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Backup battery bank? (different types)

RoySalisbury

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Apr 24, 2022
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After I build my new LiFePo4 bank I will have a larger FLA bank (16 6v@400a AGM's) that they will replace. However, these batteries are still perfectly good (only about 3 years old and very well temp regulated.

I'm trying to decide what to do with these batteries. Could they be used as a "back up" bank somehow? Or perhaps keep the FLA's as the primary and use the LifeP04 bank as the backup (sort of like a backup generator). I know I don't want to mix the banks together .. that would be bad.

Anyone have thoughts or ideas? I already replaced my original FLA's with these AGM's and let the older bank sit idle for so long they will probably never charge again, so would not like to have the same happen to this AGM bank.

I also have the option of keeping the current system (battery bank, inverter, charge controller) hooked up to a much smaller array and just use that for a smaller load (like perhaps a freezer or nighttime security lights/cameras).

Roy
 
After I build my new LiFePo4 bank I will have a larger FLA bank (16 6v@400a AGM's) that they will replace. However, these batteries are still perfectly good (only about 3 years old and very well temp regulated.

I'm trying to decide what to do with these batteries. Could they be used as a "back up" bank somehow? Or perhaps keep the FLA's as the primary and use the LifeP04 bank as the backup (sort of like a backup generator). I know I don't want to mix the banks together .. that would be bad.

Anyone have thoughts or ideas? I already replaced my original FLA's with these AGM's and let the older bank sit idle for so long they will probably never charge again, so would not like to have the same happen to this AGM bank.

I also have the option of keeping the current system (battery bank, inverter, charge controller) hooked up to a much smaller array and just use that for a smaller load (like perhaps a freezer or nighttime security lights/cameras).

Roy
There is a link in this thread to a Youtube video where a guy talks about mixing lead acid and LiFePo4 in a single bank. It is important to understand both battery types and how they charge and discharge before setting up such a system. It might be easier to use your option, of a secondary smaller system where these batteries would take a lot less cycle life hit and should continue to provide a service.
 
I know I don't want to mix the banks together .. that would be bad.
Not necessarily. It depends on the application, the condition of the lead acid batteries and how you do it. There are several threads on this topic.


I'm very close to adding some LiFePO4 to my existing bank of lead lead acid. Seems like a really nice fit together for my use case.

Mine is a 380 Ah 48 V bank of Enersys SLA batteries which are mostly kept at float ready for home backup duties. I plan to add either 100 Ah or 200 Ah of LiFePO4 (in 51.2 V / 16 S configuration) to it and begin to make more regular use of the system.

The LiFePO4 will, because of its lower resistance, preferentially discharge and charge first meaning it will manage the day to day cycling while it will also keep the lead acid batteries at float overnight while there is no solar. The lead acid will be there as a supplemental energy source for extra deep discharges and also as a buffer/ballast for charging.

But you can always sell your old kit and leave it behind you.
 
Not necessarily. It depends on the application, the condition of the lead acid batteries and how you do it. There are several threads on this topic.
The LiFePO4 will, because of its lower resistance, preferentially discharge and charge first meaning it will manage the day to day cycling while it will also keep the lead acid batteries at float overnight while there is no solar. The lead acid will be there as a supplemental energy source for extra deep discharges and also as a buffer/ballast for charging.

I'll have to look into this. This sounds interesting.

But you can always sell your old kit and leave it behind you.

That is defiantly an options.. and one I would love to do .. One system is enough.
 
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