Charge 12v LifePO4 with 30 watt panel?

mattadata

New Member
My 12v LifePO4 battery (20Ah) says I should charge it with 14.6 volts. My goal is to charge this with a 20~50 watt panel. Most of the charge controllers that come with these panels are intended for lead acid batteries and don't reach that voltage. Would it work to put a buck boost converter to get it up to 14.6 v?

I am running my router/modem with this battery. I have a 12 volt regulator on there. It draws 14 watts continously. My goal is to top of the battery each day to keep it running.
 

snoobler

Solar Honey Badger
My 12v LifePO4 battery (20Ah) says I should charge it with 14.6 volts. My goal is to charge this with a 20~50 watt panel. Most of the charge controllers that come with these panels are intended for lead acid batteries and don't reach that voltage.

My 12V lead acid batteries require 14.82V. This isn't a lead-acid issue.

Would it work to put a buck boost converter to get it up to 14.6 v?

I am running my router/modem with this battery. I have a 12 volt regulator on there. It draws 14 watts continously. My goal is to top of the battery each day to keep it running.

Your idea of using a 20-50W panel will mean you will tap out your battery every 24 hours.

14W * 24h = 336Wh

20Ah * 12.8V = 256Wh

Your battery can run your router/modem for 256/336 *24 = 18 hours

336Wh / 5 hours (you get EXCELLENT sun all day long) = 67W

Given the crap efficiency of cheap PWM controllers, I wouldn't consider this workable with less than 100W of panels (80W actual).

Again, this assumes you get excellent sun, tilt the panels optimally, and they are not shaded at any point between shortly after sunrise and shortly before sunset.
 

mattadata

New Member
So you are saying don't worry about the voltage....any charge controller will be fine?
Thanks for correcting my numbers....I can bump up to 100w panel.
 

snoobler

Solar Honey Badger
So you are saying don't worry about the voltage....any charge controller will be fine?
Thanks for correcting my numbers....I can bump up to 100w panel.

I'm not saying that that specifically. Any charge controller that can supply a bulk/boost/absorption voltage of 13.8-14.6 and a float voltage of 13.6V or less will typically work. Boost/absorption time of 1 hour or less is best.

LFP doesn't NEED to be charged to 3.65V/cell. You can easily get them to 98%+ full at 3.45V, it just takes a little longer.

Consider that even with 100W, if you have a cloudy day, you're likely going to shut down at some point. I would double the battery.
 
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