Mppt settings for sun xtender batteries

Are these for 2x 6 volt batteries in series (and 2x parallel strings)? 7.2 volts vs 14.4 volts (charger does not work on 6 volt battery bank, as far as I know).

How deeply do you cycle these batteries? Where are they installed (roughly--hours of sun)?

AH of battery bank? Wattage of your solar array?

For wiring your batteries in parallel, take a look at this website:

http://www.smartgauge.co.uk/batt_con.html

Setting #2 or #3 is probably your best bet... #2 if you do not deeply cycle your batteries. #3 if you really deep cycle your battery bank and need to get it back full every day (harder on battery bank).

If there is a switch you can set to turn off equalization, then #3 would be fine (high voltage charging are not good for AGM batteries).

-Bill

Equalization for AGM batteries should either be set to "OFF" (no equalization), or typically no more than the 14.4 volt charging set point (again for a limited amount of time). AGMs if over charged, will tend to out-gas or "wear out" the catalyst used to recombine hydrogen+oxygen. Out gassing (very much at all) and/or worn out catalyst are the end of your "useful" battery life (you cannot refill AGMs, in general).

I would only use #3 when you deeply cycle the bank because of the "float voltage" setting. The Concord batteries are supposed to be "better" able to withstand higher voltage settings--But I would not push it. 14.6 volts is a bit high for AGMs (in general at 77F).

What is the Amp*Hour rating for your battery(ies)/Battery Bank (in total)?

How much power do you want from the system, on average? Say you are near Phoenix:
http://solarelectricityhandbook.com/solar-irradiance.html

Phoenix
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.92	5.55	6.45	6.83	6.74	6.57
Jul	Aug	Sep	Oct	Nov	Dec
6.08	5.78	6.03	5.82	5.24	4.74

And it is not used in winter, gives you an average of ~5.55 hours of sun per day:

• 2 * 265 solar panels * 0.61 DC system eff * 5.55 hours of sun per day avg (Feb) = 1,794 WH per day (Feb break even month)
• 1,794 WH per day * 1/12 volt battery bank = ~150 Amp*Hours per day (avg Feb day)

-Bill

The 14.3 and 13.7 volts are fine, it is the last float voltage that I am a bit worried about:

off-off-on 2 - Sealed* 14.15 13.70 14.40 28
off-on-off 3 - Sealed* 14.30 13.70 14.60 28
off-on-on 4 - AGM/Flooded 14.40 13.70 15.10 28

Once every 28 days, the controller goes into "Equalize" at 14.6 volts.

On page 58 of the PDF file for a "random" firmware version of the Midnite Classic:

http://www.midnitesolar.com/pdfs/classic_manual_Rev_1933.pdf

Turn S1.8 to "off" and it will go to manually initiated equalize (as I understand)... Then you can use #3 or even #4 just fine... Those two settings will better charge your battery bank and avoid the (usually unneeded) Equalize function (unless you need to equalize your AGMs--And that is another issue).

If the batteries are 305 AH (we usually use the 20 or 24 hour capacity settings). When you add batteries in series, it just adds voltage. When you add strings in parallel, they add in Amp*Hours.

So, your bank is 12 volts * 610 AH rating. Normally I would suggest a 5% to 13% rate of solar panel charge:

• 610 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 570 Watt array minimum
  
• 610 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,141 Watt array nominal
  
• 610 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,483 Watt array "cost effective maximum"
  

You pretty much have a minimum array for a full time off grid system that is cycled at least 25% per day.

For AGM batteries, if you cycle at less than 25% of battery capacity per day, or only is cycled occasionally, a 5% rate of charge can work "OK".

If you use 25% or 50% of capacity per day:

• 610 AH * 0.25 discharge = 153 AH discharge per day "nominal daily usage"
• 610 AH * 0.50 discharge = 305 AH discharge per day "heavy daily usage"

Of course, it depends on the amount of sun per day and size of array too (location, by season, stretches of bad weather, etc.).

-Bill