Please see the attached circuit. Could someone please help me?

For a solar thermal project, I would like to build this circuit. (That requires only a soldering torch and the will to follow a recipe.) As a power source, I'd like to use an AC-to-DC wall adaptor transformer with output of 12V and 830 mA. The pump will be 12V, 600 mA.

Several people have suggested adjustments to the circuit. The 1M ohm resistor, connected around pin 3 to pin 1 of the LM393, to control hysteresis, should be 10M ohm. There should also be a 1N4001 connected 'backward' around the pump, to protect the circuit from surge when the pump is stopping. The STP60NE06 is obsolete, but a preferred replacement HUF75337P3 is available; its datasheet says this mosfet is good up to 15A and 55V.

So, the difficult question. Does my AC-to-DC transformer have enough amperage, with 830 mA, to run the circuit as well as the pump?

Thanks very much.

Attached Images

differential thermostat diagram.jpg (114.3 KB, 18 views)

 

Hello nyoo,

your power supply should be sufficient if the motor doesn't require more than the given 800mA.

Afraid of false polarity? If not save 3Cents and omit D1.

Boncuk

 

Thanks.

Does this mean the circuit uses 30 mA?

I thought the D1 was there to limit the amperage and guarantee the flow direction. Are you saying I don't need it if my 12V source is a transformer?

 

A flyback diode around the pump would be a good idea, as was suggested. It will prevent high voltage spikes to backfeed into the circuit when the pump is shut off, kind of like the sparks seen when you yank a vacuum cleaner out of a wall socket while its still running (inductive kick). Looks like you'll have enough current for the motor. The op amp is connected as a comparator, and the amount of hysteresis is dependent on your needs. Changing the feedback resistor will obviously affect this.

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Thanks.

If I had enough amperage, I was thinking of building two similar circuits:

1. the one I attached at the beginning, to turn off the pump when Sensor2 is hotter than Sensor1; and
2. a second one, where Sensor1 is replaced by a low dropout linear regulator that guarantees a 3.3V output. Something like an LP2981-33. This second circuit would turn the pump off when the temperature at Sensor2 is above 60 Celsius.

Is 830 mA enough to run this all in series? I'd hook them up as
830 mA source ->
differential thermostat ->
limiting thermostat ->
600 mA pump.