Float Charging Flooded Lead Acid Batteries?
Is it hard on Flooded Lead Acid batteries if they do not receive a full float charge periodically?
I find when my batteries go through a bulk, absorb and then into float charge, the amps required to float charge slowly drops as the batteries reach full saturation. If I leave the power on them, in float charge, it can take 24 hours or more before the charge amps no longer are dropping. At this point the batteries are fully charged, but doing so regularly when off-grid would not be be possible in the sun and not economical when charging from the generator.
Comments
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
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Do you have AGM or Flooded?
Can your battery bank accept more amps during Bulk Mode?
Can your battery bank accept more voltage during Absorb Mode?
With Solar ...
a) The short time to recharge the battery bank is your enemy.
b) Some days you may not get back to 100% SOC.
Describe your ...
a) Battery Bank
b) Charging Parameters
c) PV Array
d) Daily Depth of Discharge
Float should have very little if any charging going on. In float the voltage is high enough that the charge controller can increase energy from the array before drawing from the battery bank when sensing a load.
In cool/cold temps, a fully charged battery can be left with no float (or loads, including controller self-consumption) for weeks/months. In warm temps or with even small loads, floating would be wise.
If sitting floated, a bulk/absorb cycle is only needed monthly or so to prevent stratification in flooded batteries.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
In reasonably cool conditions, 3 months is probably ok. In hotter, maybe not.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
To fully charge a FLA battery, the charge voltage should be raised above the Gassing voltage of that battery. This is in the range of reasonable Absorb voltages.
Gassing is the friend of FLA batteries, as it does help mix the electrolyte, de-stratifying the battery. Tall batteries require more electrolyte mixing, than do short ones.
The ideal Float voltage will just barely keep, a fully charged battery, fully charged.
On the Flooded banks in use here, the battery charge current, an hour after the end of Absorb, is about 0.1% of 20-hour Capacity.
FWIW YMMV, and so on. Vic
As Vic notes, absorb voltage should be high enough to get some gassing. Not boiling but more of a fizzing with an occasional "burp".
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
Keep in mind however the most common battery failure mode with lead scid is undercharging, as previously stated it's a fine line, lead acid, so simple in concept but complicated in reality.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
-Bill
The proper EA on these banks varies considerably vs DOD in the previous discharge. This is one reason that I'd like to see CCs like the MN Classic have the ability to use Rate-Of-Change in battery charge current as an option to end Absorb.
The deeper the battery discharge, the higher the EA setting needs to be, or else, Absorb will not be terminated by the EA setting, but (with most good CCs) the Max Absorb time will cause the termination.
We try to choose an EA setting that is far out on the diminishing battery charge current curve, where one wonders if the average finishing current will EVER drop any more. Measured finishing current can have a reasonable amount of current Jitter. This Jitter can make the human averaging a bit difficultto see, and so on.
Of course, there is some Surface Charge effect at the very beginning of the transition to Float, from Absorb, so, this results in the CC providing 0.0 A at that time. The battery charge current, early in Float is a bit difficult to describe, should really graph it ... (but, not now).
More later, FWIW, Vic
It is why I keep raving about my new Duracell chargers. Only 4 amps but they keep charging for ~half a day after hitting the proper voltage. So I wind up at 13 volts instead of 12.7 volts.
Interesting that so many posters are whipping out math formula's this year. I know a professional solar installer with years and years of experience. I don't think he uses a single formula.
Maybe Softdowns installer friend can divine cold Voc somehow, but mere mortals like me have to do some arithmetic (or use a string calculator).
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
Small
Medium
Large
XLarge
Etc.
So you do the math and think that you need a 968 watt inverter with a 2349 watt surge. 1441 watts of panels. 731 pounds of deep cycle batteries. You find stuff that is close yet it is still way off for several reasons. Then the wife has twins and your brother develops cancer and has to be taken care of - along with his family.
What really determines many solar arrays:
Roof space
Battery room
Well pump surge
Budget
Anticipated future
Deals
Life has curve balls. Nothing but curve balls. We are talking about energy creation and adding more can be problematic. If we are going to live in a place it may be a good idea to install more than we theoretically need need. How many people regret an abundance of energy storage or ability to harvest that energy?
If numbers were crunched a 67hp Lada might be recommended. Would I be happy with its limitations? Often it is better to get more than you need. I wonder how many people have lamented to D Angelini that they wish they had less power. Or told Marc K that they wished they had less storage capacity. Does it happen? Of course. Is it the norm?
I would not want to be sitting here yearning for more storage capacity when dealing with common -15F temps, savage winds, and darkness. Luxury is appreciated at times.
And spend your $$$ on more solar panels and solar charge controllers... 5% rate of charge (20 hour battery capacity specifications) can work for standby/summer weekend systems--But for daily cycling, start with 10%-13% rate of charge minimum, and adding more panels is very helpful too (especially in Winter for most folks not near the equator). (and sizing for hours of sun per day by season, no shading, etc. too).
Using "cheaper" flooded cell batteries for your first bank or two until you get things working well--Then look at AGM or LiFePO4 batteries longer therm (for fixed/cabin/home installations).
As all rules of thumbs--The above is a good starting point. If you have something "different' (RV, not much room, not much extra weight capacity, tools, etc.), then details on the loads are critical to figuring out what your "optimum system" may be...
Over-sizing the battery bank, without appropriate charging capability (more solar panels, more genset/AC mains charging capacity, etc.) can be an expensive way to cause a shorter than normal battery bank life.
If you have a good working bank and 2x oversize it... Yes, it may last upwards of 2x longer, but it also cost you 2x as much. Obviously, less battery change outs (6-10 years vs 3-5 years) is not a bad thing for more people... But you are also "risking" your expensive "over-sized" battery bank being killed by other things that may sneak up on you (guests leave everything on when going out for a couple days, lighting kills charge controller while you are away, somebody leaves inverter on over winter at the cabin, etc.).
-Bill
For more or less full-time off-grid, the rule of thumb is to design for two days no sun to ~50% max DOD. Mine is designed that way, and the way it works out is it mostly cycles between ~80-100%. In gloomy stretches I use the genny to cycle between ~60ish and 85-90%. Having much more bank wouldn't really change that much. The genny could run less often, but for longer to recharge a bigger bank.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
The "standard" reply is to cycle to >90% once per week. However, one major mfg (Rolls/Surrette?) had said that >90% is only needed every 4 weeks (if daily 50-80% cycling).
If the batteries are not cycling (you leave the cabin for a week at 50% SoC and bad weather)--You do really need to get upwards to 90%+ State of Charge before putting the cabin/batteries "to bed"--When there is no immediate solar charging available (days/weeks of assumed bad weather/missing sun) getting the bank charged will help reduce Sulfation (which is, more or less, permanent battery damage).
-Bill "I am not a battery engineer" B.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter