# Off grid upgrade checking parameters

Registered Users Posts: 1
I upgraded my off grid system from 4 rolls surrette s605 6 volt batteries in series to 8 s550 6 volt batteries in series parallel and I just wanted to make sure my charge parameters are correct. I have 2 outback charge controllers a fx60 and fx80 with 16 220w solar panels plus a 1500w bergy wind turbine. The fx60 is set at 40 amps and the fx80 is set at 47 amps which seems fine for the old 600 ah batteries but now that i have 2x550ah=1100ah  do i need to be at 110 ah to get the recommended 10% charge rate?

Normally we use the 20 hour rate for our rules of thumb... Assuming 24 volt battery bank:
• S605 bank, 4x series => 468 AH bank
• S550 bank, 4x series x 2 parallel => 428 AH * 2 parallel => 856 AH bank
Typically, for a battery system.. Suggest minimum 5% rate of charge (weekend cabin, emergency backup) to 10%-13% for full time off grid...
• 856 AH * 5% rate of charge = 42.8 Amps minimum
• 856 AH * 10% rate of charge = 85.6 Amps nominal
• 856 AH * 13% rate of charge = 111 Amps typical "cost effective" maximum
I suggest that 13% and over rate of charge you should have the remote battery temperature sensors setup so that the banks don't over heat from too much charging (Lead Acid battery bank charging voltage drops as the batteries get hotter).

And something like 20-25% maximum rate of charge.
• 856 AH * 20% = 171 Amps "starting to worry about too much charging current for "daily charging"
Your solar array, I would expect:
• 16*220 Watt panels = 3,520 Watt array
• 3,520 Watt array * 0.77 panel+controller deratings * 1/29.0 volts charging = 93.5 Amps approximate cool/clear/noontime maximum charging current
So at this point, I would not "current limit" your Outback charge controllers... Set them for full rated output current and you should be fine for solar.

The wind turbine is a wild card here... Guessing:
• 1,500 Watt / 29.0 volts charging = 51 Amps from turbine rated output
How much current do you typically see?

The max (math wise) output from solar + wind:
• 93.5 Amps solar + 51 Amps wind = 144.1 Amps max Wind+Solar (best case)
Depending on your weather conditions--You probably rarely see full 25+ MPH wind and Noon Time sun (cool/clear day)--And even so, you probably would never exceed the 171 Amps (assuming 20% rate of charge) into the battery bank anyway.

And remember that FLA batteries tend to start "throttling back" on accepted charging current at >80% state of charge--So that you have more charging current available will not accept more than "safe" charging current for batteries.

And FLA batteries when charging below 80% SoC tend to be more efficient, so they should not overheat when charging at high currents at low SoC conditions. Assuming you have the correct charging voltages programmed...

Rolls has their recommended charging voltages (and detailed charging recommendations):