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Pump protection circuit


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Hi all,

I would like to build a circuit to protect a 12v pump from running dry, or even better to change to a second pump once the first pump runs dry. The current the pump draws when pumping water is approx 1A and when running dry approx 0.3A.

Any help or advice would be greatly appreciated,

Thank you in advance

Steve

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Hi all,

I would like to build a circuit to protect a 12v pump from running dry, or even better to change to a second pump once the first pump runs dry. The current the pump draws when pumping water is approx 1A and when running dry approx 0.3A.

Any help or advice would be greatly appreciated,

Thank you in advance

Steve


Cool idea,

If it were me, I would use a cheap PLC from www.automationdirect.com, you can get a cheep one for $129.
I would probably monitor the water flow with some flow sensors and write a bit of logic to decide what pumps to use.


Flow sensor - http://cgi.ebay.ca/Flow-Sensor-Air-Water-0-5-Vdc-Output-Omega-FLR1010_W0QQitemZ200071635353QQihZ010QQcategoryZ67003QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
PLC - http://web4.automationdirect.com/adc/Shopping/Catalog/PLC_Hardware/DirectLogic_05/PLC_Units
Software - http://web4.automationdirect.com/adc/Shopping/Catalog/Software_Products/Directsoft_PLC_Programming_Software/Directsoft_Software - there is a free version

I am a Power Electronics guy, so I tend to use a sledge hammer to solve these problems, I am sure one of the electronics guys will have a smaller idea :)
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Hi,

Thanks for your help. The current sensing idea is the way in which I was thinking of approaching the problem was to sense change in current using and A/D converter and a PIC microcontroller. I've been searching the internet for ideas, I think what I basically need to build for the current sensing side of the circuit, is a simple digital Ammeter, but this is where I'm having touble.

If anyone has any info that would help me to build what is essentially a digital ammeter, I would be very grateful. I have searched the internet for digital ammeter designs, but I'm struggling to work out what value of shunt resistor I would need.

Thanks again for the advice,

Steve

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Hi Steve,

The current sensing could be kept simple by using a low value resistor in series with the pump motor wiring. Some experimenting will reveal suitable threshold values (voltage drop) where to switch the pumps off and on. You probably need to make some delays (analogue or digital) for start currents and any other extreme condition that might occur. The shunt resistor value can be calculated from the motor current and the voltage your A/D converter can work with (don

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Am I right in thinking the value of the shunt resistor is calulated by simply dividing the maximum input voltage for the A/D converter by the current through the motor, ie: 5Volts/1.03A = 4.85ohms. As a 4.85ohm resistor would slow the motor down, would it then be possible to use a smaller resistor and an amplifier to between the A/D converter and the shunt resistor?

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