Charging a LIFEPO4 battery in multiple configuration

Hello, I would like to ask. I have two 12V, 100ah Redodo LIFEPO4 battery. Bought the two batteries thesame time and I have been using them in a parallel configuration to get 12v, 200ah. Of recent I ran into an issue… I have a 40A mppt charge controller. But at 12V, the maximum wattage that the controller will deliver is 600W. This takes about 5hours to fully charge the 200ah battery. I will like to shorten the charge time. Redodo states that their 200ah battery can safely accept 100a(1200w, shortening my charge time to about 2hr30mins) However since my battery is in a 12v configuration, my 40A controller will only deliver 600w max - (40A at 12V) and I do not have the budget to buy another separate controller so I am thinking, can I wire the two batteries in series to change their configuration to 24v 100ah so that my controller can harvest 1200W of solar Pv(40A at 24v). And then when the battery is done charging, I can change them back to parallel connection(revert them back to 12v, 200ah) because I dont have a 24V inverter. I know the safety rules
1. When I am charging the batteries at 24V, I intend to remove my 12V inverter to avoid the voltage from spoiling the inverter
2. The batteries are thesame brand, thesame capacity, bought at thesame time.
3. The max recommended charging Amp for the 24v 100ah is 50amp(1200w) for charging the batteries so I wont go above 50amp. My controller is even 40amp. So I cant go above it.
But I was just wondering, will charging the battery in 24v configuration(series) and then discharging in 12v configuration(parallel) have any negative effect on the batteries?

Easyyokefilms said:

But I was just wondering, will charging the battery in 24v configuration(series) and then discharging in 12v configuration(parallel) have any negative effect on the batteries?

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If the two batteries are both at true 100% when fully charged in the 12V configuration, you'll probably be fine.

When putting 12V in series for 24V, if either battery hits 100% first, then the BMS will enter protection mode and stop charging. This may prevent you from fully charging both batteries, BUT they will likely be at a very high state of charge.

Issues:

1. Inconvenient.
2. Opportunities for poor/broken connections - They are not designed for multiple daily disconnect/reconnects.

It's not clear how much solar you have, so I can't say if there's major benefit to be had.

IF they are "12V" panels (Vmp 16-20V), it may make more sense to remove the surplus panels above 600W and install them on a cheap PWM controller.

sunshine_eggo said:

If the two batteries are both at true 100% when fully charged in the 12V configuration, you'll probably be fine.

When putting 12V in series for 24V, if either battery hits 100% first, then the BMS will enter protection mode and stop charging. This may prevent you from fully charging both batteries, BUT they will likely be at a very high state of charge.

Issues:

1. Inconvenient.
2. Opportunities for poor/broken connections - They are not designed for multiple daily disconnect/reconnects.

It's not clear how much solar you have, so I can't say if there's major benefit to be had.

IF they are "12V" panels (Vmp 16-20V), it may make more sense to remove the surplus panels above 600W and install them on a cheap PWM controller.

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Thank you. I have thought about the inconvenience too. I should have started out with a 24v system in the first place. 12v batteries are less expensive but turns out every other thing in the system will be expensive in the long run.

When charging, without a BMS there is no guarantee that the batteries are within a certain voltage of each other. When they are taken out of series, and put into parallel, there could be a surge of power from one battery to another. Doing the connections safely on a daily basis is a PIA. You could setup switches to make the connections. Make sure you do it in a way that makes user error impossible.

DIYrich said:

When charging, without a BMS there is no guarantee that the batteries are within a certain voltage of each other. When they are taken out of series, and put into parallel, there could be a surge of power from one battery to another. Doing the connections safely on a daily basis is a PIA. You could setup switches to make the connections. Make sure you do it in a way that makes user error impossible.

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You're already considering a series/parallel swap, so put on a good 8S active balancer while charging. BTW, a 2nd charge controller sounds like a better option...

Would it be within your budget to run everything in 24v, and use a step-down converter to run your inverter? I feel your situation. My system is 12v, but only because my 2kw inverter keeps running.

Every other part of my system could be converted to 48v, if I choose, but, frankly, it does everything I need it to do, right now. I have enough generation, enough charge controller, enough inverter, enough storage.

I just don't want to buy a 48v inverter right now, or a step down converter to run my 12v inverter.

If the day comes when my inverter dies, or I want more pv, I will convert to 48v.

In addition to the inconvenience of flip/flopping the connections, you will not have a 12V source during the time that they are wired for 24V charging. I agree with the get another solar controller to use the panels.

Yurtdweller said:

Would it be within your budget to run everything in 24v, and use a step-down converter to run your inverter? I feel your situation. My system is 12v, but only because my 2kw inverter keeps running.

Every other part of my system could be converted to 48v, if I choose, but, frankly, it does everything I need it to do, right now. I have enough generation, enough charge controller, enough inverter, enough storage.

I just don't want to buy a 48v inverter right now, or a step down converter to run my 12v inverter.

If the day comes when my inverter dies, or I want more pv, I will convert to 48v.

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I am in exactly the same situation, I build my battery packs in multiples so that they can feed 24v or 48v inverters in the future when my 12v 2k inverters don't cut it anymore

I'm going through voltage selection decisions now myself over SHiB LTO 2-3v 20ah prismatic cells

One issue that may occur…

Your mppt solar charge controller will be switching from 12v to 24v and back to 12v a lot.
Is the settings to make that change easy to change?

Good luck