Instructables

How to properly power LED Strip Lights using battery for mobile sign?

Hello and thank you in advance for any assistance you can offer me here.  I'm clueless here...

So, here is the plan, I have purchased a strip of LED lights (see them here:  http://www.amazon.com/dp/B005EHHLD8/ref=pe_385040_30332190_TE_tr_3p_M3T1_ST1_dp_1) and am attempting to place them on a mobile sign.  Imagine a person walking around on the street after dark with a sign that is nice and bright with LED strip lights.

Obviously, these need to be battery operated, and I have seen it done with something like a cell phone battery and charger type thing and would like to duplicate that.  I do not know how much power the battery would need, or if resistors would be needed (or even how a resistor works).  Can anyone provide more insight for me?

Thank you again!

I have a similar situation, but will only be using 2 feet of the 16 foot long strip. Is it a linear dropoff?

i.e. if it requires 2A to power 16 feet, can I assume it will only require 0.25A to power 2 feet? And then, would 8 AAA batteries @ 1000mAh ea (8Ah total) power my setup for 32 hours (8Ah/0.25A)?

Sorry to burst your bubble you only get 8Ah if the batteries are in parallel.

When you put the batteries in series you get 12V @ 1Ah for a run time of 4 hours.

OK, thank you. Am I right that the amperage required is linear (provided the strip is uniform throughout)?

That seems crazy that 8 AAA batteries would only power 2 feet of LEDs for 4 hours. I thought LEDs were ultra power consumption?

Could this have something to do with the internal resistances built in to the strips? I'm wondering if it would last a lot longer if I built my own (lower voltage) strip, with smaller resistors.

Linear YES but only on multiples of a group of 3 LEDs at a time.

Each group of 3 LEDs is 1.968" long and needs .017A at 12V.

The circuit is 3 LEDs and a 150 ohm resistor in series.

Each 3 LED string can dim operate down to 7.5 volts until they turn off .

The entire 300 LEDs ( 100 groups of 3 ) is 16.4' == 196.8" and uses 1.7 Amps ....

So a two foot ( about 23 5/8" long ) will use 12 groups of 3 and o.204A

Time for a 1AH battery is 4.9 hrs or 4 hrs 54 min depending on what kind of battery used.

The regular Lead based AAA batteries gradually lower the voltage as they discharge.

The NiCad AAA maintain the output voltage until just before discharge, but they have a flaw, that annoying memory which delivers only the amount used on the next recharge cycle, ergo you must make sure to use up all of the battery before recharging.

The lion AAA has charging difficulties but half the weight and ten times the energy of the Lead AAA...

Great detailed explanation! Thank you.

It seems all the strips I've seen are intended to be run at 12V, off a car battery or wall adapter. I'd love to see some (shorter) strips built to run off a lower amperage / voltage (say 3V, or 2 batteries). Is there a reason why such a thing doesn't exist or isn't readily available?

You can build a single led and resistor to run from 3v @ 17ma but 36 leds equal to the 2 foot strip will be pulling o.017 x 36 = o.612 A that is three times the current of the 12 volt strip.

The exchange is simply a multiplier ie divide the voltage by 3 and multiply the current by three.

No Magic winner .... try ELwire = Rope light .

steveastrouk11 months ago
How long do you want to operate the lights, and how much of the strip do you want to use. To run the whole length will take nearly 25 watts. If you run it off a modest car battery, it wouls run for around 24 hours perhaps.
jenneee (author)  steveastrouk11 months ago
Hi Steve and thanks for your interest in helping me!

The most I would need this to run would be 3 or 4 hours. I've seen it done with something as small as a rechargeable cell phone battery that is actually attached to the sign. It would be hard for a person to carry a car battery and this will be a mobile sign that someone would be holding.
A phone battery wont supply the necessary voltage. You need 12V, and around 10Ah from the battery. If weights a major issue, here's a perfect solution.

http://www.ebay.co.uk/itm/KDQ4-EU-plug-9800mAh-DC-12V-Super-Rechargeable-Lithium-ion-Battery-SPC-2261-/331039702802

I am sure you can find an Ebay.com equivalent.
jenneee (author)  steveastrouk11 months ago
This is exactly what I was looking for! But let me ask you this if I can, there is another one that is a 6800mAh... would that be sufficient, OR IS THE 9800mAh the requirement? There is about a 15 dollar price difference and the reviews of the 9800 say that they really don't carry that charge amount. Thanks again for your help!
It will run your full strip for at least 4 hours. I don't necessarily say THAT battery is the one you should get, but its certainly one that ought to meet your spec.

For every hour you want to run the lights, you need 2AH, 2000mAh of capacity in your battery . 6800mAh will give you 6.8/2 hours of life.

The spec on my link IS pretty stupid ;-)
iceng jenneee11 months ago
Then get a 1/6 of a modest car battery.
You should be able to carry that weight for 4 hrs :-)
You will need a 12 volt 12 amp hour battery and just connect + to + and - to -.

Joe