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Emergency lighting with LEDs and a 120VAC relay ?

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Hello guys, I want to buy a relay but don't know what one.

I want to make a simple solution in case of a loss of power (which happens often here).

I would use a 120V Relay (N.C) that could, when not energized, active a 9V battery and an super-bright LED discretly mounted beside the light switch.
I'd probably use 3-4 LEDs to have one for every room.

Now, I try to buy a relay on ebay but really don't know what to use. I figure I need a 9VDC & 120VCA 15A (since lights are probably on the same breaker as a few outlets? )
 

Menticol

Active Member
Take a look of the cover of this example relay. 12V means how much voltage you need to power up the magnetic coil that connect and disconnect the relay's contacts.

12v-10a-relay.jpg

There are different coil voltages, including 5, 6, 12 or 24VDC. You can find 120VAC coil types, like the following one.

View attachment MHA.jpg

On the first picture, the second marking CONTACT 250V/10A indicates the maximum voltage and current that the relay contacts can handle. As far as I know doesn't matter if it's AC or DC, someone more experienced will correct me if I'm wrong.

Now, some relay types require that the current that powers the coils must be DC. If you try to power that type of relay using AC, it will turn on and off 50 or 60 times per second, rendering it useless (and maybe destroying the unit).

I understand that you want an extremely simple design, but using only a relay presents some flaws.

1. Your lights may turn on during a daytime outage or when they are not really needed, wasting the batteries.
2. If you decide to use disposable batteries, changing the batteries of every room of the house would be tedious.
3. Using rechargeable batteries require a charge controller circuit to avoid overcharging and over-discharging.
4. I'm not sure if i'm correct of this one, but I think that continuous energization of the relay coil may shorten its life.

Spending a little more money on a proper circuit may be a better investment.
 
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alec_t

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KeepItSimpleStupid

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I think if you are going to run all of the LED's and a relay off a 9V battery, you will have problems with run time.

You do need to select a battery that will supply the current you need for the required amount of time.

9V coils are rather uncommon.

12 VDC and 24 VDC are common systems that you can buy which use a Sealed Lead Acid battery and incorporate a charger, but it is likely more than you want to pay. 24 VDC is common for fire alarms and 12 VDC for camera's.
 
Thanks for your replies

I plan to use a 9V batteri for all the LEDs, not multiple batteries and also have a switch to turn the circuit off once we've lit candles heheh

Alec_t (trevelian?) thanksi man, but I don't understand the schematic fully ? :/
 

crutschow

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The easiest is to use a SPDT or DPDT relay with a 120VAC coil (not contact rating) and connect the normally-closed contacts in series with the LEDs and battery. When the AC power goes off, the NC relay contacts turns on your LEDs. If you use a continuous-duty type relay there will be no problem with it being continuously on.
 
The easiest is to use a SPDT or DPDT relay with a 120VAC coil (not contact rating) and connect the normally-closed contacts in series with the LEDs and battery. When the AC power goes off, the NC relay contacts turns on your LEDs. If you use a continuous-duty type relay there will be no problem with it being continuously on.
Thanks ! exactly what I was looking for

How do you plan to distribute the current from one single 9V battery into different rooms?
wires...
 

Menticol

Active Member
Oh, I was thinking about a wireless over-unity enabled explosively-pumped flux capacitor, but wires will work fine too.

Keep in mind the voltage drop, and the cost and complications of embedding the wires on the wall.

In turn, you can get some of this cheap rechargeable LED lamps on a nearby dollar store, and install a relay on each of them as Crutschow instructed. Plug a lamp on every room, and it's done.
 
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