dsgashi
Posts: 12
Joined: Fri Oct 24, 2014 7:02 pm

230v current sensor

Thu Oct 30, 2014 12:11 pm

Hello PI users.

I have 5v relays that will be used for switching 230v device on and off. What I need is a relay that will be used to monitor 230v devices if are left on or off.

Relays that have as input 230vAC does not seem to be common. Where can I find these that can be used safly with PI?

BMS Doug
Posts: 3824
Joined: Thu Mar 27, 2014 2:42 pm
Location: London, UK

Re: 230v current sensor

Thu Oct 30, 2014 1:53 pm

dsgashi wrote:Hello PI users.

I have 5v relays that will be used for switching 230v device on and off. What I need is a relay that will be used to monitor 230v devices if are left on or off.

Relays that have as input 230vAC does not seem to be common. Where can I find these that can be used safly with PI?

Search your preferred supplier for: Relay 230V SPST or Relay 230V SPDT. I think this one is probably about as good as you can expect but there is plenty of choice.
Doug.
Building Management Systems Engineer.

RaspISteve
Posts: 98
Joined: Wed Oct 24, 2012 9:15 pm
Location: Cheltenham, UK

Re: 230v current sensor

Sun Nov 02, 2014 6:19 pm

dsgashi,
Your thread title is for a 'current sensor' which I assume you're wanting to confirm current flow in the target application and feed this information back into the Raspberry. A 230vac relay across the switched supply will only confirm that it should be working. If this is good enough but you don't want to use a relay consider using a mains neon and a photo diode/transistor to sense when the neon is powered. This will also ensure isolation from lethal voltages.

If sensing the current is really what you want consider a small transformer, ideally a toroid, that you can wrap one or more turns around the core using the wire you want to current sense. You need to be very sure that the voltage in the chosen sense winding isn't too high for your input to the Pi. A resistor or two and a carefully chosen Zener diode should be in there somewhere. Remembering also that it'll be AC and the current in the sensing circuit will be proportional to the sensed circuit current so some sort of fiddle factor could be necessary.

Remember that supply voltages are usually lethal when you shake hands with it and don't underestimate what damage current can wreak on the unwary.
Share and Enjoy.

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