Flooded Lead Acid Battery Management Wall Chart
STANDARD RESTING CHARGES, 2 VOLT CELLS, SLI & Deep Cycle @ 25C (.01-.05v FC vpc difference is OK, all vpcs drift over time, and cells will trickle discharge also, when not in use)
|SOC %||12 VOLT||24 VOLT||VPC||max||2.583vpc @15v and 30v resp.|
|90||12.50||25.00||2.08||20%||SLI battery cycle maximum|
|60||12.20||24.40||2.03||40%||solar battery optimum DOD|
|40||11.90||23.80||1.98||RULES of THUMB:|
|30||11.75||23.50||1.96||SG+0845= vpc, resting charge|
|20||11.58||23.16||1.93||80%||Ohms pc = 7.5, full resting charge|
|10||11.31||22.62||1.89||(both @ 25C, normal acid range)|
@ 20 amps to 30v, briefly, full charge @30v is 2.583 vpc, including
Absorption 27.2v to 28.4v, charge rate may slow slightly. Then for
Equalisation take to 31v, taper amps to maintain venting 30-31v, 30 to 180 mins.
Float Drop amps, taper to 25.6v-26.4v, maintain 2.15-23 vpc.
Rest Being fully charged 25.4v, @ 2.12-15vpc, EMF
DETAIL: Advance charge @ <20 amps, and
raise only when needed to initiate equalization at 31 volts, and for
de-sulphation, when amps are then tapered, to enable vpc of 2.4/5v.
Both may be concurrent.
Bubbling and venting at
30-31v will be sufficient for equalization. Bubbling begins at 2.2vpc, so beware of
overcharging beyond 31v, damaging and unnecessary, causing heat and
plate breakage. (An electronic desulphator is recommended?)
TRUEST VOLTAGE READINGS ARE TAKEN DIRECTLY FROM BATTERIES WITH A RELIABLE HANDHELD DIGITAL VOLTMETER
|good SLI 1275 to 1300||
good DC 1220 to 1240
|Test for SG peak during equalisation, then discontinue charging; add or subtract .004 for|
|satis " 1225 to1250||
satis " 1200 to 1220
each 5C above or below 25C for SG correction.
|poor " 1150 to1200||
poor " 1100 to 1150
hydrometer readings should always be concurrently optimum. Battery capacity is progressively limited
with cold, so factor this into winter usage calculations. Freezing
point means 35% capacity reduction, plus the limitations caused by age
and condition. Heat and/or poor plate condition cause
resistance, and cold limits capacity.
Battery temperature and state will influence charging, by PV or generator. Battery life is halved by every 9C over 25C, if unregulated. Capacity to receive charge v temp: F/C & good SG: @ 27C, 100%; @ 0C, 65%; @-18C, 40% . Temperature regulation for battery banks is strongly recommended.
The quicker and
higher the charge return and hold,
the healthier the battery. Regular top-ups and/or trickle
charging are needed when batteries are not in use, see FLOAT above, and
the normal charge routine still applies. Always use 4-stage regulators
to taper any charge, especially for unattended operations.
Slow and steady C10 charge and C20 discharge best, 20-40% discharge only, for longer battery life, no large quick drains or shallow cycles under 5%, and use a generator for high demand periods, for PV charge cycle lag and/or equalisation. Allow adequate time for plate reformation, the key to optimum battery charging and long-term health. When fully charged, the anode, PbO2, should be noticeably chocolate in colour, and the lead cathode, Pb, should be grey.
Battery temp 25C for optimum performance, 25C max for PV panels. A brewstrip thermometer on the battery, plus calibrating wall thermometer, account for temperature lag. Ensure adequate ventilation of batteries at all times. Rotate end battery positions minimum once per annum, ad hoc, to maintain uniform condition.
Make a chart to track individual battery health, record readings regularly. Check connections and wiring first when faultfinding, before more complex steps!
these Wall Chart figures according to ambient temperatures,
manufacturers specifications, plate chemistry, and/or individual PV
systems, when necessary. AGM
and Gel VRLA battery maximum charge input is only up to 2.35 vpc, use
dedicated VRLA regulators!
Free PDF and WORD versions, PDF
of this Wall
Chart, and of the 72 page booklet, Home Solar Power Management, and Why
are availble at the Home Page: