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Author Topic: 3VAC on coil side of relay. What's going on?  (Read 716 times)
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Victoria, Australia
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Hi, attached a diagram showing  how to connect the arduino side of your relay.

Tom...... smiley
PS, Sorry forgot to show the relay 5V supply ground connected to the arduino gnd.


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« Last Edit: June 23, 2014, 08:35:29 am by TomGeorge » Logged

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This post has been awfully quiet today....
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So tonight I re-soldered my board. The transistors are on the negative side of the coils and I have 1k resistors on the inputs pins.
I soldered a fuse to a wire and stuck it into my arduino's ground. I checked the AC voltage between the arduino ground and the floating coil ground and it was only .6vac this time (idk if this is a useful measurement but I'm glad it's lower)
Took a deep breath and plugged in the ground...
Nothing blew up this time.
Next step is mounting the board on the outlet box and making it safe. I'm thinking I should slather it with epoxy.
Thanks for the input guys, there's a lot of good info in this thread.

Bonus question: the resistors on the input pins are for current limiting right? Could I use an LED with the right forward voltage? It would be nice to see which relay was turning on.
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Manchester (England England)
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You should not be measuring the voltage between the arduino ground and the mains, it is a meaningless value you will get because they are floating with respect to each other.

You will get about 6V between the mains neutral and ground and you can use that voltage for free, it does not get metered. Although you will possibly get put in prison if the electricity company catch you doing it.

Any LED with a resistor wired across the coil will show when the relay is on.
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You will get about 6V between the mains neutral and ground and you can use that voltage for free, it does not get metered. Although you will possibly get put in prison if the electricity company catch you doing it.


Come, come Mike you really shouldn't encourage this sort of behaviour.

If a neutral feeder fault (open circuit) occurs anywhere in the domestic distribution side between the substation and the home then the neutral line within the house could rise to line voltage.  Not a happy scene for anything using neutral-ground potential as a power supply.
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Hi can you post a copy of your circuit please, including the mains wiring so we can see if we are all on the same page.
A circuit diagram is worth a thousand words. (to miss-quote)


Tom...... smiley
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Come, come Mike you really shouldn't encourage this sort of behaviour.
I did not consider my warning of prison as an encouragement, just a technical observation.
  
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If a neutral feeder fault (open circuit) occurs anywhere in the domestic distribution side between the substation and the home then the neutral line within the house could rise to line voltage.
Then we have another candidate for the Darwin awards   smiley smiley smiley
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Can you post a revised schematic of how it wired now (that doesn't use yellow ink please)
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Hey guys, I had a great time at the maker faire today!
Here's a little sketch of my updated board. It's only half the circuit, but it's symmetrical. (Sorry about the size, I'm on my phone and can't resize)
I found a strange problem though. When I turn my pump on, it'll cause my usb devices to reset. It'll cause the arduino to jump to ttyACM1 instead of ttyACM0. It doesn't do it when I activate the other relay that doesn't have anything plugged in. I imagine it's something  to do with the voltage spike when the coil discharges.


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What is ttyACM0 & ttyACM1 ?
I don't see any code. Did you post it ?
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I found a strange problem though.
This is not strange it is veery common.
It comes from interference from the inductive load. The soloution is to use more power supply decoupling.

It is not the arduino that jumps but your computer.
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What is ttyACM0 & ttyACM1 ?
They are USB ports that the arduino appears as to the computer.
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