Re: [CAD_CAM_EDM_DRO] Re: Info on Jumping a PC power supply?

Sam...,

I believe that this is only the case, if you don't meet the minimum
loading requirements on the various output lines, which includes
avoiding "crossloading". Crossloading happens when you pull a lot of
current from the +5 side, and not a "balanced" amount from the +12 side
(or vise versa).

If all the minimum loading requirements are met, and there's no
cross-loading, I'm not sure why using an ATX supply wouldn't work.
(It may be hard to achieve this goal, however).

The appeal, of course, is that ATX supplies can be so darn cheap (<
$20 US), and produce so much current (more than would be needed for
small motors). I think it would be hard to find a brand-new, assembled
linear supply for that price. (If you are aware of one, please let me
know!)

Mike

sam3216549872003 wrote:

> --- 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
>
>