Help identify Christmas light wiring - Page 1
Forum section: electronics / repair

author: Mikey5791
author_rank: Contributor
timestamp: September 21, 2020, 01:56:10 am
content: Hi,Yesterday i found this old christmas light setting but the neon bulb and wiring had been pulled off.Fyi, i need help to identify the 3 output wires and how to connect to light those neon bulb.I noticed the first 2 output wires are connected to third leg of transistor pcr406 while the 3rd output wire is connected to either live or neutral input. This is a 230v ac setup.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: September 21, 2020, 02:20:30 am
content: Very similar to a simple Chinese garland. I think the scheme is like this. But you need to make sure that the neon lamps have a limiting resistor or are designed for direct voltage.

author: Haenk
author_rank: Super Contributor
timestamp: September 21, 2020, 06:23:07 am
content: Looks like a deathtrap to me.There are so many things wrong with this "construction" (aka "POS"), smash it to pieces and throw it away, before somebody gets hurt (or, more likely, killed).

author: james_s
author_rank: Super Contributor
timestamp: September 21, 2020, 06:27:25 am
content: That's not a neon bulb, it's incandescent. There are several common voltages ranging from 2.5V to 12V bulbs and they are wired in series with enough bulbs to add up to the mains voltage. In the US the most common are 35 and 50 light segments using 3.5 or 2.5V bulbs powered by 120V. The chaser controllers use triacs or SCRs to switch the AC mains voltage directly.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: September 21, 2020, 04:21:02 pm
content: Quote from: Haenk on September 21, 2020, 06:23:07 amNot all countries live well enough to buy expensive things and throw away what can be repaired.

author: SeanB
author_rank: Super Contributor
timestamp: September 21, 2020, 05:12:50 pm
content: Yes the diagram by S. Petrukhin is correct, though there are only 2 outputs used. The lights are run on half wave rectified DC, so you can run any sort of lamp you want, provided power draw per string is under 100mA, and it will work off DC. Typically 20 12V incandescent lamps in series, or 60 white LED's in series, with a resistor of 220R every 5 lamps to limit current, also in series with the lamps. This is for 230VAC use, for 120VAC you use half the number of lamps or LED's.

author: Mikey5791
author_rank: Contributor
timestamp: September 22, 2020, 02:31:51 am
content: Hi,Thanks all for the respond and the diagram from S. Petrukhin.Say if i have a string of 20pcs incandescent lamps, do i connect one end to line 1 and the other end to common.Leave line 2 empty and not connected to anything unless i have another string of lamps.Will the above work safely without burning the house down?Any suggestion and advice is appreciated with thanks.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: September 22, 2020, 04:20:26 am
content: Quote from: Mikey5791 on September 22, 2020, 02:31:51 amYes, you can connect it this way. But we need to make sure what kind of lamps. 220V will be divided in half because a diode is installed on the board, and then they will be divided into 20 lamps. I.e. each lamp will receive 220/2/20=5.5 V. If neon lamps are used, then this is a low voltage for them. If these are incandescent lamps, then make sure that they are designed for 5.5 V, most likely their rated voltage is 6.3 V. Connect the lamp to a 3V battery, if the lamp does not light up at full intensity, then everything is fine - you can connect them in a chain to one output.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 22, 2020, 04:41:04 am
content: Quote from: S. Petrukhin on September 21, 2020, 04:21:02 pmBeing poor makes the impact of a house fire even worse. So be careful. I don't see anything horribly dangerous about the pictured part of this device, but there are failure modes that could lead to a fire and thus it would be wise to keep the box away from flammable materials and better yet not operate it unattended.My personal experience with dealing with this grade of device is that the biggest problem is the poor quality connections to each light of the string. Most likely failure is an open which isn't dangerous, but a line to line short can also happen. Here the current limiting provided by bulbs upstream of the short tends to keep this from being disastrous, but a careful inspection each time these strings are set out makes good sense.