Lifepo4 vs lead acid battery rating

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rickdemers
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Posts: 73
Joined: Mon Nov 23, 2020 1:31 pm
My RE system: Two outback fm 80, Royal 12 volt pure sine inverter , with 8 roll S550 batteries , 8 panels of 220 watts each ,4 strings of 2 in series) ,. second set up for DC freezer and DC fridge 4 rolls S550 in series =24 volts with fm 60 and currently with 1320 watts array

Lifepo4 vs lead acid battery rating

Post by rickdemers »

i see lead acid rate the batteries at C20 are the lifepo4 rated the same or rated to total dischrge as they are capable ,i have 8 roll S550 batteries set up at 12 volts because inverter is a 12volt these batteries are rated at approx 428 amphr C20 x 4 strings =1700 or so what lifepo4 battery would i look at for size to comparable output

also if i go to 24 volts would i only need half of amphr rating because i am doubling voltage and 1/4 amhr rating for 48?
i read they say on some battery sites that if lifepo4 batteries are put in series that they should have seperate charging , but is not a lifepo4 48 volt batteries simply cells in series so whats the difference ?
raysun
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Re: Lifepo4 vs lead acid battery rating

Post by raysun »

rickdemers wrote: Wed Oct 05, 2022 9:05 am i see lead acid rate the batteries at C20 are the lifepo4 rated the same or rated to total dischrge as they are capable ,i have 8 roll S550 batteries set up at 12 volts because inverter is a 12volt these batteries are rated at approx 428 amphr C20 x 4 strings =1700 or so what lifepo4 battery would i look at for size to comparable output

also if i go to 24 volts would i only need half of amphr rating because i am doubling voltage and 1/4 amhr rating for 48?
i read they say on some battery sites that if lifepo4 batteries are put in series that they should have seperate charging , but is not a lifepo4 48 volt batteries simply cells in series so whats the difference ?
The C20 rate is a practical benchmark for capacity measurement, as it reflects how most deep cycle batteries are discharged in many cycling applications, like home power. Though LiFePo4 capacity varies a bit less with discharge rate, it follows the same relationship. When sizing a LiFePo4, however, the battery's allowance for deeper discharge can be taken into account. A conservative DoD of 80% v.s. Lead Acid 50% is significant.

All things being equal, the higher the system battery voltage, the lower the discharge for given power. Not just the V*I math, but also Peukert's Law.

The series connection issue with some LiFePo4 has to do with the Battery Management System, rather than the cell chemistry. Some BMS permit series connections, some do not. Others claim to, but seem to cause issues in practice. Since there is no natural inter-block balancing as with series connected Lead Acid blocks, if connecting LiFePo4 in series, each battery block should be individually charged fully before connecting in series. Most all LiFePo4 batteries have the cells internally connected to a BMS that balances them to some degree within the block. This is true for 12V, 24V, or 48V blocks.
rickdemers
Forum Expert
Posts: 73
Joined: Mon Nov 23, 2020 1:31 pm
My RE system: Two outback fm 80, Royal 12 volt pure sine inverter , with 8 roll S550 batteries , 8 panels of 220 watts each ,4 strings of 2 in series) ,. second set up for DC freezer and DC fridge 4 rolls S550 in series =24 volts with fm 60 and currently with 1320 watts array

Re: Lifepo4 vs lead acid battery rating

Post by rickdemers »

Thanks again Raysun
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