# Powering multiple devices from a single power supply

I am learning electronics on my own and have been having a lot of fun. I am currently working on creating a Nerf sentry gun for fun with my son. I am at a point there where I need to power multiple devices and am not sure about the best way to go about it. I want to power a Raspberry Pi (RPi), two servos and a 12V relay that controls an air solenoid (12V). I bought a battery pack that supplies 12V and max of 3000 mA current. I am confused though on how to efficiently convert the power to each of the devices using the single battery pack.

I originally purchased a breadboard power connector that would convert 12V to to 5V on each of the rails. The problem I ran into was the breadboard power connector will max out at 700 mA and I cooked the first one when I hooked up my RPi.

I also purchased some 5 volt regulators that seem to be most common but I run into the issue of wasting the excess voltage to heat. This also leaves me with the problem of how to split the voltage between two rails.

I guess my question is how can I take the 12V input from a battery pack and split it into 2x5V outputs to power each side of my bread board. My idea is that I want to power the two servos on one side and my RPi on the second from a single 12V input. I can create my own second battery pack to power the 12V relay outputs to control the air solenoid.

Sorry if my verbiage is not correct but I am trying trial by fire.

Extra links for the stuff I am trying to power in case I am completely off base:

• Search for "DC-DC converter" look for 12V to 5V. The popular 'selling websites" should have something which will step down 12V to 5V efficiently. They sometimes say 'switch mode'. Avoid 'linear' which is the parts you have been using, They will need to convert the power of the 7V voltage drop, and 700mA for the R-Pi to heat, which is about 5W. The other parts sound okay at 12V. Oct 2, 2014 at 16:21
• I found a 96% efficient dc-dc converter that appears like it will work well. It is rated up to 3 amps so that should be fine for my little project. Thanks for your help. Oct 2, 2014 at 16:50
• You are welcome. I believe shopping questions are off-topic. However, it can be vey hard to find something on the web if the name is not known! 3A sounds way more than enough. It may be better to use two, one for the R-Pi, and one for the servos. Some servos (which look like the ones you link to) take a huge stall current, and might dip the R-Pi voltage enough to make it erratic. The R-Pi should be okay with 1A. Oct 2, 2014 at 17:06
• Thanks again, I was thinking that and did order two of them. I wanted to isolate the power for the R-pi onto its own leg. Appreciate the help again. Oct 2, 2014 at 17:37
• BTW if you want to add an answer, I will send the reputation points your way. Oct 2, 2014 at 17:44

Search for "DC-DC converter" look for "12V to 5V".

The popular 'selling websites' should have something which will step down 12V to 5V efficiently.

They sometimes say 'switch mode'.

Avoid 'linear' which is the parts you have been using, Linear voltage regulators will need to convert the power of the 7V voltage drop, and 700mA for the R-Pi to heat, which is about 5W. A waste of energy and battery charge.

It may be much better to use two DC-DC converters, one for the R-Pi, and one for the servos.

Some servos (which look like the ones you link to) take a huge stall current, and might dip the R-Pi voltage enough to make it erratic. The R-Pi should be okay with 1A

A cheap and simple solution that is by no means elegant would be to offload the excess voltage handling from the regulators to other components. A series array of rectifier diodes like 1N4001 could be used to drop voltage to a level more easily handled by the 5V regulators (perhaps 6V or 7V). Use one array for each regulator, and use at least 3 parallel sections so that the 3000mA max current of the PS is divided down to 1000mA or less to respect the max current ratings of the diodes and the regulators.