L-16s like higher voltages [RE-wrenches]

David Palumbo, Independent Power & Light ipl at sover.net
Thu Jan 17 06:30:25 PST 2002



>2. The report's conclusion that its necessary to EQ at 15.3 v (2.55v/cell)
>for up to 20 hours on a regular basis ( weekly or less) is totally
>impractical offgrid. They mentioned using a generator to do this, but that
>would totally negate any  environmental or cost benefits from going solar
>in the first place.

<<I am puzzled when I read of this practice too.  It sounds as if some
people do this.  They use a charge controller to deliberately limit
the voltage of the batteries when running on solar power (or wind)
and then burn fossil fuels to wildly overcharge them from time to
time.  It makes more sense to me to use a higher voltage setting on
the controller, or no controller at all, if the batteries need more
charging.  Equalisation should then only be needed as a last resort
if some cells are getting low.  Hugh>>

I agree with Hugh.
I have working with L-16's, and similar batteries for over seventeen years
and have seen various people and systems get good results (equivalent of 900
to 1,000 deep cycles, or 8 to 12+ years of useful life in a properly sized
system )by following some simple basic rules.
1.) Make sure batteries are fully charged (100% on a accurate amp hour meter
or hydrometer) at least once per week.
2.) Check each cell to make sure they are relatively equal (within .010 on a
hydrometer, or .05 on a voltmeter). If some, or one cell, is out of wack
then charge the battery bank (with an RE source if possible) until it comes
up with the others. If it does not come up "exactly" equal to the other
cells do not worry about it. Close is good enough in this game. Just make
sure that you keep up with the checking so they do not drift apart too much.
There are a few reasons why some cells will not catch up all the way with
others in the same bank. Such as unequal sulfuric acid in the electrolyte.
Upon shipping some cells spill a little; or when they were first filled they
were shorted a bit. I also suspect that internal resistance may vary
slightly from cell to cell as battery manufacturers tolerances are not as
tight as facilities that work on electronics.
3.) Rotate the batteries within the pack (especially true with larger cell
batteries where you are expecting a very long service life). Get the
batteries that are on the + and - ends rotated into the middle every year or
two.

I have also found that the recommended high voltages (above 15v) are not
necessary to completely charge (what an equalization charge really is) lead
acids if you follow the above rules. The length of the charge at 14.6 to
14.8v (at 78F) is what accomplishes the complete charge (all cells
relatively equal). What's the point in heating up your cells if you don't
have to?
For instance you can tell when your batteries are well charged when charging
with a Trace SW by the amps charging into to your batteries. After you have
been in the absorption stage of charging for a while (1 hr more or less) at
14.6 to 14.8 at 78F you should notice your amps tapering off as the cells
become fully charged. The amps will get lower the longer you charge. The
cells should be equal (again, relatively) when the AC amps on the Trace
meter read below 4 amps. You can also follow this on a good amp hr meter
with a correspondingly higher DC amp number depending on system voltage.
A good three stage PV charge controller and ammeter work the same way.

Best,
Dave

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