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LED Strip (SMD5050) Unexpected Current Measurements

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audioguru

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Alright, that makes sense :) So if I'm understanding correctly, 3 AA's would just run a 5V strip for (3/8) as long as 8 AAs would run a 12V strip.
But only if the LED strips have the LEDs in each type using the same current for the same brightness. I am guessing that the LEDs in the 4.5V strip are much dimmer and use much less current than the LEDs in the 12V strip then they will not work in your application.

In which case, just for convenience, since portable cell phone chargers are so much more plentiful than 12V battery packs, it seems 5V would be a better choice. Much easier & more cost-effective to find 5V battery packs than 12V, all else equal. Again, if I'm understanding correctly ;)
I am guessing that a 4.5V LED strip will work a little brighter when powered from a 5V cell phone power bank. You need to try it to see if it is bright enough.

You never told us the length of the LED strip needed (therefore the number of LEDs and the amount of battery current needed).
 

Tony Stewart

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Best compromise is to match LED voltage to battery range from full to no power
LiPo = 3.7 to 3.5
LED=3.1 to 2.8 typ 2.9 for medium brightness , better efficiency.

Then string as many in series as possible to matchup and give more tolerance.
Such as 6 LEDs and 5 Lipos.
 

Justin Klein

New Member
You never told us the length of the LED strip needed (therefore the number of LEDs and the amount of battery current needed).
Well, my original intention was, to some degree, to adjust the length of LEDs in the costume based on the battery size it'd require - i.e. if I could get away with more length at a given physical battery size/cost then I would, otherwise I would shorten it. So I didn't really have an explicit strip length. All this confusion just started because the current measurements I was getting made no sense as compared to the numbers I expected based on calculation.

I still see all kinds of wild claims about how long this stuff will last too. i.e.:
*Glowhut claims 4ft strips will run for 4-5hours off of a single 9V battery (4ft->0.2439 of a spool, 0.2439*21W=5.122W/9V=0.5691A. Since a standard 9V battery is around 550mah, I'd again expect it to run for less than an hour. But they say 4-5hrs.
*Electricstyles says their hood runs 12-36hrs off of a 9V. The fact that the hood changes color to me means it's 5050 (vs 3528 or something), and just looking at it the strip has to be at least a couple feet. How this could possibly go for up to 36hrs on a 9V when a 9V only has ~550mah is beyond me.
*Even during my own testing, my 5m spool has definitely run for *way* over an hour on this 8-pack of AA's, whereas the calculations my first post (which reflect every how-to-calculate reference I've seen - i.e. https://www.reddit.com/r/DIY/comments/3abnek/trying_to_fix_my_electrofur_running_led_strips) show it should draw 1.75A and thus kill the batteries in barely over an hour.

At this point I've pretty much given up on trying to make sense of the numbers, and am just going to design with the shortest length possible, and test to see what happens. I expected this to be a super quick division problem, but unfortunately it turned into hours of research & confusion :p

In any case, I very much thank everyone on here for their help :)
 
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KeepItSimpleStupid

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I would urge you to look at www.batteryuniversity.com It has lot's of info about batteries. Battery technology determines the voltage and it's a multiple of a single cell.
NiCad's being 1.2, Alkaline being 1.5, Lithium being about 3.6.

So, 3.6 V is a common cell phone battery. Switching power supplies are known generically as an SMPS power supply. They are buck (step-down) and boost converters (step-up) and buck-boost (both). Efficiencies are getting pretty high these days.

I don't even think any one paid attention to the possibility that the current meter introduces a series resistance!
 

Tony Stewart

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Single RGB LED strips have individual series current limiting R that are are chosen to run off 4.5~5V
Every 5050 strip is not the same, as some are designed for 9~15V using 3 LED's in series and a series current limiting resistor.

Since Red has a Vf near 2V and B/G near 3.4V ( +/-?) the resistor for voltage drop is different and using Ohm's law can help you determine the current from the voltage drop/ Rseries.

Each LED is typically rated at 20mA each and driving all 3 at the same time will drain 3x the current.

Since each Chip & 3R's are in parallel with the others, you can multiply the load current by number of LED's, which would limit you to a very small strip.
Anything more , means they aren't telling you everything, like... it is only pulsing 1 colour at a time for a blink of the eye for 4hrs or they are actually using Lithium primary cells.

1st be realistic about your expectations, then redefine what you want.
LIthium batteries are your only good option.
 

Tony Stewart

Well-Known Member
Most Helpful Member
Buy some CR123 3V Lithium cells in bulk and get the 12V strings.

Single RGB LED strips have individual series current limiting R that are are chosen to run off 4.5~5V
Every 5050 strip is not the same, as some are designed for 9~15V using 3 LED's in series and a series current limiting resistor.

Since Red has a Vf near 2V and B/G near 3.4V ( +/-?) the resistor for voltage drop is different and using Ohm's law can help you determine the current from the voltage drop/ Rseries.

Each LED is typically rated at 20mA each and driving all 3 at the same time will drain 3x the current.

Since each Chip & 3R's are in parallel with the others, you can multiply the load current by number of LED's, which would limit you to a very small strip.
Anything more , means they aren't telling you everything, like... it is only pulsing 1 colour at a time for a blink of the eye for 4hrs or they are actually using Lithium primary cells.

1st be realistic about your expectations, then redefine what you want.
 
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