Christmas bulb repair

[sdancer75]

I want to replace some bulbs from a Christmas lights. The input voltage is 220v and there are 25 bulbs in each of total four rows. Making the calcs, each bulb is at least 220/25 =8.8 volts for it's brightest point.

I tested one good bulb with a 12v battery but the light it wasn't so bright as I expected. Why?

Regards,

Ps: Despite the fact these Chinese lights are advertised as led they are not.

[james_s]

What kind of 12V battery? Is it possible that the voltage is sagging? Are you sure it's actually arranged in series groups of 25 lamps?

[sdancer75]

What kind of 12V battery? Is it possible that the voltage is sagging? Are you sure it's actually arranged in series groups of 25 lamps?

I attached a battery photo.

 Yes, there are four lines (parallel) with 25 bulbs each in series, total of 100.

[james_s]

That's a very small battery for 12V, those internally are usually a stack of little button cells and can deliver very little current, try measuring the voltage of the battery with the bulb connected.

My first guess would be they are 12V bulbs run a bit under to extend their life. 240V / 25 bulbs is 9.6V. What's that green box? Are you sure that doesn't drop the voltage too?

[sdancer75]

The green box is the power supply, with a blinking program for each line. Line 1-4 are the bulb lines (25 bulbs each) and line 0 is the phase. The left most two wires are the wall socket.

I will check the voltage drop tomorrow and I will let you know.

[gorge441]

I guess the reason for the lower brightness is voltage dropping. Please check carefully...

[sdancer75]

Yes, you have right, the battery voltage drop is about 6v, that's why...

I got bored to use my bench power supply which is closed in my store closet.

Thanks to all.