Wiring up cotton string lights with LEDs?

StickyIcky

Hey guys. I have a few of these kinds of cotton string lights around the house and I've only realised that getting spare bulbs for them is a bit of a pain.

I thought it would be a good idea to replace the fittings and bulbs with led lights instead of the regular fairy lights that christmas trees etc use.

These 12 volt G4 LED bulbs look like they would do the job and the fittings are something like this which also look suitable.

Has anyone any experience with this type of thing?

The current Fairy light bulbs that came with the cotton string lights are 12volt 0.84 watt and there's 20 of them which = 20 x 12 = 240 volts. There's no transformer or anything.

However these LED's seem to be DC so I think I need a converter for it as well?

Any info appreciated. Am I daft? Should I just stick with the regular bulbs?

Tokyo

Seems like it'd be a lot more straightforward/cheaper/safer to just buy a string of 20 LED fairy lights, complete with its own transformer, and transfer the cotton string lampshades over onto them...

StickyIcky

Yea Mike. You're totally right that it's probably easier/cheaper/safer that way and it's an excellent point.

The pros with the DIY route are
The learning aspect of it / can custom make it to size etc / something to keep me occupied and off the streets / sourcing the parts from china means it's not actually expensive in money, just in time

The difficult part is making sure I get the right bulbs and transformer I'm guessing.

I can imagine if I had all the bits and I knew what I was doing I could string one up in about 45 minutes which I watched the telly.

Tokyo

If you are to do it then you need to bear in mind that it's not just a matter of plugging in 20 LEDs in place of the fairy lights and hooking up a transformer. IF you take a closer look at a set of LED fairy lights you will see that they aren't all in series - there are groups of LEDs in series, and each group are then connected in parallel back at the transformer.

So, for example, based on the figures for a standard white LED, if you had 21 LEDs connected to a 24V transformer, you'd end up with three arrays of 7 LEDs each wired in series, and the three arrays connected in parallel at the transformer.

What this means in practical terms is that you're not going to be reusing any of the wiring or holders from your original fairy light cluster. You're going to be replacing all of the wiring with three parallel arrays, soldering on new bulb holders at each point on each array, sourcing a transformer to suit the setup, gluing on the lampshades, so on and so forth. So practically you'd be better off buying a cheap LED fairy light chain from ebay.

Tokyo

Handy LED calculator to illustrate the point.

http://www.ledcalc.net/?betriebsspannung=12&led_anzahl=21&led_spannung=3.1&led_strom=20&enorm=24

For the average white LED, 3.6V voltage drop at 20mA are good numbers to work with.

StickyIcky

Thanks Mike. For someone who has not much experience wiring things up wiring up a mixture of both series and parallel arrays does sound complicated alright.

I looked and looked on ebay again and all I could find where AA battery powered 20 string LED lights (I want the plug in kind).

However then I found someone in Thailand how makes the same Cotton String Lights but using plug in LED's instead. So I've emailed this person to see if they can send me just the LED string without the cotton balls (I can use my existing cotton balls and toss the rest )
http://cgi.ebay.ie/ws/eBayISAPI.dll?ViewItem&item=331040842912

Thanks Mike... I think I'll get it sorted this way fingers crossed. Love boards

indie armada

Most electrical shops will soon have mains powered led lights for christmas.
We usually get them in around november and at present only have the outdoor heavy duty types.

StickyIcky

True that, thanks Indie Armada, I shall put it on my list and keep my eye out when ever I'm going into shops. Might be cheaper, quicker and easier (see I'm learning Mike haha) than importing from Thaliand!

Tokyo

Good job - glad you got it sorted.