FLOODED LEAD ACID BATTERY FAQ.
not for SLA Sealed Lead Acid batteries
What size should my battery bank be?
Balance is the key issue here. Your bank should be large enough to handle your input(s) and not suffer from deep discharges, yet a larger sized bank can suffer from a lack of charging. A good rule of thumb is to size the system to keep charging at a rate of 10 to 20% of the battery bank size. (This does relate to overall system sizing which is beyond the scope of this FAQ)
.
What voltage should my batteries be at?
A normal 12 v battery system should be between 11.8 (35% charge) and 14.8 (100% charge). Or between 12.1(35%) and 12.7 v (100%) at rest, no charging and no load. Other voltage systems can be scaled accordingly.
What should the specific gravity of my battery be?
State of Charge Specific Gravity Voltage
12V 6V
100% 1.265 12.7 6.3
75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.8 6.0
Testing should be done at 75 to 80 F or 24 to 26 C other temperature require correction.
What tools should i have to maintain my batteries?
EYE PROTECTION,a good float type hydrometer, a good terminal brush, steel wool, or light sandpaper, a volt/ohm meter, baking soda for spills. A load tester for larger systems can come in handy too. Also a battery filler bottle is handy. If you do just take your batteries in for load testing, make sure they do not overload the battery during the test, remember they want to sell you a new one!
What should i do to maintain my battery bank?
Check your connections ACROSS the connection for resistance, (battery terminal to clamp) clean and keep all buildup and corrosion off the terminals. High resistance is a major cause for battery failures. Keep the batteries CLEAN, dirt will pick up moisture and cause a "short" between the terminals, slowly draining your charge. A solution of baking soda and water is best for cleaning. Keep the water levels topped up.
Batteries like a good constant temperature of around 70-80 deg F. Keep the area well ventilated to minimize hydrogen buildup. Keep terminals and wires covered or insulated to prevent short circuiting,keep wring runs neat.
DO NOT place anything on top of the batteries, ESPECIALLY METAL which can short the terminals. Keep all sensitive electronics such as converters and controllers away to prevent corrosion on them.
Some people report good results using a thin coating of silicone sealer at the base of the terminals to keep corrosion down, and some use terminal "doughnuts" to soak up and neutralize any excess electrolyte gathering at the base of the terminals. Also a protector spray is available for spray coating to reduce corrosion, Do not use a grease to do this, as it can melt and run between the terminal and lug, insulating them.
OK, how often should i perform maintenance?
At least check water levels once a month, if not the full maintenance routine.
Where should the water/acid level be?
At all times the solution should cover the plates, and in most batteries there's a line or "ring" to indicate a high level mark, do not exceed this. A battery should always be able to breathe so do not fill to the top of the "slot" on the ring this will cause sputtering and acid spillage outside the battery.
What should i add to my battery when it is low?
CLEAN distilled water is best. Do not use ordinary tap water as the minerals contained in it will contaminate the plates.
How do i test my batteries?
First, fully charge the bank, or battery, and let it sit unattended to equalize a bit, an hour is sufficient. Then test voltages across each battery, Then do a specific gravity reading for each cell. These tests should be done between 75 and 80 F. Readings at other temperatures must be compensated for.
I just want to keep my batteries charged up, how much charging do they require at a minimum?
2% of the capacity of your battery amperage rating. Batteries self discharge at a rate of 1% a day at 80 deg F.
How do i keep my batteries from undercharging/overcharging?
Dump load protection is usually used in RE wind power applications to limit excess charging. MPPT or charge controller in PV situations limits excess overcharging.
There should also be protection circuitry to shut down your battery bank for undervoltage. This is incorporated into a lot of inverters.
How do i wire up my battery bank?
two 6 v batteries run in series=12 v,4 24 v, 8 48 v.
Two 12 v batteries run in series = 24v, 4 48 v
Batteries run in parallel equal either the single battery voltage or the series string voltage.
Series wiring pos in then neg to pos. then neg out.
Parallel wiring, pos to pos neg to neg.
How do i resurrect a bad battery?
First off, it depends on what the problem is, first thing to do is perform a maintenance properly then fully charge and test.
Some people have had decent luck with desulphators/pulse chargers, however i personally cannot guarantee results from
this.
Can i just use old automotive batteries?
In a nutshell, no. You do want some sort of deep discharge battery, a lot of people have had good luck using golf cart batteries, other good ones are forklift types, heavy machinery batteries, and those specifically designed for deep discharge storage.
What is battery equalization, and how do I do it?
During the charge cycle the voltages of the different batteries will vary. In order to bring them all to the same level it is necessary to give some a slight overcharge in order to bring the other up to full charge.
Equalization is done by allowing the voltage to rise while allowing a small constant current to the batteries. The voltage is allowed to rise above the normal finish voltage in order to allow the weaker batteries/cells to draw more current. The stronger batteries will not be adversely affected providing the current is gentle and the period and frequency of overcharging are not too high and great respectively. The stronger batteries will absorb the overcharge by giving off heat by gently boiling and gassing more heavily. Once the weaker batteries have absorbed the required energy, the equalization charge can be halted. The equalization time should be long enough to bring all the batteries up to a full state of charge. As the time factor will vary the most reliable way to check the charge states is by a voltmeter and hydrometer on each cell or individual battery.
Equalization should be done at least 2x/year and for heavy usage or bad test results, more often.
What are acceptable voltage differences between cells, and different batteries?
My rule of thumb is 5% difference. Efficiencies start dropping off at greater than this variance.
Why should I keep my batteries warm/cool?
A battery over 100 F self discharges at a much higher rate, also causing sulfation on the plates shortening the lifespan dramatically. Battery voltages drop off below 65 F and a discharged battery can freeze, causing permanent damage!
What shortens battery life?
Overcharging, and deep discharging do the most harm, especially on RE systems. Excessive heat can kill them too,as can extreme low temps such as freezing especially on a low charge state. Dirty conditions will shorten their lifespan. High resistance in connections and leads contribute, also.
What are indications that my battery(ies) are going bad?
Widely differing voltages, cells that need frequent topping up, (more than the others) excessive boiling or heat during charging, one cell being warmer than the others, widely varied specific gravity readings.
How can i resurrect my failing battery?
Some people have reported good luck using a pulse/desulphator charger. I've been known to totally flush a battery out (after dumping the acid), rinse with clean water until all silt and minerals dissapear), and adding a fresh , clean charge of electrolyte.
Battery repair used to be common long ago, but only larger expensive batteries would be even worth this consideration today. Most battery tops are not designed to be removed to allow access to the individual plates and cells.
Safety considerations,
Batteries produce hydrogen gases which in a high enough concentrations ARE EXPLOSIVE, maintain good ventilation. Battery acid burns exposed skin and eats cotton (and other fabrics) like no tomorrow! ALWAYS WEAR EYE PROTECTION when working around a battery, one small drop can burn an eye badly,( i know, just one teensy drop burned like hell) FLUSH ANY acid spills or contact as soon as possible.
