# Can I charge individual lifepo4 batteries while in series?



## onegreenev (May 18, 2012)

No need to remove them from the string if you plan on charging one at a time.


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## deckofficer (Apr 3, 2012)

I have discovered for balancing cells what works best is run them down to 2.9 volts, and put all the cells in parallel and slowly charge to 3.7 volts. Might be a PITA for high voltage packs, but for low voltage pretty easy. If your cells are banded and you don't want to un-band to line up all the negative and positive posts, build some jumpers.


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## Ziggythewiz (May 16, 2010)

You can either top or bottom balance them. Plenty of threads arguing about each.

I prefer top because it's much less effort with the cells already mostly full. The standard process is to bring each cell up to 3.65V @ a current of C/20, but it depends on exactly what cells you have.


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## Elithion (Oct 6, 2009)

dpatriot said:


> Do I need to remove each from series before charging individually with 3v charger to balance them?


No.

Also, you can use multiple chargers, each charging a different cell individually.
The chargers have to be isolated (pretty much every charger is isolated, except for Manzanita Micro).


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## dpatriot (Jan 31, 2013)

Thank you all. 

Also.. I made lots of reading in here on how best batteries are cared... I think everyone agrees that the battery will last if you don't overcharge and not go beyond a maximum discharge level of the cell. In order to do that, the battery pack must be balance all the time, and that is where the disagreement pops up. Some say you must have a bms in order to maintain a balance pack and the other says not necessary. 

I choose not to use a bms for simplicity and lower the cost of the system and see if the packs maintain its balance. It did not, so I need to charge them individually to balance. I don't know why it did not remain balance after use, any idea why? I also use my my existing LA charger, monitor the charge and will stop before it is full. I don't understand why there is a difference between FLA charger and lifepo4 charger as long as it has the same voltage output as the pack I am charging. Btw, I did buy a lifepo4 charger from china but after inspecting it it looks like very low quality and could cause a fire so decided not to use it.


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## Ziggythewiz (May 16, 2010)

How was the pack balanced to begin with? What cells are they?

A lead acid charger usually has a gassing cycle where the voltage goes much higher than the full resting voltage. Lithium only goes a little above the full resting voltage.


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## deckofficer (Apr 3, 2012)

I just use a cell logger with alarms set at 2.9 low, 3.9 high, but never hit the high anymore since I did a bottom to top balance. I don't care for BMS either. I fast charge just like most EV'ers at 3.7 VPC X cells in the series string.


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## Elithion (Oct 6, 2009)

dpatriot said:


> the battery will last if you don't overcharge and not go beyond a maximum discharge level of the cell.


Yes.



dpatriot said:


> In order to do that, the battery pack must be balance all the time.


No.

Balancing is done to maximize battery capacity. I doesn't prevent overcharging or over-discharging. 

What prevents overcharging is to stop charging when ANY cell reaches its maximum voltage. What prevents over-discharging is to stop discharging when ANY cell reaches its maximum voltage. (That's not disputed.)

A correctly installed BMS does prevent overcharge and over-discharge (that's not disputed). A BMS does top balancing (that's not disputed).

What some dispute is that you can do that even without a BMS. 

If you do not have a BMS, most of those same people say that bottom balancing is best (but that is disputed).


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## dpatriot (Jan 31, 2013)

Ziggythewiz said:


> A lead acid charger usually has a gassing cycle where the voltage goes much higher than the full resting voltage. Lithium only goes a little above the full resting voltage.


Oh ok. I checked that the charger on board the ev is designed to charge gel cell batteries, and gel cell battery are charge with lower voltages... so I assume this charger should be ok with lifepo4 batteries as well?

Thanks


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## Ziggythewiz (May 16, 2010)

Set for GEL it should be fine as long as the finish voltage matches your pack. What voltage does it charge to and how many cells do you have?


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## dpatriot (Jan 31, 2013)

Ziggythewiz said:


> Set for GEL it should be fine as long as the finish voltage matches your pack. What voltage does it charge to and how many cells do you have?


Hi, Output is 72v... I have 24cell, 3.xV each. btw, I am using the cells as a replacement for gel cell batteries on my th!nk neighbor.


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## Ziggythewiz (May 16, 2010)

That should be good. Be sure and monitor it the first few times to see exactly how high it goes.

I think someone else had issues upgrading from gel to lithium with a think neighbor, will have to find the thread.


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## dpatriot (Jan 31, 2013)

I charged the pack for 8 hours and it seems the voltage of each of the battery stopped at 3.27 - 3.30v range. I charged it again to try to bring the voltage to at least 3.5 but it remains at the same voltage range. Something wrong with the charger/controller?


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## Ziggythewiz (May 16, 2010)

3.27-3.3 is a huge range for lithium.

What was the peak pack voltage while charging, and what is it resting?


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## dpatriot (Jan 31, 2013)

I was planning to balance them when it reaches around 3.5 but they won't go there. How will I measure the peak pack and what is resting? Sorry, really don't know about these.

Thanks


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## Ziggythewiz (May 16, 2010)

3.38 is full so they'll never get to 3.5

Pack voltage is the voltage from the negative post of the most negative cell to the positive post of the most positive cell.

If you're not charging them in series, just one at a time all but that one will be at a resting voltage.


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