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PICList Thread
'Battery Charging Techniques'
1997\08\06@081902 by Scott Walsh


    I know this is off topic, so please repsond via email.

    I need to implement a battery charger for NiMH cells, the battery has
    three cells.

    The battery needs to be fast charged in about 1 hour, the obvious
    thinsg I need to know are how do I determine when the battery has been
    charged. What time period did people take a measurement of the battery
    voltage ... 30secs, 1min maybe 2mins? Do I need to wait that long for
    the battery voltage to have change enough to be detected by an 8bit
    ADC. That of course raises the question as to whether 8bit ADC is
    enough ... I may be able to get a 10bit one.

    I am in the process of buidling a test rig with GPIB equipment to
    collate the data I need, but if anybody would care to enlighten me
    form their own experiences I would be very grateful.

    kind regards,

1997\08\06@101436 by Garrick A Kremesec

I'm attempting to use a LTC1325 microprocessor-controlled battery
management system from Linear with a PIC.  It appears to be a versitile
chip and can be used to charge just about any type of battery you desire.
It requires several external components to drive the charging/discharging
of the battery, but the devices suggested are fairly common IRF devices.
It also has a "gas gauge" mode which measures the average voltage accross
a sense resistor to determine the average battery load current.  Or so
goes the advertisement.

Has anyone else used/attempted this controller?  How accurate is the "gas
gauge"?  Oh, it does a a 10 bit deep ADC to perform all of the various
measurements required during charging as measuring load current.

Garrick Kremesec
Beckman Institute - RA

1997\08\06@121416 by Harold Hallikainen

picon face
       There are, of course, chips just for this purpose.  I think they
generally watch for either a zero or negative dV/dt, depending on battery
chemistry.  They will also often watch battery temperature, since there
is a rapid rise in cell temperature on continued charging after the
battery reaches full charge.  Each of these techniques assume a constant
current charge.
       Comapnies that come to mind are Maxim and maybe Linear
Technology.  You could, in the interest of reducing chip count, do
soemething similar with a PIC.


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