Can a Mac Portable battery be "trickle charged"?

From: Gary Oliver <go_at_ao.com>
Date: Fri Apr 28 01:22:19 2000

At 10:44 4/27/00 -0600, you wrote:
>I have one of those "universal" AC adapters that can do 7.5 V, but only 300
>mA. If I plug in this adapter to the Portable, will the internal battery
>eventually obtain a usable charge (assuming it's not totally dead, as so
>many are)?
>
>Any suggestions gratefully received.
>
>Mark Gregory

Two more cents worth: I've seen basically three types of chargers (or wall-wart
power supplies.) At the cheap end are those using fairly high impedance
primary
transformers (with rectification and possibly filtering if DC
supplies.) Better
supplies contain a better quality transformer and a linear regulated DC output
driver. The best supplies are the newer, high efficiency switchers.

The cheap warts are designed to provide the rated current at the (approximate)
rated voltage continuously. At a lower current, you get a higher voltage -
it's
all open loop. At a higher current, you get a lower-than-nominal voltage, but
you also will get a premature burnout. These supplies are designed to
self-destruct when the transformer core exceeds a rated temperature - burns out
the transformer instead of burning down your house. In my experience, most of
these DO NOT use a fusible link - they rely on the transformer primary opening.
Those that do use a link usually bury it deep in the primary transformer
winding.
You will have to rewind the transformer to fix the open circuit in either case.

For the linear and switcher type supplies, they usually just current-limit
and/or
shut down if you attempt to exceed the rated current.

In the case of the cheap supplies, where the required current greatly
exceeds the
rated capacity of the supply, it will probably work for while and then the
power
supply will die. For the other types of warts, they will probably survive but
the outcome of the charging is dependent on the circuit providing the battery
drive - can it provide a proper charging voltage when operated at with a lower
current supply?

-Gary
Received on Fri Apr 28 2000 - 01:22:19 BST