"Jim Wilkins" wrote in message
...
On Oct 12, 11:04 pm, "RogerN" wrote:

Some of the chargers description described as charging and then monitoring
the voltage, when it falls below a certain point it charges again. This
had
me thinking that it monitors voltage with almost no current flow. I'd
guess
it also monitors voltage during charge with current flow. I thought if I
were brewing my own, I would use shielded 4 conductor, 2 wires for charge
and 2 others for measuring voltage.
/
/Kelvin connections won't help you with lead-acids. They charge to an
/artificially high voltage due to "surface charge", which takes time to
/dissipate. This article says 4 - 8 hours:
/http://www.batteryuniversity.com/partone-13.htm
/

I was thinking of charging to a 14.2-14.4 charge voltage, the voltage would
be sensed by 2 wires with very low current. The reason is because if I ran
a wire from my house to my batteries in vehicles, the wire would drop some
voltage on the current carrying charge lines. The idea is the same as using
a 3 or 4 wire connection to a platinum RTD. The current carrying leads of
an RTD only carry 1mA but that's enough error to throw the reading off. If
I did use something like a LM317 regulator I could adjust it for 14.4V and
as the battery charged, and the current decreased, the voltage drop in the
wire would also decrease.

/I have found that I need a "dumb" charger to start batteries who have
/been seriously discharged and then allowing the smart charger to
/finish...again that little chip in the smart charger being a bit too
/"smart".
/
/Agreed. I need the homebrew lab-supply chargers for older batteries
/whose cells have become unequal or sulphated.
/
I would think that would be the best way to get the ultimate charge
without
overcharging.

I've played with an adjustable regulator circuit in Electronics Workbench
simulator. I used the typical voltage divider circuit to set the open
circuit voltage and used an inline resistor so that the voltage goes down
as
the current goes up. I got an open circuit voltage of 14.201V, .19A at
14V,
2A at 13V.

RogerN
/
/You don't need the series resistor, the exact shape of the knee
/(constant-current to voltage transition) doesn't matter.
/http://www.national.com/mpf/LM/LM317.html
/
/jsw

By using a series resistor I can make the supply current go to zero as the
voltage approaches full charge voltage. This gives a power source that is
limited in both voltage and current.

RogerN