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Why does a 48V100Ah LFP battery have a capacity of 5,120Wh instead of 4,800Wh?

Banjohn

Banjohn

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Hi Everyone,

I am new to the whole DIY battery thing.
Only have experience with portable power stations.
I was doing my research on some LFP batteries, and I can't understand the logic.
Why does a 48V100Ah LFP battery have a capacity of 5,120Wh instead of 4,800Wh?
LFP battery cell has a voltage of 3.2V so connecting 15 cells in series results in 48V(3.2*15=48).
If the 51.2V is 16 cells in series, then why not use 15 or call it 51.2V?
1716534065140.png1716534137626.png
 
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The 48 volt comes from the older systems before LiFePo4, those systems have a wide variety of voltages depending on the state of charge. and most things that are designed for 48V will work fine with 51.2V as they had to deal with those fluctuations. Sodium-ion batteries, which might be cheaper for home storage also fluctuate far more depending on their state of charge.

So basically, it is just convention and it works well enough...
 
It’s “48V nominal”, no “48V” battety is actually 48.0 volts. As Bongbong points out the loads work on a range of voltages. Do you talk about 13.8 volt car batteries?
 
Bongbong said:
The 48 volt comes from the older systems before LiFePo4, those systems have a wide variety of voltages depending on the state of charge. and most things that are designed for 48V will work fine with 51.2V as they had to deal with those fluctuations. Sodium-ion batteries, which might be cheaper for home storage also fluctuate far more depending on their state of charge.

So basically, it is just convention and it works well enough...
Click to expand...
Thanks for the reply.
Is there a range for 48V batteries?
 
wpns said:
It’s “48V nominal”, no “48V” battety is actually 48.0 volts. As Bongbong points out the loads work on a range of voltages. Do you talk about 13.8 volt car batteries?
Click to expand...
Thanks for the reply.
What's the range then?
Did any organization set the rules for 48V nominal?
 
Banjohn said:
Does that break any standards or regulations?
Click to expand...

No, you can build whatever you want depending on your goals. They just won't be compatible with 16s. Pylontech was quite early in the market and they went with 15s (likely because cells were expensive, or other reasons), the rest of the world went 16s. It's not a standard or regulation issue at all, since both stay under 60V DC. Once you go over 60V, certain regulations apply depending on where you are.
 
wpns said:
It’s “48V nominal”, no “48V” battety is actually 48.0 volts. As Bongbong points out the loads work on a range of voltages. Do you talk about 13.8 volt car batteries?
Click to expand...
They're not 48v nominal, they're 51.2 nominal
lifepo4 chemistry is 3.2 nominal per cell. 3.2* 16 cells = 51.2
lead acid made everyone normalized with multiples of 12 for decades, that is literally the only reason everything is 12/24/36/48.

oh also your 13.8 volt is the "max charge" of a 6 cell lead acid. (yea they can go higher)
lead acid is 2.1-2.2 per cell
each "12 volt" battery has 6 cells
2.1 * 6 = 12.6 nominal
you'll see on 99% of car batteries it is 12.6 nominal and 12.7 on the other 1%... not 13.8
 
Banjohn said:
then why not use 15 or call it 51.2V
Click to expand...
I'm going to assume there's some marketing psychology reason

Two facts I know:
1. humans prefer even numbers
2. humans would be confused if their "48v system can use a 51.2 battery"

I can't imagine the amount of emails customer service would get if they listed the battery with only 51.2v and no mention of 48v
"CAN I USE THIS IN MY 48 VOLT SYSTEM WITH MY INVERTER?"

In the spec sheets everything says their voltage range, for most people too much info just gets them to leave the page.
 
Banjohn said:
Hi Everyone,

I am new to the whole DIY battery thing.
Only have experience with portable power stations.
I was doing my research on some LFP batteries, and I can't understand the logic.
Why does a 48V100Ah LFP battery have a capacity of 5,120Wh instead of 4,800Wh?
LFP battery cell has a voltage of 3.2V so connecting 15 cells in series results in 48V(3.2*15=48).
If the 51.2V is 16 cells in series, then why not use 15 or call it 51.2V?
Click to expand...
Battery watt-hour capacity is a bit of fiction. It is just the normally charged voltage times the amp hour rating. You might get more or less depending on your loading and environmental conditions. People want it to be a volume type measurement like a gallon or liter of something. Batteries are chemical devices.
 
gotbeans said:
They're not 48v nominal, they're 51.2 nominal
lifepo4 chemistry is 3.2 nominal per cell. 3.2* 16 cells = 51.2
lead acid made everyone normalized with multiples of 12 for decades, that is literally the only reason everything is 12/24/36/48.

oh also your 13.8 volt is the "max charge" of a 6 cell lead acid. (yea they can go higher)
lead acid is 2.1-2.2 per cell
each "12 volt" battery has 6 cells
2.1 * 6 = 12.6 nominal
you'll see on 99% of car batteries it is 12.6 nominal and 12.7 on the other 1%... not 13.8
Click to expand...
I still don’t buy 12.6 V car batteries, and when I bought the parts for my 48 V off grid system I knew which was a generally accepted term, and which was an engineering value that I needed to do an analysis on. I still have a 48 V system.

I had a t-shirt: Does Anal Retentive Have A Hyphen?
 
gotbeans said:
I'm going to assume there's some marketing psychology reason

Two facts I know:
1. humans prefer even numbers
2. humans would be confused if their "48v system can use a 51.2 battery"

I can't imagine the amount of emails customer service would get if they listed the battery with only 51.2v and no mention of 48v
"CAN I USE THIS IN MY 48 VOLT SYSTEM WITH MY INVERTER?"

