Circuit for emergency lighting?

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warmbells
Posts: 6
Joined: Thu Jan 09, 2020 10:58 pm

Circuit for emergency lighting?

Post by warmbells » Thu Jan 09, 2020 11:58 pm

Hi,
I have a couple of portable LED emergency lights which have an internal 6v sealed lead acid battery. The unit was left connected to the mains and the battery would be trickle charged, whn the mains failed the lamp would light fo about four hours. I have a 12v suply I could use so would need a circuit to drop the voltage, trickle charge the battery and sense when the supply had failed and switch the LED unit on. Any ideas?
Thanks,
Gerald

David
Posts: 202
Joined: Sun Oct 04, 2015 6:18 pm

Re: Circuit for emergency lighting?

Post by David » Mon Jan 13, 2020 5:19 pm

I'm not 100% sure what you are trying to do here.

Do the lights work as you want now, with a 6V supply (which I presume they do)? If you just want to run two emergency lamps off a 12V supply, then you might like to try with the lamps connected in parallel, but with a suitably rated 6V Zener diode in series with the supply to each light. (i.e. each lamp has a separate supply.) Take care to see that the 12V supply will cope with the loads.

A little bit more info, such as pics, schematics, ratings, and where they are to be used would be very helpful!

warmbells
Posts: 6
Joined: Thu Jan 09, 2020 10:58 pm

Re: Circuit for emergency lighting?

Post by warmbells » Wed Jan 15, 2020 9:42 am

The lights work when connected to the 6v battery, the problm is on both units the boards have failed and do not charge the battery or switch to emergency when the supply fails. I have not been able to source a schematic for the units which are LLoytron D1002GR LED Emergency Rechargeable Lanterns. I'm basically looking for a circuit that will trickle charge the battery and detect supply failure and switch on the LEDs, a bank of 18 in 3 banks of 6 in parallel drawing 20ma at 6v and a circular bank of 7 LEDs in parallel drawing 8ma at 6v. These banks can be one or the other or both off via a dptw switch. These banks can be one or the other or both off via a dptw switch. Sorry I cannot be more specific but I think the switch does not control the LEDs directly.

David
Posts: 202
Joined: Sun Oct 04, 2015 6:18 pm

Re: Circuit for emergency lighting?

Post by David » Wed Jan 15, 2020 11:59 am

OK. I think that you might be approaching the "mend-it-with-a-new-one" threshold here. I have had a quick search for "emergency lighting" on Google, and it throws up a huge number of LED emergency lights of varying specifications with price tags from less than £5.00 upwards.
If these are suitable, I would be inclined to say cut to the quick, and move on.

On the other hand, if you wanted to make a device that works as you mention, I would suggest that you start with a small relay (only one c/o contact is needed) which is kept energised when the source is on, and when the source fails the relay drops back to its non energised condition which then connects the batteries to the LEDS. You may well need a diode to isolate the charged batteries from the dead feed. You may well have to do some experimenting.

Hope this helps.

warmbells
Posts: 6
Joined: Thu Jan 09, 2020 10:58 pm

Re: Circuit for emergency lighting?

Post by warmbells » Wed Mar 25, 2020 11:58 pm

Sorry I've not replied before but I've been in hospital. I've bought a cop;e of new ones that use the same battery and am keeping the old batteries as standby replacements as they are about £10.00 each.
Gerald

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