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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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  • 0 in reply to Former Member

    Some other alternatives for diodes

    pump - 6A05-T from Diodes Inc

    relay - 1N4002 from Micro Commercial, Diodes Inc or any other mfr

     

    The inductive current spike will just recirculate through the diode and coil until it is dissipated as heat.

  • 0

    1n4002 is a PS diode, its okay but not really manufactured for this application.  Early ones were quite slow, now they are average.  The 1n914  is gold-doped for minority carrier lifetime suppression and is much faster.  Because you are using a relay, you will be fine with it, only better than nothing protecting a transistor.  Say, why are you using a relay rather than a transistor?

  • 0 in reply to D_Hersey

    Good point Don, picking the best diode depends on the specific circuit and objectives. Even the choice of using a flyback diode may not be the ideal way to control flyback pulses in some applications since using a flyback diode can delay the relay turn off until the coil has discharged.

    The specific relay may also impact diode choice - for example some 12V relay coils have an impedance of 28 ohms. This would result in a coil current of over .4 amps. Since the current through the coil cannot change instantly, the flyback diode would see the same current, which is above the rated current for a 1N914 - so its life would be shortened if it were used with this relay.

    Conversely the 1N4000 series diodes can take higher current, but may allow a short spike up to 500 ns as they turn on.

    You can of course get high speed, high current diodes - if the application justifies the price.

     

    For those who haven't seen these flyback voltages, here is a video...

    (Note he calls it back EMF which is not an accurate term for flyback voltage or inductive spike)

    https://www.youtube.com/watch?v=43HFng0CVKg

  • 0

    Boy, brain fart!  (It was me)  Somehow, it got into the back of my cabasa that those signal diodes of yore could handle an ampere, wrongo! 200mA, 300mA are the types of numbers I am seeing.  Anyway, you want an HVish diode that has low capacitance.  Let me step back from discussion of specific p#s to one point about circuits that switch reactors.  Charged, in the case of capacitors, they initially max out at the potential ya' left 'em at.  Inductors at the current you inserted.  This is a point of analytic simplicity, in what can look like a spaghetti bowl (all metaphors turn to food at a certain hour) of equations. 

     

    Sorry, I should have looked that up before I posted.  Didn't realize I didn't know what I didn't know.  In the many places where they are applicable the 1N4XXX diodes are an excellent value and quite robust.  I certainly keep a drawer-full that I replenish often.  Reliable, cheap, and easy to find a DS for, something I must train myself to do more often.  Parts are generally much better now than when I became accustomed to them.

  • 0

    If electronic parts come to you by yak, caribou or reindeer, you can make a fine suppression diode in a pinch by degenerating a transistor.  There are a buncha ways to do this, but in this case connect the collector to the base.

     

    With a transductor its a flyback, with just an inductor I think they call it boost, sorry for my prior imprecision.