Wired LED Strips w/9v batteries & switch, but batteries are hot & draining... I know i did something wrong but what?

I am building a 3dimensional box with LED strips on the verticals to light the inside.  The strips are a foot long, and have 12 LEDs. I asked for instructions when I bought the parts (this is my first project of this nature!) and did as described, I think... 4 9-volt batteries and a push button switch later, the lights go on, but then the batteries get very very hot... and when I turn the switch off, it's slow to come back on again.

any ideas?

sort by: active | newest | oldest
frollard7 years ago
The strips expect 12 volts, so get a battery that spits out 12 volts! (an 8x AA holder would be vastly superior to 9v batteries).

Wire the battery @ 12 volts in series with a switch (either side, doesn't matter) - and have the 4 strips in PARALLEL across this switched battery circuit.

thats: Battery +, connected to switch, switch to all 4 + ends of the led strips. All 4 - ends of the strips go to the other end of the battery pack.

It will draw 25mA per 3 leds, so 100mA per strip at 12 volts
4 strips = 400 mA, at 12 volts = 4.8 watts. This will nearly destroy a 9 volt battery - hence the heat. Stick with bigger batteries.
http://www.allelectronics.com/make-a-store/item/BH-342/BATTERY-HOLDER-4-AA-CELLS//1.html 2 of these in series will make 12 volts.
dizzyvondamn (author)  frollard7 years ago
that makes a lot of sense and is very clear- unfortunately the reason i am using 9Vs is the portability factor- this is a costume with no where to put a 12V battery or 8AAs lined up.

knowing that, can i still do the above?
Sure can. There are several options.

1) Ditch the 12v setup and make your own. Not as turnkey a solution, but each individual led would gladly operate on 2-3 volts each. Since your design constraint is the power source, you may need to redesign around that. One thing to keep in mind, regardless of driving for more voltage or more amperage, the wattage will always stay the same for the same amount of light. (give or take given the nature of resistive current control). Don't worry if that doesn't make sense yet.

2) Hide the batteries elsewhere and run a wire.

3) Go to lithium. If you lack space, there is the option of lipo batteries. They are the stuff that makes cel phones and next gen hybrid cars go. The beauty is they can come in most shapes and sizes, and in this case, a nice flat pack that is only a few mm thick. They require additional circuitry to use and charge, but they offer much higher power density. (they'll still need to be converted to 12 volts from whatever their native voltage is, depending on the pack)

4) *shudder* use multiple 9 volt batteries in parallel (+ to +, - to -) such that each battery shares the load and sees only a portion of the total current -- OR just wire one battery for each strand.

I STILL recommend getting rid of 9 volt batteries. They are terrible in pretty much every way, and are not at all suited to lighting applications. Lastly, they will underdrive your led strips and make baby jesus cry.

If either of the above are options for you, let me/us know and we'll try to figure something out for you.

dizzyvondamn (author)  frollard7 years ago
oh goodness, this all sounds terribly complicated, i wasn't prepared for this!

1. that sounds too hard.
2. that won't work, there's not really an elsewhere in this sort of costume.
3. are these pricey? readily available in los angeles? simple enough for me to hook up in an evening or two?
4. this sounds best right now since i have the stuff to do it, but i understand it's not a great solution. would the batteries be in parallel but the LED strips in series? because right now i think i have it all in parallel and clearly that's not working right.

i really appreciate all this help!
1: It's really not if you're willing to do a little soldering :) I can understand not wanting to go that deep into it though.
2. I think a 4xAA battery pack (linear or sideways mounted) can be hidden in a lot of places, perhaps even on the verticals where the led strips are mounted. Concept/prototype photo?
3. They're not bad, you'd be looking in the 20-40 dollar range for battery and charger. It would last quite a long time and would be the way to go if it was a permanent/professional costume rig. Not so suitable for a one-off. Also, slow to ship from (likely) china for a decent price. Shopping local (hobby stores) you would likely pay a lot more.

Sounds good. As a temporary/less than ideal solution: see what happens when you wire 1 strip directly to 1 battery. Is it bright enough? Does anything get hot? It's a quarter of the current draw compared to running all the strips at the same time on 1 battery, so it should be a lot more good-er-est.

What form factor are we dealing with? does it need to fit in a skimpy costume or be otherwise unnoticed? a small lump of battery covered in fabric of whatever the costume is on the lower back/spine can be pretty easy to conceal (presuming that area HAS costume on it) ;-)
dizzyvondamn (author)  frollard7 years ago
yes, you've hit the nail on the head. this is a burlesque costume, so there's not really much costume at all. normally i hide batteries in my wig, but i'm wearing a fingerwave for this act, which is close-fitting to the head.

if i wire 1 strip to 1 battery, how to do utilize the switch?

here's a picture of the setup: http://farm6.static.flickr.com/5210/5202318901_5efb65c455_b.jpg

it's PVC piping. the LED strips are on the verticals, and i would like the switch to be in the front right, and the batteries in the back if possible.

disregard the long wire on the floor, that's my cable.
This is really coming along! Are the tubes big enough to get AA or AAA batteries in there? If so, you can make a REALLY easy battery holder out of neodymium magnet disks. If you run on AA's, it 'should' easily handle the load and you can run all the strips in parallel off one switch.

