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how quickly / hard should batteries be recharged?


SilverNodashi
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Hi, 

 

I wonder if someone can please shed some light on this matter. 

Once a battery pack reaches say 50% or 30%, how quick / hard should it be recharged?

 

As a reference to the system in question, I have an Axpert 5Kva inverter + 16x 6v P6V1700 batteries (setup in 2 banks of 48V) with a total of 244Ah, and 4x 260W solar panels on the roof. This gives me an average of about 600W solar power during the day and we draw about 300-400W average. During the night it drops to about 240W. The battery bank is 11,712W (is this correct? 48V x 244A) and can thus provide power for 39hours @ 300W, or 48.8hours @ 240W. 

 

Obviously, there could be spikes so the usage could differ. 

 

Now, what would be a safe recharge? As quick as possible, or a bit slower and "easier" on the batteries? i.e. would a 30A recharge be fine, or should I rather increase it to 70A or even 90A?

 

This is the battery in question: https://www1.elfa.se/data1/wwwroot/assets/datasheets/laSprinterP_t_en.pdf

 

P.S. Does anyone know how many cycles I can get at 30% DOD, 40% and 50% DOD? I can't quite figure it out from the tables on that PDF, and can't find any other info on this battery. 

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Hi, 

 

I wonder if someone can please shed some light on this matter. 

Once a battery pack reaches say 50% or 30%, how quick / hard should it be recharged?

 

As a reference to the system in question, I have an Axpert 5Kva inverter + 16x 6v P6V1700 batteries (setup in 2 banks of 48V) with a total of 244Ah, and 4x 260W solar panels on the roof. This gives me an average of about 600W solar power during the day and we draw about 300-400W average. During the night it drops to about 240W. The battery bank is 11,712W (is this correct? 48V x 244A) and can thus provide power for 39hours @ 300W, or 48.8hours @ 240W. 

 

Obviously, there could be spikes so the usage could differ. 

 

Now, what would be a safe recharge? As quick as possible, or a bit slower and "easier" on the batteries? i.e. would a 30A recharge be fine, or should I rather increase it to 70A or even 90A?

 

This is the battery in question: https://www1.elfa.se/data1/wwwroot/assets/datasheets/laSprinterP_t_en.pdf

 

P.S. Does anyone know how many cycles I can get at 30% DOD, 40% and 50% DOD? I can't quite figure it out from the tables on that PDF, and can't find any other info on this battery. 

 

Batteries should ideally be charged at rates between C10 and C5.  If you have a 100Ah (20h) battery you should charge it at a rate of between 10A (100Ah/10) and 20A (100Ah/5), preferably at a lower current. Just keep in mind that at a lower current it will take longer to fully charge the battery and especially if you are charging it by means of solar, you'll have to make sure that the batteries will be charged fully during the day.

 

According to your batteries' datasheet, they are 122Ah (10h) and you have two strings in parallel, so you effectively have a 244Ah (10h) battery bank, which should be a bit more at 20h, but without getting too technical, lets round that to 250Ah. Your ideal charge rate would thus be between 25A (250Ah/10) and 50A (250Ah/5). Depending on how deeply the batteries are discharged in the morning, you'll have to determine at what rate you'll get them fully charged during the day. I would suggest that you experiment with different charging current settings and monitor the level of charge. Maybe start with a 30A or 40A setting and monitor the batteries' state of charge - if they are fully charged by 11:00 in the morning, then lower the current, but if they are not fully charged by about 15:00, then raise the current etc. etc.

 

The datasheet does not contain a graph indicating cycles @ DoD.  It only mentions 10 year design life at 20

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The max charge rate should be in the document or sometimes written on the battery. In the doc there is a graph that show .1C and .2C charging, so I would not go above that.

 

On the cycles at a certain DOD, if the document do not specify, assume that battery is not really made for that. :) This one look like it is meant to be used as a "normal" ups battery, ie. most of its life is on a float charge and only very occasionally is it required to actually do work.

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The max charge rate should be in the document or sometimes written on the battery. In the doc there is a graph that show .1C and .2C charging, so I would not go above that.

 

On the cycles at a certain DOD, if the document do not specify, assume that battery is not really made for that. :) This one look like it is meant to be used as a "normal" ups battery, ie. most of its life is on a float charge and only very occasionally is it required to actually do work.

 

ditto

 

These batteries should not really be cycled daily.

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So the original battery choice seems to be a bit unfortunate. How would the OP maximise his battery life in his current situation? Just a thought as it may be useful to use the batteries "up" before replacing them.

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So the original battery choice seems to be a bit unfortunate. How would the OP maximise his battery life in his current situation? Just a thought as it may be useful to use the batteries "up" before replacing them.

 

Discharge as little as possible during a cycle and cycle as little as possible.

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