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 Post subject: Wiring a relay
PostPosted: Thu Mar 07, 2019 11:55 pm 
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I am planning the installation of a 65" television that will be mounted on the wall inside a fireplace recess (the fireplace has been removed) and am looking for ways to hide this big black beast when it is not in use. I have already bought a motorised wall bracket that will retract the TV to the back of this recess, but I am also thinking about using a roller blind to cover the TV in its retracted position.

This creates a risk that someone will accidentally activate the wall bracket motor while the blind is down, so I want to find a way to prevent this from happening. My first thought is to fit a reed switch to the wall at the upper position of the roller blind, activated via a magnet on the bottom bar of the blind, and use this to trigger a relay that controls the power to the wall bracket.

The attached PDF file shows my proposed circuit diagram. I've never designed a relay circuit before, so would appreciate any comments.


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Reed switch and relay wiring diagram.pdf [62.97 KiB]
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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 5:44 am 
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The wiring is correct.........
Providing (as the drawing implies) that the motor will only work when the blind is fully out of the way.

The other thing to note, is that you have a transformer. Transformers give out A.C. but your "relay" (according to your drawing) is D.C. You would be better off with a plug in power supply. (Example only select a 12v one.)

You may also find one of these useful (Connect to the two silver screws)

* Your RS part number is not correct click here so I can not be too specific.

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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 9:30 am 
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These are awesome relays

https://www.discountfiresupplies.co.uk/ ... _60Hz-Coil)-in-White-or-Red-Single-Gang-Box#149

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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 11:01 am 
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someone-else wrote:
The wiring is correct.........
Providing (as the drawing implies) that the motor will only work when the blind is fully out of the way.

The other thing to note, is that you have a transformer. Transformers give out A.C. but your "relay" (according to your drawing) is D.C. You would be better off with a plug in power supply. (Example only select a 12v one.)

You may also find one of these useful (Connect to the two silver screws)

* Your RS part number is not correct click here so I can not be too specific.

Thanks for your feedback and apologies for sloppy wording on my circuit diagram. I did in fact mean a rectified power supply rather than a transformer and was thinking of buying a power supply normally used for 12v LED lighting.

I don't know how close the magnet will need to be before it triggers the reed switch, so some experimenting will be required to establish the correct position of the reed switch, so that it will only operate when the blind is fully raised. Is your suggested 'surface mount burglar alarm contact' a reed switch?

Your RS search failed because you had used the 'wrong' sort of hyphen/dash/minus symbol. The search works if I use the minus sign key on my PC keyboard, but it fails if I copy the symbol you used (if you are using an Apple device then perhaps it is generating a different code than my PC). Try copying Stock No 102-5544 from this post to see if that works. A search for Mfr Part No KSIM380D10-L should also find the same item.


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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 11:04 am 
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Razor wrote:
These are awesome relays

https://www.discountfiresupplies.co.uk/ ... _60Hz-Coil)-in-White-or-Red-Single-Gang-Box#149

Thanks for that suggestion. It has the advantage of being very easy to install.


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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 12:02 pm 
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It seems over engineered I would use a simple micro switch Image no need for transformers and relays.



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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 12:47 pm 
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ericmark wrote:
It seems over engineered I would use a simple micro switch Image no need for transformers and relays.

I'm all for simple solutions, so your suggestion is much appreciated.

Without having one of these switches in my hand it is difficult to visualise exactly where it would be positioned to ensure that it is turned on when the blind is fully raised and turned off as soon as the blind has dropped by a centimetre or two. Can you please expand a little on exactly how this switch would be physically activated by movement of the roller blind.

Note that I would want the microswitch to be hidden by the blind at all times.


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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 4:37 pm 
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I selected one with a roller as was expecting it to role over the door all the way down, often roller blinds have switches built into the motor so it will stop either fully up or down, have you looked?


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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 5:22 pm 
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ericmark wrote:
I selected one with a roller as was expecting it to role over the door all the way down, often roller blinds have switches built into the motor so it will stop either fully up or down, have you looked?

Your use of the word 'door' suggests that you might be assuming a heavy-duty roller blind with wooden slats. I was actually planning to use a fabric blind, to minimise the diameter when retracted. I've no idea how much pressure is required to push in your proposed micro switch, but I suspect that a fabric blind might not do the job in a reliable fashion. Even if it did, the micro switch would have to be mounted below the top position of the blind to allow the switch to spring out after the blind has passed over it and I was hoping to avoid any visible switches.

