How long should a battery be in floating charge

bigbrovar

Hello guys. I have a battery bank of 220ah @C20 12 x2 connected in series. The batteries are charged from a 30a Mppt controller and also from the Inverter built in charger.

My neighbour gets very little grid power hence the system is meant to provide me with electricity when the grid is down (and it is almost always down) before starting this project I did a lot to reduce my consumption and make it efficient. As a result my daily dod is about 30% mostly less than 20%. As a result my batteries gets charged quickly and remain in floating charge for a very long time. Sometimes the grid power comes up and the battery remains in float for hours.

I read somewhere about batteries having rest period when the battery is full and no load or charge is put on it. I also read batteries should never been left with no trickle charge for a long time. How can I balance the two statements. Can a battery in floating charge with no load be considered in sleep/rest period?

vtmaps

The answers to your question depend upon the type of battery.  What batteries do you have?

Hint: put the details of your system in your signature.

--vtMaps

Photowhit

All things are relative, Likely your system is never at 'rest' Do you have a inverter plugged into it? Is it switched on? Even with out an A/C load the inverter will be a small load. The battery doesn't need a rest period. We often talk about 'rest' periods, when people are trying to determine the State of Charge of their battery by it's voltage.

There is no conflict in the statements, but the statements are likely for different types of batteries. AGM batteries can be left with out trickle charging for longer periods than flooded lead acid batteries. Flooded, deep cycle, lead acid batteries 'Like' to be used, held in any state for long periods of time will diminish it's capacity.

For a battery to be at rest, it must be taken out of the system. No charging or discharging.

Dave Angelini

If you are using the battery overnight, then whatever your battery states as a float voltage can be used. In summer my bank is full some days by 9 am and floats until just before dusk. Been doing this 24 years with this bank and the previous one.

BB.

Trickle Charging is also the question... Inexpensive trickle chargers output, more or less, unregulated voltage (i.e., they output 1 amp all the time). If the battery is not being cycled, even 100-200 Amp*Hour 12 volt battery bank fed 1 amp 24 hours per day 7 days per week will use lots of battery water and probably not have a long float life.

The more expensive "trickle chargers" have a voltage regulated output (like 13.5 volts)--Those are capable of X amount of amps current, but hold the battery voltage at "float" -- A voltage that is high enough to overcome self discharge current, but not over charge/boil away the electrolyte (flooded cell batteries you can refill with distilled water--AGM batteries will "recombine" gasses, but the recombination process generates heat, bad for batteries, and does "wear out" the catalysts inside the AGM--so will be a cause for shorter battery life).

And there are "trickle chargers" that have both charging mode (14.2-14.4 for sealed GEL/AGM, 14.5 volts or so for flooded cell) and float mode (13.5 volts). I.e., a good "standard" battery charger--If a bit on the small side (not intended for regular deep cycle operation of batteries).

-Bill

bigbrovar

@vtmaps oops I forgot to add battery details. Basically here is my system setup.

PV 240w x 2 connected in series.

30A mppt charge controller

Battery 220AH 12v x 2 @ C20 FLA battery the Tubular plate type

1200w pure sinewave Inverter. 24v.



My daily load is about 1200w tops.

Load is spread across 10 hours at a discharge rate of not more than 8amp. My batteries stay well below 50% dod of daily use.

I basically turn on the Inverter on demand. It's comes on between 18:00 to 04:am on week days.

By time I am home battery is floating (in fact battery gets to floating charge by around 12-13:00.

On weekend. I use the system from 9am till 03:am the next day. On weekends my panels general enough to keep battery in float and power my load at least from 12pm till like 17am.

Although the Inverter is not always on. The battery is always connected to the controller. My fear is that because it is always connected to the controller it might not be good for its health. Often time the battery is always on trickle charge mode.

Floating charge for my cc is about 13.6v x2

Hope this answers all questions

vtmaps

To answer your question about whether too much floating is bad for a flooded lead acid battery: yes, if done wrong. 

What you are doing is OK, because you are cycling the battery every day.   The problem occurs when you have grid powered battery charger keeping the batteries at float for days at a time.  Stratification develops.  The cure is to do a full absorb cycle.

Several battery charger manufacturers have a mandatory automatic equalization of the batteries.  The popular Iota battery chargers do an automatic equalization after a week of floating.  Iota calls it an equalization, but their manual shows that it is just an absorb cycle at the normal absorb voltage.

--vtMaps

Masterjoe

Right now automatic equalization is disabled.  I have the option to enable it.  Would that be suggested to do and let it equalize on its own?