"Larry Jaques" wrote in message
...
On Mon, 22 May 2017 18:39:59 -0400, "Jim Wilkins"
wrote:
...
I haven't seen that remaining for an hour or so at full discharge
would further harm a battery and want to record the voltage it
recovers to without any load as an indication of true remaining
capacity and a safety check that I haven't set the disconnect
voltage
too low and drained the battery too far.
Yeah, that's a fly in the ointment of capacity measurement. Are
you
saying "full discharge to cutoff point" there?
(Which you didn't answer.)
Here's the problem:
http://batteryuniversity.com/learn/a...tate_of_charge
"To get accurate readings, the battery needs to rest in the open
circuit state for at least four hours..."
The AGM I discharged at a little less than the 20 hour rate (0.5A)
tripped at 10.0V (twice) and then recovered to 12.15V, which is over
40% State-of-Charge on that chart.
Thus taking the battery down to 10V cutoff at the 20 hour rate wasn't
a full discharge, so I couldn't answer. There was still capacity left
that was unavailable for some reason, perhaps one higher resistance
cell that I might be able to bring back by slow equalizing. I've had
some luck restoring a weak cell in a flooded battery and had popped
open that 12V 12AH AGM to add water, but it didn't appear to help
enough.
And you thought the tripping was from the internal resistances,
didn't
you? But the deeper the DOD, the shorter the battery life. (Loved
the Hot Tip on the Fridge and Solar site. Batteries love to be
charged but don't much like being discharged, etc.) Speaking of
which, what's the difference (other that price) between the standard
Ford style starter relay @ $12.99 delivered and the $80 Enerdrive
VSR
super-duper battery disconnect switch? As I look at it again, I see
that it has voltage-sensitive engagement. ($0.37 worth of old 7400
series chips?)
I had bought some LM324s and a relay to build one before I found the
Battery Isolator for $5. It's a hand-drawn circuit board in a Radio
Shack grey aluminum box, like the stuff I built as a kid, though it
seems to work well enough.
IIRC, I recently read that EQ can be good, but frequent EQ shortens
battery life.
Since I don't cycle my batteries daily I can afford to experiment with
slow charging from the solar panels at a few percent of the Amp-Hour
rating current. Rather than adding a current limiter which would cut
into the already minimal voltage overhead of solar panels, I've been
charging with simple, rugged LM317 and LM350 regulators with meters
and bumping the voltage up a little when I walk by and notice the
current has dropped. Before long the battery charges high enough that
an AGM draws only C/100 current at 15V and a flooded battery at around
14.0V, though they all are different. The current lost to electrolysis
seems to decrease, as shown by the battery drawing little more current
above 14V than at 13.6V.
I built a homebrew power supply whose current limiter adjusts from
1mA to 0.4A. I use it to restore old electrolytic capacitors at about
5mA and to desulfate free batteries that need to be hit with over 16V
to accept any current. For them the current needs a limiter to avoid
pegging the ammeter as they recover. I've been using one such free
"dead" battery in my tractor for two years.
I'm equalizing as gently as appears effective. The goal is to
determine if a variable voltage source with high resolution volt and
amp meters is enough to prolong and restore batteries IF operated
properly, which is the tricky part; the hardware is cheap except for
the Variacs that I already had.
It may be the sort of gizmo that only the inventor can make work, too
troublesome to be commercially valuable. I've come up with several
ideas that work fine for me but no one else.
I know I can make them last much
longer than usual, but is it worth the effort?
Good question. Perhaps with a more expensive battery, it would be,
or
in a top-down situ where the grid is and stays out. I rather doubt
it
with UPS batteries otherwise, though. Q: are the internal plates
and
connections in the larger glass mat batteries the same as the
smaller
AGM UPS batteries? I do know that the larger, PV-rated LA batteries
are more up to the task, and they're really heavy (massive lead
plates) and pricy.
AFAIK flooded batteries can be nursed to live longer than
maintenance-proof ones, so I lack the experience to answer that. I
don't own batteries larger than I can carry down the stairs and
outdoors to let them gas freely when I equalize them.
This isn't New Orleans; after a natural disaster the local governments
quickly clean up and repair and only expect FEMA to arrive afterwards
and write checks to cover the cost. My father was the CFO of one of
the state's departments that participated.
The dump trucks and loaders the towns need to clear snow can repair
flood washouts and push fallen trees off the roads, really everything
except paving and building bridges. My one-week storm preparations
could stretch to two weeks but I don't think any longer is likely with
the high level of response I've seen here.
It seems like this would have been done and written about by many a
battery manufacturer by now, or by their ad people. "Our batteries
and chargers are better because..." But I grok the "need to know"
function, too. I believe I'll be getting a lot of experience and
experimentation in the next decade, too, playing with solar.
Neon John posted a good reference to actual experience maintaining
backup batteries. I haven't found much else that gives hard technical
details instead of wishful copywriter promises. I did some work once
on 48V telco battery banks, otherwise my industrial experience is
mainly with Lithiums which are still overly expensive.
-jsw