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Comment on Sanity check for LiFePO4 Charger Design

There are really charging curves that should be followed to avoid damaging the cells.

You want to charge up to a certain voltage at a current (related to the battery capacity I believe) and when the cutoff voltage is hit, you switch to constant voltage (the max voltage of the cell) and then slowly drop the amperage as the battery is topped off.

I’m not sure about your cells, but some LiFe are 95-98% full at 3.45-3.5 volts, but the problem is that the voltage curve is really flat from 40-50% charged up to 95%. So you need really accurate measurement if you want to charge to 95%. The last 3-5% is when the battery ramps up to 3.65v and really is the riskiest part of the charge. It’s also the highest wear part of the battery use, if you can avoid charging it all the way up to that your cells will last much longer.

Decent video explaining charge/discharge here, though he’s using big LiFe prismatic cells.

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ColeSloth@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
My normal lithium battery charger automatically slows its charging speed as battery voltage nears its capacity. I could set it at 1000mah and it will step down to less than 1/10 of that before charging is complete.

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HewlettHackard@lemmy.ca ⁨1⁩ ⁨year⁩ ago
LFP cells have excellent cycle life anyway (2000+ cycles); is it worth worrying about staying at 95%?

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- nilloc@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
  It’s just that it’s really tricky to charge the final bit because the middle 80% is such a flat voltage curve. They have a 1000x life when they’re taken care of.
  
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  - Eheran@lemmy.world ⁨1⁩ ⁨year⁩ ago
    It is in no way tricky. Simply apply a constant voltage.
    
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    nilloc@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
    It’s tricky to stop at the right point, because lithium iron only have a very small voltage increase between like 40% and 90% and they ramp up to full voltage right near the limit of their capacity.
    
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Eheran@lemmy.world ⁨1⁩ ⁨year⁩ ago
What you are talking about is nothing special at all and not following a charging curve. The curve automatically looks the way it does when charging CCCV. Constant Current -> Constant Voltage.

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