Powering 12v and a Pi from the same battery

Question

I'm building a game that contains:

• rpi (5v)
• 2x 9g micro servos (5-6v)
• 5m RGB led strip (12v)

Right now I use 3 different sources:

• 4xAA battery packs (6v) for the servos
• 8xAA battery pack (12v) for the LEDs
• 1x power bank (5v) for the raspi

This is totally wasteful. My plan is to buy a rechargeable battery (something like this :link to aliexpress) and power the LED's straight from there.

Then add a voltage step down like this one (link to aliexpress) and hang the servos and the Pi from there.

Do anyone foresee any problems in the setup? Will the servos draw too much current from the voltage regulator and therefore reboot the Pi? Will the sum of all tree components just be too much for the base 12v battery?

Answer 1

Two words of warning:

• Don't underestimate startup currents of motors. It's not uncommon for a stalled motor to draw 10 times the current it consumes during normal operation (only for half a second, but half a second is plenty to reboot your Pi). Check the specs or measure this value before you decide how much current you need.

• Don't try to save every last penny on powerful Li-ion batteries. I've seen cheap batteries with very poor charge balancing between the cells, which either stop working much earlier than they had to (because there's one cell charged to the max and another one which is nearly empty so the battery would neither charge nor discharge) or become a fire hazard as they age. If possible, try getting a battery with electrical safety certification logo valid in your country (like FCC in the US). The last thing you want is explaining to the insurance company how a fire started in your house due to an uncertified electronic appliance.

Answer 2

From the battery link:

Output current:1-2.4A

So, you will need to check out current consumption of all devices.

I've found online that the servos consumption is between 0.25 to 0.75 A. Led consumption depends on the led itself. The current needs will be modified by how much resistance it will face.

Raspberry pi depend on what are you using. Assuming Typical bare-board active current consumption will be 400mA.

So, you'll be drawing, at minimal power consumption 250x2 + 400 + led_number*led_drawing. = 900 + LED mA which gives you only 1.5A for the leds, which I assume is too low for powering the 5 meters of the led strip.

Then add a voltage step down like this one (link to aliexpress) and hang the servos and the pi from there.

Regarding this, the output is 3A. So, it must be ok.

Personal approach to this:

I do recommend get some 3S (11.1V) or 4s (14.8V) lipo battery, which will give you much room (in terms of current) for powering the leds, but you'll need to get a lipo charger (can be found for about 10€ some times at chinese websites)

If the game is permanent and doesn't matter how much it weights (ie: not a handheld device) I'll recommend get a car-like battery. There are some with a small footprint than can provide lot of current, but I'll go with the lipo

Answer 3

I would suggest using some SEPIC (Buck/Boost converter), one for each voltage you want. They are inexpensive, operate at 90% or better efficiency and the output is adjustable. This necessitates having a meter of some type to set it. You can get them well under 1/3 the cost of a pi.