# Lifepo4 3.2vdc 20ah pouch cells BB



## TexasCotton (Sep 18, 2008)

Does any1 know what the value(lower) that should be used to bottom balance a Lifepo4 3.2vdc 20ah pouch cell.I realize that value will be within a range . I am thinking like 2.5 to 2.6vdc.


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## rwaudio (May 22, 2008)

TexasCotton said:


> Does any1 know what the value(lower) that should be used to bottom balance a Lifepo4 3.2vdc 20ah pouch cell.I realize that value will be within a range . I am thinking like 2.5 to 2.6vdc.


When bottom balancing my A123 pouches, I had good results with a cc-cv discharge to 2.4v (PowerLab6) which gave an OCV of 2.75 - 2.8V I brought the high ones down manually with a resistor.


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## onegreenev (May 18, 2012)

2.75 OCV is an excellent level. I use the PowerLab 8 with my own custom version to charge/discharge. I do both cc/cv when bottom balancing. Works great.


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## Red Neck (Feb 1, 2013)

Go to 2.5 and even then don't just trust it. After a charge, go down again and measure under load. You will see one or two cells lower than the rest under load (heater, lights... on) and give them an extra 1 Ah charge from a separate charger, to protect them a bit..

Then, you'll be OK.

My 50 cents. Without the lousy music


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## TexasCotton (Sep 18, 2008)

onegreenev said:


> 2.75 OCV is an excellent level. I use the PowerLab 8 with my own custom version to charge/discharge. I do both cc/cv when bottom balancing. Works great.


 I am slow but does cc(constant current) and cv(charge voltage) what your abbrev mean


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## Red Neck (Feb 1, 2013)

cv is constant voltage. In that phase, the charger will keep a steady voltage while the current slowly drops as the battery takes less and less charge as it fills up.


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## TexasCotton (Sep 18, 2008)

rwaudio said:


> When bottom balancing my A123 pouches, I had good results with a cc-cv discharge to 2.4v (PowerLab6) which gave an OCV of 2.75 - 2.8V I brought the high ones down manually with a resistor.


 Thank you ever one..Last question what kind and rating on the resitor?


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## rwaudio (May 22, 2008)

TexasCotton said:


> Thank you ever one..Last question what kind and rating on the resitor?


I use 0.05ohm 250 watt resistors, I got a batch of them off ebay very inexpensively. They do get hot after tweaking a couple cells so I just grab a cold one and let the hot ones cool.
For a single LiFePO4 cell somewhere in the 0.05-0.25ohm range should work, but the lower the value the higher the power rating required or it could burn up. (the lower the rating the more current drawn, and faster you can do the balancing)
IE 0.05 = 200-250watt
0.1 = 100-125watt
0.25 = 40-50 watt

Higher power rating doesn't hurt (just cost more)...
http://www.ebay.com/itm/100W-Power-0-1-Ohm-5-Aluminum-Wirewound-Shell-Resistor-/321061415339?pt=LH_DefaultDomain_0&hash=item4ac0c069ab


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## TexasCotton (Sep 18, 2008)

onegreenev said:


> 2.75 OCV is an excellent level. I use the PowerLab 8 with my own custom version to charge/discharge. I do both cc/cv when bottom balancing. Works great.


discharge voltage for Lifepo4 3.2vdc 20ah pouch cell range 2.5-2.7vdc or there about thank you everyone.
Charge voltage(CV) range 3.4 -3.6vdc will this range work?


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## onegreenev (May 18, 2012)

TexasCotton said:


> discharge voltage for Lifepo4 3.2vdc 20ah pouch cell range 2.5-2.7vdc or there about thank you everyone.
> Charge voltage(CV) range 3.4 -3.6vdc will this range work?


3.5 volts to 3.65 volts for the charge is fine. I think ending at 3.4 is too early. They will after charged settle to 3.35 to 3.4 volts. Mine settle at 3.34 volts. 3.4 volts under charge is not much into the charge curve but 3.5 fits nicely. Any more than 3.5 or 3.5 volts is just a waste. Takes long to charge that top up for a measly little range increase like around maybe 1 mile or so. Its not worth going higher. Time wise and cell stress wise. 

Pete


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## TexasCotton (Sep 18, 2008)

onegreenev said:


> 3.5 volts to 3.65 volts for the charge is fine. I think ending at 3.4 is too early. They will after charged settle to 3.35 to 3.4 volts. Mine settle at 3.34 volts. 3.4 volts under charge is not much into the charge curve but 3.5 fits nicely. Any more than 3.5 or 3.5 volts is just a waste. Takes long to charge that top up for a measly little range increase like around maybe 1 mile or so. Its not worth going higher. Time wise and cell stress wise.
> 
> Pete


 Thanks 
I should have stated this much early in thread. I am attempting to salvage 3.2vdc Lifepo4 20ah pouch cell from a damaged pack. How do I measure the AH(amp hour) of the cell. Never measured a cell before > I am thinking a meter, leads , and resistor will work.(hopefully) Or do I invest in ah meter with shunt?


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## onegreenev (May 18, 2012)

TexasCotton said:


> Thanks
> I should have stated this much early in thread. I am attempting to salvage 3.2vdc Lifepo4 20ah pouch cell from a damaged pack. How do I measure the AH(amp hour) of the cell. Never measured a cell before > I am thinking a meter, leads , and resistor will work.(hopefully) Or do I invest in ah meter with shunt?


Might be cheaper to just replace the cell 

I use my PowerLab. It can do it all or you can get the JLD 404 with shunt. I don't like it for small batteries. The readings are not fine but coarse. The powerlab will do a bang up job but the cost is more than a cell Im afraid. 

I don't think you are going to actually salvage the cell if it has been damaged. Once damaged there is no magic that will revive it.


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## onegreenev (May 18, 2012)

Actually reads voltage coarse not the counting of AH in or out. I use the JLD Volt meter for fine voltage reading. 

http://www.lightobject.com/Programmable-Digital-DC-Power-Watt-Meter-red-LED-w-control-P237.aspx

Buy them here.


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## onegreenev (May 18, 2012)

Here you go.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> Actually reads voltage coarse not the counting of AH in or out. I use the JLD Volt meter for fine voltage reading.


I'd be surprised if the circuits are actually different. Did you just have the resolution set for high voltage?


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## onegreenev (May 18, 2012)

Could be!. I'd have to go check it out. Easy to miss if not paying attention. Ill check later. But even so buying the components to check the cells will cost more than replacing a single one. But for fun it would be cool to check it out. I have a bloated pouch cell and it still works. Have not checked the capacity of that one. No leaking. Just puffed from over voltage.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> But even so buying the components to check the cells will cost more than replacing a single one.


Certainly for a 20AH cell, but running lithium it's good to have an AH counter anyway. If you wire it for easy in/out you can use it both in the lab and in the car.


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