# DC Power Supply

Discussion in 'Electronic Basics' started by servozoom, Dec 31, 2005.

1. ### servozoomGuest

I was sent a power supply for a unit that requires 9 volts DC with
180ma.
The power supply says input 220v AC, not 110-220v, so I guess that
means non switching, and is supposed to supply 300ma of current. . I
checked the voltage output and it is 9.5 volts, so I'm good with that,
but I do not have an amprobe, so I couldn't check the current.
Basically the power supply does not have enough "juice" to power the
unit (a CCTV camera).

Here is the question. Since I can't check the amperage from the
power supply, could the fact that I'm pluging it into 110v and not 220v
be the reason that I am having a problem? What would the amperage
output of the unit be? Is there a conversion formula? Is it half?
It appears to be the situation. Thanks in advance.

2. ### Walter HarleyGuest

Cheap power supplies often put out much more than their rated voltage, when
they have no load. There is no way to determine what the voltage it's
putting out with full load and 110V input is, except to test it. There are
too many variables. You could guess "half the rated voltage" but you'd
probably be wrong.

9VDC power supplies cost what, \$10 if that? Go to Radio Shack, or
http://www.jameco.com, and buy the right one. Or buy a 110VAC to 220VAC
step-up transformer if you're really attached to this particular power
supply for some reason (such as an oddball power connector).

3. ### Jasen BettsGuest

measure the voltage again with the camera attached (or use a 50 (or 47)
ohm resistor) it'll probably be less than 9v under load.

a generic replacement powersupply should only cost a few dollars.

Bye.
Jasen