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Discuss Simple Electrical Query in the Electrical Forum area at ElectriciansForums.net

S

sophos9

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Hi, good to have found this forum... I'm after some help on a simple relay switching 240v from a 12v feed.

Basically, I have a feed from a microcontroller which under certain conditions will provide a 12v feed to a pump. What I would like to do is remove the pump and connect a relay so that when 12v is supplied, a 240v pump is activated.

I presume a would need a spst relay capable of switching 240v - would I need a diode etc?

Can some one help put something together?

Many thanks :)
 
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W

wattsup

  • Thread Starter Thread Starter
  • #2
I'm not sure what you mean, why can't you use 12v coil feed to a 230v contactor?
 
S

sophos9

  • Thread Starter Thread Starter
  • #3
I'm not sure what you mean
:) Sorry, as you may have gathered - I'm not much good with the bits I need

why can't you use 12v coil feed to a 230v contactor?
I dont know? If I take the diagnosis out of it - it may help... The microcontroller controls a 12v pump which is activated by a optical eye (sensing fluid level). I want to remove the 12v pump (inadequate flow and head height) and replace it with a 240v peri pump

How can I get the 12v output from the microcontroller to activate the 240v pump?

Thanks
 
W

wattsup

  • Thread Starter Thread Starter
  • #4
just take the output from the 12v mp to a 230v contactor, of course the contactor needs a 12v coil to activate.

Basically, you need a 230v contactor (amps I don't know) with a 12v coil. You need to take care with the circuitry, all in one. Where isolation would kill all circuits

It is really dead simple, just make sure the whole is fed from one supply point only, ie coil feeds (even if through transformers) and mains are from one source only.
Accidents occur because coil feeds and mains transfer are from separate sources. In other words, the coil feed is fed via a different breaker. Sometimes this cannot be done, if so, then interlocks must be used for isolation
 
Last edited by a moderator:
M

mkmukok

  • Thread Starter Thread Starter
  • #5
I presume a would need a spst relay capable of switching 240v - would I need a diode etc?
Yes , you need a diode on the coil, because the coil is inductive load for the transistor in the controller and may damage it.
The inductive load creates peaks in the voltage.

Diode have to be connected in reverse polarity.

copy/paste from another forum
flyback diode (sometimes called a snubber diode,
freewheeling diode, suppressor diode, or catch diode[1]) is
a diode used to eliminate flyback, the sudden voltage spike
seen across an inductive load when its supply voltage is
suddenly reduced or removed.
 
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