12 volt differential controller [RE-wrenches]

[Mark Downing, Hurshtown Alt. Power]

Darryl,

This is what I was looking for, in the event I can't get something ready
made.

I'm not sure what I really need in the way of degrees of hysteresis, maybe 10
to 12 degrees?  This is a 30 tube Thermomax and it heats up REAL fast.
If you have the time you can send a schematic to FAX: 413-793-2031.

Thanks loads,
Mark
--- Darryl Thayer <daryl_solar at yahoo.com> wrote:
> hi Mark 
> I put together a simple op amp comparator "schmitt
> trigger" circuit from radio shack parts and the
> circuit board.  It seems to work.  I used the LM324 op
> amp, and 10 k resistors, and a 100 K positive feed
> back resistor.  I hooked it up to a 12 VDC power
> supply.   give me the temperature range you would like
> and I will tell you how it works, by doing some
> calculations.  Send me your Fax number and I will fax
> a drawing.  This is not a refined circuit and cost
> about $8 or so. This is not a refined circuit, and the
> differencial will vary with temperature.  The
> selection of the feed back resistor determines the
> switching hysterisis.   Please note I am not a circuit
> designer and only took a couple of design courses at
> school, about 42 years ago.  So I was never good and
> now am forgetfull.  If some one else who has a young
> brain would like to help. please do so.  
> 
> Daryl 
> PS the LM324 can only source 40 mills, to drive a
> relay you should use an emmetter follower and free
> wheeling diode.  


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