Christmas lights - Something I am doing wrong

[Francesc V.]

Hi:

i am trying to repair this Christmas lights from my parents. They are incandescent lights, no led lights.

I have tried with 12V a 24V small lights that I found in Aliexpress but is obvious that are not the right ones. They last microseconds connected. Do they blow because of Amps or Volts?

If I measure the Amps in the string........it's only 90mA. If I measure the Volts in the "green box"......it's between 0 and 190V, but doing a little bit of maths from the number of bulbs in series.......it's only about 6V per lamp.

Could you please explain me "the basics" and recommend me the right bulbs?
I never thought that changing a light bulb would be that difficult.

Thank you in advance,
Francesc.

[eccerr0r]

Re: Christmas lights - Something I am doing wrong

Light bulbs burn out when they are expected to dissipate more watts than they can at the time. Watts is volts times amps.

These tiny lamp Christmas light strings are usually run in series to reduce the number of connections needed and hence cheapen the light. Since they all are in series, they all need to pass the same current.

However how much current will pass through depends on the characteristics of each bulb and the one that can pass the least current will end up getting the most voltage and if it can't deal with the volts times amps it will burn. So to keep things simple, the lamps all need to match, perfectly.

Also note that most Christmas light strings' lamps are specially designed such that they sort of short out when they burn out so they appear to not light yet the rest of the lamps light up - until it is removed from the socket. So, watch out for that.

BTW usually these strings are not rectified and are all AC lamps, so you will barely get any current reading in DC ampere modes as the average current will be zero in AC.

[Francesc V.]

Re: Christmas lights - Something I am doing wrong

Thank you for the feedback.

Did same test, but now measuring AC Amps.......and results are quite different. There are 3.4A peaks there.

Where the heck they sell these bulbs? Not able to find it anywhere. Anybody knows?

Regards,
Francesc.

[eccerr0r]

Re: Christmas lights - Something I am doing wrong

That's yet another issue with these bulbs, they peak for a very very short time a fairly high current. The bulb you get needs to survive this for that very short period but does not need to sustain it. I would imagine they would be no more than 300mA or so steady state.

You should search for "Christmas Tree replacement bulbs" or something like that, don't try looking for generics as they may not be designed for these strings.

[stj]

Re: Christmas lights - Something I am doing wrong

back to basics.
you have 3 wires so 2 or 3 strings of lamps - probably 2.
how many lamps are there?

[redwire]

Re: Christmas lights - Something I am doing wrong

Many of these chinese Christmas light controllers use SCR's to drive strings, each 1/2 wave. Some have a diode stashed inside the string as well. It depends on the patterns and colours. Three wires in the string could give a mux. of 4 possibilities.
OP your multimeter might not be true-RMS and give wrong readings for current and voltage with 1/2-wave AC.
Also, if there is no fuse in the controller box, I would not use these, too dangerous.

[jiroy]

Re: Christmas lights - Something I am doing wrong

From its end , when you get chinese , that what you get ...

[Francesc V.]

Re: Christmas lights - Something I am doing wrong

Yeap.........I think I will suggest my parents to throw them away and move it to "LED".