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Basic circuit with relay

Former Member

Hi.

First of all: I hope this is the place to post.

 

I am gonna make an easy circuit with a relay to control a pump.(see attachment)

I understand the principal, but I wonder if there is anything more I gotto think of, like resistors or something?

 

It is not to be used in a car.

 

I am thinking of using an car relay: 12V, Max 30 amp.

The pump use 12V and 4 amp.

The fuse need to be 4 amp?

 

Can the switch for example be wired directly to pluss and minus on the car battery or do I need a  resistor there?

Thanks!

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    Some loads have a significant inductive component.  Motors in particular, other stuff.  A passive, linear load can be modeled upon a complex number.  The first term is resistance.  The second is reactance, which if it is positive in signum represents an inductance, negative signum indicates capacitance.  Your load is a relatively small resistance (high conductance) + fairly great inductance.

     

    Inductances source and sink potentials to oppose changes in the current through them, by establishing or diminishing magnetic fields in their surround.  When you first turn on your pump, a magnetic field is established by taking energy from your battery.  When you try to turn it off, the field collapses, inducing energy back into your wire.  The saw is that it (our inductor of interest) sources potential in an attempt to maintain the current going through whatever tried to break the circuit.  Initially, the potential will rise to whatever it takes to maintain the current, which is a function of the new (high) resistance of your switch.  The snubber diode is to protect the switch.  The 'area under the curve' of  the spike is going to be a the product of load inductance and load current /2.

     

    If this doesn't make sense, blame me, just woke up.

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  • 0

    Some loads have a significant inductive component.  Motors in particular, other stuff.  A passive, linear load can be modeled upon a complex number.  The first term is resistance.  The second is reactance, which if it is positive in signum represents an inductance, negative signum indicates capacitance.  Your load is a relatively small resistance (high conductance) + fairly great inductance.

     

    Inductances source and sink potentials to oppose changes in the current through them, by establishing or diminishing magnetic fields in their surround.  When you first turn on your pump, a magnetic field is established by taking energy from your battery.  When you try to turn it off, the field collapses, inducing energy back into your wire.  The saw is that it (our inductor of interest) sources potential in an attempt to maintain the current going through whatever tried to break the circuit.  Initially, the potential will rise to whatever it takes to maintain the current, which is a function of the new (high) resistance of your switch.  The snubber diode is to protect the switch.  The 'area under the curve' of  the spike is going to be a the product of load inductance and load current /2.

     

    If this doesn't make sense, blame me, just woke up.

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