Pixels on a battery

[Johnnyboy]

Hello,
up to now I had my Xmas light show mobile arround munich with the use of standard 220V current. I in most cases use the 5V-Versions of the RGB strings and stripes. (4800 Pixel tree, 4800 Pixel Matrix, and arround 4000 pixels in other objects like stars, singing trees, snowflakes aso.). Therefore i need a lot of power supplies with many cooling fans making noise.
I would like to expand more and be more mobile and independent.
So I plan to Use LiFePo4-Batteries and think of using them directly without inverter and power supplies. LiFePo Batteries fully charged have about 13.5 Volts. Do the LEDs survive that? I know the controller would.
I have inverters but it would be nicer without those power supplies.
So if bert-nc wants to consider LiFePo4-Batteries, they would make a huge difference than lead batteries.
I use 3 LiFePo Batteries parallel with 200Ah each, wich makes 7.5 kWh capacity and I can discharge with 600 amps continious. I even Plan to have 8 of these LiFePos with a total capacity of 20kWh (solar powered)
greetings from Munich

Running pixels at 13.5v may survive in the short term but the would degrade the life significantly.

You also have to consider that batteries loose voltage when they discharge, this may or may not be an issue depending on how your wired it all up. I would suggest looking at something to step down the voltage a litle

 

[Skymaster]

Running pixels at 13.5v may survive in the short term but the would degrade the life significantly.

I tend to disagree slightly - 12V pixels are not "12V" in the sense that this is a fixed voltage, that is their nominal voltage.

For WS2811 based bullet pixels, they use either a regulator to drop the voltage down to 5V, or a set of resistors to limit the current through the LEDs.

The voltage regulator will have no problems with 13.5V, and will drop the voltage smack on to 5V with a slightly higher thermal output.

The resistor pixels will have a slightly higher current flowing through the LEDs, but this will be limited to the 16mA per colour by the 2811 chip. Internally the power rail to the chip runs through an LDO Regulator, with an external voltage divider resistor. The small change in external voltage will not affect this.

For 12V strip, they use 3x LEDs in series rather than a resistor to handle the higher voltage, and therefore have no issues on the LED side. The power to the 2811 chip is the same as bullets.

GS8208 based 12V drivers have an inbuilt regulator, and and rated for up to 15V as their standard specification.

 

[merryoncherry]

I tend to disagree slightly - 12V pixels are not "12V" in the sense that this is a fixed voltage, that is their nominal voltage.

These are all reasons you'll probably get away with it, yes, at least using the common designs on the market today. The 12V regulators will generate 20% more heat at 13.5V than they would at 12V, but that may well be within their rating. especially if you don't run 100% white for long. The typical 12V resistor pixel from the last few years runs at 10mA max per color at 12V, and would probably hit 12mA max per color at 13.5V, which is well below the electrical rating for the components, again depending on heat. So I agree it is probably OK to do this for all the components I own, but there were reports from a few years ago (2018) of pixels that were much more sensitive (
View: https://www.youtube.com/watch?v=ur77Hv1cFfw
). so I wouldn't wave off the risks completely.

 

[OG-Munich]

You also have to consider that batteries loose voltage when they discharge, this may or may not be an issue depending on how your wired it all up. I would suggest looking at something to step down the voltage a litle

No, with LiFePo Batteries you do not have the voltage drop issue. The Battery will only drop voltage unter 12 V , if the charge level is below 10%

And even with 5% left it ist at 11V

Discharging with 1C (means with 1 times of capacity e.g. 200Ah with 200 Amps discharge) affects voltage a little bit but that means 2.4 kilowatts of power draw per battery and i plan to use at least 3 Batteries up to 8. So i could draw at least 7 kilowatts up to 19 kilowatts of discharge power. That would be a powerful big lightshow..

You can not compare lead batteries with LiFePos. That is a huge difference. Here they used 4 Batteries in a row.

 

[Johnnyboy]

Discharging with 1C (means with 1 times of capacity e.g. 200Ah with 200 Amps discharge) affects voltage a little bit but that means 2.4 kilowatts of power draw per battery and i plan to use at least 3 Batteries up to 8. So i could draw at least 7 kilowatts up to 19 kilowatts of discharge power. That would be a powerful big lightshow..

You can not compare lead batteries with LiFePos. That is a huge difference. Here they used 4 Batteries in a row.

My experience in LiPo batteries was with RC helis where the batteries are rated at 90-120C. Peak draws while doing hard pulls would result in current draws in excess of 250A+. In those situations the there is significate voltage drop, though this would recover after the heavy load was removed.
I was mostly using 6S batteries that have a nominal voltage of 22.2V with a peak charge of 25.2V and a low safe cut-off of 19.2V. Thats where my experience of change in voltages comes from.

LiPo/LiFe/LiPePO4 all have slightly different characteristics and use cases. I admit my experience is mainly with LiPo and LiFe types.

In saying all that, my comment about running pixels above the 12v specified voltage is based on my reading of the issues people have been having in the last few years. Why drive something harder / generate more heat if you don't need to. In my case I am undervolting slightly at 11.7V for pixels. Given very few people drive their pixels at 100%, the choice to undervolt doesn't have any impacts on perceived brightness.

 

[OG-Munich]

I fly RC models and drive RC-cars. I even had 3 T-Rex Helis. I even jump started a car with a 3S 4000mAh LiPo. Yes hard draws result in voltage drops, but not with 1C. Think about that: A 3S 5000mAh drawing 120C means you draw 600 amps and 6.6 kilowatts.
With a 5kWh pack I discharge it (charging my PHEV SUV car drawing 3000 watts. At the end of the discharging cycle I have bigger voltage drop, but at the configured 10.5v power cut there is only 6% of charge left and it should shutdown then.
How many Kilowatts does your lightshow draw in average? I guess my Xmas light show with about 14000 LEDs draws less than 2 kilowatts. That is no problem for the batteries. Shure the peak power consumption probably could reach 4kW, but even that is within the specs of my batteries (with 3 batteries 7.8 kW) for continuous draw.

not having to use power supplies would be a big advanate for mobile usage.