Remove the Heating Function From a Corning PC420 Hot Plate Stirrer

Intro: Remove the Heating Function From a Corning PC420 Hot Plate Stirrer

This instructable involves the modification of a laboratory instrument powered by main voltage. If you choose to make these modifications, you will endorse the full responsibility of these modifications. The instructions described here will most likely void the warranty of your hot plate stirrer. If something goes wrong, there is a risk of major damages to properties and persons, including death.

Disclaimer: Please revise the legal section of this site.

I recently received a safety notice from my institutional Health and Safety Department about Corning PC420 hot plate stirrer. Apparently, there is a risk that the plate will start heating by itself even if the heating button is turned off. I did a quick web search and this problem could be caused by a defective microcontroller sending a heating signal while it should not. More info is available here.

This instructable will show you how to disconnect the heating element of a Corning PC420 hot plate stirrer and convert it into a stirring plate with no heating function.

STEP 1: Getting Started

First things first, do not electrocute yourself and remove the power cord from the stirrer hot plate.

You will also need these tools and parts:
- Corning PC420 stirrer hot plate
- Screwdriver, Phillips head #2
- Tie wraps
- Heat shrink tubing
- Heat gun

STEP 2: Under the Hood

You will need to flip your hotplate upside down and remove the three identified screws. Then you can remove the bottom cover and access the internal parts of the hotplate.

STEP 3: Disconnect the Heating Element

The heating element is connected with the two thick white wires. Pull on the blue end of these wires to disconnect them from the main board. Now, the two wire ends and the two headers will be exposed and need to be secured.

STEP 4: Secure the Disconnected Wires

First cover the exposed wire ends and the two exposed headers using heat shrink wraps. The secure the wires using tie wraps. Make sure to keep the white wires within the high voltage area of the casing. These wires should not protrude within the low voltage area of the casing (lower area with integrated circuits in the picture). If the wires are not properly placed, they will be pinched and will constitute a hazard when you will put the cover back in place.

STEP 5: Finalize

Double check the position of all wires before closing and screwing  the cover back in place. It is also important to place a label on your stir plate to make sure nobody will try to make it heat.

Comments

[tkurrle1]

Hi Dr L. I am repairing a similar model Corning hot plate, I am having difficulty finding the specs of these specific potentiometers. Do you know what the specs are for these or do you know where I can find one to replace a bad potentiometer?

Best,
Taylor.

[dj_nme]

Maybe instead of totally diconnecting the heating element, you could put a switch on one of the leads going to the heating element?

At least that way you can have the best of both worlds, a heating stirrer when you want and totally non-heating the rest of the time.

[kymyst]

I fully agree with your switch suggestion, why disable the heater permanently ? Hotplates should never be left on for long periods while unattended, this is the cause of most laboratory fires originating from a hotplate. Unplugging the unit from the wall socket when not in use is also a safety precaution which should be observed with all electrical heating devices. If overnight heating and stirring is necessary,an external thermal safety switch should be used with the device.

[Dr_L]

Good point. You could even add a relay and activate it using the existing potentiometer. This would avoid having two controls for the same function. The potentiometer has a off state. Currently the off state is processed by the microcontroller, but if it was also enforced by a relay, it would add an additional layer of safety in case of microcontroller failure.