On 28 Apr 2014 at 15:04, Chad Bush wrote:
I believe the correct parameter to measure a full charge would be the
current
output of the charger, so that once it met a minimum amperage (floating
current), the charger/controller would begin to maintain, restarting ONLY
IF
the voltage dropped below a given level. Voltage can be misleading due to
weak
or bad cells in the entire pack.
You're on the right track, except that the maintenance phase is unnecessary
and even detrimental.
Here are good basic battery charging instructions:
http://www.evdl.org/pages/hartcharge.html
If you're holding voltage constant at the acceptance voltage (2.4-2.5vpc),
when the current falls to < 0.02C (2% of the battery's rated amp-hour
capacity expressed in amps), the charge is complete. Then you STOP. At
this point, continuing to charge the battery will only degrade it by
overcharging. For a battery in cyclic use, as ours are, float or
maintenance charging is nothing but slow battery murder - "battricide."
Mr Landis's device is an interesting design. He is looking at battery
charging from a different angle. It's sort of a modified cycle-dropping
charger.
A cycle-dropping charger has an output voltage high enough to charge the
battery fairly rapidly. During charge, it monitors the battery's on-charge
voltage. When the on-charge voltage reaches a threshold (typically around
2.4 to 2.5 volts per cell), the charger shuts off its output and waits for
the battery voltage to fall. When it falls below some threshold voltage
(there is some hysteresis in these voltages), the charger restarts.
In theory, at some point as the charger off time approaches 100%, the
battery is considered fully charged.
Cycle dropping is about the cheapest and crudest form of charge control.
It's better than none at all, though, and it's easy to implement. I've
used
it for years in simple chargers with quite a bit of success.
Anyway, if I understand Mr Landis's algorithm aright, its approach is sort
of similar. He specifies a *minimum* voltage to turn *on* the charger,
instead of a *maximum* voltage to turn it *off*. Any time the battery
falls
below some voltage value, he starts the charger and runs it for a fixed
time
(5 minutes, IIRC).
As a charge controller, I'm not sure what advantages, if any, this approach
has over the more conventional design. But then AFAIK it's not really
meant
to be a charge controller for daily use, though some folks use it that way.
It's a battery maintainer.
And I come back to what I said before. In my experience, battery
maintainers are just not necessary or even a good idea.
I think that folks who want better battery charging and longer battery life
for their ETs would be better off with a good smart charger. A modern 3-
phase charger with temperature compensation would be a good choice.
Delta-Q
is one example, but there are many others.
Another good choice (and one you can probably find used) would a golf car
charger with a DV:DT algorithm such as a Lester Lestronic or Lestronic II.
A
DV:DT controller (Lester has a patent on it, I think) watches the slope of
the battery's voltage on charge. When the voltage is above a threshold and
is no longer rising, it considers the battery fully charged and shuts off.
The advantage is that the DV:DT algorithm naturally compensates for
temperature, battery aging, and even a few questionable cells in the
battery. Maybe that's what Chad is looking for?
David Roden - Akron, Ohio, USA
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