In the spec sheets everything says their voltage range, for most people too much info just gets them to leave the page.
Click to expand...
Thanks for the explanation.
Is there an acceptable voltage range for 48V systems?
 
Mattb4 said:
Battery watt-hour capacity is a bit of fiction. It is just the normally charged voltage times the amp hour rating. You might get more or less depending on your loading and environmental conditions. People want it to be a volume type measurement like a gallon or liter of something. Batteries are chemical devices.
Click to expand...
Yes, if temperature is considered, the calculation would be much more complicated.
 
gotbeans said:
They're not 48v nominal, they're 51.2 nominal
lifepo4 chemistry is 3.2 nominal per cell. 3.2* 16 cells = 51.2
lead acid made everyone normalized with multiples of 12 for decades, that is literally the only reason everything is 12/24/36/48.

oh also your 13.8 volt is the "max charge" of a 6 cell lead acid. (yea they can go higher)
lead acid is 2.1-2.2 per cell
each "12 volt" battery has 6 cells
2.1 * 6 = 12.6 nominal
you'll see on 99% of car batteries it is 12.6 nominal and 12.7 on the other 1%... not 13.8
Click to expand...
1716603591538.png
Enjoybot's 5,120Wh battery has a nominal votage of 48V without mentioning 51.2V.
That's confusing.
 
Banjohn said:
Thanks for the explanation.
Is there an acceptable voltage range for 48V systems?
Click to expand...

The acceptable range is actually at the cell level so it would be different for a 16s versus a 15s battery.

A conservative cell voltage operating range is from around 3V to around 3.5V with an absolute max of 3.65V per cell. There’s not much capacity to be gained by charging above 3.5 or discharging down below 3.

Multiply those numbers by 15 or 16 depending on your battery.
 
48 = 12 x 4

But there is no exact 12V with 3.2V LFP cells. 4 of them gives you 12.8V for your "12V" battery.

Then you put 4 of them together for your "48V" battery, but 4 x 12.8V gets you 51.2V.

So there ya go.
 
gotbeans said:
They're not 48v nominal, they're 51.2 nominal
Click to expand...
They can be both. Nominal literally means ‘in name only’. They’re acceptable for 48V systems, so nominally 48V. The average voltage from fully charge to fully discharged is 3.2V per cell, or 51.2V, so nominally 51.2V.
Both can be useful information in the right context.
 
SparkyJJO said:
48 = 12 x 4

But there is no exact 12V with 3.2V LFP cells. 4 of them gives you 12.8V for your "12V" battery.

Then you put 4 of them together for your "48V" battery, but 4 x 12.8V gets you 51.2V.

So there ya go.
Click to expand...
This. ^
 
Banjohn said:
Why does a 48V100Ah LFP battery have a capacity of 5,120Wh instead of 4,800Wh?
Click to expand...
As others explained the voltage of 4 or 16 LFP cells more closely resembles the common 12 volt Lead Acid battery voltages which is also not 12 volts. We are stuck with that nominclature. None of it makes sense because a 12 volt battery is actually six 2.25 volt cells which is 13.5 volts. On the other hand a "12 volt LFP battery is four 3.2 volt cells which is 12.8 volts.
 
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Banjohn said:
Thanks for the explanation.
Is there an acceptable voltage range for 48V systems?
Click to expand...
no, it depends on inverters
it's gonna be like 45-60volts or something for most stuff
data sheets will tell you
There are some older inverters, for example, that pre-date the lifepo4 batteries and thus won't say they are compatible with them... not sure if they are or aren't as far as voltage goes

Banjohn said:
View attachment 217479
Enjoybot's 5,120Wh battery has a nominal votage of 48V without mentioning 51.2V.
That's confusing.
Click to expand...
yep I saw that, that's likely non technical person writing that or they did it on purpose for confusion reasons I said previously
 
16S LFP better matches the operating range of 48V lead acid, which is what almost all of this equipment was designed for (lead acid).

15S LFP (48V nominal): 37.5V - 54.75V
16S LFP (51.2V nominal): 40V - 58.4V
24S lead acid (48V nominal): 42V - 59.2V

Operating range of 48V systems depends on the battery chemistry and equipment. My Victron inverter states a 38-66V operating range. My 14S NMC Lithium battery has an operating range of 42-58.8V.
 
SparkyJJO said:
48 = 12 x 4

But there is no exact 12V with 3.2V LFP cells. 4 of them gives you 12.8V for your "12V" battery.

Then you put 4 of them together for your "48V" battery, but 4 x 12.8V gets you 51.2V.

So there ya go.
Click to expand...
That explains a lot.
Thank you for the help.
Seems like it's an old habit people don't want to update.
Just like Apple's lighting cable and the Imperial system.
 
sunshine_eggo said:
16S LFP better matches the operating range of 48V lead acid, which is what almost all of this equipment was designed for (lead acid).

15S LFP (48V nominal): 37.5V - 54.75V
16S LFP (51.2V nominal): 40V - 58.4V
24S lead acid (48V nominal): 42V - 59.2V

Operating range of 48V systems depends on the battery chemistry and equipment. My Victron inverter states a 38-66V operating range. My 14S NMC Lithium battery has an operating range of 42-58.8V.
Click to expand...
1716630689981.png
Trying to understand Enjoybot's spec.
What's the difference between charge voltage and operating range?
 
Banjohn said:
View attachment 217507
Trying to understand Enjoybot's spec.
What's the difference between charge voltage and operating range?
Click to expand...

Charge voltage is the voltage you charge to.

Battery voltage changes between full and empty.

The operating range includes the peak charge voltage AND DIScharging the battery to its minimum safe voltage.
 
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