12 volt differential controller [RE-wrenches]
Darryl Thayer
daryl_solar at yahoo.com
Tue Oct 14 20:28:55 PDT 2003
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 woth 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 coursed 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.
--- "Dean T. Newberry" <deant at dcn.org> wrote:
> Quick note the LM 335 will work just fine on 12VDC,
> you don't need the
> AT power supply.
>
> Dean T. Newberry wrote:
>
> > Hi Mark,
> > I think the basic comparator is the LM 335 from
> National Semiconductor.
> > A google search for "comparator LM335" found the
> webpage, download the
> > pdf for sample circuits. If you can read and build
> from schematics
> > you've got it. I'll bet you can buy singles at
> Halstead or Fry's, some
> > Radioshacks have them too. The rest of the stuff,
> resistors,
> > capacitors, case and relay's can be got from most
> radio shack's or off
> > their website. I think I would just use a power
> supply form an old AT
> > computer to get a nice regulated 12Vdc and +- 5
> too if you want it.
> > If you cut off all the computer pigtails and toss
> the fan, there
> > probably is enough room to pack your components in
> the PS case, RS has
> > some nice breadboards too for this kind of stuff.
> >
> > good luck. deant at dcn.org
> >
> > Mark Downing, Hurshtown Alt. Power wrote:
> >
> >> I am in dire need of a 12V differential
> controller that uses 10K
> >> thermisters
> >> for use on a Solar DHW system.
> >> Does anyone have one or know where I can get one?
> >> Can anyone supply a fairly simple circuit I can
> build to accomplish this
> >> function?
> >>
> >> Mark, Hurshtown Alternative Power
> >>
> >>
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