# Quick Current Consumption Question

Discussion in 'Electronic Basics' started by CoogarXR, Jan 29, 2004.

1. ### CoogarXRGuest

Hello,

I have 2 cameras that have 12v 1000ma "wall warts". I have a 12v 4a regulated
power supply that I would like to use in it's place. I plan to add more cameras
to it some day, so the current will be a closer match, but for now my question
is this: If I hook both cameras up to this power supply, will they draw only
the current they need, or will the power supply damage the cameras by "forcing"
the extra available current through them?

I know this is a very basic question, but it has been many years since my
electronics classes

Thanks
CoogarXR

2. ### Costas VlachosGuest

This is a very common beginner's question, and a perfectly legitimate one.
Your 12V 4A power supply is able to supply 12V at *up to* 4A of current. The
load will draw as much current as it needs (1A maximum per camera in your
case). So the supply will provide a total of 2A to the combined load. Even
if it was a 100A supply, it would still provide the exact same amount of 2A.
For the supply to be able to "force" 4A through the load it *must* increase
the voltage to a value higher than 12V (which it won't). As you can see,
of the capabilities of the power supply. In resistive loads, the
relationship between V and I is given by Ohm's law:

V = I x R

So, for a fixed load R, the voltage and current are linked together and
nothing in the world can "force" a change in one without affecting the
other. Your cameras are not entirely resistive loads and hence will not
generally obey that law, but the idea is qualitatively similar.

So, don't worry about the 4A supply rating. It just means it can support up
to 4 cameras at the same time. Just make sure it's regulated and the
connection/polarity is right - you don't want to fry your expensive cameras!

cheers,
Costas

Hello,