Vintage Christmas Tree Lights question

Tiger31

I have a quantity of very old screw in type decorative Christmas tree lights. I can test the individual bulbs on a small battery.

How do I calculate the minimum quantity of bulbs that should be on a loop plugged into the mains socket to avoid blowing any or all?

Capt'n Midnight

"I'm a firestarter, twist-in firestarter"

Get LED's instead.

They will blow, it's only a matter of time. Incandescent bulbs typically halve their life if run 5% over voltage, ie. by skipping one bulb in 20. Bypassing bulbs is NOT recommended.

IIRC it was 20 x 12V bulbs in series for 240V mains. Note : all wires are live mains voltage , tinsel and fake trees are metal...

Even if the bulbs have a heavy transformer it's probably unregulated so skipping a bulb will still allow the voltage to increase. and paper decorations don't like heat...

John.G

I have a ancient set as well, in three unequal sized translucent "boxes", they are wired in series so if one bulb blows you have to go through the lot which I have just done to replace one blown one . The bulbs are 5V 20ma 0.35W to a total of 17.5W. By calc (as I didn't count them) means 50 bulbs in this particular set.

No traffo on mine.

2011

As above it would be best to replace with LEDs and far cheaper.

Bruthal.

https://www.boards.ie/discussion/comment/118361983#Comment_118361983

Just in a sort of factual note, not quite mains voltage the whole way along the string while the bulps are all working. With reference from neutral/Earth point, from Live side, 230 at first, 218 at second and so on. 0v at neutral side of last one, 12v on other side, 24v on other side of second one and so on.

Bulb fails, now its 230v on one side, 0v on other according to volt meter tested to a N/E point.

Capt'n Midnight

https://www.boards.ie/discussion/comment/118372007#Comment_118372007

It's only a matter of time before a blub blows and then like you said there'll be full mains voltage across that bulb.

Bruthal.

https://www.boards.ie/discussion/comment/118372665#Comment_118372665

Yes it was never a great setup.

John.G

I thought that if connected in series that the volt drop through each is 230/bulb numbers although I have another fairly ancient set that are lighting with two blown bulbs but will extinguish if any one of the blown ones is removed.

Going back to the 50 bulb set above, I can track down a blown one reasonably fast by removing any bulb say 7 or 8 from the live end, and probing the two contacts with the other end of the m.meter probe to N, if I get 230V, then I replace the bulb and move down another 7 or 8 until NO 230V and so narrow it down that way.

Esel

https://www.boards.ie/discussion/comment/118372933#Comment_118372933

Would it not be more efficient to start in the middle?

Bruthal.

https://www.boards.ie/discussion/comment/118372933#Comment_118372933

It is 230/bulb numbers.