Powering LOTS of LED's with 9v batteries for longer

Thread Starter

Bioniclekolacz

Joined Aug 21, 2019
7
I need to power a bunch of RGB LED strips on my cosplay, however, the batteries seem to run out extremely fast no matter if there is 2 or 6 9vbatteries powering the LEDS. the LEDS are 12v, however since there are so many of them, they are quite dim with only 18v. I feel like there is something I am missing electronically, like, some sort of bottle neck so that adding more batteries will actually increase the duration, not just the brightness.
 

jpanhalt

Joined Jan 18, 2008
8,080
A 9V battery has at most 500 mAh. How many LEDS are you driving? How much current for each at 18V? (just use the 12 V current, as you will/should be using a very energy wasteful resistor to drop 18V o 12V.
 

Thread Starter

Bioniclekolacz

Joined Aug 21, 2019
7
A 9V battery has at most 500 mAh. How many LEDS are you driving? How much current for each at 18V? (just use the 12 V current, as you will/should be using a very energy wasteful resistor to drop 18V o 12V.
I'm running around 30 feet of led strips that are 60 LEDs Per Meter
Working Current: 5A
Working Input Voltage: DC 12V
I don't really know anything about current, as of right now I just have 4 9v battery harnesses connected together and then soldered to the leds.
 

paulktreg

Joined Jun 2, 2008
770
They are not suitable for your application. They can't delivery the power needed.

I don't know how long you need these LEDs to work but you need to be looking for a different power source. An option is 12V sealed lead acid.
 

Thread Starter

Bioniclekolacz

Joined Aug 21, 2019
7
They are not suitable for your application. They can't delivery the power needed.

I don't know how long you need these LEDs to work but you need to be looking for a different power source. An option is 12V sealed lead acid.
I need them to be able to run for around 8 hours before needing to be replaced or recharged. I can't use those giant sealed lead acid batteries since the LEDs are being used for a costume, and there isnt room anywhere for something that big.
 

Thread Starter

Bioniclekolacz

Joined Aug 21, 2019
7
5A is 5000 mAh. Thus your 500 mAh batter can light them for 6 minutes at most. How much time are you seeing?
They usually work bright for about an hour but then they really start to dim down, and colors such as Yellow are mostly red due to not being able to power green.
 

djsfantasi

Joined Apr 11, 2010
5,690
Out of curitousity, if a 9v battery is 5A, why is 4 9v batteries not 20A?
Depends on how you wire the batteries.

If you wire them in series, the voltage adds (4*9=36V) and the current remains the same. (.5Ah)

If you wire them in parallel, the voltage remains the same (9V) and the current adds (4*0.5Ah=2Ah).
 

WBahn

Joined Mar 31, 2012
24,853
I'm running around 30 feet of led strips that are 60 LEDs Per Meter
Working Current: 5A
Working Input Voltage: DC 12V
I don't really know anything about current, as of right now I just have 4 9v battery harnesses connected together and then soldered to the leds.
You are probably running well below 5 A if you are powering it with 9 V instead of the intended 12 V depending on the circuit powering the LEDs -- and that's ignoring the likelihood that you could get anything approaching 5 A out of a 9 V transistor radio battery in the first place.

A typical alkaline 9 V battery is about 500 mAh capacity, so at 5 A that would come out to be about 0.1 hours (assuming that it could actually achieve that capacity at that heavy a current draw, which it couldn't). So four batteries in parallel would give you something on the order of 0.4 hours (being optimistic) so about half an hour. You are probably down in the couple of ampere range, so you might get twice this amount of time or a bit more. Call it an hour or so.
 

WBahn

Joined Mar 31, 2012
24,853
I need them to be able to run for around 8 hours before needing to be replaced or recharged. I can't use those giant sealed lead acid batteries since the LEDs are being used for a costume, and there isnt room anywhere for something that big.
You may well be asking for something that simply isn't achievable with today's technology.

8 hours at 5 A is 40 Ah. To put that in perspective, that right in the range of a typical car battery, which are usually between about 20 Ah and 50 Ah.
 

WBahn

Joined Mar 31, 2012
24,853
A 9 V Duracell Coppertop has to have the current draw down in the 50 mA range in order to get a service life in the 8 hour range. So you would need 100 of them in parallel to get 5 A for that long. You can probably get by with about half of that or perhaps less since I don't think you are actually pulling anything close to 5 A. But I suspect that's still going to be a lot more batteries than you want to be slogging around in your costume (not to mention paying for).

I would recommend spending time trying to find more power-efficient LEDs and determine just how low you can get the current and still have an acceptable costume.
 

DickCappels

Joined Aug 21, 2008
5,936
One possible area in which to search for a solution is in Sealed Lead Acid Batteries, sometime sold as Gell Cells. Like a car battery, they need to be recharged, and they are a bit on the heavy side.

https://www.amazon.com/s?k=gell+cell+12v+battery&crid=25F0SPIQQBYYR&sprefix=gell+cell,aps,1147&ref=nb_sb_ss_i_1_9

If you want to use a single-use primary (one-time use) battery, put six alkaline D cells in series for 9V or 8 D cells in series for 12 volts. You can, of course use smaller cell sizes -C, A, AA but capacity goes down as the cells get smaller..

Battery holders are available for the most common cell sizes.
 
Have you actually measured 5A? You are probably not really drawing 5A because 9V batteries, even in parallel, will supply that for only a very short time and then go flat. That's not what they are designed for. A 9V alkaline battery is really just 6AAA batteries in series, squashed into a smaller space (with a lower capacity.
30 feet of led strips that are 60 LEDs Per Meter
Let's assume 10M @ 60LEDS/M or 600 LEDs. Rule of thumb tells us that at full brightness white (all colors on) a single LED will draw 60mA ~20mA per color). So 600 LEDs x 60mA per LED = 36A -- but that is only if you are blinding everyone with your lights.

As has been suggested, there are 12V solutions, but one thing to do is to make sure that you are NOT running your LEDs at full brightness. Since you didn't say what kind of LEDs they are or how they are being driven, I can't comment on how that might be done (I have a fair amount of experience with LED strips and controlling them). For improved batteries, search your favorite online retailer for "12V battery bank". I use something as is shown in the attachment. But before you strap on a big gel cell or lead acid battery (HEAVY), reduce your current draw.

Feel free to ask more questions.

upload_2019-8-27_12-27-54.png
 
Any Details other than about 10m @60led/m?
Steady on for 8 hours or changing in some way like it blinks, they are chasing lights, etc.?
Will you be using all white or different color(s)?
Is the project too far along to redesign to use fewer leds?

Just looking for more details to ensure the smallest/lightest power solution possible.
 
One trick to help out - persistence of vision. Pulse the LEDs at a bit over their rated DC current, but cut the duty cycle to less than half. Power used goes down to about half, yet the eye perceives almost no change in brightness. You will have to investigate the best combination of operating voltage/current and duty cycle for the LEDs and battery you have.
 
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