Voltage limit LiFePO4 charging

[energyi]

Doing a recumbent e-trailer project which includes carrying some old recycled solar panels, 150 watts at 48 volts (open-circuit voltage is ~80), and want to charge my LiFePO4 20 amp-hour battery which tops out at a 58 volt limit charging.

A charge controller could be used for my needs to optimize the battery. The solar panels were so inexpensive that the cost of a charge controller begins to dominate the project budget. My question is, does it make sense to just use a voltage limiter on charging the LiFePO4 pack, say to 54 or 56 volts and have the I-V curve of the PV ride the ups and downs of battery voltage and clouds to that point? And if yes, does anyone know of a good one with a 10 amp rating? I would include a blocking diode so there would be no reverse flow. Is there a reason why LiFePO4 should be charged to full? I don't see much energy storage above 54 volts anyway. Yes, LiFePO4 has a BMS.

As always, thanks for endless-sphere.

Best Regards,

Energyi

PS: Great discussion on charge controller for such a scenario in this thread https://endless-sphere.com/forums/viewtopic.php?f=2&t=75232&p=1141076; I also found a less expensive charge controller at http://www.ebay.com/itm/SL03-4810A-10A-36V-48V-60V-Wincong-solar-panel-charge-controller-regulator-LCD-/261853354706 which enables a set-point for charging.

 

[amberwolf]

Is there a reason why LiFePO4 should be charged to full? I don't see much energy storage above 54 volts anyway. Yes, LiFePO4 has a BMS.

With the BMS, unless you charge to full, most don't do any balancing, so if your pack needs that....

 

[energyi]

Thanks amberwolf. If I understand this correctly, LiFePO4 BMS don't initiate a balancing procedure till fully charged. Same question then, with a higher voltage. Can a 58V voltage limiter be a successful alternative to a solar charge controller?

Best,

energyi

 

[energyi]

Follow up post, I did purchase the 10 amp charge controller Wincong SL03-4810A, currently less than what I paid, http://www.ebay.com/itm/10A-36V48V-60V-PWM-Solar-Controller-Charge-Regulator-100V-Max-Input-With-USB/141943518483

This can be set for stop-charging voltage, Floating charging voltage, under voltage recover (if using load output) and under-voltage protection (again, if using load output). I was able to customize the stop-charging voltage for 58.1 volts for the LiFePO4 48 volt pack. And was able to set the temperature compensation voltage to zero.

Challenge is that when the charging is approaching the 58.1 volt cut off, it is charging fast. My 3 amp wall outlet charger slows down after around 55 volts. This charge controller is set up for lead acid, or possible LiPo, but I think it isn't perfect for LiFePO4. I am thinking of setting the stop-charging voltage around 55 and periodically use wall outlet charger to bring it up to 58.1 volts and then the BMS should be able to balance the cells.

Shipping was free, quick, arrived as promised.

Any discussion is welcome. Thanks in advance. Hope this helps.

energyi