Help with alternatives

Hi all,

I'd like to build this device -

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but the transistors don't seem available anymore, can some one suggest alternatives?

Thanks all!

Steve

Reply to
Mr Sandman
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BC546 and BC556 should do. I would suggest putting a revese biased diode across the relay coil, 1N4001

martin

Reply to
Martin Griffith

Thanks Martin...got another problem you may be able to help with... I am trying to solve a problem with a submersible pump running dry....someone has suggested that rather than use the other circuit, one could detect whether the pump is pumping water or running dry by looking at its current consumption. I have tested the pump and it draws 2.6A @12V when pumping water and 0.4A when running dry...would it be easy to design a simple sensor to switch off the pump if the consumption drops below 1Amp say? Can you suggest any circuits already out there I can easily build that do this?

Thanks for your help!

Steve

Reply to
Mr Sandman

This might give you some ideas

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You may need to have some extra logic, so that when the pump starts up it doesn't think that it is running dry. ie a 1 second Resistor Capacitor time constant. that feeds another "switch off" transistor I don't really know that much about dc motors

martin

Reply to
Martin Griffith

Thanks Martin, those suggested circuits don't look like they can handle

2.3amps through them, but I don't really understand all the facts and figures given! Which one looks most appropriate for my application to you? ...will look into this resistor-capacitor setup..see if I can make head or tail of it!

cheers

Steve

Reply to
Mr Sandman

It is the current sense resistor that handles the power, the amplifier is just to give a bigger more useable signal. Say the sense R is 0.1 ohm and you pass 1 amp through it, the power dissipation is very small ( current squared times R) =0.1 watt, but the voltage generated across it is also small, so you just need a little amplifier to get a more usable signal

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P 15 LHS for the circuit. They use 0.003R, so it can handle higher currents, and then they boost it with the amp, in this case 10000/10, which is 1000, which you feed to a comparator to do the yes/no testing.

martin

Reply to
Martin Griffith

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