# Is running two voltage regulators in parallel safe?

Components

• Battery (7.5V 6A Max)
• D24V25F5 (5V 2.5A step down)
• U3V50F12 (12V 5A step up)
• Raspberry Pi 3 (5V 2.1A-2.5A)
• Motor (12V 3A stall) (Using H-Bridge)

Would the setup be suitable? I much prefer to use one battery instead of two batteries in which one battery runs to each of the voltage regulators. Below I have included a drawing of how I'm going to solder them onto a prototyping PCB.

Do the math on your power budget:

• The Pi needs up to 2.5 A @ 5 V = 12.5 W
• The motor needs up to 3.0 A @ 12 V = 36 W

That's a total of 48.5 W

Taking the efficiency of the converters into account, which is going to be 90% or less, that becomes at least $$\\frac{48.5 \text{ W}}{0.90} = 53.9 \text{ W}\$$ that you need from the battery.

But you say that the battery can only supply 6 A @ 7.5 V = 45 W.

This will work only if you can tolerate overloading the battery each time the motor starts or stalls. (Motors generally pull their stall current when starting from a dead stop.)

And just to clear up the misconception in the title, the regulators are in parallel, not in series.

• I think it should be added that there is nothing wrong at all with the concept of connecting a battery up to multiple voltage regulators, it's just that in this particular case the power doesn't work out. – Hearth Sep 14 '19 at 19:09
• Yeah. I forgot to account for the efficiency of the conversion. – parkcandy Sep 15 '19 at 6:17