Recently I was given a number of
cartridge heaters and was thinking of a project to put, at least a few of them, in good use. The etch tank idea on that thread would be better off with a low power, low power density immersible heater.
What I have decided to use them for is as the heating elements of a hotplate/stirrer combo.
Despite the classic chemistry lab applications, I know many use such hotplates to reflow SMT components. So I will keep a high level, mostly pictorial log of key stages in this project to chat over.
Firstly to lay down a few requirements. I expect these to get 'massaged' during development.
Must have:- Heating area: 300x300 mm
- Max temperature unloaded: 450-500 degC
- Max temperature non-uniformity: 10 degC
- Temperature control method: PID
- Stirring speed: 100-2500 RPM (TBC)
- Stirring capacity: >= 10L water
- Single power outlet: 3kW (13A 240VAC)
Would like to have:- Coated surface for chemical splash resistance
- Hot surface indicator - Active when the surface is too hot to touch
- Secondary immersible process temperature sensor
Design drivers:- Low profile
- Split construction - plate and controller are separate
- Robustness
- Electrical safety
Flexible on:- Weight
- Cost
- Time
- Heat up/cool down duration
Already available components- 11x Watlow tubular cartridge heaters: 750W 240VAC each. Ceramic bead termination insulation and fibregalss wiring insulation
- 1x K type thermocouple panel connector
- 1x 10A and 1x 25A Celduc SSRs
The bar is quite high - there is a lot of work to be done and stuff to be purchased! So stay tuned for the next update where I plan to look at what is available and other peoples' hotplate design.
Alex.
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