Some Dc Power Calculations Again

[EdRedBird]

Hi I am looking at these:
Amazon product ASIN B07JWCQMDM
When looking at the Adapters on the different lengths I see
10m 100 lights - Adapter reads 4.5V 2.7W 600mA
30m 300 lights - Adapter reads 12V 500mA 6W
To me that reads as R for 10m 7.5Ohm R for 30m 24 Ohm ( and 3x10m = 21Ohm close enough)

Can I add 15 Ohm to a 10m string and connect it to 12V

 

[DBK]

If the 100 light string is made up of 4.5v leds then they won't be happy running on 12v.

You should be able to join two 300 light strings together, making sure to maintain polarity, then just cut it to a shorter length if that's what you need.

I'm assuming all the bulbs in a string are wired in parallel, which I think they must be otherwise if one failed they would all go out.

The only worry is whether the in-line controller can take a higher load. It probably can but I can't be sure.

 

[68c]

Why not run it of a USB supply, that is typically 5vDC @ 1 to 2 Amps.

 

[autorouter]

Can I add 15 Ohm to a 10m string and connect it to 12V

Yes that would work, but not ideal. You'll need a substantial resistor, capable of handling 600mA (0.6 x 0.6 x 15 = 5.4W). And you would be wasting 5.4W of precious battery power to get 2.7W of LED light.

I think 68c has the best idea. Alternatively if they are cuttable (many are) you could cut it into 3 sections and wire them in series. They will require 3 x 4.5V = 13.5V, which is about right for the average 12V supply.