Basic Battery Questions

BB. wrote: »

Here is a thread on Hydrometers and how best to use them.

I understand that some tropical locations will use a bit weaker electrolyte (batteries will have a longer service life?).

From this thread, the range of Electrolyte Specific Gravity seems to be:

Specific Gravity vs Applications
1.285 Heavily cycled batteries such as for forklifts (traction).
1.260 Automotive (SLI)
1.250 UPS – Standby with high momentary discharge current requirement.
1.215 General applications such as power utility and telephone.

As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

...

Higher Gravity = vs Lower Gravity =
More capacity / Less capacity
Shorter life / Longer life
Higher momentary discharge rates / Lower momentary discharge rates
Less adaptable to "floating: operation / More adaptable to "floating" operation
More standing loss / Less standing loss

So, where do your readings fall in the above scale... And I would guess that a difference of 0.030 SG or less is nothing to panic over.

Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
Or
Single-cell open circuit voltage = specific gravity + 0.845.

• 150 AH * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 705 AH @ 24 volt battery bank

• 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,695 Watt array minimum
• 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 3,390 Watt array nominal
• 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 4,406 Watt array "cost effective maximum"

Month      Solar Radiation(kWh/m2/day)
1      2.57     
2      3.62     
3      6.03     
4      5.48     
5      5.21     
6      5.31     
7      5.48     
8      4.89     
9      3.96     
10      3.78     
11      2.70     
12      1.80     
Year      4.24

• 150 AH * 25 volts avg batt voltage = 3,750 Watt*Hours per day (DC side of inverter)
• 3,750 WH per day * 1/0.77 panel+controller derating * 1/0.80 batt eff * 1/3.62 hours of sun = 1,682 Watt array minimum

• 740 Watts * 3.78 hours of sun * 0.77 panel+controller derate * 0.80 battery eff * 1/29 volts batt charging = 59 AH @ 24 volts per day