Reed switch motor

[otaio]

Dear all,

Your observations and comments are invited.

CONTEXT
A magnetic reed switch is used to control a fractional hp motor which drives a domestic shower pump.

The reed switch is the electrical part of the flow switch.

When the shower valve is opened the water begins to flow. The water flow displaces a small magnetic which in turn closes the reed switch causing the pump to operate.

The flow switch has two leads. In the normally open position the dc resistance is infinite. In the closed position the reading falls to 470 ohms.

The flow switch is in series with the motor and operates reliably at mains voltage.

PROBLEM
I have a spare set of the flow switches which I intend to use for a different application.

This application works at 16 volts dc.

While the prototype works fine with a simple switch simulating the flow switch the circuit doesn't function properly when the actual flow switch is substituted.

The flow switch closes on simulated flow however it refuses to open when flow ceases. However the flow switch resets itself when disconencted from the circuit.

The flow switch is in series with a relay coil. I have put a diode across the coil but to no avail.

Plainly, I'm missing something and so the call for help as it is easy to miss something obvious when working on your own.

Thanking you all in anticipation

Bob B

 

[cbarn24050]

Hi, it looks like your flow switch has a built in triac, try it on an ac voltage with a lamp.

 

[otaio]

CB

Thanks for taking the time to reply. Much appreciated.

I've checked the leads for 'diode' action. The indication is that there are no semi -conductor junctions present.

It is purely resistive.

I have done further rsearch about the application of reed switches and their protection. See:

http://www.reed-sensor.com

I note with interest that one application recommends including a series resistor with the reedswitch to protect the contacts from over current due to capacitive discharge with a 50-500 ohm resistor.

So the incorporation of such a resistance in a commercial product is consistent with this recommendation.

I can get the flow switch to reliably change state by using it first to switch a transistor which in turn switches a relay coil. I will develop this route further.

Of course this has prompted an issue with the circuit being controlled...

Again thanks for your help.

Otaio