crazyboy
Hazard to Others
Posts: 436
Registered: 31-1-2008
Member Is Offline
Mood: Marginally insane
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Stirrer/hotplate too hot
I have a corning magnetic stirrer/hotplate. The problem is even when I turn the heat to the absolute lowest setting it gets too hot to touch. By heat
setting 2 it boils water. What can I do to fix this problem?
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zed
International Hazard
Posts: 2283
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
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Mood: Semi-repentant Sith Lord
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Open it up, take a look. Whats with yer rheostat?
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peach
Bon Vivant
Posts: 1428
Registered: 14-11-2008
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Mine gets very warm even with the resistor for the PWM supply literally against the off position.
It can occur because a number of PWM schematics have a minimum value of 10% due to the way the circuit works, so it can never go entirely to 0% and
instead goes off -> 10% to 90%.
The solution is to suspend the flask over the plate. You can easily control the number of joules of heat reaching the flask, and so it's temperature,
by moving it closer or further away. Another trick is to wrap a foil skirt from the neck, draping it around the flask and onto the plate to act as a
t-p. Do not touch the base of a round bottom directly against the plate.
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protem
Harmless
Posts: 8
Registered: 19-5-2006
Location: South Africa
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Mood: improved
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sticking points
Recently a stirrer/hotplate showing lack of response to low heat setting of the temp pot was repaired by (very) carefully cleaning the points of the
thermal regulator with abrasive paper. So - sticking points can cause this kind of problem.
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