[Elecraft] RF Hash from IBM Laptop

[Jack Brindle]

BE VERY CAREFUL DOING THIS!!!!!

This advice is specific to a single product form one manufacturer. Each  
laptop manufacturer has different battery maintenance circuitry, and  
they operate off different voltages, usually NOT 13.8V! Input voltages  
tend to vary between 12 v and 30 v depending on manufacturer. As an  
example, Apple PowerBooks and iBooks need about 25 volts. Applying 20V  
to a 12V input WILL cause undesired effects. Applying 12V to an 18V  
input MAY cause undesired effects.

Also, be sure that any power adapter you use will provide enough power  
to run the laptop. Laptop power supplies started out at about 20 watts  
many years ago, and generally run around 45-65 watts these days.

I would STRONGLY advise that anyone wanting to run their laptop from a  
12V battery source purchase a commercial power adapter for their  
laptop. These are available from many sources, including your local  
neighborhood computer store.

On Aug 29, 2004, at 11:14 AM, Bob Tellefsen wrote:

> Hi don
> I have two laptops here, and both can be run from an external battery
> source.
> HOWEVER, I need to run them through a small inverter to bring the
> voltage up to around 13.8v.  I checked this with my variable
> voltage bench power supply to find out where the laptop switched
> from external power to internal.  It is usually above normal
> battery voltage by 1-2 volts, hence the small inverter.
>
> I built the one from Sam Ulbing, N4UAU.  It was written up in QST
> as "My All-Purpose Voltage Booster".  He sells the kit for a very
> reasonable price.  You can find him on the web under his call.
>
>  I used mine on Field Day, and it was extremely quiet.  Not a trace of  
> hash
> anywhere.  A side benefit in running on batteries in the field is that  
> the
> converter is regulated.  As the input voltage drops, the output stays
> pretty near constant.
>
> This would not be a problem in the shack with a fixed supply.  I  
> suggest
> you check your laptop using a variable voltage power supply and find
> out how low you can go before it switches over to the internal battery.
>
> Good luck and 73
> Bob N6WG

- Jack Brindle, WA4FIB
------------------------------------------------------------------------ 
---------------------