relay circuit diagram

Thread Starter

sajelectric

Joined Aug 19, 2011
15
I need to operate a 12v d.c pump and a fan using a 12v50ma relay by the open collector signal from a power supply. Can somebody send me a circuit.
 

praondevou

Joined Jul 9, 2011
2,942
by the open collector signal from a power supply.
It's not clear what you want. A DC-power supply has a plus pole and a minus pole. You certainly mean a component with an open collector output that is somehow triggered/switched on, right?

How is it triggered? If by a switch your circuit could be in it's simplest form an NPN transistor with switched base current, which allows you to control the emitter/collector current. The relay would then be connected from plus to the collector. Is that what you want? http://terpconnect.umd.edu/~toh/ElectroSim/relay.html
 

SgtWookie

Joined Jul 17, 2007
22,210
5v/500 Ohms means that the LM339 would have to sink 10mA; where it may only be able to sink 6mA. It might work, but I wouldn't guarantee it.

An LM311 would be a better choice.
 

Thread Starter

sajelectric

Joined Aug 19, 2011
15
thanks for your response.
Here I have a power supply unit which is programmable type and supply power to an heating element. simultaniously i need to start my 12v cooling pump using a relay.
4 wires are available from the power supply.2 main lines and 2 signal lines. Hope one relay only is enough to start the pump.Please give me the suggestions and circuit.
 

SgtWookie

Joined Jul 17, 2007
22,210
You really are not giving us any helpful information.

We don't know how much current your 12v pump needs.
We don't know how much current your fan needs.
We don't know how much current you have available.
"2 main lines and 2 signal lines" really does not tell us much; we would have to simply guess. Are the two signal lines for remote voltage sensing? What voltage and current does the power supply output?

And why do you need to use a relay?
 

Thread Starter

sajelectric

Joined Aug 19, 2011
15
its a 12v 3amps power source.
pump drags around 2amps and fan 0.8amps.
relay needed to automatically operate the pump and fan.(realy coil should be 50ma.)
Hope you can help me with this info.
 

SgtWookie

Joined Jul 17, 2007
22,210
OK then,
Is your open collector current sink of 50mA enough to energize the relay that you have selected? The relay contacts must be rated for at least 3A at 12v, and the coil should have a resistance of 250 Ohms or more. Many automotive relays will be suitable for this application.
 

iONic

Joined Nov 16, 2007
1,650
5v/500 Ohms means that the LM339 would have to sink 10mA; where it may only be able to sink 6mA. It might work, but I wouldn't guarantee it.

An LM311 would be a better choice.
SGT. I was being facetious, kinda mead I guess. He wanted a relay circuit so I gave him one. Since there was almost no supporting information as to specific requirements I just googled and posted a "relay circuit!"
 
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