Powering mains LED fairy lights from batteries

[neglected_goldfish]

Hi,

I have a string of 50 fairy lights that are fitted with a UK domestic plug. I'd like to know if it's reasonably possible to power these by battery. My partner needs some LEDs for some table centres she's making for a wedding. Its likely that the LEDs will be on for up to 12 hours.

Here's what information I have on the LEDs:

230v ~ 50Hz
50L x 2.4V 0.12W
50mA / Total: 6W

Transformer output:
24V 250mA / 6VA

Regards,

Fish

 

[Iggifer]

I would just go with something like:

http://www.tlc-direct.co.uk/Main_Index/Xmas_Lights/Christmas_Battery_Lights/index.html

http://www.amazon.co.uk/Lights-Battery-Operated-Static-Action/dp/B000W6T5DU

Might be much more straightforward and hardly bank breaking

 

[Taylortwocities]

Or use a small inverter, like this:
http://www.tlc-direct.co.uk/Products/TLINV300ST.html

 

[mattylad]

It would be cheaper to buy a set of 12v led lights.

 

[Space cat]

A simple calculation shows that you need 3 A.hrs of battery capacity. That's easily achievable from D-cells, though you'll need sixteen of them. Can you rustle up a pair of old car batteries instead?

Are these LEDs static or flashing? Static ones probably have nothing more in the circuit than a simple bridge rectifier and something to regulate the current. These will work just fine on DC. The electronics in a flasher unit might be counting AC cycles to do its work, in which case there's a fair chance that a flashing set won't work on batteries.

Edit: I've just read your post more carefully and there's a chance that the 'transformer' is already putting out DC. If this is the case then your LEDs will work but MAKE SURE YOU GET THE POLARITY RIGHT!

LEDs don't like being driven in reverse.

Double edit:

If you do use car batteries - or any other beefy source or DC power for that matter - PLEASE put a fuse in there somewhere. You'd be amazed how much damage a hundred amps can do.

 

[bernardgreen]

The figuresd

2.4V 0.12W

suggest the lamps are taking 50 mA at 2.4 volts.

A string of them in series with a resistor will enable them to be run from a battery if the resistor value is chosen to allow 50 mA to flow.

Assume a 12 volt battery and 4 LEDs in the string. The LEDs will take 9.6 volts ( 4 x 2.4 ) leaving 2.4 volts across the resistor. The value of the resistor will need to be 48 ohms ( R = V / I ). Nearest standard value is 47 ohms but I would try it first with 100 ohms ( 24 mA current ) as it is most likely that when working on mains the LEDs are only lit on one half cycle for less than half the time. They [1] may not take 50 mA continuously and [2] may be very bright if fed 50 mA continuously.

 

[big-all]

The figuresd

2.4V 0.12W

suggest the lamps are taking 50 mA at 2.4 volts.

A string of them in series with a resistor will enable them to be run from a battery if the resistor value is chosen to allow 50 mA to flow.

Assume a 12 volt battery and 4 LEDs in the string. The LEDs will take 9.6 volts ( 4 x 2.4 ) leaving 2.4 volts across the resistor. The value of the resistor will need to be 48 ohms ( R = V / I ). Nearest standard value is 47 ohms but I would try it first with 100 ohms ( 24 mA current ) as it is most likely that when working on mains the LEDs are only lit on one half cycle for less than half the time. They [1] may not take 50 mA continuously and [2] may be very bright if fed 50 mA continuously.

i have several different leds running from power tool batteries
a string off xmas lights cut into strings off 6 wired in parallel[series parallel] on an 18v[up to 20] so giving 3-3.3volts

i also smaller 1 w 3v on rechargable batteries
i have 2 off the 10w 9-12v leds connected in series connected to a 18v nmh battery
and another one connected to 10.8v bosch li-ion battery interestingly the battery goes flat after 1 hour even though its 1.3ah
the dewalt will last all night at 2.6ah

am i likly to dammage the batteries without resistance in the circuit or would i get better performance with one

 

[Space cat]

am i likly to dammage the batteries without resistance in the circuit or would i get better performance with one

1) Your batteries will last longer if you add some resistance in series but your lights will not be so bright. It's a trade-off.

2) Given the kind of current that some rechargeable batteries can put out when shorted, I would definitely put a fuse in there!

 

[big-all]

thanks for your answer
the wire i am using is the really thin 3 or 4 strand that came with xmass lights so would expect it to burn through in a few seconds but will put a weak link in in when i finalize the design somthing like a 250ma

 

[ban-all-sheds]

His customary idiotic and pointless smattering of smilies.

 

[ricicle]

His customary idiotic and pointless smattering of smilies.

And the more you comment on it, the more he will do it !

 

[ban-all-sheds]

Why?

Just how pathetic and immature is he?