedy, you'd struggle to make a cup of tea with that. What are you planning to use for heat?

L

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gmoon

8 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.