Solar and battery powered LED question

[Mikey B]

Can anyone help explain this to me. Battery Voltage is 13.1V (measured with my Multimeter) there is nothing connected to the battery.
When I measure the current in a 5M strip of LED's connected to the battery with my multimeter it shows 1.3A.
When i cut the strip to 1M long and measure the current it shows 0.65A
I would have expected it to be around 0.25A?

 

[Mrjmegson]

How powerful are the LEDs and how many in your long strip and how many in your short strip?

 

[Mikey B]

LED strip details/spec – 12V (300 LED’s code 5630), current 0-5A, power 60W (from Ebay add) I would guess there are 60 LED's in the 1 Metre strip.

 

[Geoff1946]

Assuming it is similar to the stuff I've used, that specification is for a five metre length. i.e. the full five metre piece you buy is rated 60 watts and will take 5 amps at 12 volts. Hence your one metre length will take 1 amp.

 

[Mikey B]

Thanks for your reply Geoff,

Yes I understand that, but what I have found is when the full 5M strip is connected through my multimeter it shows 1.3A with the battery at 13.1V so doesn't that give me 17.03 Watts? the 1M strip shows 0.65A so is that 6.5 Watts?

I cannot figure out why I am not getting 3.4 Watts for the 1M strip (17.03/5)

Cheers Mike

 

[Geoff1946]

0.65 X 13.1 = 8.5 not 6.5

Assuming your meter is reasonably accurate then the answer is that the led strip is less powerful than specification. Not really a surprise with some of the cheap rubbish sold on e-bay.
The tracks along the strip are also of significance for it's resistance, so there is volt drop along the length, meaning that each segment, usually of three leds, is at a slightly lower voltage than its upstream neighbour. I think this probably explains your non-linear test results.
Long pieces of led strip are best fed from both ends to get optimum output. There is nothing you can do about it not meeting specification in the first place.

 

[Mikey B]

Thanks for that Geoff,

Mis-typed calculation - Doh

Makes sense to me now.

I will allow 1A or 12W per 1M cut strip length to be on the safe side in my calculations.

Cheers Mike