how to power led strip

I bought a strip of 60 led lights, they are 12 volts and draw 2 amps. I am using them where i cannot just use a 12v power adapter and plug them in so i was wondering about using battery power. What would be the best way to go so i am not replacing or recharging batteries all the time. they would only be running 2-3 hours a day so i was hoping to get a few weeks to maybe a month on whatever power source i go with.

Thanks

Where will you be installing them?

2-3A is quite a bit of current - you'll need a decent size battery to go a month without recharging.

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Kevin Pierson

A month was just wishful thinking, I would be using them in my horse trailer. The storage compartments don't have any lights in them.

12V at 2A = 24AH (per hour of operation).
(aka 24W - a bit more than a brake lamp; almost half a headlamp or about 2.3rds if a single HID lamp)

But how are they wired?
60 LEDs at 2A means 2/60 = 33mA per LED.
Normally LEDs are only 20mA, but they can be higher.

But also, for 12V, they would normally be series connected.

Assume worst case that they are 3.4V LEDs (not 1.7V), then 3 in series = 3x3.4V = 10.2V with a resistor to drop say 12.7 battery volts to 10.2V meaning drop 2.5V @ 33mA (or whatever current they are).

That means 20 "strings" of 3 LEDs.
If they really are 33mA LEDs, then that is now 20x33mA = 660mA (ie, 2/3 Amp).

We are now down to an 8 AH load.

Find out what LEDs they are - ie, voltage and current; and how they are wired.
Is it 60 LEDs each with their own 12-volt dropping resistor, or series connections of 3 or 4, or maybe 6 - 8 if 1.7V LEDs?

Just to be clear, this horse trailer will be totally stand alone and not hooked to any vehicle for weeks at a time? Days?

It has no provision for tail lights and no 12v harness of any kind?

If you can't LEAVE the pwr there, you may need to just bring it with you when you need it.

Or supplement with solar...
But if full time 24W, that's probably over $500 of solar panel etc.

or you can do a 6volt batt with solar panel from autozone or something?
even a 12v if u want, thus its not an actual charger, just a maintainer. its cheap, and since u wont be using it 24/7 don't have to worry about having to start a car or anything. :)
~wolf

Yep. But if they are 12V strings....

Wait for c_frank to provide the connection/LED info to see if we can reduce the consumption.

Otherwise is just sizing a battery or whatever to provide 24W = 2AH per hour = 6AH per (3 hour) day = 42AH (504W) per week or ~180AH per month.

And I just realised I confused Watts with AH in my reply above....
A 2A load is 2AH per hour etc.
The power is the AH x voltage (2AH is 24W per hour).

Damn shame I can't post-edit. Let's hope readers get this far....

All the info i could find for the led's is in this ebay listing

click here

That link is broken, use this one. I cant get the hyperlink to work right so it's just copy and paste.

https://#/ws/eBayISAPI.dll?ViewItem&item=250587661043&viewitem=&sspagename=STRK%3AMEWAX%3AIT

That link doesn't work either (notice the # after https://?) - but all that is ever needed for eBay is the magic item number (250587661043). Yes sir - we have the technology....!

First comment - I hate sites that do not include IMHO is basic data - like connections else individual LED data.

However, at least they state "High brightness 3528 60 SMD warm white LEDs" and 3258 leads me to $0.18c 3258 (1205 sized) White hi-intensity SMD LEDS with Forward current: 60mAh (sic!) & voltage: 2.9 to 3.3V.


So they are 3-ish volts.
So again....
60 LEDS (ie parallel strings) @ 2A = 2A/60 33mA per LED, hence they are wired 2 in series, so 30 strings @ 60mA = 1.8A (ie, their 2A).
2 max-3.3V LEDs means 6.6V, so the resistor is dropping about half the supply voltage.
Half of the energy consumed is being wasted in resistors as heat.

But being SMD etc, and being 30 parallel strings, I doubt that you'd want to rearrange the strings (eg to 4 in series for a total of 15 strings and hence 0.9A consumption).   

It's back to the 2AH per hour of operation.
6AH per 3-hours day (or 6AHx12V - 72 Watts per day which might get by with a 35-40W solar panel with reasonable 12-hour sunshine....).
Or one 12V-7AH battery per day (~$35 for an AGM).
Or ~40AH for 1 week ($140)
Or 160AH for a month... hmmm (Odyssey 65-PC1750 is only 74AH ~$280), or 31-PC2150 or 31M-PC2150 (90AH) ~$350 or PC2250 (100AH) ~$450.

But be aware that those AH ratings are over a 20-hours discharge period aka the C-20 rate. You really want a C-90 rate for a month at 3 hours per day (sort of), and AH capacities increase with longer discharge times (ie, lower discharge currents).
EG - those C-20 100AH rating become 92AH at the C-10 10-hour rate.


You get an idea for what your are up for....
Unless I have boob'd again in my calcs and approach (any sanity checkers out there?).

You may find that halving the current per LED (ie, to 30mA) makes little difference for what you want, etc.

So if you removed all resistors and replaced them with the "remaining" 2 LEDs from other resistor-less strings (hence from 30x60mA to 15x60mA strings = 1Amp (900mA)...
And ran at half current (is 3/4 or half or 1/4 brightness?)...
That's 450mA - 1/4 the original current draw (40AH per month).

Otherwise just replacing the resistors with 2 LEDs halves the current draw.