Date   : Wed, 15 Aug 2007 14:22:04 +0200 (BST)
From   : johan@... (Johan Heuseveldt)
Subject: Master battery packs

Hi,

On Wed 15 Aug, Alex Taylor wrote:
> On 14/08/07, Eelco Huininga <eelco@...> wrote:
> 
> > Wouldn't it be possible to replace the batteries with NiCd's?
> 
> It ought to be possible, although the voltage of three normal NiCd
> cells in series would be 3.6V, not 4.5V.

I think your point of start is incorrect. Originally a rechargeable
cell was planned, but the danger of explosure had it changed by 3 AA
non-rechargeable cells. I think the original was 3 Volts?

The diode was placed to prevent charging non-chargeable cells!
(There's also a resistor in line with the diode)

There are newer cells which are 3 Volts exactly, but have no idea how
suited they are for the charging-circuit present.

> This could be increased if
> necessary by adding a fourth cell to make it 4.8v, or using 1.5V cells
> which I have seen available somewhere.
> 
> Whether these could be charged by the Master when switched on is
> another matter. In my (limited) knowledge, a 4.5V NiCd battery pack
> would need 6 or 7V to charge, so some regulation circuitry would be
> required. It should be possible but with my limited knowledge of
> electronics, I'll leave discussion of the details to the experts...

I suppose the voltage charged with is more of a result from the charging
current, which is the important factor. E.g. that current should/could be
1mA, so constant trickle charging is allowed.

If the charging circuit is very well designed, the rsulting voltage is
automatically adjusted to the correct value. Perhaps the Master version
is simpler - commercial reasons - and a certain voltage, exact or a small
range, is designed for/expected.


Greetings,
Johan

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
If you're going to do something tonight that you'll be sorry
for tomorrow morning, sleep late. - Henny Youngman