Sciencemadness Discussion Board

Is there any feasible way to PID control a hotplate power without effecting the stirring?

Sidmadra - 29-9-2018 at 16:25

Or would doing this properly require taking apart the entire hotplate and adjusting the internal wiring so the stirrer circuit isn't affected? The PWM output of a PID to the AC power of the hotplate would interfere with the stirring I would presume. All of the digital temperature controlled hotplates with thermocouple inputs are $300-500, right now I'm working with a $100 hotplate. If I can avoid spending some $500, it would be ideal.

macckone - 29-9-2018 at 16:59

It would require taking the hotplate apart.

If it is bi-metal controlled then the temperature stability is probably shit as is.
If it is a PWM controlled already then it should be easy to convert.
But if it cost $100 it is probably bi-metal.

You may want to get a $15 hotplate and use overhead stirring.

Sidmadra - 29-9-2018 at 17:45

I believe it is PWM because it heats in short bursts on and off, if I'm not mistaken. I'd have to check. Could be confusing it with my other hotplate (that broke)

monolithic - 29-9-2018 at 17:45

No, there is no simple way to do it. You need to separate the circuits for the stirring and the hot plate functions. I ran into the same issue with my hot plate and I think I'm going to sell it and just buy a digital hotplate, because I don't want to hack up a perfectly good hot plate stirrer.

macckone - 29-9-2018 at 20:37

If it is short burst it is using an integrated time proportioning controller.
It is a type of PWM but it isn't discreet enough.

If it has a hum that changes frequency when you adjust the heating dial then it is true PWM.

If it isn't heating satisfactorily then it really isn't perfectly good.
It is the cheap controller.

Sigmatropic - 29-9-2018 at 23:32

In the old ikamag stirrer hitplate I have the stirring and heating circuits are physically separated from each other. Joined only by the transformer. So I would say it all depends on what kind of stirrer-hotplate you've got, open it up and see.

Sulaiman - 30-9-2018 at 00:41

Yes, open it up and post photo's here.