John wrote:
>>
A fellow list member, and I've been unable to find who it was after
scouring my email archives, gave a number of suggestions, including deep
cycling it several times and simply leaving it on trickle charge for a very
long time.
<<
Likely me, I have designed high performance chargers for Sealed Lead Acid
batteries professionally, and have cycled them to life and death many times,
while optimizing chargers. Generally SLA's are used in mainly inexpensive
equipment so the chargers are often poorly designed to save cost. The battery
quality/price/ performance varies a lot between vendors. With care they can be
rapidly charged and achieve better cycle performance than even the most
optimistic claims of the vendor. For example I once cycled (~full discharge)
some Hawker brand (Cyclon) batteries to 1500 cycles (4 cycles/day ~14 months =
over 2000 Watt hrs!). Near the end, they started to loose capacity fast as
parts of the plates internally were starting to disconnect. The vendor's claims
under their recommended charge regime was 200cycles at that time. The most I
ever did for the Sonnenschein batteries (like are used in Metz) is 700cycles,
but I stopped testing (the capacity was still over 85%). The pris
matic
(flat)sonnenschein plates likely wear out earlier than Hawker (rolled).
There are actually a number of different SLA technologies. The Sonnenschein is
termed an excess electrolyte design, using fumed silica in the gelled
electrolyte to enhance gas recombination. It has relatively good sulphation
recovery, as long as you don't ever leave it deep discharged for a really long
time (>30days). Charge the sooner the better and float charge in the Metz
charger for days
To recover the batteries it helps to cycle them with a charger having a little
higher regulated voltage supply than that used in the Metz charger cct (which
is actually in the 60CT box, not the wall wart) . The voltage used by Metz
(2.33V/cell ) is really more appropriate for float use than cycle use. It
would be better to use a smarter charger and 2.5V/cell (i.e. 7.5V for Metz 6V
battery) or use a current source capable of 5-10mA to top up the cells after
normal charge. If you use the higher voltage, you need to be careful not to
leave it on charge too long or it may thermally run away. Use a timer or put an
outdoor thermometer on them and keep an eye out! You can make a crude current
charger for topping up batteries using a 12V wall wart, and hook up a resistor
to limit current. (~560 Ohms, ~8mA). You can comfortably leave it on top up
current for a few days without a problem when recovering.
Regards,
Tim Hughes
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