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Author Topic: Li-Ion charger behavior with LiFePO4 cells CC mode / CV mode fully illustrated  (Read 1423 times)

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Offline Kiriakos GR

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For some time I wanted to data log the constant current mode of my charger, and get a graph of the charging curve.

Constant current mode is when the charger working at max current which is labeled at the top of it.
At that step it is like feeding the cells with raw energy and voltage peak is not important.

If we divide the sum of charging time in five parts of equal time (five periods), the four of them belong to constant current mode .
The constant voltage mode engages in the fifth period in which the DC current in use is much less because the batteries are all ready charged at 90%.
The green light comes ON later on in which the fifth period has ended but even so the charging is close to 95% and therefore is not really ended.
 
All our batteries are active chemistry, and chemistry has much slower response rate so to activate at 100% when is activated by a DC voltage source.
The so called as balancing or better described as finalizing recharge stage is the unknown factor which this measurement is going to in light me about.

One simple to build DIY cable splitter with compatible input/output power plugs and a pair of banana plugs was the only needed accessory.
 
This U1272A is still my favorite meter as self-data logger and I programmed it to take a sample of the action every 5 minutes (300 seconds).

BM-257 has an easy job to do here and this is volt output monitoring and is connected by alligator clips over my accessory extension cable.

According rough (by memory) statistics of the last five recharge cycles, my 36V 10Ah Lifepo4 with 30120LE cells, was needed about five hours up to green light.
This translate to 1.9Ampere per hour => times five = 9.5Ah
   
The result of these measurements will illustrate or answer my very own question marks.
a)  How long I will have to wait after the Green LED regarding additional time so the battery to be considered as fully charged?

b) Which is the sum of energy in Ampere hours which my charger supplying to my battery?
The answer in this second question can be considered as good evidence of battery cells capacity capability, and this info can assist even further if battery cells evaluation becomes first as priority in your application. 
 
Today that you reading these text lines, the job of making the measurement and the results has been completed.
My battery definably is in top shape and the graph which includes a bit of artwork as assistance about better illustration of the action to hobbyists readers it can definably help them to raise their understanding of how a Li-Ion charger behaving.
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