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paulpic
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Joined: 09/10/2010
Location: Australia
Posts: 2

Posted: 09:23pm 08 Oct 2010

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http://www.zen22142.zen.co.uk/ronj/rt3.html

Attached is a link to small cicuit i want to make to control a small pump to recirculate water in my solar hot water system,It will turn on and off 5 minutes at a time when sun comes up etc.
Im hoping that i can remove the relay and use a fet.Can some recomend what i need to do please if possible.
The pump load is 6 watts or so.

home heater

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Joined: 03/03/2010
Location: Australia
Posts: 9

Posted: 10:37pm 08 Oct 2010

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There are a few alternatives. If you are an electronics wiz then build your own for sure, but a non working home built cct can be a bugger to fault find if you are not an expert.

A differential thermostat to turn the pump on when the source is hotter than the storage.

A thermostat to turn the pump on at a preset temp.

Or save yourself time and buy something like this thermostat on Ebay, http://cgi.ebay.com.au/Mini-Digital-Temperature-Controller-T hermostat-Aquarium-/400159019018?pt=AU_B_I_Electrical_Test_E quipment&hash=item5d2b56100a

I have a couple of these controlling my solar air and water heating system. They are very reasonably priced and give a constant readout of temp and pumping status.

They are easily settable from the front panel and give precise temp control. They have contacts for heating and cooling. Different settings are required for summer / winter.

Allan
Portland
Vic

do it yourself

Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 03:17pm 10 Oct 2010

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You might find trouble sourcing the 4M7 pots, as 1 meg is about as high as most places stock nowdays.

For 6 watts at 12 volt you could just replace the present transistor with a BD139 transistor and forget the relay and drive the pump from the BD139 transistor.

It is a very simple circuit but could be a right buggers muddle to sort out if you need to subsutute some components.

If it was me, i would just do it with a Picaxe, at least then any adjustments needed are only a software change, and not a hardware redesign.

Pete.

Sometimes it just works

Robb
Senior Member

Joined: 01/08/2007
Location: Australia
Posts: 221

Posted: 10:50pm 10 Oct 2010

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paulpic said http://www.zen22142.zen.co.uk/ronj/rt3.html

Attached is a link to small cicuit i want to make to control a small pump to recirculate water in my solar hot water system,It will turn on and off 5 minutes at a time when sun comes up etc.
Im hoping that i can remove the relay and use a fet.Can some recomend what i need to do please if possible.
The pump load is 6 watts or so.

Put something like an IRFZ44 in place of Q1.

Add a 100k from the junction of Q1 & R5 to ground.

Replace D3 with something higher current to deal with motor spikes eg 1N4004 etc

Connect the pump where the relay was.

paulpic
Newbie

Joined: 09/10/2010
Location: Australia
Posts: 2

Posted: 09:37am 11 Oct 2010

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Thanks Allan,Rob and Pete,Rossw helped with me with pretty similiar
circuit as Robb.
Now to go and attempt to make it and hope it works. Edited by paulpic 2010-10-12

Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 10:02am 11 Oct 2010

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I would think a reliable old 555 timer would do just as well and could even be easier.

You could use the ldr to control the trigger pin or even the reset pin.

Good luck with your circuit.

Pete.

Sometimes it just works

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