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Charging LiFePO4 battery from car

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danielandrews

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Hello all,

I have a LiFePO4 battery that I would like to keep charged from my car battery.

My problem is that the alternator runs about 13.75V, to fully charge the battery I need a source of at least around 14.6V. Charging with the 13.75V source only gets the battery to roughly 10% of its capacity.

Would it be easiest to find a boost converter that outputs 14.5V? An off the shelf LiFePO4 charger that runs off 12V?
Any suggestions or experience would be appreciated, Thanks
 

Hi I have the same question and i made this conclusion: You need a boost converter. Best is to step down the voltage to say 5 VDC and then step it up to about 17V or 18V DC. This voltage then you applied to your charging circuit and you are guarantee a full charge every time.
Hope this helps.
 

Hello all,

I have a LiFePO4 battery that I would like to keep charged from my car battery.

My problem is that the alternator runs about 13.75V, to fully charge the battery I need a source of at least around 14.6V. Charging with the 13.75V source only gets the battery to roughly 10% of its capacity.

Would it be easiest to find a boost converter that outputs 14.5V? An off the shelf LiFePO4 charger that runs off 12V?
Any suggestions or experience would be appreciated, Thanks

13.75V sounds really low for an alternator unless you made the measurement at idle. Usually they run around 14.0 - 14.5V. You might have a loose connection.

In any case, charging any lithium battery should only be done through a proper charger that can babysit the battery and cut off the charge at the proper voltage. I'm sure you can find one that's powered from 12V.

Ed
 

13.75V sounds really low for an alternator unless you made the measurement at idle. Usually they run around 14.0 - 14.5V. You might have a loose connection.

In any case, charging any lithium battery should only be done through a proper charger that can babysit the battery and cut off the charge at the proper voltage. I'm sure you can find one that's powered from 12V.

Ed

how hight is the max voltage I can safe and efficiently charge my 12.8v LiFePo4 battery, is there step for different state of the battery capacity to charge efficiently. have seen many charge curve with constant current level. but that not show the charge requirement. I also have another LiFePo4 that say "do not pulse charge" does anyone have a application note to follow with guidelines ?
 

Ordinary Li-Ion and Li-Po battery cells have a maximum voltage of 4.20V. When their charging voltage reaches 4.20V then they are only about 70% fully charged. Considerable more charging time is needed at 4.20V until the charging current is detected to drop to a low value then the charger should disconnect the cell.

Your battery manufacturer should tell you the maximum recommended charging voltage and how long it needs to be at the maximum voltage.
 
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