nuckolls.bob(at)cox.net
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 Posted: Tue Sep 30, 2008 6:40 pm Post subject: VDC Battery Minders (follow up) |
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If one insists on plugging the battery in for storage
every night and the battery was put away charged, the
charger won't even have a chance to do a full blown
recharge, top-off-drop-to-float cycle. This
slicing and dicing of float voltage from a charger
is mostly smoke and mirrors. Open circuit on a SVLA
battery at room temperature is right at 13.0 volts.
Ideal float voltage would be right at 13.0 volts too.
All you're wanting to do is externally offset the
internal leakage of the battery. Now if you really
screw up and float it at say 13.4 volts, the current
that flows into the battery will be somewhere around
30 mA on a 17 a.h. battery.
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Just took one of my instrumentation SVLA batteries that
have been off the charger for several months. The open
circuit voltage was 13.03 volts. I hooked it to a
power supply set for 13.5 volts. As soon as the clips
touched, the 'charge' current jumped to over 1.5 amps.
Came back in 20 minutes at it was down to 0.013 amps
or 13 milliamps.
I raised the power supply to 13.6 volts. Again, charge
current jumped up to about 400 mA. But after 20 minutes,
it was again down around 0.022 amps or 22 mA.
This suggests that if I "floated" this battery anywhere
between 13.1 and 13.6 volts, it would be just fine.
In my shop, I used to keep the instrumentation batteries
all clipped in parallel on a single Battery Tender Jr.
That was several years ago. Now, after using a battery
to some task, I put it on the SC2500 (super-duper smart
charger with a switch for "deep-cycle", "AGM" and
"regular". I think the charger defaults to "regular"
when plugged in. I hook it to the battery, come back
in the morning and put the battery back on the shelf.
All of my batteries are still above 80% of new capacity
after 6 years with no special pampering to "optimize"
service life. Walmart generally stocks the Schumacher
SEM1562A for under $20. This is a fine low rate,
charger maintainer at a very attractive price. See
page 11 of
http://www.schumacherproducts.com/assets/pdf/sec_catalog.pdf
Bob . . .
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