Christmas LED lights connections

Question

I have several Christmas lights with different AC adapters.

First case

In the label of one of them, I read:

Primary: 220-240 V ~ 50/60 Hz
Secondary: 31 V DC 3.6 W

In the label of the cable connecting this AC adapter to the LED array:

Lamp: 3.2 V
0.064 W
80 LED

I can not understand if this is referred to the single LEDs, but the total amount of LED seems to be 80.

How are they connected, then?

In the case of a series connection, each of them would have a 0.3875 V voltage drop, which maybe is too small for a LED. If they were parallel, 31 V seems too much for each of them, and the total available current 3.6 W / 31 V = 0.1161 would be 0.00145 per LED. So, neither of these solutions seems correct.

Second case

In another LED string, I have a 4.5 V battery power supply, with no labels and therefore no indication about the current and the number of LEDs. Do they have a parallel connection?

Answer 1

The LEDs must be connected in series strings of LEDs. A string of 8 LEDs would work, with a single small resistor to linit the current. Connect ten strings in parallel, and you have 80 LEDs.

Alternatively, connect eight strings of ten LEDs, and rely on current limiting in the power supply. This will work if the LEDs in the strings are all matched.

For the 4.5V version, connect all the LEDs in parallel, with a single current limiting resistor. Again, all the LEDs need to be reasonably well matched.