12 volt system - battery dilemma

rancher0

when I started out I thought a 12 volt system would be perfect so I bought a couple of 100 ah gel batteries and connected them up in parallel. After quickly upgrading the size of controller and inverter, I also added 4 more 12 volt 200 ah gel batteries to beef things up.

Having read some other post’s about adding to many batteries in parallel will lead to heavy battery maintenance; not wanting to buy new inverters to accommodate a higher voltage unless necessary, I’m not sure what the remedy is.

icarus

Live with what you got, consider if a learning curve, and when your batteries need replacing, weigh your options of going with larger AH capacity 12v series parallel or upping the voltage of the system?  That said, mixing the new and the older batteries will eat to trouble, as will mixing the larger 200 AH batteries with the 100 ah pair.  I would consider cutting loose the two 100 ah batteries, keep them on a different float charge and use them for something else?


tony

BB.

Welcome to the forum Rancher0,

Assuming you are in California (in/around California City, Ca?), typically the GEL batteries you get here can have a maximum rate of charge of C/20 or 5% of the battery 20 Hour Capacity. If you have 400 AH @ 12 volts of battery, that is:

• 400 AH * 0.05 rate of charge = 20 Amps

GEL batteries have many good properties... High surge current, low self discharge, "No" maintenance, no spill, efficient. All that AGM type batteries also do well.

What USA GEL batteries don't do well--Is take high charging current (or tolerate over charging). When GEL batteries are gassing (bubbling electrolyte in flooded cell lead acid batteries), this creates gas pockets (bubbles in the gelled electrolyte) and reduces the capacity of the battery bank.

GEL batteries are fine for UPS systems, charging overnight for wheel chairs, etc. when you have >8-12 hours of charging time.

With solar, you may have 6 hours or even less (particularly in winter, farther northern latitudes) where is it difficult to fully recharge the GEL battery at such a low rate.

Typically, for an off grid solar power system, we want to put something like 10% to 20% rate of charge into the battery bank to quickly get them charged (bulk charging) and to voltage set point (absorb voltage) and hold it there for ~2-6 hours (depends on how deeply the battery bank is discharged). Flooded cell, AGM, Lithium Ion (like LiFePO4 type for off grid homes) are good at taking the higher charge currents.

This is a really a broad brush, and I am certainly not a battery engineer. Look for the manual for your battery bank/Mfg charging specifications and see what is needed.

And, it is difficult for us to guess at what "is a good system/voltage" for you without some details about your energy needs (average and peak surge Watt loads, Watt*Hours per day, full time off grid, emergency backup power, weekend RV, where the system will be installed--roughly, etc.).

I like to start with your loads and energy needs, then define the battery bank (AH, Voltage, chemistry, etc.). After that, hanging on solar panels and backup AC/Genset charging sources is pretty straight forward.

-Bill

rancher0

I’m out near cal city running a Coleman 440 hvad with a freedom 4 raptor to harvest wind and a Pv combiner on 1000 ah of renogy gel configured in parallel with 4 ea 200 ah batteries and 2 ea 100 ah batteries; might take those 2 ea. 100’s off.

mvas

To use all 6 @ 12v batteries .. create two (2) battery banks ...
Bank #1 = 4 @ 200 Ah Batteries 
Bank #2 = 2 @ 100 Ah Batteries

Add the Renogy 12v-to-12v Charger between the 4 @ 200Ah Battery Bank and the 2 @ 100 Ah Battery Bank
Then connect your older / smaller DC-to-AC Inverter to the 2 @ 100Ah Battery Bank.

http://www.smartgauge.co.uk/batt_con.html
Use Method #3 or #4 for the 4 @ 200 Ah Battery Bank
Use Method #2 for the 2 @ 100 Ah Battery Bank

GEL = Set Absorb to 14.1 - 14.2 volts to prevent gassing issues per mfr