MPPT or PWM charger? For LiFePO4 battery?

[T1 Terry]

PWM is best for LiFeP04

Hi, new here, found this forum while looking up PWM v MPPT. I have a 360ah Winston Battery prismatic LiFeP04 battery pack I charge with a PWM style Plasmatronic PL20 with an expansion relay modification. There are 12 x 80w poly Solarex panels, 6 X 50w mono "Rich Solar" from evil bay and a 120W mono no name panel also from evil bay. 1380w in total, not angle optimised at present but still puts out 65 plus amps at mid day.
The PWM type controller is better suited to Li batteries if the sun is good and the ambient temp short sleeve or better during the sun periods. I've tested heaps and they just don't live up to the makers claims when it comes to Li batteries. I think the reason for this is the Li batteries in a 12v nom. configuration hold 13v or higher till deeply discharged, the difference between the MPP of a 12v nom panel in full sun with a temp of 40degC or more isn't enough to be of any value. The claim of better output in poor light or rain conditions has never happened either, the PL20 starts putting amps into the battery long before any of the MPPT unit do. I really wish their 30% better output claim was true but unfortunately it must only happen in a lab with cold panels into a load cell held at 12v or lower, it doesn't happen in the real world with Li batteries that's for sure.

T1 Terry

[john p]

The 12 v "drop in" replacement lithium ion phosphate batteries are available in 12.,24.,48. and 144v

If you arenot wanting to spend much money you can use a PWM charger with an adjustable end of charge voltage.14.8v that also allows you to turn off the "equalize " setting.. IE the old Steca ones and their new chinese copies.and if you are using the smaller cylinder 10a cells you can make a simple BMS using a zenner 3.9v and resistor across each cell to balance against overcharge and a low voltage cut off switch to prevent over discharge.. set point about 10v..

This does work ok as I have done 3 systems like this and they have now worked perfectly for over 3 years .

[Mike90250]

....I am keen to integrate LiFePO4 into my system in order to replace the Lead acid type. ...

The easiest way for you to do that, is to obtain the 12V automotive "drop in" replacement batterys that have the BMS built into their case. They are quite pricey !

[Thomas Lai]

LiFePO4 battery charger for solar panel

Hi Williams,

I'm also looking for a charger solution or provider. Would you please share with me once you get any update? I'll do the same for sure.

Since I'm designing a standalone solar generator for disaster recovery, I am keen to integrate LiFePO4 into my system in order to replace the Lead acid type.

with kind regards
Thomas

[Sunking]

I doubt you will get any answers, because there are so few if any using LFP batteries for solar. It is not that it cannot be done, there is just no demand for it right now and thus no one is manufacturing charge controllers targeted at LFP batteries. I recall one manufacture that has a LFP setting, but I would not recommend using it because it is not accurate enough. Lithium batteries are very expensive and need Battery Management Systems (BMS) to charge each cell or group of cells to precise voltages. No one makes that for Solar yet and it is very expensive.

You can buy BMS charging systems but they are designed for the Electric Vehicle markets and require a very hard power source, and solar systems are not hard power sources and never will be.

So for now the only way is a custom design/build which very few are capable of, and those that can will not give any clues.

[Mike90250]

( moved post to it's own thread )

The MPPT is always more efficient when you have a higher voltage PV array. Like a low loss DC-DC transformer to match high voltage array to low voltage batteries.

BUT that's not what LiFe batteries care so much about, as they need a very precise way to balance the charge to each cell in the battery, and not to overcharge. So being able to set precise voltage set points is the most critical thing.

Hi, Everybody,

Is anybody here experienced with LiFePo4 battery bank in off grid solar system?
Can the LiFePO4 battery bank be working with the MPPT charger or PWM charger?

Thanks

William