LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[CatNewBee]

Nothing wrong with Ah, it is the right unit used world wide for battery capacity, or Amperehours.

[Cpt Pat]

Originally Posted by john61ct

These are actually pretty rare units, native metric, apparently no USA-imperial equivalent!

Understood.

I'll stick to ampere hours here.

"Ah" has too many multiple meanings for people who can't grasp context. https://www.abbreviations.com/AH

[CatNewBee]

I am not aware of imperial equivalent units for electricity so no problem there, it is pretty international.

Edison, Tesla and Wesinghouse used also Volt, Ampere and Watt from the beginning and all the time.

[Cpt Pat]

Originally Posted by CatNewBee

I am not aware of imperial equivalent units for electricity so no problem there, it is pretty international.

Edison, Tesla and Wesinghouse used also Volt, Ampere and Watt from the beginning and all the time.

Yeah, right. Don't get me started on how the U.S. has lost much of its industrial base because we (and only two other non-industrial countries) refuse to fully adopt the metric system. People don't want to have to own two sets of tools - like we are forced to do in the U.S. So they don't buy our products based on that ancient system of measures. (And they don't torture their children by forcing them to learn how to perform math with fractions.)

Of course there're no Imperial equivalents for electrical measurements. Everything in electrical engineering is and has always has been metric.

And, since I have enough connected brain cells to understand context, I won't criticize you all over the use of the symbol "C" to denote "battery capacity." In electrical engineering, that symbol is reserved for the unit "coulomb" and to symbolize capacitance (expressed in Farads); distinguished, of course, by context. https://en.wikipedia.org/wiki/Coulomb

I can see how Fanboy wannabe electrical "engineers" might be offended by having to learn something outside their narrow range of interest, but broadening your understanding of the field might be useful.

Feel free to sling scat. I've given up on this thread. The signal-to-noise ratio is too low, and it's consequently a waste of time.

[newhaul]

Originally Posted by Cpt Pat

Yeah, right. Don't get me started on how the U.S. has lost much of its industrial base because we (and only two other non-industrial countries) refuse to fully adopt metric. People don't want to have to own two sets of tools - like we are forced to do. So they don't buy our products based on that ancient system of measures. (And they don't torture their children by forcing them to learn how to perform math with fractions.)

Of course there're no Imperial equivalents for electrical measurements. Everything in electrical engineering is and has always been metric.

And, since I have enough connected brain cells to understand context, I won't criticize you all over the use of the symbol "C" to denote "battery capacity." In electrical engineering, that symbol is reserved for the unit "coulomb" and to symbolize capacitance (expressed in Farads). https://en.wikipedia.org/wiki/Coulomb

where has anyone on this thread used "C" to denote battery capacity?
I have missed that one

[Cpt Pat]

Originally Posted by newhaul

where has anyone on this thread used "C" to denote battery capacity?
I have missed that one

(Long sigh..) You're kidding, right? How do you denote a current that's 50% of the battery's rated ampere hour capacity? "0.5C"

Yes, I know you don't mean 0.5 coulombs. I can grasp context.

Arguing over symbols? Really? This is all just childish banter.

I am so outta here... "There is no greater fool than someone who argues with one."


bye

[newhaul]

Originally Posted by Cpt Pat

(Long sigh..) You're kidding, right? How do you denote a current that's 50% of the battery's rated ampere hour capacity? "0.5C"

Yes, I know you don't mean 0.5 coulombs. I can grasp context.

Arguing over symbols? Really? This is all just childish banter.

I am so outta here... "There is no greater fool than someone who argues with one."


bye

If you have an issue with listing of charge rates like that aka 0.5C or any rate listed as anything by C rate perhaps you should direct it at the manufacturers of the batteries .

For instance here is the spec sheet from the manufacturer of my camel cells that my bank is made up with.

[john61ct]

He was not saying doing so is IRL incorrect.

He's saying pedantic corrections when the meaning is clear, is just silly and

especially to imply that the "offender" knowledge of electrickery principles is therefore not trustworthy.

[gscriba]

Arrived!
Cell 6887: 3.263
Cell 6888: 3.263
Cell 6889: 3.263
Cell 6900: 3.264

Waiting to hear back from REC so I can order my ABMS and accessories.
Next step...top balance.
Fun.

[john61ct]

So sweet, well matched, at least voltage on arrival.

[andyalford]

Originally Posted by gscriba

Arrived!
Cell 6887: 3.263
Cell 6888: 3.263
Cell 6889: 3.263
Cell 6900: 3.264

Waiting to hear back from REC so I can order my ABMS and accessories.
Next step...top balance.
Fun.

If you can get those compression plates on, can you tell me how you did it. I have discarded mine.


Also, I notice you have the same copper connectors - made of many laminated thin copper sheets. Is this normal, or would we be better to cut connectors from solid 5mm copper?

[andyalford]

Originally Posted by Dockhead

Bingo!


That's it exactly, and must be what CatNewBee was talking about.


It's not in my Multiplus manual -- guess it's a feature of newer ones, than mine:



Attachment 199806

It won't be in the paper manual. You need to load an Assistant. Check the web site for details....


https://www.victronenergy.com/live/a...ble_assistants

[CatNewBee]

Originally Posted by Cpt Pat

(Long sigh..) You're kidding, right? How do you denote a current that's 50% of the battery's rated ampere hour capacity? "0.5C"

Yes, I know you don't mean 0.5 coulombs. I can grasp context.

Arguing over symbols? Really? This is all just childish banter.

I am so outta here... "There is no greater fool than someone who argues with one."


bye

I understand your confusion, the charge rate C is not a unit like Ampere or volt, but a constant defined as following:

Chargerate C = Battery Capacity in Ah / 1 hour and the unit is Ampere

It is the theoretical constant current for charging the full capacity of a battery from 0% to 100% in 1 hour.

Similar to Speed V = distance S / 1 hour with a unit like km/h or mph.

0.5C in the equiation for a 100Ah battery means a current of 0.5 * 100Ah / 1h = 50A

3C for the same battery would mean a current of 3 * 100Ah/1h = 300A

It is a representation of a constant current and not of the capacity.

Manufacturers could of course write instead of 0.5C a current 50A in the specs. Keeping it relative makes things easier with variable capacities and voltages when using more than one battery, e.g. You connect 4 batteries in parallel to get a 12V 400Ah battery, 0.5C means then 200A, connecting 2 batteries in series means you have doubled the voltage from 12V to 24V with a capacity of 100Ah, so the capacity remains the same, the charge current would also remain at 50A.

[mikedefieslife]

Originally Posted by yachtshah

If you can get those compression plates on, can you tell me how you did it. I have discarded mine.


Also, I notice you have the same copper connectors - made of many laminated thin copper sheets. Is this normal, or would we be better to cut connectors from solid 5mm copper?

I have these connectors too. I'm told by the community that they are better than solid copper. 1) there is more surface area. 2) They are flexible to theoretically put less strain on terminals.

[CatNewBee]

I have made mine out of a solid copper bar.

Surface area is bigger and the connection can carry higher currents. The disadvantage is, they are rigid and there is no mechanical play except by the holes on the screws.

It is only the contact surface between the poles and the copper that needs to be as big as possible.

Multiple layers add more connection surfaces with resistances, so the connection is worse than a connection made by a solid bar, also the size of the bridges is afaik smaller than the available pole surface. Another advantage of my DIY bridges: the crosssection of my bar is at least twice the size of the laminated bridges.

I tried to order the cell bridges from the supplier but they could not provide the right size and crossection for the 1000Ah cells, so I decided to make my own.