A simpler push-button micro switch pointing downwards just above the retracted position of the blind might prove to be a more reliable and unobtrusive option, as it could be pushed up by the bottom bar as it rises.

Motorised roller blinds will obviously require an internal switch to turn off the motor when the blind has retracted, but I'm rather doubtful that this switch circuit could be easily accessed for other purposes. However, I will check that point with a supplier of such blinds.


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 Post subject: Re: Wiring a relay
PostPosted: Fri Mar 08, 2019 6:56 pm 
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The relay Razor mentioned is no use to you as it has a 240v coil, you want one with a 12v coil.

I would say a microswitch is of no use in this instance as it needs to pressed or released at the end (when the blind is up)
If you had a microswitch at the bottom as soon as the blind starts to raise it will no longer be "closed" so the blind will stop.

Yes, the contact I suggested does contain a reed switch (which is why I suggested it) that and the fact as it is in a plastic housing it cant get broken easily, and will not look that bad if seen.

Your solid state relay does not have change over contacts, and it costs £11.00

I found just what you want for only £3.02 Click here This one has a 12v coil and change over contacts.

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 Post subject: Re: Wiring a relay
PostPosted: Sat Mar 09, 2019 12:06 am 
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someone-else wrote:
The relay Razor mentioned is no use to you as it has a 240v coil, you want one with a 12v coil.

I would say a microswitch is of no use in this instance as it needs to pressed or released at the end (when the blind is up)
If you had a microswitch at the bottom as soon as the blind starts to raise it will no longer be "closed" so the blind will stop.

Whatever solution I decide to use, it will only be for controlling the power to the motorised wall bracket and the TV. The power to the blind will be on a separate circuit. The microswitch suggestion is appealingly simple, but I suspect that the use of a reed switch and relay will offer greater reliability.

Quote:
Yes, the contact I suggested does contain a reed switch (which is why I suggested it) that and the fact as it is in a plastic housing it cant get broken easily, and will not look that bad if seen.

Your solid state relay does not have change over contacts, and it costs £11.00

I found just what you want for only £3.02 Click here This one has a 12v coil and change over contacts.

Thanks for tracking down those cheap options for both reed switch and relay. As far as I can see, they appear to offer everything I need. I'm not sure what strength of magnet would be needed to operate the reed switch, but there is a wide choice available online.


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 Post subject: Re: Wiring a relay
PostPosted: Sat Mar 09, 2019 8:15 am 
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haggis999 wrote:
I'm not sure what strength of magnet would be needed to operate the reed switch, but there is a wide choice available online.


When you buy an alarm contact (Flush or surface) it comes in two parts (Since one part is of no use without the other) One part is the reed switch, the other part is the magnet.

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 Post subject: Re: Wiring a relay
PostPosted: Sat Mar 09, 2019 9:15 am 
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someone-else wrote:
haggis999 wrote:
I'm not sure what strength of magnet would be needed to operate the reed switch, but there is a wide choice available online.


When you buy an alarm contact (Flush or surface) it comes in two parts (Since one part is of no use without the other) One part is the reed switch, the other part is the magnet.

I was beginning to suspect that was the case, but it was not always made clear in the reed switches I have viewed so far. Another thing that is not always specified is the operating distance between magnet and switch, though this seems to be typically in the range of 3 to 10mm.


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 Post subject: Re: Wiring a relay
PostPosted: Sat Mar 09, 2019 12:45 pm 
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That will be because you are looking for reed switches, not alarm contacts.

Yes a bigger magnet will help, but you can always buy two, and put the magnets side by side, same pole to same pole

i.e NN...............SS

NOT

NS.................NS

You can also get "Heavy duty" contacts, basically, they have bigger cases and bigger magnets, but some will look out of place in your project.

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Fret not, a forum is a collection of opinions. Above, are mine.

Which is correct? Metre or Meter? Click the link to find out more.

Working on anything electrical? have you got a multi meter? why not? Would you hit a nail with a shoe?

If gloom had a voice, it would be me. :mrgreen:

:idea1: How to post a picture on this forum Click here


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