LED strip power supply

[pelvisp]

Hello all,

I am getting pretty confused with this maybe someone has experienced this before and can help me understand what i need to do to get this LED lighting meet my requirements.

Well, my sis is trying to light some empty box with a led strip, but wants it to be portable (so using batteries). something simmilar to these LEDs **broken link removed**

what source would I use to get best lighting and longest battery life?.
the sheet say 12V , but at what current , and which batteries can supply that for atleast a couple of hours?
do i need to add a resistor to limit the current?
would simple wristwatch batteries do?

seems every time i connect them to a source , in some configuration i get different results (even if i repeat the same configuration).

Id apreciate any insight on this , so i can understand this bettter and give my sister a usebale solution.

Ofcourse if there are any details that are missing , feel free to let me know.

Thanks in advance, pretty frustrated,
pelvsip.

PS ,
I posted this in elementary electronics...Im assuming this is elemenatry..

 

[alexan_e]

If your leds are like the ones in the datasheet then it says 12v/1.9w or 1.6w depending on the color
1.9w/12v=0.158A and 1.6w/12v=0.133A

The datasheet is not clear but i suppose that since the leds are in groups of three (1 section) this rating is also for one section
so depending on the length you need to multiply the current.

Or maybe the rating is per unit which has 10 sections, i don't know what kind of led it uses.
can you use a 12v psu and an ampere meter to measure it or if someone else has experience with leds like this can tell us.

Alex

---------- Post added at 20:21 ---------- Previous post was at 20:07 ----------

I think it is per unit (10 sections 0.5m ) because I see about 50 lux illumination per unit,
it the watt rating was for 3 leds thay would have to be 0.6w each so these are probably small leds.

Alex

 

[pelvisp]

Hey Alex,

Thanks for the quick reply. yes it is confusing , about the power consumption (1 section or unit)... if i would have to guess , i think the 0.133A u calculated is for 1 section , meaning 3 leds... I think my sister wants to use all 30 (10 section) , so that would be 1.33A.
I might be able to get to test with a 12V psu(i dont have one at home) , what exactly should i be looking for? measure 1 section current consumption? dont i have to worry about the current output of the PSU so it would fry the leds?...

Until i do measure it , assuming a 12V 1.33A battery supply is needed for the 30 leds, any suggestions on what batteries to use?
- I would need them to be in compact size.
- and probably have them on about 2-3 hours straight, if they arent that expensive , replaceing them once a week could be fine (meaning a battery life of approx 20 hours under 1.33A operating)
-As a best solution , if it is not to complicated to rig , it would be nice to use some battery with a battery charger, like a cellphone battery (again not to big in size)

It would defenitely be great if someone who had experience with this type of strip would add a comment or two.

anyway, Alex thanks for the help

EDIT:
just saw ur edit , about thinking its per unit....which does change everything...
and yes, the leds are quite small in size

 

[alexan_e]

Can you check if the small smd resistor value is visible?
Maybe you can measure a voltage drop on that with a voltmeter.
To measure the current you can use an amp meter in series with the psu (or battery ) to see the current.
For 12v you can probably use 8AA (1.5v ) batteries but i don't know if they will last 2 hours,
the smaller the battery the less capacity it will have so i don;t know.
Maybe even rechargeable batteries but they are more expensive.

I still think that these are not 0.6w leds and that the rating is for 0.5 m, in that case the current will be small and can work for many hours

Alex

 

[KJ6EAD]

As Alex says, this type of LED strip is designed to run from a regulated voltage supply. The good points of this design are: inexpensive to build, can be connected end to end to create longer strips, can be cut at marked subcircuit lines to shorten. The bad points are: when run from a battery the current and light output will drop as the battery voltage drops, some power is wasted in the resistors.

New AA alkaline batteries will supply ≈1AH when drained at a high rate (≈800mA) and ≈2AH when drained at a low rate (≈100mA): Discharge tests of AA batteries.

If this were my project, I would probably bypass the resistors on the strip and build a small current regulator for each subcircuit.

I think for your purposes, as Alex has also said, you first must determine the total current draw of the strip at it's rated voltage with an ammeter. Then some reasonable powering method can be decided.

It would be helpful to know the exact make and model of the strip in question if that information is available of course. Many are sold here: LEDtronics | LED, LED Lights, LED Light Bulbs, LED Lamps, LED Indicators, Super Bright LEDs. A clear photograph of each side is a good second choice.

 

[enjunear]

Since these LED strips have a built-in current limiting resistor, you're probably safe to run them from any relatively stable 12V supply. The spec sheet shows an absolute max of 13V, so check any power supply's unloaded voltage with a voltmeter before hooking these up.

