Alt-BEAM Archive
Message #01043
To: Wilf Rigter Wilf.Rigter@powertech.bc.ca
From: Bob Shannon bshannon@tiac.net
Date: Fri, 26 Feb 1999 19:44:07 -0800
Subject: [alt-beam] Re: Li-ion cell charger
Wilf Rigter wrote:
>
> Speaking of 4V lithium-ion cells, they are ideal for our robot applications:
> very light and high energy density. What is the recommended charging circuit
> for these cells?.
First understand that an 18650 Li-Ion cell has about the same explosive
energy
as a thimble full of gasoline.
Unless your charger is accurate to within 1% of the cells true capacity,
you risk dammaging the cells and risking a major malfunction.
A Li-Ion cell must be charged with a constant current for the majority
of the cycle, and then switch over into a constant voltage mode.
Charging MUST be terminated within 1% of the full cell capacity.
Charging must also be terminated if either the change in voltage over
time, or change in current over time exceeds very specific limits.
And that aint all...
You must stop discharging within 1% of the cells empty state. If you
over discharge the cell, extracting more than its rated energy, you will
cause a permanent loss of storage capacity.
So to charge and discharge a Li-Ion battery, you need to constantly
track the energy entered and taken from the cell. If you don't know the
cells current
capacity, you need to watch the cell voltage like a hawk to prevent a
disaster.
If you need a charger for a Li-ion battery, you simply must get a
dedicated charger chip, probably from Benchmarq microelectronics. Do a
search for their web site, and you'll find the Li-Ion charger chip you
need.
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