UK Socket - Relay

Hey.

Been searching the internet for a few hours now and I'm at the point where searching is just making me a bit more :~ so, My aim is that I want to control a UK Extension lead (13 Amp) with an Arduino.

I've come accross the following item: http://www.ebay.co.uk/itm/New-1-Channel-5V-Relay-Module-Shield-for-Arduino-ARM-PIC-AVR-DSP-SRD-05VDC-SL-C-/221005545219?pt=UK_Sound_Vision_Other&hash=item3374f4ff03

Now, I'm just a little confuised on the fact that if I was to wire this up, I'd connect it to a 13Amp UK plug, then pass this through the Relay before it reaches the Extension. Reading this, It says it's rated at 10Amps (Correct?/Incorrect?) - I can't seem to find anything higher than 10Amp. Am I just looking at this part wrong?

Secondly, I've seen this one: http://www.ebay.co.uk/itm/NEW-5V-2-Channel-Relay-Module-Board-PIC-AVR-MCU-DSP-/320759929632?pt=UK_Computing_Other_Computing_Networking&hash=item4aaec81b20

It's still a 10Amp one, but it has the extra LED's on here, which I'm sure I read some where that this can be an advantage? Because of how you control it and really your only telling the Arduino to only turn the LED on, which in turn, turns on the Relay?

Looking forward to your comments :slight_smile:

Thanks

The spec says 30A low-voltage DC, 10A for 250V AC. At high voltages the current rating is less because of the larger sparks that occur on switch-off - too high a current and voltage and the arc will weld the contacts together.

For more than 10A you'll be looking at a physically larger relay that takes a larger current to operate it, and thus need a driving circuit as well as the relay.

Be safe with mains voltages - enclose all high voltage contacts (insulated box or earthed metal box), and as that relay doesn't claim to be double-insulated you must earth the Arduino ground.

So, Taking another look on eBay and I stumble accross: http://www.ebay.co.uk/itm/Solid-State-Relays-SSR-Output-48-480V-AC-25A-DC-3-25mA-/261032791550?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item3cc6c44dfe

This one would be more suitable?

Is there any other way possible of just controlling a socket. I'm in the UK so would require the items to be within the UK. I've tried researching into Remote Control Sockets, but haven't been able to find hardly anything regarding this.

Solid state relays are good.

You might like to check one of my favourite suppliers - Rapid.

Here's a nice one: Panel Mount Ssr 4-32vdc, 0-240vac 25a Load with Led, Zero Cross | Rapid Online

It's nice to have a "Zero Crossing" SSR to make things like incandescent bulbs last longer. The main reason bulbs blow when you turn the light on is because a traditional switch isn't zero crossing. It does make it more expensive though...

I'm not sure if to say expensive or not hmmm :slight_smile:

If I was to purchase one of these, what extra would I need to get this to work with the Arduino? Will the Arduino have enough power to trigger this relay?

If not, I might just go ahead and purchase this now.

A solid state relay is basically an opto-coupler and a triac.

If you can light an LED, you can turn on this relay. That's the beauty of solid state ones - there's no coils, no moving parts, nothing that consumes massive currents.

You can treat it just as you would an LED. It states you want 4V at 25mA in the data sheet (after some hunting and deciphering), so treat it as a 4V LED that uses 25mA and link it to an IO pin using a 47? (or close to) resistor.

How did you work out the resistor needed?

Ohms law. The device is 4V. It draws 25mA. The IO pin gives 5v.

You need to loose 1V (5-4=1). R=V/I, so R=1/0.025 = 40. 47? is the closest "normal" resistor.

That's how you calculate the resistor for an LED.

Of course, it may not need it - it's a bit of a grey area (the data sheet is a bit sparse). It says the input can be between 4 and 32 volts - that's a huge range. Personally I'd have a resistor just in case. (Can any one else with SSR experience confirm the requirement for a resistor?)

Am I right in saying these: Royal Ohm CFR0W4J0471KIT 470R Carbon Film Resistor 0.25W - Pack of 100 | Rapid Online are the right ones?

EDIT:

Infact, Just going to go for this kit, and get free Delivery: http://www.rapidonline.com/Electronic-Components/CR25-Carbon-film-resistor-kits-28374 - Is 0.25W ok?

0.25W is perfect. They're the "normal" size ones you see everywhere.

Is there anything that I could use with this to control the voltage? Looking at the same 13Amp again. Would like the Arduino to control the voltage allowed through, not manually.

Not easily. Yes, it can be done, but it's not as easy as dimming a DC signal. You can't PWM it, you can only slice the AC waveform, or reduce it resistively. The latter is very hard to do safely with high voltages, and the former is technically difficult.

There's another thread on it here: http://arduino.cc/forum/index.php/topic,109339.0.html

Some things you need to be aware of when using a solid state relay:

  1. They usually pass a small amount of current (a few mA) when they are off. Typically, this doesn't matter, unless the load is very light.

  2. They have a small voltage drop (maybe around 2v), so they get warm. To run them anywhere near their rated current, they need heatsinks.

  3. Sometimes they have trouble switching off if the load is inductive. This can be fixed with a snubber network. Many SSRs already include snubbers.

dc42:
2. They have a small voltage drop (maybe around 2v), so they get warm. To run them anywhere near their rated current, they need heatsinks.

UK mains is rated at 13A max without special plugs and sockets. The mentioned 25A SSR would not be running at any more than about 60% of its maximum, even under exceptional circumstances.

majenko:

dc42:
2. They have a small voltage drop (maybe around 2v), so they get warm. To run them anywhere near their rated current, they need heatsinks.

UK mains is rated at 13A max without special plugs and sockets. The mentioned 25A SSR would not be running at any more than about 60% of its maximum, even under exceptional circumstances.

Yes, but at 13A it will probably be dissipating around 20W - so will very likely need a heatsink.

[EDIT: the datasheet for the 25A part you suggested shows the rating without heatsink as about 9A or a little less. The 40A version is not much better, 10A without heatsink.]

dc42:

majenko:

dc42:
2. They have a small voltage drop (maybe around 2v), so they get warm. To run them anywhere near their rated current, they need heatsinks.

UK mains is rated at 13A max without special plugs and sockets. The mentioned 25A SSR would not be running at any more than about 60% of its maximum, even under exceptional circumstances.

Yes, but at 13A it will probably be dissipating around 20W - so will very likely need a heatsink.

That's over 3KW of power being pumped through it. The only thing that springs to mind that would draw that much is an electric heater. It's going to get hot anyway :stuck_out_tongue:

What if I was to use a computer fan for safety to keep the temp down?

Couldn't find a suitable heatsink with Rapid Online

Hi,

Been a while. Didn't realise that these SSR allow a small voltage through. I currently have a DC Adapter attached to the Extension lead, which the DC Adapter is attached to an Electromagnet. I have noticed it because the Magnet comes on and of for a short delay of approx one second, even if the SSR has 0V.

I obv. can't connect the SSR inbetween the DC Adapter and Magnet, as the SSR only allows AC and not DC.

Try connecting a 25w or greater incandescent bulb in parallel with the mains side of the adapter. Or use a mechanic al relay instead.