# Powering 5v LEDs with 6 or 12 volt batteries

I'm building an art piece that uses about 2000 RGB LEDs. They are WS 2812b LEDs, and I expect the normal draw to be around 200-300 watts. If all bulbs go full white at the same time, it could pull up to 500 watts.

I have power supplies that can handle this when I'm running off of 110v AC, but I'm trying to come up with a battery powered option.

Some concerns - the amount of light emitted will be highly variable. So I want to make sure the voltage stays within safe bounds given that reality. Also, it should be able to run for around 16 hours between chargings.

What battery configuration would you recommend for this piece?

6 volt batteries? 12 volt batteries and build a voltage regulator?

Thank you for your thoughts!

• What voltage and current do you usually deliver with the power supplies you already have? this is in order to know the voltage and current that you LEDs need. – berto Mar 30 '16 at 0:10
• I'm currently using a small 3 amp, 5 volt power supply. But I'm picking up 60 amp ones for the main project. I should probably get three instead of two. – chrispitzer Mar 30 '16 at 0:13

Power

According to the WS2812 datasheet (I can't find a WS2812B datasheet and you didn't provide a link) the integrated LED chip and controllers run on a supply voltage of 6 to 7 V and a current of 20 mA per R, G and B LED. Total all-on power demand given by $P = VI$ will be $2000 \cdot 3 \cdot 6 \cdot 0.02 = 720 W$. You have underestimated on your power budget.

Current

Max current is simply the sum of all the currents when all LEDs are on. $I_{MAX} = 2000 \cdot 3 \cdot 0.02 = 120 A$.

Battery

Batteries are typically rated in Ah (ampere-hours). The manufacturer will provide an amp-hour rating at a specific discharge rate. If you discharge at a higher rate the amp-hour rating decreases.

Ignoring that for a moment, at 6 V (no voltage conversion) you need 120 A x 16 h = 1920 Ah capacity. Let's round it up to 2000 Ah. We can de-rate, for example, if we assume that on average 50% of the LEDs will be on, to 1000 Ah.

As an example, the 6 V Yuasa battery pictured above has a 12 Ah capacity. You would need $\frac {1000~Ah}{12~Ah} = 83$ to give 1000 Ah capacity. Weight: 83 x 2.05 kg = 171 kg. Guide price: 83 x €16 = €1,328 from Farnell.

Charging

Charge current for an ideal battery will be $\frac {Ah~capacity}{charge~time}$. For an 8-hour charge time that would work out at $\frac {1000}{8} = 125~A$.