Steptoe,
a few points regarding charging SLAs.
1) Agree with Gannon re: series vs parallel.
2) Charging with a solar cell is dependent on positioning, season, day (sun or rain), shadow, bird poop, etc. Make sure you get enough charge, as...
3) ...12V SLAs, once discharged below ~11V are regarded as completely discharged. Further discharging will damage the battery and reduce its capacity.
4) Unless regulated a solar cell also tends to ramp voltage with light. Cheap solar cells not only may not be as efficient, last less time, be non-hailproof and don't tend to have the solutions to the following two effects:
a) Too much light- too high a voltage. Damage to battery can result (just like any lead-acid battery overcharging). Solution: solar charger regulator. Something like Jaycar CAT. NO. AA0348 should suffice, I have used these to charge car batteries from an unregulated 15VDC power source, too.
b) Too little light- too low a voltage (ie less than the SLA). The SLA now has more V than the cell, resulting in a net back-current discharging your battery through the solar cell (every night). Solution: solar charger regulator or a simple diode at the solar cell output to prevent the back-current (have we visited this somewhere before:-) ) Note the diode will produce a slight voltage drop, reducing the net output voltage of the solar cell.
5) You're better off with one SLA of total capacity rather than 5 connected in parallel if you can. Why? Assuming you're using 12V SLAs:
- each SLA is actually a bit more than 12V at full charge, perhaps 12.5 to 13V.
- charging generally takes place at 13.8 to 14.4V. The higher, the quicker but damage will result above ~14.8V.
-each SLA actually has 6 ~2V cells connected in
series.
- when a SLA fails, either it has been abused (loses some capacity), REALLY abused (damaged), cycled too may times (worn out) or a cell 'drops out'.
- when a cell 'drops out' then that cell effectively goes short circuit (if the cell went open circuit, you're battery would be open circuit and 0V). This gives you 5 functioning cells with a total output of ~10V.
* but you're charging with ~14V! So the 5 working cells are being overvoltaged and tend to fail more quickly or the fluid gets boiled off (and the battery fails).
* the other batteries are still running 12V or more. So there is effectively a 2V back-voltage across the 'dead' SLA. This can discharge the good SLAs, damaging the bad SLA further and causing further damage. Further cell drop-outs can occur, accelerating the process, exacerbating the voltage differences and in extreme cases perhaps causing fires or explosions form released hydrogen. Especially in enclosed spaces (100mm square metal container?)
6) Don't buy Jaycar (Diamec) SLAs. In my experience, they are not much chop at all. If Murray County is around Canberra can I recommend Alpine Batteries (have changed their name recently to R & J Batteries) in Queanbeyan. Good prices and batteries, they specialise in SLAs for alarm systems too so they know which ones are good And I assume have high turnover (no stale batteries). On display they also have some interesting examples of lead-acid batteries gone wrong (or charging gone wrong). In my experience all battery manufacture moved to Chinese production just didn't last, this includes good brand names such as Century, Yuasa and Panasonic. May be better now but won't still be Japanese quality.
7) When wiring there will be a slight drop at each terminal/connection. So if you have 5 batteries in parallel and the charger connected to one end,there will be a slight voltage drop to the other end through each connection. This can mean differential charging of batteries.
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[/noparse] Don't use too small a fuse in line with the charger. The voltage drop across the fuse can be too large and prevent proper charging. E.g. if expecting a 1A charging current, use at least a 5A fuse. Ditto for wiring.
9) If you search around and spend you should get an intelligent controller that will optimally charge your batteries from the solar panel by e.g. pulse width modulation method, may accept an auxiliary power source for those grey days, may detect battery faults and prevent further damage and may turn off the output if the battery voltage goes too low.
10) Charging rates for SLAs are generally recommended at a current that is equal to 1/10th of the Ah (Amp-hour) capacity, for 14 hours (I think) for a full charge: i.e for a 5Ah battery charge at 5/10=0.5A, for 14 hours for a full charge. For 5x5Ah batteries =25Ah that would be 2.5A.
Good luck!
