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6L6 30th May 2012 01:37 AM

Mains relay help please :D
Hello all!

I have a chassis that I salvaged, it's quite nice, and it has a small front-mounted power switch and LED. It was originally for a relay on a 100W SMPS or something of that ilk.

Anyway, what I would like to do is use the small momentary switch to trigger a relay on the primary side of the mains transformer.

I have no idea where to start, and there may be a very simple answer to this, I am just ignorant of it -- I have only ever used big beefy switches on the mains.

Any info, part numbers, links, etc.. will be very welcome!

imix500 30th May 2012 02:11 AM

I am using a tiny little board from Sparkfun to control an SSR from a momentary pushbutton in the F5T I'm building. Maybe worth checking out the board.

6L6 30th May 2012 02:19 AM

Do you have a produce name or a link?

I looked at the Sparkfun website, but nothing is jumping out at me...

imix500 30th May 2012 02:37 AM

There are two versions. Here's one.

Pushbutton Power Switch LV - SparkFun Electronics

The only cavat with it is the switch terminals cannot be tied to the supply terminals i.e. a three terminal illuminated switch.

6L6 30th May 2012 02:50 AM

So one of those would be used to control the coil on a relay? Is that the basic idea?

AndrewT 30th May 2012 12:28 PM

Use a latching relay in the primary circuit.
There are various ways to implement latching using an ordinary non-latching relay.
Some use one or two extra low current, low voltage relays to control the main Power high voltage relay to allow for latching and unlatching using a momentary Make switch controlling a low voltage current.

imix500 30th May 2012 04:47 PM

Yup, the board turns a momentary switch into a latching output to drive your choice of relay. It also has some de-bouncing built in and has a garunteed output state on power up.

Andrewt's method works well too. I have also done it with more relays.

6L6 30th May 2012 09:47 PM

Andrew - I understand what you are saying, but if you have any schematic or links to the general idea (or specifics) of what you are talking about it would be greatly appreciated. :)

imix - So the sparkfun module turns into a 'latch' for a standard relay. Momentary switch -->sparkfun board --> relay coil. Right? Do you have any examples of what would be a suitable relay?

imix500 31st May 2012 01:31 AM

Yes, it's the same as building a simple two transistor latching circuit or using a couple relays, except this is already done in a tiny little board that seems well suited to the purpose of using a momentary switch to act like a push-on, push-off switch.

The two versions are two ranges of operating voltages. The supply voltage is the output voltage.
I am driving a 30 amp SSR with 12v and it works great at such a low current, but it will switch unto 10A according to the data sheet. So, it should be able to drive most mechanical relays as well.

AndrewT 31st May 2012 05:02 PM

This last could be done with low voltage and the output could then drive a mains relay.

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