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I'm participating in an art show soon in which I am making "sculptural light paintings" of which require a few 12v LED strips. They're the kind that work in aquariums and car's taillights and whatnot, and look like this;

green led light strip

I have about 3-6 lights being used per sculpture. So far my idea is to solder each one of them to an individual battery pack (so 3-6 battery packs per sculpture) that holds an A23 12 volt battery, and then connect each battery pack to a communal switch to turn all lights on and off at a whim to conserve energy. The LED strips vary in length (despite all being 12v) ranging from 20 inches long to 6 inches long.

As this is an art show, I prefer to not have any kind of outlet going into the wall as it really takes away from the look of the work, hence the battery packs. That being said, i also need the LEDS to be reliably powered for 2 weeks and active from 9-5 each day. Do you all think that this may be possible or will a different energy source be more efficient?

So far i have a test led strip lit up via 12 volt A23 battery that has been going for about 2 days now with no problems, but that's my only finding. I'm quite lost as I know this will all work in theory, but I'm not sure it's reliable in duration.

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  • \$\begingroup\$ Here's a tip. Actually measure the current draw of your light strips, and edit your post to include it. With a real number to work with, and assuming 6 strips per sculpture, only then can people give you accurate recommendations. \$\endgroup\$ – WhatRoughBeast Jul 11 '15 at 21:56
  • \$\begingroup\$ Is recharging the batteries and cycling them out of the question? If you know a battery will easily last a day popping in to change the battery, or assigning curators to do so, would perhaps be doable, depending on circumstances. It's asking a lot to expect it to last two weeks and the amount of battery needed to power something two weeks is just fourteen times the amount (size, cost, etc), of battery needed to power it for a day. And if you get recyclables, you could have a significant saving. \$\endgroup\$ – Dan Sheppard Jul 12 '15 at 0:50
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One single large battery will be easier to deal with, and will also make it easier to switch all the lights on and off.

To determine how big a battery you need, do the math. Add up the current requirement of all the lights. That's the current the battery must deliver. Now divide the battery capacity by that current to get a time. That's the time, in theory, that the battery can deliver your current for. However, for off the shelf 12V lead-acid car batteries, you want to avoid running them very low because that will cause permanent damage. Either get a larger "car" battery, or a lead-acid battery specifically designed to be able to be drained to nearly empty. Such batteries are called deep cycle, or are sometimes sold as marine batteries.

For example, let's say all the lights together draw 1.3 A (just picking a number out of the air). A 50 Ah car battery can supposedly run the lights for (50 Ah)/(1.3 A) = 38 hours. However, let's consider only half that actually usable for a consumer level car battery, so 19 hours. You'd need to get a bunch of such batteries to last the 112 hours you want. In fact, (112 h)/(19 h) = 6, which is how many 50 Ah "car" batteries it would take.

Since you say you only need to run the lights 9:00-17:00 each day, a better solution is to use a single battery and charge it overnight. Presumably the gallery or whatever is closed during the off hours, so it doesn't matter how it looks with a cord running to a outlet during this time.

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You would still have the wiring to the battery, and switch so this isn't really about eliminating wires, and then you have a bulky battery or array of them which is larger than a SMPS.

There has to be a way to integrate an AC power source into the art, perhaps run an extension cord under the floor or in a concealment strip that lays flat, or painted to match the floor color, and/or routed behind the LED lamps so it is lost in the shadows, or beneath carpet or a false (raised) floor.

You might even be able to position mirrored panels as a channel the cord passes through or simply a flat length reflecting the empty floor in front of the cord. As others have mentioned it seems practically impossible that your A23 battery has powered one for 2 days as it needs many times that much current to work at all as an A23 is quite current lmited to the extent that it can't operate those light for even ONE minute unless you mean only a very faint glow. Is a very faint glow what you are shooting for? It is possible these lights have current limiting resistors in them and by modifying them you could significantly increase their efficiency but an A23 cell as a power source is still not enough, at least in the practical sense that it would take far too many of them in parallel to do the job.

If you are in fact only wanting it very dim then how about integrating solar panels into the art work, or will the room be too dim? We need some numbers such as how much current the lights consume, at what voltage, that you find an acceptable amount of illumination. From there one of the most power dense solutions without excessive cost might be an array of 18650 Li-Ion cells configured as 4 in series, then enough series in parallel so their sum equals current * working hours between recharge opportunities if there are any, per light. Without numbers specific to your illumination goal the question cannot be answered.

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In your application you want to operate the LED lights for 8 hours per day, for 10 workdays (80 hours)? Or 8 hours a day for 14 days (112 hours)? How much current does the LED lamp require? More current will drain the battery faster. It's hard to give a clear answer to this question without knowing details about the load.

A23 battery datasheet http://www.energizer.com.cn/pdf/ts/A23.pdf This is a 12V battery with 55mAh rated capacity. Under "Typical Discharge Durations": after 81 hours, the A23 battery will be down to 8.8V, and after 115 hours, it will be down to 6.0V. This is assuming continuous discharge at 0.48mA. So this battery can last long enough, but it's not clear whether or not it can drive those lamps for the duration.

The miliAmp-Hours capacity rating at 15mA (which is more likely for LED lamps) is about 30mAH, so at that rate, the battery will only last about 2 hours. At 2mA, the battery will last about 25 hours.

For a 15mA load, the A23 battery is rated for about 30mAH (discharge to 6V)

I assume you don't have much electronics equipment available, but you should at least get a cheap DMM (digital multimeter or digital voltmeter). Without turning off the LED lamp that's been on for 2 days, measure the voltage across the A23 battery and see how low it is after so many days. If it's down around 7V or less, the battery is rapidly nearing the end. Compare with the "Discharge Characteristics" graph in the lower left of the datasheet. This isn't a life-critical design, worst case if the batteries run out after 3 days then you just have to replace the batteries. If you do notice one of the batteries reach its end, most likely they will all need to be replaced. So budget for that. Looks like they are about $1 each through internet distributors, and $2 each if you buy them retail. But ideally you'd like to see the battery last for the length of the show. (If the A23 doesn't last long enough, you could use a large 12V lantern battery.)

About the switching, it will be simpler to just have individual on-off switch for each battery pack, that way they are all independent. Less wiring, simple cheap SPST switch, simpler circuit. You could even go simpler and just take the battery out of the battery holder when it's not in use.

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These lights are about 15 watts per meter. 1 meter is roughly 40 inches. So you can calculate how much each unit is consuming.

Now individual battery is good idea in case your operating time was less but for 2 weeks 120 hrs operation a big single battery would be more reliable.

Load Watts /12 = current. Current * running time (120) = battery capacity

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Assuming each led strip you are using has a current need of 160mA, based on the pictured strip listed as 24 SMD 5630 leds at an amazon seller with the same pictures, a A23 battery will not cut it. A typical A23 has 55mAh nominal capacity, and will drop down from 12V to 6V quickly. You will not get any reasonable amount of time on those.

8 AA batteries will provide 12V and 2000 mAh, giving you about 12.5 hours full brightness. C have 3~4x that capacity, and D batteries have 8~10x that. At 18000 mAh, you get 112 hours from D batteries (14 days of 9-5. But voltage will drop along the way). This is 8 D batteries per led strip. At 3 per sculpture, lets assume 5 sculptures, that 120 D batteries!

A better solution would be a larger battery. You can get a Car battery. Even a used car battery should work as long as you have a charger for over night.

Of course this highly depends on the actual current draw of your led strips

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