On Mon, 22 May 2017 18:39:59 -0400, "Jim Wilkins"
wrote:
"Larry Jaques" wrote in message
.. .
On Mon, 22 May 2017 08:34:11 -0400, "Jim Wilkins"
wrote:
...
Previously I was using a rewired Battery Isolator I bought from
Quicksilver Radio for $5 at a hamfest ...
....
Those I've seen only engage the relay to switch to the secondary
battery. Are you talking about when the secondary battery is
discharged/cutoff and the relay continuing to be engaged? I see
that
as a problem, too. Perhaps rig up a kickout relay to disengage when
the cutoff hits on the secondary?
This one remains powered by the main battery when it switches the load
to the second one, perhaps to avoid the glitch while the
break-before-make relay contact is moving. It drives the relay with an
SCR and won't release and revert to the main battery until the user
pushes a disconnect button, regardless of how high the main battery
may have recovered or been recharged. This means that connecting NO to
a charger won't make the relay turn off when the battery voltage
rises.
I cut and jumpered the traces to redefine COM as the battery instead
of the load, which is now NC. Originally COM was the load, NC the main
battery and NO the secondary one. As you said it would simply allow
the secondary battery to die, but retain whatever capacity the trip
point left in the main battery.
Maybe running the anchor light as long as possible is more important
than preserving a battery that sinks when the boat is hit?
That would do it.
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.
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?)
The point of knowing the full capacity is to find out why I'm not
getting it, and see if anything I can do makes an improvement. I can't
fix bad interconnects but a discharge - charge - equalize cycle
reforms the active material. Only measurements will show how well
equalizing and desulfating work.
IIRC, I recently read that EQ can be good, but frequent EQ shortens
battery life.
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.
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.
--
I started out with nothing and
I still have most of it left!
--anon