[ltp] auxiliary battery packs for A/T/X series

[James P. K. Gilb]

You may need a voltage regulator to make the DC port of the laptop 
happy.  In fact, you probably should avoid overvoltage of that port, it 
could cause problems.

You can get a project board and variable output linear voltage regulator 
at Radio Shack (or Frys or Digikey, etc.).

My IBM adapter indicates it it 16 V at 4.5 A, which is pretty sizeable 
power.  If you drop 2 V at 4.5 A that is 9 W of power.  The regulator I 
have from RS is 15W, if you tie down the ground to enough metal to 
spread the heat.

Also, alkaline batteries have a useable voltage range of about 1.5 V to 
0.9 V (in order to get 70% of the power.)  Thus, 12 cells will range 
from 18 V down to 10.8 V before you really start to run out of power. 
If you limit the drop to 15 V, (probably too little low), you will have 
used only a small percentage of the mA-hours of the batteries.

NiMH, Litium or NiCad cells would work better (in terms of a more stable 
voltage) than alkalines, but they are more expensive.

You could try to get a buck/boost regulator (i.e. one that either 
increases or decreases the voltage depending on the input voltage) that 
would take 12 to 18 V and regulate it at 16 V, but that will be somewhat 
more expensive, especially at 4.5 A of current.  If you are going to do 
that, you may pursue using only a buck regulator and use less cells, say 
6 alkalines (i.e. 5.4 V to 7.2 V input).

If you decide to try, post your results, it sounds like an interesting idea.

James Gilb

Brian Beattie wrote:
> A while back, there was some discussion of auxiliary battery packs. The
> little reasearch I have seen indicates that some of this packs may be
> unregulated, meaning that the output of the battery pack is the raw
> battery voltage.
> 
> This has lead me to wonder, what the requirements for the DC power input
> of the thinkpads are and if it would be possible to use a battery pack
> made up of disposable cells (D or C cell alkaline for instance) by using
> say 12 cells to cover Alkaline and NiMH, 18V - 15V nom.
>