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Trickle Charging LifePo's

R

Roop

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Feb 11, 2024
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UK
I watched this video:

He suggests that trickle charging is bad but doesn't explain why.
So I googled: lifepo4 trickle charge issues and got this:


For those who don't have any test equipment more advanced than a Seeley multi-meter how would one decipher from the controllers instructions that it charges a LiFePo battery as intended? NB: I watched that particular video because it uses what I presume is a pretty generic chinese version of the controller I have.
The instructions for which can be found here:

I have disconnected the solar panel from my setup as a precaution.

Oh, the instructions say: float charge- gel (mine has gel/lifepo in this column) but the voltage is the same. Is this the voltage that it charges until it reaches this value?
Also, mine's the 10A version ecopower one.
 
'Trickle Charge' can mean a lot of different things. 10 amp solar controller is fine as long as the voltages are correct.

Float charge for GEL/LFP probably just eliminates the equalization of lead-acid.
 
Roop said:
. Is this the voltage that it charges until it reaches this value?
Click to expand...
The controller should charge to a target voltage, boost volts, ( absorbtion voltage), then after a period at constant voltage drop to float volts.
The concern discussed in the video is that the controller does not drop to the lower float, but continuously charges at the higher boost volts. This is common with the low cost PWM controllers . I have tested several and all exhibit the same performance, ( I expect the control ' chip' is common).
For reliable controllable safe charging profiles for lithium batteries, a quality MPPT controller is recomended. With the price reduction the Victron Smart range is recomended,
www.12voltplanet.co.uk

Victron SmartSolar MPPT Charge Controller 75/10

Victron Smart Solar 75/10 MPPT Charge Controller with Bluetooth built-in. For 12V & 24V systems in motorhomes, caravans, campervans & boats.
www.12voltplanet.co.uk
 
As I understand it:
- Lithium chemistries have very low self-discharge - virtually zero, and especially just after fully charged.
- So trickle charging will overcharge them.
- Overcharging, rather than just leaking charge and heating the cell, tends to deposit metallic lithium - which no longer "plays the game", reducing the capacity, and may grow whiskers back toward the other side, eventually puncturing the separator and shorting the cell.

(This is why you balance strings of Lithium cells with a BMS that routes current to discharge the higher charged cells, while lead-acids can be balanced by a moderate overcharge, which just electrolyzes some of the water in the fully-charged cells as charging current is driven through them to bring up the low cells.)

Different lithium chemistries are differently prone to the failure modes. (I understand one in the lab starts eating the end of the whisker when it gets too long.) I'm not sure how the LiFePO4 chemistry fits in, but I do note that BMSes shut down charging when any cell in the string reaches fully-charged voltage. So I wouldn't use a charger that trickled on a lithium battery of any chemistry unless I was sure that it had a good enough BMS to protect it from the overcharge. (Preferably, not even then.)
 
Ok. Well, the LifePo batt is won't be connected until I take the bike and trailer out.
That charge controller is exactly the type of second purchase I'll be going for, if not a little on the small side- slightly OT but can I connect panels in 24v mode to charge a 12v battery or does it have to be 24v all the way through?
 
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