best protocol for carging a Laptop Battery

  • Thread starter Thread starter Rahul
  • Start date Start date
OK, thanks for the links. There seems to be a set of advantages and
disadvantages for each type.
 
Bill in Co. said:
Interesting - thanks.
But is this because they weren't available in the identical size packages,
with the same electrical capacity (i.e., voltage, ma-hrs, etc)? Or
because of the external charging circuitry (if any) possibly having
different requirements?
Click to expand...

Although the electrical characteristics are pretty similar (apart from the
greatly increased mAh capacity), Ni-MH has an exothermic charge reaction
(Ni-Cd was endothermic). This means that when rapid charging the cells, it
is necessary to have temperature monitoring and cutout which was unnecesary
with Ni-Cd. However, a temperature sensor could be used to detect the end
of charge condition for Ni-Cd (as the charge power had to be disipated as
heat once the battery stopped absorbing it's charge). This cannot be so
easily done in Ni-MH as the cells get warm anyway.
 
M.I.5¾ said:
Although the electrical characteristics are pretty similar (apart from the
greatly increased mAh capacity), Ni-MH has an exothermic charge reaction
(Ni-Cd was endothermic). This means that when rapid charging the cells,
it
is necessary to have temperature monitoring and cutout which was
unnecesary
with Ni-Cd.
Click to expand...

Interesting. And what a pain...
However, a temperature sensor could be used to detect the end
of charge condition for Ni-Cd (as the charge power had to be disipated as
heat once the battery stopped absorbing it's charge). This cannot be so
easily done in Ni-MH as the cells get warm anyway.
Click to expand...

I would have thought the end of charge condition (for any battery) could
have been sensed by a dropoff in the charging current when the battery is
nearly fully charged.
If, for example, one used a fixed charging voltage source, and charged the
battery through a resistor, the current would start off high, and then drop
as the battery got charged. Apparently they don't do it that way.
 
Bill in Co. said:
Interesting. And what a pain...


I would have thought the end of charge condition (for any battery) could
have been sensed by a dropoff in the charging current when the battery is
nearly fully charged.
If, for example, one used a fixed charging voltage source, and charged the
battery through a resistor, the current would start off high, and then drop
as the battery got charged. Apparently they don't do it that way.
Click to expand...

Both NiCd and NiMH cells are charged with a constant current. A
slight drop in cell voltage, at least with NiMH, indicates full
charge.
 
Måns Rullgård said:
Both NiCd and NiMH cells are charged with a constant current. A
slight drop in cell voltage, at least with NiMH, indicates full charge.
Click to expand...

OK, with later retrospect, I was guessing that might be the way they
actually do it, since it's probably safer (since there is no huge initial
current inrush, like there would be for a dead battery).

But the problem with that method is that you can't tell when its fully
charged as easily as you could if you were to use the constant voltage
source method (and just monitor the charging current), from what I can see.
 
OK, with later retrospect, I was guessing that might be the way they
actually do it, since it's perhaps a bit safer (since there is no large
initial
current inrush like there would be for a dead battery). But....

But the problem with that method (constant current charging) is that you
can't tell when
the battery is fully charged as well as you could if you were to use the
constant voltage
source (with a series resistor) method, and monitor the charging current
(from I what I can see).

So I still don't see why they don't do it this way.
 
Bill in Co. said:
OK, with later retrospect, I was guessing that might be the way they
actually do it, since it's perhaps a bit safer (since there is no large
initial
current inrush like there would be for a dead battery). But....

But the problem with that method (constant current charging) is that you
can't tell when
the battery is fully charged as well as you could if you were to use the
constant voltage
source (with a series resistor) method, and monitor the charging current
(from I what I can see).

So I still don't see why they don't do it this way.
Click to expand...

Actually modern charge monitoring circuits have got quite sophisticated, and
are quite adept at detecting end of charge condition using the electrical
characteristics of the cells. However, the best of them still use some form
of temperature monitoring as an extra clue.
 
Bill in Co. said:
OK, thanks for the links. There seems to be a set of advantages and
disadvantages for each type.
Click to expand...

The two main differences that affect choice are:

Mi-MH: Has a greater capacity per unit volume (at least 4 times these days -
and rising). Because they are lighter, an even greater energy capacity per
unit weight.

Ni-Cd: Can deliver very high discharge currents with practically no loss of
capacity. They can even deliver what might be regarded as short circuit
currents with little damage. Ni-MH suffer damage with even moderately high
currents (but even this is improving as we type).
 
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