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Author Topic: 5V relay for switching 120VAC  (Read 2804 times)

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Typefighter01

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5V relay for switching 120VAC
« on: August 18, 2013, 10:23:49 am »
I am building my own Mach 3 CNC pendant and I incorporated an on and off switch for convenience, without it, I will have to get down on my knees and reach behind the PC tower to toggle on and off. I want a simple one wire solution from the pendant to the tower, so I was going to use a DB9 cable. I need four pins for USB, two pins for E stop switch and this leaves three pins for power. I am not daft enough to think I could run 120v thru a DB9 cable, but even with proper gauge wire, I don't want high voltage running beside my communication wire, so I was going to send 5V from my computers PSU to the pendant and have it trigger a 120v relay.

Is this relay http://www.ebay.com/itm/Relay-Module-for-Micro-Controllers-Arduino-5v-3-3V-125V-Switch-Large-Loads-/231032621473 up to the task?

I want to switch my normal 120v house hold current on and off to the 48VDC power supply that powers the stepper drivers and the steppers here is a link http://www.aliexpress.com/store/product/Good-quality-wantai-single-output-350W-48V-power-supply-CNC-Router-Kit/711241_616408438.html.

Side note, if I install a 5V LED after the switch on pendant to show the CNC is getting power, will the LED draw enough current to not trigger the relay?

DaOld Man

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Re: 5V relay for switching 120VAC
« Reply #1 on: August 18, 2013, 08:20:57 pm »
No, you definitely do not want to run high voltage (120) with low voltage wiring. I mean it can be done, but it is not safe and can shock you or damage your equipment, so I say don't do it.
Looks like that relay will work.
And an led should be fine but you may need to run three wires, one +5VDC (can probably get it off the usb port).
A ground for the LED (also off usb, possibly. usb is good for about 500 ma, so figure what kind of load will be on it.)
And the wire back to relay to turn it on.
Wire +5 to your switch.
Other side of switch goes to the relay, also to the led.
Other led wire goes to ground. (Also suitable resistor in line with led.)
I can give you a simple diagram if you need it.

Typefighter01

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Re: 5V relay for switching 120VAC
« Reply #2 on: August 19, 2013, 06:12:34 am »
No, you definitely do not want to run high voltage (120) with low voltage wiring. I mean it can be done, but it is not safe and can shock you or damage your equipment, so I say don't do it.

Don't worry DaOld Man, theres no way I would run 120V thru a DB9 cable, thats why I was looking into using 5V to trigger a relay  :o

Looks like that relay will work.

Good to know.

I can give you a simple diagram if you need it.

Only if you have time, don't go out of your way, I am sure I can figure it out with your detailed description.

Thanks for the help...

DaOld Man

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Re: 5V relay for switching 120VAC
« Reply #3 on: August 23, 2013, 05:28:23 pm »
I think you can figure it out, but we are here to help, if you need it.
And please post pics and schematics when you are done, someone else might benefit from your work.

  
 

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