From: muratlanne@gmail.com
wrote in message
news:03a03e1ug859be4l3lgbjvu43lk1mj7sqb@4ax.com...
> On Fri, 4 Jan 2019 12:41:49 -0500, "Jim Wilkins"
> wrote:
>
> ...
> I've yet to try the "recover your AGM battery" process of opening
> the
> battery up and adding water to the low cell. While I can see that
> it
> might work in the short term, whatever caused that cell to fail is
> still there and I'd expect it to fail again in the not-too-distant
> future.
>
Adding water didn't improve the one weak 12V,18A AGM I tried it on.
The valve caps were soft rubber and easy to remove.
My discharge test loads are an assortment of large rotary rheostats,
up to 1 Ohm 1000W (31A). Their advantage is a steady current that
doesn't confuse the ammeter with switching noise, the disadvantage is
that the intended constant current or power ramps down between
unevenly timed readjustments. Successive capacity measurements can
vary around +/- 10%, possibly due to this procedure, which obscures
small changes.
A DC-AC inverter makes a pretty good constant-power load with a
built-in but non adjustable low voltage cutoff. My crock pot draws
100W from the inverter without becoming dangerously hot, while the
rheostats approach 600F at their rated power. An inverter does produce
switching noise that seems to randomize the low voltage trip point.
The run time of an AC-powered refrigerator is hard to estimate because
the inverter will trip out on a starting surge voltage drop although
the battery could still provide the running current. My datalogger
uses PC-linked multimeters which can't sample faster than once per
second, and miss spikes. The DC Alpicool's ramped soft start is a help
here.
-jsw
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