# Beginner Question - Choosing a Power Source Option for Circuit with Multiple Loads

Thread Starter

#### Scott Unknown

Joined Apr 13, 2020
3
I'm working on designing a circuit with two distinct loads - one being a DC motor and another being an LED strip. I want to run both off the same power source, but they have different voltage requirements. The strip requires a fixed 5V and the motor will require 12V+.

I'm currently planning to wire them in parallel. My question is, is it better to choose a power source with a higher voltage and add a step down to the LED strip or choose a lower voltage power source and add a step up to the motor? Is there a current impact/trade off between these two options? Is there a trade off in overall power consumption from the source?

If there's not a big trade-off either way, then what criteria should I consider when choosing a power source?

Thanks for the help!

#### MrChips

Joined Oct 2, 2009
27,646
12VDC -> buck converter -> 5VDC

Power OUT = Power IN x efficiency
V x I OUT = V x I IN x efficiency

In other words, when you step up the voltage you lose current capacity. Which means if the motor demands a lot of current, the 5VDC source will have to provide 2.4 times more current and some more.

Also 12V supplies are more common than 5V supplies.
12V heavy duty batteries are very common. Not so for 5V batteries.

#### crutschow

Joined Mar 14, 2008
31,091
How much current does the LED require?
Is the power source a power supply or a battery?

Thread Starter

#### Scott Unknown

Joined Apr 13, 2020
3
Thank you both for the quick reply!

The LED strip requires .3W per LED and I plan to use about 128 LEDs, so it will be 7.68 Amps.
I haven't decided whether to use a battery or a power supply. Though, given that the LED strip is pulling quite a bit of current, a battery may not be practical.

The motor is one that I've salvaged out of a power drill. I don't have the data sheet, but the model is an RS-550SH-8017. I'm guessing it's from Mabuchi Motors (https://www.mabuchi-motor.com/) based on my internet searches?

The fact that Power is conserved makes A LOT of sense (and resolves my implicit confusion about energy magically coming from nowhere). I'm surprised the articles/videos I came across did not state the current impacts explicitly.

#### ElectricSpidey

Joined Dec 2, 2017
2,177
Sounds like a job for a salvaged ATX supply.

#### Reloadron

Joined Jan 15, 2015
7,059
Allowing a margin with 5.0 volts and 7.68 amps you may as well call it 5 volt 10 amp supply. That's a pretty beefy 5 volt supply. This would go much better if you had a 12 volt LED string which would better than half the current for the same wattage. Finding a 5 volt out 10 amp buck converter may be a challenge Here is an example. Be wary of stuff off the boat as many do not make their specifications and fall short on current. Depending on motor current you can find your 12 VDC source.

Ron