Power outage - relay switch

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Mr_B
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Mon Jun 01, 2015 9:12 am

One more question for the electrical fundis...

I'm looking for a 220v / 12v relay switch that will close the 12v circuit when the current is lost on the 220v side? Not sure what the correct terminology is for a component like this? What I want to do is run my 12v exterior lighting circuits through a relay like this, with a 12v day/night sensor... so that when it's dark enough and loadshedding strikes, the exterior lights automatically switch on. Any advise?

Many thanks... B :subscribed:

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Stef
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Mon Jun 01, 2015 9:44 am

B,

Any relay with a 220V coil can work, provided it has normally closed contacts, i.e when energised the contacts are open circuit and when the power fails contacts are closed.

Give a bit more info...are these additional light or do you want to run them either on mains or batteries?

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Mr_B
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Mon Jun 01, 2015 10:00 am

Stef wrote:B,

Any relay with a 220V coil can work, provided it has normally closed contacts, i.e when energised the contacts are open circuit and when the power fails contacts are closed.

Give a bit more info...are these additional light or do you want to run them either on mains or batteries?
Hi Stef, these are 12v LED lights running directly from my backup battery system. The idea is that when loadshedding strikes, and it's dark outside, these exterior 12v lights will come on automatically. Obviously I'll install a 12v day/night sensor switch as well.

B

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ChrisF
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Mon Jun 01, 2015 12:08 pm

actually not that straight forward .....

How many amps will you be drawing on this circuit ?? If it is only a few outside lights it may be possible to use a normal relay, for a system that includes your inverter etc you may well need a more heavy duty cole hearsey type relay ....


Get a 220/12V power supply. Use this to power the relay - to keep a normally CLOSED contact in the OPEN position. As soon as eskom does its thing the power to the relay is dropped and the relay switched OFF, thus the normally closed contact will now let power through for your 12V lights.


now to go find a 12V relay with a normally closed contact ....

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Stef
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Mon Jun 01, 2015 1:50 pm

Kinda where I was getting to Chris ;-)

Personally I do not like using relays for mains monitoring because the coils do not last,especially if that relay coil is going to on the mains permanently and not from a light switch that get switched on occasionally for a few hours.

My suggestion would be more electronic i.e an optocoupler together with a NAND gate and a fat power transistor that powers the day/night switch directly. The Motorola MOC3019 is a nice package. You could use a Triac or 12V relay instead of a transistor, the wiring of the triac in the circuit will differ though due to it remaining active once triggered on DC.

Basically a reverse version of a solid state relay.

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Stef
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Mon Jun 01, 2015 4:00 pm

Something like this...just 12V
Optocoupler mains detect.jpg
Optocoupler mains detect.jpg (18.74 KiB) Viewed 2009 times

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ChrisF
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Mon Jun 01, 2015 4:19 pm

Uhm jaaaaa.......


anything less than heavy current and I say "not so easy"


Hehehe...


I also hate the idea of relay permanently powered.

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Mr_B
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Mon Jun 01, 2015 5:25 pm

Whooooosh... sorry Stef that's gone right over my head... haha! :oops:

I'll start with Chris' suggestion, then in a few years time when I'm more intelligent and possibly wiser I'll take a look at that spaghetti drawing again.

I do like the colours! :thumbup:

:surrender:

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ChrisF
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Mon Jun 01, 2015 5:56 pm

Mr_B wrote:Whooooosh... sorry Stef that's gone right over my head... haha! :oops:

I'll start with Chris' suggestion, then in a few years time when I'm more intelligent and possibly wiser I'll take a look at that spaghetti drawing again.

I do like the colours! :thumbup:

:surrender:
Stef actually KNOWS what he talking about :)


Your best bet is to wash his Hilux and beg he builds you that multi colour contraption ....

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Stef
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Tue Jun 02, 2015 9:20 am

Haha I wish...there are more cleverer okes than me LOL (talking about the colours :lol: ). That's the only circuit I undestand...welll... sort of :mrgreen:

That opto is actually just a fancy relay that works with light rather than a magnetic coil, this type of circuit commonly used by the Raspi & Arduino type guys to monitor the presence of AC mains.

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Tue Jun 02, 2015 3:04 pm

Mr_B wrote:Whooooosh... sorry Stef that's gone right over my head... haha! :oops:

I'll start with Chris' suggestion, then in a few years time when I'm more intelligent and possibly wiser I'll take a look at that spaghetti drawing again.

I do like the colours! :thumbup:

:surrender:
+1

Bretton, why not run your LED's strait from you batteries , using a day/night switch for on/off ? Security lights will stay on for the whole night, right ?( With a switch to turn them off when you want to use your night vision before you start shooting. lol )
Word te vinnig oud en te stadig wys.

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