RE: Even more homebuilt charger madness

["Roger Stockton" <rstockton@delta-q.com>]

Hi Lee,

Valuable feedback, as usual; thank you.

I had described a SOC monitor that would monitor series discharge
current (since all batteries see the same discharge current), and
monitor individual charge currents.  Since there would be only
one flying charger, this would mean one shunt in series with the
charger output, one in series with the pack, and a software Ah
accumulator per battery.  So, there wouldn't really be "individual
monitors".

You mention that your Balancer only shuttles charge around the pack
so the E-Meter tracks things fine; is this really true or does it
only seem so due to the E-meter's limits of accuracy?  That is,
since the Balancer itself is less than 100% efficient some of the
energy it shuttles around is lost; if the E-meter sees the Balancer
input power leaving the pack but not the power returned to an
individual module, then surely it is not tracking SOC accurately?
Conversely, if the E-meter doesn't even see the energy drawn from
the pack by the balancer, nor how much of that is returned to an
individual module, then it will mis-represent SOC by the amount
lost in the Balancer's inherent losses.

How difficult would it be to modify a Balancer to power the Batmod
from an AC-derived source when present and the pack the rest of the
time?  How about beefing up the Balancer to use several paralleled
Batmods for ~60A output?

Cheers,

Roger.

-----Original Message-----
From: owner-ev@listproc.sjsu.edu [mailto:owner-ev@listproc.sjsu.edu] On
Behalf Of Lee Hart
Sent: August 30, 2001 3:04 PM
To: EVlist - Electric Vehicle Discussion List
Subject: Re: Even more homebuilt charger madness

[snip]

How you measure state of charge has a big effect on the results you get.
If you charge dissimilar batteries in series, you overcharge some of
them. If you monitor and charge them individually, you can eliminate
this overcharging. But if your individual monitors don't monitor
amphours removed (to save money), then they can be as bad or worse than
a single series charger that *does* monitor amphours and controls
charging accordingly.

And as you say, knowing state of charge is considerably more difficult
when batteries aren't charged/discharged in series.

I faced many of these problems with my Battery Balancer. I chose to take
power from the pack as a whole to charge individual batteries.
Basically, it is redistributing power within the pack; no power going
out (like Rudman regulators) or in (like individual chargers). This
means a single E-meter and single shunt still correctly indicates the
number of amps, amphours, and watthours that go in or out of the pack.
--
Lee A. Hart                  Ring the bells that still can ring
814 8th Ave. N.              Forget your perfect offering
Sartell, MN 56377 USA        There is a crack in everything
leeahart_at_earthlink.net    That's how the light gets in -- Leonard
Cohen