- Last Active
- Registered Users
Rewinding to your original questions, your batteries manufacturer states minimum charge current of 8 amps, you have ~11 amps, but you have 2 batteries in parallel, so assuming internal resistance of each are equal, the current flow would be equal or 5.5 amps through each battery, below the minimum requirement. To add to this the minimum guidelines are based on grid charging, where unlimited hours are available, not just a small window of opportunity per day, so you need much more charging capacity to account for this. You really don't want to be on the fine line of battery failure where you currently are, sure lowering loads to almost nothing may help, but what's the point of having a system that can't support the loads you require.1
Think about the statement, 8A minium, 20A maximum, per battery, in parallel that is 16A minium, 40A maximum, you can exceed the maximum for short periods of time with no ill effects,as soon as the voltage climbs the current will reduce. Focus on the maximum, because there are only so many hours of productive sunlight per day.1
The percentage has nothing to do with the self discharge, it is a recommended figure to provide sufficient PV capacity to support the battery. For every 100Ah of battery capacity, 10A or more, of charge current would be required . So in the planning stage of a system for a 310Ah 12V nominal battery bank, the PV array should have the ability to provide 31A thereabouts, so rough calculation 12V×31A=372W, panels generally produce 75% of rated output, so 372W×1.25=465W, this is the wattage of panels required, round it off to 500W.
In addition geographic location has to be taken into account, many overestimate the hours of useful sunlight, use this link to find the hours at your location, http://solarelectricityhandbook.com/solar-irradiance.html pay particular attention to winter months as this will be a determining factor. Please note all the above is a rough calculation there are many more contributing factors not included, the purpose is to point out that perhaps you have over estimated the amount the 2 ×100W panels are capable of supporting. Sometimes it's better to start from the beginning again with the loads, battery capacity needed to support them, charging system to support the battery, geographic location etcetera, etcetera. Most have made the mistakes, me included, with the help offered from various members, a successful system can be developed.
In order to maintain a battery in daily use a charge current of 10% of the battery capacity Ah rating should be applied, so for your 310Ah the charge current should be ~31A, keep in mind if there are loads during charging these will subtract from the charging current, don't forget the inverter tare load if applicable.
With the panels you have, 200W, the most you will actually get is ~150W which equates to ~10.5A, so without loads during charging your panels are only able to supply 30% of what is required, so no amount of air gapping or tilt can make up the deficit because the calculation above accounts for that already. The addition of PV to meet the requirements will help during the cloudy days, by my estimate around 500W minimum of PV are required, more if a load is present during charging and assuming the batteries are sized according to the night time loads, something not discussed.
Can you give more details about loads, inverter if applicable.1
I estimate the bank charge status by observing the voltage before the sun is out and the load is none/minimal. I usually expect voltage to be above 12.8V. I've calculated that value by reverse extrapolating manufacturer's specs that state top 50% of charge are in 12.4-13.0 range.Also my charge controller provides daily statistics which I can use once the batteries hit float stage (voltage drops from 14.8V to 13.8V the values I've configured the controller with).In order to estimate SOC using voltage, the battery must be disconnected from all loads and charging for about 4 hours before measurements are taken.