Festoon lights outdoor

[Gktssm82]

Hello gents I need your help plz.

Lets suppose we have 15 led lights bulbs on a 2 core cable. I chopped 5 of them coz it was too long for the job. Now 7 out of 10 work and the last 3 don't work. When I touch the two ends together the last 3 switches on and the first 7 turns off.
How can I make them all work.

 

[Lucien Nunes]

Seems they are in series-parallel groups with the first seven in series, the last eight in series, and those two groups in parallel across the driver. When you cut off the last three, you broke the circuit of the second group and only the first group lit. When you completed the circuit by shorting the two ends, the group now consisting of only three lamps had a much lower forward voltage than the group of seven, so the current supposed to be flowing in the first group was diverted to the second as well (with the lamps probably running at double their rated current.)

The series-parallel connection makes things much harder to modify. If the driver's voltage compliance range includes the forward voltage of five lamps, you could rewire as two parallel groups of five. Alternatively you could ballast the second string to compensate for the missing lamps, but with heat dissipation and energy wastage equal to the power of the missing five lamps. Or maybe just extend the leads to reconnect the original 5 lamps in a position that their light can be utilised.

 

[Gktssm82]

Seems they are in series-parallel groups with the first seven in series, the last eight in series, and those two groups in parallel across the driver. When you cut off the last three, you broke the circuit of the second group and only the first group lit. When you completed the circuit by shorting the two ends, the group now consisting of only three lamps had a much lower forward voltage than the group of seven, so the current supposed to be flowing in the first group was diverted to the second as well (with the lamps probably running at double their rated current.)

The series-parallel connection makes things much harder to modify. If the driver's voltage compliance range includes the forward voltage of five lamps, you could rewire as two parallel groups of five. Alternatively you could ballast the second string to compensate for the missing lamps, but with heat dissipation and energy wastage equal to the power of the missing five lamps. Or maybe just extend the leads to reconnect the original 5 lamps in a position that their light can be utilised.

Thank you,
That is exactly what it is. We tried to connect a 800ohms resistor at the end which actually worked.

 

[OnlQQker]

As long as you know what you're doing...