Microcontrollers > Data Logging

LiFePO4 repurpose with Arduino

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Bruce S:
Folks;
With a nice task requested of me. I thought it best to begin at the beginning and document it here so other trying to get a better understanding of the Arduino as it relates to it usefulness.


Here is one of the battery packs that I have been asked to repurpose into a 12V pack that is able to run a SIM card based router.

The current battery is from an old DeWalt hammer drill, the battery pack is a 36V system with no real way of telling what the Ah rating is.
Opening the pack up I am happy to see the A123 sized LiFePO4 cells. There's 10 of them with numbers A123 & ANR26650M1A.

I looked up the information which tells me they are 3.2Vdc at rated at 2300mAh.

Knowing this; I quickly realized my little USB based 18650 could be a hazard since the cut-off voltage is 4.2

frackers:
LiFePO4 can be charged to 4.2v without catching fire but its not recommended. Stick a  1N4004 diode in series to loose 0.7 volts (unlikely that USB will be charging at more than 1 amp).

Bruce S:

--- Quote from: frackers on September 27, 2017, 08:08:21 PM ---LiFePO4 can be charged to 4.2v without catching fire but its not recommended. Stick a  1N4004 diode in series to loose 0.7 volts (unlikely that USB will be charging at more than 1 amp).

--- End quote ---

True, these little gems top out at ~1A with a solid incoming voltage at ~5Vdc using a diode is what I have on a lone LiFePO4 cell, but where's the fun in that.

Cheers
Bruce S

Bruce S:
The pic I have here isn't the best quality and it certainly does not show how well these cases are built.
 
This is the case top showing how everything is covered.


This hopefully can show how they use the idea of coiled battery connections to maintain those tight connections and how they inter-connect each sets



Here are the batteries with the case covers removed.

Ten of these batteries and so far 3 packs, will allow me to reconfigure them into 13Vdc packs. I plan on building at least two packs from each of these giving 13Vdc@2.3Ah each. IF I get lazy, I'll have 2 batteries left on each of these units that won't be used to their fullest , but will still have a total of 13Vdc@ 12Ah back that will weigh in at less than 3Kgs.

Bruce S

OperaHouse:
Not sure if you are talking about a drop from 5V or from a 4.2V charger. Think I would go with a Schottkey diode for less drop if from a charger. Incidentally, choose one with a reverse voltage of less than 30V and preferably in the several amp range. Forward voltages of Schottkey diodes over 30V approaches that of plain silicon.  At lower % currents the forward drop is also less.

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