Sunday, Apr 03, 2011 at 08:20
Hi Folks, If one parallels a charged battery with a 50% charged state battery, what will happen is a little current from 100% to 50% but not a balance of
75% to 75% as ,when on charge from a panel or charger, the applied voltage raises the terminal voltage of battery say, from 12.2v to 13.2v @ around 5-10 amps on a 100AH battery. A charged battery at rest will exibit about 12.6v. so there is not a high enough voltage to drag the other battery up to itself.
To cut a long story short, with the different charge states, the fully charged battery will supply most of the current to the load while system is not being charged & 50% charged battery will accept most of the current while batteries are on charge from an external source. If a reasonable amount of capacity is cycled this way, the batteries will quickly equalise.
By the way, cycling of batteries from full state of charge down to say, around 70% & then recharging back up to 100% within a few days is good for the cells & will keep batteries more "active". Keeping cells in a float state for long periods (say many weeks) is not recommended & leaving them in a discharged state will damage them.
NOTE:If you are wondering how to pick a poor battery, from a dicharged state, they will come up to a high terminal voltage prematurely (say 12 up to 14 volts in an hour with a charger probably supplying only a few amps or so).) when on charge & draw less current than expected doing it. Remember, that current over time that you want from it can only be obtained by current over time when charging it.
Some technical info for those who can use it:
cells disharged= 2.05v. cells @ 50%=2.25v. cells fully charged=2.35cv. (readings taken @ no charge or load)
Charge rate for best performance should be about 10% to 20% capacity for first half of charge from a flat state. Then no more than 10% at half way point (2.35v/cell on charge). You will find the current dropping throughout charge so these are guide points. Towards end of charge the battery should be gassing & at this point charge current should not exceed 5% of capacity & be allowed to run in this state for 3 hours. This will equalise the cells to each other. This gassing proceedure should be done at least once a month.
I'll stop pratteling on now, I recently went into the do's & dont's of batteries from several sources & thought it might be helpful to some.
Best to all,
John.B.
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