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NO or NC contacts

Community Veteran
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Registered: 16-02-2009

NO or NC contacts

For several months I have been trying to get a NC magnetic switch. (NO= normally Open, NC = Normally Closed)

EVERY one I have received has been NO.

Now to me NO = open when no magnet near, NC = closed with no magnet

Wikipedia agrees with me. Wink

 

But to the China suppliers it is with the magnet that they take the version, so NO=NC for all 3 I have received so far, even though they are advertised as NC.

I can't find one from the UK (not without paying ££'s for a few p's worth of kit)

I just know if I order a NO one from them it will actually be!

Edit:

just checking and very confused:

Switch Type: NO(normal open type), the circuit is open normally, and, that if a magnet comes near it, the circuit closed.

 

Switch Type: NC (normally closed type), circuit is connected when magnet closes to the switch

 

27 REPLIES
Community Veteran
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Registered: 06-11-2007
Community Veteran
Posts: 16,820
Thanks: 1,112
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Registered: 06-11-2007

Re: NO or NC contacts


HairyMcbiker wrote:

Edit:

just checking and very confused:

Switch Type: NO(normal open type), the circuit is open normally, and, that if a magnet comes near it, the circuit closed.

 

Switch Type: NC (normally closed type), circuit is connected when magnet closes to the switch

 


 

 

 

However.... in the Maplin item, listed in my post..... it says...

 

 

______________________________________________________________________________________________

 

What does the reed switch do?
When a door or window has been affixed with the surface mounted reed switch and is closed, a circuit is created with the connected alarm system.

 

When you open a door or window (with the alarm system activated) this once completed circuit breaks, sounding the security alarm.

 

This means that even if someone were to cut the wiring that connects the reed switch to the alarm system’s panel, the alarm will still sound.

 

____________________________________________________________________________________________

 

Community Veteran
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Registered: 16-02-2009

Re: NO or NC contacts

I'm trying to retrofit a light to a caravan fridge, so 12V and using led's they take 4-500mA.
My idea was to fit a reed switch to the door and when it opens the light comes on (simple eh?)
But every contact I have ordered even though stating NC have bee OPEN.

Those ones from Maplin look good bar the fact they are discontinued and so are all the others linked to from them.

My thoughts now are a power transistor fed from the switch, this will reverse the output.
Will have a further look at the instuctable.

 

Edit:

the instrtuctable works however the distance is very critical. placement will be interesting, however will try it out.

Community Veteran
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Re: NO or NC contacts

A quick check in relation to replacement fridge light switches indicates that many are mechanical - have you considered one like that

Community Veteran
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Re: NO or NC contacts

i was about to go into full pedant mode and tell you that every "reed" switch I have ever encountered have been NO then I read this  https://en.wikipedia.org/wiki/Reed_switch

lol

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To be is to do - Kant
do be do be do - Sinatra
Community Veteran
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Re: NO or NC contacts

Have you considered a "Lever arm" micro-switch ?

You could araldite it to the inside of the door,    (or the inside of the fridge ) and fit a small wood block for the lever arm to butt up against, when the door is shut..

 

something like this  ? 

 

http://uk.rs-online.com/web/p/microswitches/0517656/

 

From the product details....  Ice-free lever option suitable for operation in cold damp environments where a pivoted lever may freeze up

 

 

It would be easy to wire up a battery and bulb to the contacts, to see which way the switch works before fitting it to the door...  

PowerLee
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Re: NO or NC contacts

We use a lot of magnetic reed switches on older forklifts & have both NO & NC depending on what application the switch is being used for.

 

Does it have to be magnet activated OR would a metallic sensing switch be better?

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Re: NO or NC contacts

@PeterLoftus When I was a lad I knew they were both kinds. But it seems the definitions have changed over the years. Wikipedia agrees with me but sellers seem to use what ever they feel like. (see above definitions)

@@shutter thought about it but thought magnetic would be "easier"

@Oldjim Mechanical would mean more size, fridge is quite small.

@PowerLee can't use metallic sensing as fridge is metal

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Re: NO or NC contacts

You need an Inverter circuit, where the reed switch opens, it triggers the circuit to turn on a transistor output which in turn operates the light, quite over-complicated compared to a simple switch, but, needs must and all I guess...

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Re: NO or NC contacts

An alternative solution.... keep a torch handy by the fridge ! ! ... Roll eyes

2u2me
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Re: NO or NC contacts

As @twocvbloke say`s to achieve what you want with a reed s/w is a lot of faffing, you would be better/ cheaper off wiv a mechanical door s/w, similar to this:-

 http://www.ebay.co.uk/itm/Surface-Mount-Mortice-Switch-240V-2A-Push-To-Break-replacement-Door-switch...

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Re: NO or NC contacts

2u2me
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Re: NO or NC contacts

From my recollection reed s/w`s are normally used in the monitor/control circuit and usually in the closed position when next to the magnet,if something differs in the circuit, then a relay or equivalent fires up the load circuit, to have the reed s/w in the load circuit could put excess stress on its contacts, Mind you when I did my apprenticeship relays and cont-actors had mercury  phials in them.Smiley    

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Re: NO or NC contacts

The one I linked to above is a changeover (SPDT) so suitable for both NC or NO applications and rated to 2 amps so should be ok for some in fridge lighting Smiley