From what I've seen above, to determine a good power source you need to determine how much power you will be drawing over the run-time. If we assume your lights draw 1.33 amps at 12V, then for a 3 hour run-time, you will consume 1.33A * 3 Hr = 3.99 (or 4) Amp-hours (Ah), at 12V.

A typical AA battery will hold less than 1 Ah (per KJ6EAD's post), so that is no good. Most alarm system batteries (and UPS backup batteries) are 12V and around 7 Ah at moderate discharge rates **broken link removed**. These can be tough to find, and you'll need a 12V charger in order to recharge it... they are typically sealed lead-acid, just like a car battery (generally they are AGM, so non-spillable, but still lead-acid cells).

If you can find an AC-to-DC power adapter (a "wall-wart") that will support 12V @ 1.4A +, then I'd say go that way for ease of implementation. But if wall power isn't available....

Another approach might be to use D cell batteries. They are about 12 Ah @ 1.5V. Battery Reference They are rated at 200 mA draw, so pulling 1.33 amps will significantly reduce their capacity from what it's rated. So, if you had 8 D-cells in series, 1.5V*8 = 12V, at 12 Ah... then you could run 12 Ah / 1.33 A = 9 hours at 12V. That's going to be drastically reduced because you are sucking 1.3 amps out of the cells, instead of their rated 0.2 amps. Even if the high-rate discharge takes you down to 1/3 of the capacity, that could still give you sufficient run-time to make it 2-3 hours.

If you used C-cells, that would give you 6 Ah, so 6 Ah / 1.33 A = 4.5 hours. Even that might be good enough, if they last half as long as normal with a 13x current draw (1.3 amps, compared to rated 0.1 amps).

That might be the next test I'd do... buy 8 C or D cells, tape them together (or buy battery-holders and wire them together), and see how long the lights will run with sufficient brightness. Maybe start with C's... they are cheaper. If they don't go long enough, try D's. If they still don't cut the mustard, you can run two strings of batteries in parallel to double the capacity. (i.e. make two stacks of cells, so that from end-to-end they read 12 V. Connect the negative ends of the two stacks together, and connect the top ends of the stacks together. Now you'll have 12V and twice the number of amp-hours.

---------- Post added at 22:51 ---------- Previous post was at 22:37 ----------

Hey Alex,

Thanks for the quick reply. yes it is confusing , about the power consumption (1 section or unit)... if i would have to guess , i think the 0.133A u calculated is for 1 section , meaning 3 leds... I think my sister wants to use all 30 (10 section) , so that would be 1.33A.
I might be able to get to test with a 12V psu(i dont have one at home) , what exactly should i be looking for? measure 1 section current consumption? dont i have to worry about the current output of the PSU so it would fry the leds?...

Until i do measure it , assuming a 12V 1.33A battery supply is needed for the 30 leds, any suggestions on what batteries to use?
- I would need them to be in compact size.
- and probably have them on about 2-3 hours straight, if they arent that expensive , replaceing them once a week could be fine (meaning a battery life of approx 20 hours under 1.33A operating)
-As a best solution , if it is not to complicated to rig , it would be nice to use some battery with a battery charger, like a cellphone battery (again not to big in size)

It would defenitely be great if someone who had experience with this type of strip would add a comment or two.

anyway, Alex thanks for the help

EDIT:
just saw ur edit , about thinking its per unit....which does change everything...
and yes, the leds are quite small in size

I think you are destined for a BIG battery if you want to run 1.33A for 20 hours.... that's 26.6 Ah. I've got some big PowerSonics that are 12V and 26 Ah @ 1.3 amp discharge, and measure 6.5" x 6.5" x 5". That might do the trick, but they aren't real cheap. You might invest in an old golf-cart, go-cart, car battery and a 12V linear regulator (so you don't overvolt the LEDs and pop them). A lead-acid battery should show about 12.65V open-circuit after resting for at least 4-8 hours, when fully charged. When coming off the charger, they could read over 13V for a period of time (float charge is generally at 13.5V).

 

[mopoco]

I really cannot believe that the .133 A is just for one section (3 LEDs). If you look at the circuit diagram, it looks like it is for 30 LEDs, which would make more sense to me for a typical led: in my experience, most LEDs want 10 - 20 mA to light them up nicely, and with 10 of the 3 LED strips in parallel, the 133 mA would divide down to 13.3 mA per section, which makes more sense. So, a typical AA alkaline or NiMH battery source should do you for 2/.133 = 15 hours. Have fun!

 

[KJ6EAD]

Mopoco, good point. Even if each subcircuit on the board were drawing 20mA, that only multiplies to 200mA and a set of 8 AA alkaline batteries could supply it for at least 2 hours and still be above 10.5V.