# Basic 12V DC PSU resistance & current distribution Question

#### jc29

Joined Aug 23, 2014
2
Hey guys,

Been getting into home automation as of late, but am weak on the electronics side, hoping for a bit of direction to build my foundation.
I have a basic question regarding supply multiple DC devices from a single DC power supply.
Scenario is:

INPUT:
12V 5A DC power supply DC plugs
OUTPUT:
2x 12V 1.8A DC 2wire fans
1x 12V 1A water pump

If I only have 1 of the 3 equipment running, then does the water pump only take the 1A it needs. I figure with the other fans seen as an open circuit would then mean the 3.6A would also flow into the water pump by KCL.

So correct me if im wrong, I'd need to setup a set of parallel resistors for the case when the switches are open.
If that makes sense?

#### BobTPH

Joined Jun 5, 2013
3,306
When you have two lamps plugged into an AC outlet, and one of them burns put, does the other ine double in brightness? If you can confidently answer that, you should be able to answer your question.

Bob

#### crutschow

Joined Mar 14, 2008
27,172
would then mean the 3.6A would also flow into the water pump by KCL.
If you properly use KCL, it would not show that.

#### MrChips

Joined Oct 2, 2009
23,507
A 12V car battery can crank out 200A.
One light bulb takes 1A, another takes 4A. The radio draws 2A. Yet they are all connected in parallel to the same 12V source without burning out.

#### BobTPH

Joined Jun 5, 2013
3,306
I’ve always wondered, if a powwr supply worked the way a lot of beginners think it does, i. e. put out the same current independent of the load, where do they think that current goes when no load is connected!

Bob