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Subject: Re: help with MAX712 circuit
Date: Tue, 31 Dec 2002 14:31:17 +0100
Organization: Wanadoo, l'internet avec France Telecom
References: <3E108263.305089AA@worldonline.fr> <3E1159CE.1A74C6E3@worldonline.fr>
NNTP-Posting-Date: 31 Dec 2002 13:31:24 GMT
X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.20 i686)
Alex Graham wrote:
> A.Iakovlev wrote:
> > Alex Graham wrote:
> >>Right - I forgot to mention that its switch mode.
> >>Also why is that the min charge current?
> > That is related to the maximum timeout: the timeout (264mins) is 110% of the
> > time that would be required to charge an ideal cell at the rate C/4 - it
> > assumes the charging efficiency of the cells of 10/11 or better.
> > Have you correctly adjusted the # of the cells (PGM0 and PGM1 pins on
> > MAX712)?
> > Also, there are some specific requirements on the input voltage and maximum
> > supplied current. I would expect these to be satisfied but it would be
> > better to have a look at the schematics.
> > A.I.
> Well I charged them about 4 times so far from a fixed voltage PSU, and
> it seemed to work. All the cells are from the same batch etc and were
> installed at the same time. they are bundled up in a bike water bottle
> so measuring the voltage accross each one would be tricky.
> I have charged them from the MAX circuit with voltage slope turned off,
> and I get a good voltage and constant current charging which is
> absolutely fine afaik.
> Its just this charge termination that doesnt work properly.
I have seen some cells specifying tolerance to indefinite charge at C/10 rate,
but overcharging (i.e. note properly terminating the charge) at the rate of
about C/5.7 will most probably damage your cells. Do you have their datasheet?
The early termination may and may not be a malfunction. If it is not, no problem,
it only means that the cells were not fully discharged. In that case, if ever the
charge times out (264mins), just restart the charge cycle - the second cycle
would then properly terminate before the timeout. If this is a malfunction, then
I don't think I have any other idea at this time. Does the battery look fully
charged after the early termination?
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