See attached image :)
*view full size image if necessary, might be garbled on the smaller resize.
so hook a long pigtail of wire to each strip, drill a hole in the vertical where the strip terminates, and feed that wire through the pipe so that it runs inside and follows some path to a common location, where the switch is located.

Hide the batteries somewhere. You may need to put 4 and 4 on opposite sides so that it's balanced. run the + and - from the battery to the switch. use the switch on the + or - side, whichever you prefer, won't make a difference.

then make an effort to stuff as much in the tubes as possible to hide it away :D
dizzyvondamn (author)  frollard7 years ago
AMAZING! it works! i'm done! woohoo! now i can finally get to the decorative part.

you were so helpful, thank you so so much.
dizzyvondamn (author)  frollard7 years ago
that picture totally made my night! i'm going to try this right now; i have to finish the wiring so i can cover the box frame in fabric and rhinestones. ;-)
dizzyvondamn (author)  dizzyvondamn7 years ago
i'm making a mess of this thread.

what you said above:

Battery +, connected to switch, switch to all 4 + ends of the led strips. All 4 - ends of the strips go to the other end of the battery pack.

1. does the negative not need to go back to the switch?
2. do the LED strips need to connect directly to the switch, or can it be LED+ to LED+?
seandogue7 years ago
Have you measured the current drain when the LED strips are powered?

What is the expected load current per strip?

Compare the two.

It may be "normal" fr the load, or it may reveal a flaw in your execution.

I suspect that you're simply using to little in the way of batteries for powering the desired system, and you're draining the batteries both too fast and too hard (heat for the former, and depletion for the latter)
dizzyvondamn (author)  seandogue7 years ago
that sounds very plausible; i don't know how to measure the drain though. I'm more a costumer than a technologist!

these are the strips i have:

A photo is insufficient info. Contact the seller and get the specs.

It certainly sounds like you're drawing more power than the batteries can handle, essentially short-circuiting them. Either your wiring is wrong, or these are consuming more current than the battery can provide. You may simply not be able to run them off a 9V; they may need something more like a gel-cell or other serious (and seriously heavy) battery.
dizzyvondamn (author)  orksecurity7 years ago
the specs are on that page i think?

i explained what i was doing to the guy in the store and he told me the 9V batteries would work; i guess i will try using fewer.
Ah. Sorry; my NoScript filter was blocking part of the page.

"12Vdc, 25 mA per 3-led segment."

The amount of power you can get out of a 9V depends on the exact battery you're using. Assuming you mean the small "transistor battery" form factor, a typical rating seems to be between 400 and 600 mAh nominal with short-circuit output of around 500mA .

See, for example, http://data.energizer.com/PDFs/522.pdf. By that chart, 25mA (one three-LED segment) ought to run for something on the order of 15 hours from a fully-charged 9V -- assuming that these will run from 9V at all rather than having to be stepped up (though if they didn't, they just shouldn't light up), and assuming that an external current-limiting resistor is not required.

So if it's shorting out the battery, that sounds like either a wiring error on your part (just how many of these segments are your trying to run, and exactly how do you have things hooked up?) or the product not matching its specs.

dizzyvondamn (author)  orksecurity7 years ago
hmmm now i have hooked it up and left it for 10 minutes before turning it on (since that's how it will be- i'll have to put it on a get backstage- and the batteries (only 2) are quite hot! it also took kind of a while for the lights to turn on, and they don't appear quite as bright (but that could be untrue.)

this is turning into quite a pain!

If it got hot before you turned it on, you have a short circuit somewhere.
Strips like these have the limit resistor built in every 3 leds, designed to pull the optimal current from the rated voltage...
dizzyvondamn (author)  orksecurity7 years ago
i just tried it with only one and it didn't get hot, so maybe it only needs one or two.

i'm using four strips (3 LEDs per section, 4 sections per strip... so 12 LEDs in each section) and i guess i over shot thinking that each would require its own battery.

this is how they're wired: i have a 3d box made of PVC piping. it has the strips along the vertical pieces, which are then wired down to the corners, where they meet the round (square) circuit. in the two rear corners are the batteries, and in the front right is the switch. it does work, and i just ran it with one battery and i think it could be brighter, but i'm not sure if that means i've made an error or not.

+- . . . . . +- switch
. .
. .
. .
. .
+O- . . . . . +O-

i appreciate all the input!
re battery type. Agreed. Even standard D cells would provide significantly greater load current capability, although as Ork suggests, gel cells (or perhaps Ni-Cad) would be better suited for large drains.
dizzyvondamn (author) 7 years ago
i think the problem is that they're wired in parallel not in series. i'm going to try that tomorrow and see if it fixes the problem. :-)