ChemichaelRXN
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Fixing My Hot Plate/Stirrer
I was given a Precision Scientific hot plate/stirrer that wasn't functioning properly. The problem was the heat control switch (or whatever it’s
called in smarty-pants electronic terms). The stirrer part works fine. My knowledge of electronics is not high, but I know enough to easily fix this
hotplate/stirrer, if I get a new heat control switch. It should just be a matter of swapping the damn thing out. What is this switch really called and
where can I get one to replace the broken one on the hot plate?
(I know for sure its the switch and not the element thats not working)
I have searched with no luck at all. I was thinking of using a dimmer switch used for dimming the lights in a room, but I want this to be a last
resort, since it will be quite bulky on this small hot plate/stirrer.
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obsessed_chemist
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Since it's a fairly sophisticated piece of laboratory equipment, being a combination hot plate and stirrer, I would think it's unlikely that the temp
controller is a mere bimetallic strip type thermostat, like those on cheap buffet burner hot plates. But I could be wrong.
Maybe if you can offer more spec's about the piece of equipment, someone could help. There should be wattage ratings somewhere on the back/bottom of
the device. If so, are there separate respective ratings listed for both the hot plate and the stirrer? If, for instance, the name plate rating for
the hot plate alone lists 1500W, that means that if you bypass the thermostat completely (not recommended), the heat element should only draw 1500W.
In that case, it'd be possible to control the hot plate with a triac-style light dimmer rated for 1800-2000 watts (to be safe). Of course that's only
possible if the hot plate's element runs off of unmodified mains power. Then, you might be able to control the dimmer with a potentiometer relocated
to where the temp control knob was before, mounting the dimmer somewhere else discreet, but with good airflow.
Is the hot plate shorting out, or tripping a circuit breaker/fuse in your house or within the piece of equipment?
[Edited on 11/20/2010 by obsessed_chemist]
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ChemichaelRXN
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Sorry for not being specific. The only info. I could find is below;
Precision Scientific 61695 Therm-O-Swirl Stirrer Hot Plate 5" X 5" PLATE. Temperature range 66C (51F) to 371C (700F)
•525 Watts
•120 Volts
•50/60 Hz
Its this one here: http://www.biostad.com/product_images/18751_therm-o-swirl_61...
It actually was a bimetallic strip type switch! It seems to be missing some parts, so I just took it apart and tossed the thing out. There was no
point in trying to fix it, its was in horrible shape. I put a 400watt dimmer switch on it and it works, but its bulky and ugly...and heats up. I know
I need a 500 or even better, a 600watt switch, since the hot plate/stirrer is rated at 525watts. I still would rather get a replacement switch that
looks and fits better than this dimmer switch.
Do you know where I can get a new replacement part for this hotplate or even a smaller switch that fits and looks nicer?
It seems these heat control switches are on everything, yet I cant find any on the internet. I am not sure where to find them. What would be the exact
name of them?
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ChemichaelRXN
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Okay, I was doing more searching again and I think I may have found what it is called. A Bimetallic Thermostat.
It looked similar to http://www.o-digital.com/uploads/2179/2196-2/Bimetallic_Ther...
Based on the specifications I have given on the hot plate/stirrer, what bimetallic thermostat should I purchase?
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SelfStarter
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I also have a broken hotplate stirrer combo that I am trying to fix. I had an Ice/Salt slurry bath on top of the hotplate, I left the rxn in the bath
stirring overnight. Some how during the night the plastic bin I was using for the bath cracked and some salt water leaked into the hotplate. Luckily
it didn't reach the controllers or anything. The salt water did ruin the heating element. I disconnected the heating element and the stirrer still
worked fine. Obviously, I would like to replace the heating element myself to save money. I searched far and wide for one and I've been unable to find
it. The specs for my hotplate/stirrer is below:
VWR Scientific Products 375 Hotplate/Stirrer
75C-570C
Ceramic
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ChemichaelRXN
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In my case, its a matter of finding a new bimetallic thermostat.. (I assume a 120V one)...which can be found.
In your case, it is a bit more difficult to find a new element unless you know how to make one. If your hotplate uses nichrome wire, maybe you can
open it up and replace it. I am sure you can find some nichrome wire online, but I assume it has to match exactly, which makes it more difficult. I
would look into that option and also contact VWR to see if they sell replacement parts for that model.
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