Re: Info on Jumping a PC power supply?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffspinner" <j.spinner@...>
wrote:

>
> I'm trying to jump out a pc power supply to run some stepper

motors.

> Does anyone know where I should install jumpers to power up a

supply

> that is used on a desktop PC?
>

Unfortunately a computer power supply is not a good choice for any
thing other than a computer.

Although I have heard of several people using computer power supplies
for things other than a computer. This is never a good idea.


The problem is that a computer power supply regulates the voltage on
only one output using a PMW controller, either the 5V or 12V output.

This means that if you are using the 12V, and it is regulated on the
5V output your available current will drop very quickly.

If it is regulated on the 12V side, the 5V side will tend to drift
higher and higher.

The more current that is pulled from the 12V side the higher the
voltage on the 5V side.

This can damage the capacitors on the 5V side.

On ATX power supplies the 3.3V output is normally derived from the 5V
output.

The -12V and -5V outputs are normally linear regulators.

You are better off building a transformer power supply.

It will give you a much better available current.

Sam