[mdlug] Old 386 needed - Power Supply

[Raymond McLaughlin]

Sorry I hit "Sent" prematurely before.

Jay Nugent wrote:
> Greetings Ray,
> 
> On Tue, 21 Apr 2009, Raymond McLaughlin wrote:

>> Thank you Aaron and Jay,
>>
>> I have been, and continue to mull a more detailed reply, but will here
>> quickly point out that I have, on hand, several serviceable AT and ATX
>> powers supplies. Each of these provide both a +12 (yellow) and a -12
>> (blue) output. Shouldn't this look like 24v to any DC device connected
>> to it? 
> 
>    CAUTION.  The +12 and -12 are referenced to the ground lead -- and this
> is oftentimes directly connected to the chassis of the power supply as
> well as the motherboard.

>  Sound ground *MUST* be isolated between the
> power supply and the PC/laptop if you expect this to work.  Never the two
> shall meet :(

I'm not clear on what you mean here. "Isolated between" is confusing to
me. Do you mean connected to each other (i.e. a common ground) and
isolated from, say an earth ground? Please clarify.


>> Just quickly, shouldn't the 24 volts described above provide a
>> satisfactory "first approximation" of the 22 that the laptop requires?
> 
>    I would expect 24 volts would work fine.  24 is within 10% regulation 
> of 22 volts.  I would find it unlikely to cause the magic smoke to escape.
> Be carefull though...many wall-wart supplies may "say" that they are 24 
> volts, but they usually mean they will *produce* 24 volts at rated load.  
> At less than rated load they *may* produce a much higher voltage.  Always 
> measure with a meter BEFORE connecting the laptop to it the first time.
>  
>       --- Jay
>