Old plus new
Winkstone Registered Users Posts: 1 ✭
I am living in my rv while building a home. I have four 100ah AGM SLA batteries wired in parallel, three 120 watt solar panels and a 3000 watt inverter. The inverter shuts off at 11.9 battery volts. I am somewhat limited on power and would like to add four more batteries. My batteries are only 7 months old. I know mixing old and new batteries is bad. But at only 7 months, would this be a problem?
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|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
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Since this is short term it may be best to just buy the $600 dollar Yamaha inverter genset at costco.
If your inverter does not have a charger built-in then that will not work.
Be sure and do this safely! You would not be the first to have fire while building. Too many of those lately so be aware of rodent damage and have a non flamable area for all of this gear. Get a cat! Good Luck with the build!
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Also, 11.9 volts is pretty high for a cutoff voltage... 11.5 to 10.5 volts is pretty typical (note: at 10.5 volt cutoff, the battery bank is pretty much dead and you have or may have killed the battery bank).
- 3,000 Watts * 1/0.85 inverter eff * 1/10.5 volt cutoff = 336 Amps @ 12 volt bank
I think you are expecting "too much" energy from your solar system as presently configured. Just some quick math (I have to leave soon):
A 400 AH battery bank can supply a recommended 2 days of storage, 50% max planned discharge of:
- 400 AH battery bank * 14.4 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 748 Watt array "nominal" for your battery bank
I.e., a 300 Watt AC inverter would be a much better fit here...
- 400 AH * 12 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 1,020 WH per day
- 1,020 WH per day * 1/5 hours of use at night = 204 Watt average 120 VAC for 5 hours a night
Say you are in the Dallas Texas area, and have 360 Watts or 748 Watts of solar panels. Fixed array facing south:
DallasMeasured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
Average Solar Insolation figures
(For best year-round performance)
Anyway... With a 3kWatt AC inverter you can run it at ~1,000 Watt AC load for something like 1 hour a day (on average) with your present 350 Watt array... When you have a partially sunny day/cloudy weather, much less harvest.
- 360 Watt array * 0.52 AC off grid system eff * 5.26 hours of sun per day = 985 WH per average May day
- 748 Watt array * 0.52 AC off grid system eff * 5.26 hours of sun per day = 2,046 WH per average May day
Really need to start with your loads--And design a system around those needs.
Watch the inexpensive inverter-generators... Many appear to be MSW (Modified Sine/Square Wave) AC inverters (you may have to call the mfg and ask--MSW is avoided in the literature... Or ask for THD (total harmonic distortion specifications... 5% or less is TSW. MSW may be in the 25-29% range... Not nearly as nice as the (more expensive) PSW/TSW type (Pure/True Sine Wave inverter).
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