Lifepo4 upgrade?

[rslifkin]

Originally Posted by RaymondR

I'm pretty well in the same boat myself having only started the demystifying process about two years ago and not progressed very far.

One of the things I am finding baffling myself is the allowable charge current, designated as C which appears to generally be between 0.5 and 1.0 of the amp hour capacity.
but is generally stated without any voltage limitation.

This raises the question of why one should observe voltage limitations whilst recharging since the BMS is supposed to prevent overcharging and over discharging. Is it that there might be a damaging heat buildup or is it that one should not entirely trust the BMS to remove the charging source and that limiting the charge voltage will ensure that excessive overcharging will not occur because the rising battery back voltage will prevent over charging if the charge source output voltage is set low enough to allow this mechanism to come into play.

You don't want to force a BMS disconnect when charging, so you'd want to keep voltage within the acceptable range. The BMS cutting out on over-voltage is a safety feature, not a normal charging feature.

[fxykty]

Originally Posted by Chotu

Thank you!



I was thinking the same, but I didn’t know what I didn’t know here. Brand new to these types of batteries and I have never even read about them.



installing just one will allow me to do it quickly, just changing the charge parameters on my solar charge controllers.



and of course I should change the charge parameters on my generator powered charger also.



The battery manual gives a charging voltage of 14.1V for these batteries I bought. I am guessing the BMS takes this higher voltage and manages it correctly to charge the cells properly.



I'll give it a finishing voltage of 13.2 or something. Essentially switching off the BMS for charging at finish.



Sound about right for the finishing voltage?



Also, my new batteries will be full a lot. I know. Bad.



So if I finish my charging at 13.2, turning off the BMS for charging, will the solar controllers pick up the high loads when I turn them on? Things such as microwaving? Power tools? Shop vac?

Will these run off solar during the day leaving my batteries topped off to be used at night like I had been doing with the FLA batteries?





Note:. It may have been 14.6. I'll double check that today before installing. Going off memory and my memory cup runneth over. Too many details right now.

The BMS integrated with the battery is also a charge controller? That’s not usual, but perhaps that is the case with your battery. Hmmm, better check that. Generally a BMS only monitors the battery parameters (voltages, temperature), calculates and reports SOC, and disconnects the battery in case of some out of bounds condition. Regulating the charge is not function a BMS usually does.

Can you set your solar controllers to bulk and/or absorption charge at 14.1V until tail current reduces to 2.5% C? If so, set the float voltage at 13.2V and you should be fine. The initial charge will take the battery up to a notional 100% SOC, then that float voltage will allow it to discharge to around 50% SOC and hold there, with the solar charging providing the power for loads. Don’t be tempted to set a higher float voltage to hold the battery at a higher SOC - that can lead to overcharging (anything above 13.3V is high enough to charge to and past 100% given enough time).

For your generator (a DC generator?) set it to 14.1V and turn it off when your SOC reaches 90%+. If it’s an AC generator then make sure the charger only charges bulk and no float.

Your inverter will likely overwhelm your solar input and will therefore draw from the battery while your microwave or whatever is being used. Smaller loads will draw directly from the solar input.

LFP batteries are fundamentally different from LA. One of these differences is that it is destructive to hold them at 100% SOC. Since you have so much more available capacity, with 10% SOC being just as fine as 50% or 90%, you can forget about the LA obsession to always maintain the battery at a high SOC.

[Chotu]

Now that I've been using the battery today, I'm not sure his I'm going to keep it down to 90% SOC.

It's full right now.

I was supposed to charge it all the way up first use, so I did that from the generator. After about 2 hours at various 13.x voltages (and 72-80 amps), I heard the load drop from the generator. I guess it was done.

I switched off the generator and associated charger (which has 14.7 and 13.2 as the parameters, not changeable) and went back over to just solar.

The solar was still doing 13.6 or so as read on the charge controller. But the battery was just sitting there doing nothing on the battery monitor.

Now it's starting to discharge since the sun went down. Still st 100% SOC


My charge parameters are 14.4/14.6 on these batteries. Drop ins so I think they are trying to be mor3 compatible. BMS shuts over charge off at 15.0

[RaymondR]

Tried my Victron smart battery and charger with 14.1 Volts and it would hardly accept any charge current. I know it's not fully charged as it's been running a fridge all night.