Lifepo4 cells . Initial charge or not?

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Grumpy-b
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Lifepo4 cells . Initial charge or not?

Postby Grumpy-b » Thu Sep 11, 2014 6:32 pm

Diffrenet makes of Lifepo4 cells appear to adopt different approaches to the need for a specific initial charge routine.
As part if the initialisation of the cells the cells have to be charged to certain higher than normal usage finish CC voltage, some makers do this for you, like CALB, others like thundersky did some of the work but required a final recharge to over 4v (exact voltage varied ) before being put into use.

So if you have some new cells or are looking to buy some its always worth making sure that you know what the makers require you to do with them before putting them into service.

A generic approach just isnt an option, as not only is it a do or dont charge, but if its a charge then what voltage and CC do you use.

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Rory166
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Re: Lifepo4 cells . Initial charge or not?

Postby Rory166 » Thu Sep 11, 2014 7:32 pm

Slight aside
I bought a power supply from china which appeared to be ideal for doing the initial charge.

http://www.ebay.co.uk/itm/380920543735? ... EBIDX%3AIT

Unfortunately it does not work correctly. Yes you can set 4.1 V output yes you can set 20A current limit but when you connect to say a 3.4V cell you do not get 20A you get 100mA! To get 20A to flow into a cell it is necessary to set the open circuit voltage to 9V. It would do the CC part of the charge ok but would keep on charging past the max voltage. Lab supplies do not work like this at all. To use this PSU I will need to build an external regulator.

Rory
Electric Seicento conversion, Leaf

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skooler
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Re: Lifepo4 cells . Initial charge or not?

Postby skooler » Fri Sep 12, 2014 12:16 pm

I see no reason for this.

I capacity tested a couple of cells around a year ago. From 2.7-3.5v, then 2.7 to 4.0v, then 2.7 to 3.5v again.

Guess what... same capacity on both the 3.5v tests.
Posts by Mike Schooling
Director and tech lead at indra.co.uk

Mazda RX8, Soliton Jr, 24KWH Sinopoly LiFePO4, Kostov 11alpha
http://www.diyelectriccar.com/forums/sh ... 61556.html

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Rory166
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Re: Lifepo4 cells . Initial charge or not?

Postby Rory166 » Tue Sep 16, 2014 7:19 am

Just watched the recent Jack Rickard Youtube seminar on Lithium batteries. Well tried to watch as it turned out to be an insomnia cure. Anyway I caught a remark that the initial charge should be very slow I think he said several days?

Rory
Electric Seicento conversion, Leaf

Grumpy-b
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Re: Lifepo4 cells . Initial charge or not?

Postby Grumpy-b » Tue Sep 16, 2014 7:26 am

Still product specific. Follow the makers guidelines, especially if you want any warranty.

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skooler
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Re: Lifepo4 cells . Initial charge or not?

Postby skooler » Tue Sep 16, 2014 8:46 am

Any scientific reason to do this?
Posts by Mike Schooling
Director and tech lead at indra.co.uk

Mazda RX8, Soliton Jr, 24KWH Sinopoly LiFePO4, Kostov 11alpha
http://www.diyelectriccar.com/forums/sh ... 61556.html

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Rory166
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Re: Lifepo4 cells . Initial charge or not?

Postby Rory166 » Tue Sep 16, 2014 9:28 pm

Mike

I am not sure I can do the subject justice in a post. Might be better to watch the video. To sumarise the plates and electrolyte are stable and non reactive. Only when charged do the Lithium molecules move into the plates and become highly reactive. A protective layer forms which protects the plates from reacting with the electrolyte. I assume that it is much better to build this layer gradually on the first charge and not just bang in maximum charging current. For storage and shipping it would be best to then discharge the battery to a partial level as it will degrade less.

It is possible to imagine the battery assembled and not charged then shipped then charged when about to be used. This would have advantages in delaying the start of shelf life but would mean no testing in the factory.

Rory
Electric Seicento conversion, Leaf


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