[mdlug] Old 386 needed - Power Supply

[Aaron Kulkis]

gib at juno.com wrote:
>  
> I was looking for some power supplies for some old laptops.  I noticed that JCC Computers on Inkster just South of Ford RD (Dearborn Heights) on the West side of the street had several.  
> Do you know the Voltage and amps?  Can you tell if the connector looks like a modern standard?
> 
> 

If all else fails, AC -> DC power converters are extremely
easy to make -- and you can probably make one which is
significantly more robust, both electrically, and mechanically
than what you buy at a computer store, for approximately
the same cost from parts available at any Radio Shack.



The circuit is this

                  +-------+
    o--)||(-------| ~   + |------+-----------+-------o  +
       )||(       |AC   DC|   |  |           |
       )||(       |       |   +-----+        |
 AC    )||(       |       |      ^  |    ----+----     DC  
 in    )||(       |       |     / \      ----+----     out
       )||(       |       |    /___\         |
       )||(       |AC   DC|      |           |
    o--)||(-------| ~   - |------+-----------+-------o  -
    Transformer   +-------+    Voltage   Capacitor 
                  Rectifier   Regulator   (Large)
                   ($2.50)  (Zener Diode)

The step-down for the determined by the ratio of the turns
of the windings.  For example for 120V -> 12V, a transformer
with a ratio of 10:1 is used.

The Rectifier is chosen based on voltage and current
requirements.  You want both the voltage rating and the
current rating to exceed what you need.  It will probably
have a screw hole for a small heat sink -- use it!

The Capacitor can be either one large capacitor, or
several smaller ones (the more capacitance the better).
You should aim for 1000uF (microfarads) or more.
Radio Shack sells 2200uF electrolytics.

 ------+--------+--------+--------+---     ---+---
   10uF|    10uF|    10uF|    10uF|       40uF|
     --+--    --+--    --+--    --+--  =  ----+---- 
     --+--    --+--    --+--    --+--     ----+----
       |        |        |        |           |
 ------+--------+--------+--------+---     ---+---

(Note: it does NOT work this way for resistors --
putting resistors in parallel LOWERS the resistance)




The Voltage Regulator is chosen by the desired voltage (obviously).
If you can't find the exact voltage needed, two resistors
can be put near the output terminals, like so:

---+\/\/\/\/\+---+-----o  +
       R1        |
                 \
                 /       DC
             R2  \       Out
                 /
                 \
                 |
-----------------+-----o  -
                  
To step down the voltage from the voltage of the regulator
(Vreg) to the desired voltage (Vout)


  Vout = Vreg * R2/(R1+R2)


A more sophisticated method is to replace R2 with a lower
valued Resistor in series with another voltage regulator
(Vreg2), for a voltage slightly less than Vout.

In this case:

 Vout = Vreg2 + Vreg * R2/(R1+R2)



> ---------- Original Message ----------
> From: Raymond McLaughlin <driveray at ameritech.net>
> To: "MDLUG's Main discussion list" <mdlug at mdlug.org>
> Subject: Re: [mdlug] Old 386 needed
> Date: Mon, 20 Apr 2009 14:00:43 -0400
> 
> bob dion wrote:
>> Hi all,
>>
>> My wife is looking for an old 386 laptop or desktop to run some old 
>> controls software. Apparently anything newer runs too fast.
>>
>> Anyone have something laying around?
>>
>> As a side note, any thoughts on emulation? Or would the emulator run as 
>> fast as the host?
>>
>> Thanks for any ideas.
>>
>> BD
> 
> I have an old "CompuAdd Express 325NXL" but I don't think I have the
> power adapter. The battery is, of course, ancient history. I got it from
> my brother, and I remember it working, DOS 3.x. It looks like an
> appropriate AC adapter would cost about $60 on line.
> 
> Let me know if you are interested.
> 
> Raymond McLaughlin