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

[gscriba]

CNB. Would you be willing and able to take a pic or two of your copper connections with measurements please?
RE: initial charging of my new cells...does it make more sense to use my shore power charger to bring the collective cells (12 volt) up closer to the top then dismantle to individual cells and top balance. As opposed to slowly charging each individual cell at a lower amp (15A and tapering) over a lengthy period of time (up from current resting of 3.263), then assemble the 12v battery?
I imagine that either way will work.
Thanks.

[john61ct]

Yes if you do not have a 1S power source

(nor a charger that automates balance charging)

with enough amps

Then do a higher-voltage (4S?) charge up to say 3.4Vpc, ensuring no cell is going over max spec voltage.

Then do the last bit with the balance charger, or

at 1S voltage, all in one big parallel group, to say 3.60V (or all the way to vendor max) and allow current to go to 0.02C (or even 0A)

There are many ways to get there, depends on what equipment you have. With good enough balancing gear that will be doing your normal-usage maintenance, you could even use that won't take long if the cells are already healthy and well matched.

So once you finally get there, let them all settle back to resting, in that one big parallel group, at least overnight, 24 hours better.

Break them up to let them rest an hour or two, then check they're all the same and they're ready to assemble as a working bank.

Best to also do your CC load testing for an actual-capacity peak benchmark, on a per-cell basis, within the first few dozen deep cycles.

Not sure how specifically relevant to LFP, but IMO best to keep C-rates relatively low during this "breaking in" period, if nothing else to preserve accuracy of your 100% SoH benchmark.

[Cpt Pat]

Originally Posted by CatNewBee

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.

(Very long sigh - shaking head)


Yes, I know the meaning of the "C" abbreviation in the context of expressing battery capacity. I don't need an explanation. It's a common use. I'm not arguing over use of that term. You just aren't getting it, Cat. I'm trying to say that abbreviations need to be interpreted in context!

Some of the posters here have set a tone of yelling at each other that is consistently shrill. The yelling and juvenile personal attacks make me wonder how far we have progressed from our primate cousins.

Quibbling over terms is pedantic and anal retentive. Is this tread limited to posts by obsessive-compulsives and people trying to impress others over their "correct" use of abbreviations? Apparently, judging by some of the recent posts.

I am an electrical engineer who has worked 40 years in the field as a chief engineer in broadcasting and a tech. for NASA. (Yes, I'm that old.) I am familiar with electrical concepts that are far more complex than anything being discussed here. I also hold an Amateur Extra license -- do you think I don't know what an "ampere" is?

In this tread, I feel like I've walked into a kindergarten class debate over finger painting techniques. Please continue learning, your efforts to learn are laudable, but the contributors here should refrain from embarrassing themselves with newbie personal criticisms of others. Nothing is gained by that but to force off others who are trying to carry out an actual productive exchange of ideas. This thread has become infested by trolls. Thanks moderators, nice job.

I am disgusted by some of the "contributors" in this thread, who appear to care more about criticizing other contributors for their efforts - than learning anything new. Get a life! There is nothing I can do to improve people's civility skills, except to point out how they are absent, because it's a matter of early upbringing. It's too late to redeem their personalities.

By the way, please contact and correct the engineers at Firefly Batteries, because they too are using the term amp/hours. Do you suppose they know nothing about batteries...?

[CatNewBee]

So than sorry for explaining it to you like in kindergarden.

Please just be more precise with the units, it helps the others to follow the discussion.

[CatNewBee]

Originally Posted by gscriba

CNB. Would you be willing and able to take a pic or two of your copper connections with measurements please?
RE: initial charging of my new cells...does it make more sense to use my shore power charger to bring the collective cells (12 volt) up closer to the top then dismantle to individual cells and top balance. As opposed to slowly charging each individual cell at a lower amp (15A and tapering) over a lengthy period of time (up from current resting of 3.263), then assemble the 12v battery?
I imagine that either way will work.
Thanks.

I have done it the same way, I had a lab power supply, but it was too weak to charge 4000Ah at 3.8V, so I connected the cells to a 12V battery and used regular battery chargers to get near full, then disconnected the cells and charged the last few percent in parallel with the lab psu to around 3.8V. I did not charge to 4.0V initially as recommended by Winston to not stress the cells too much.

I don't have a picture of the bars here, I am not on board at the moment. The copper bar was 30mm x 5mm x 1500mm.

[Cpt Pat]

Originally Posted by CatNewBee

So than sorry for explaining it to you like in kindergarden.

Please just be more precise with the units, it helps the others to follow the discussion.

No need to apologize, Cat. My post above wasn't directed to you personally, but instead to the trolls who are polluting the general tone of the entire thread.

[john61ct]

Yes, focus on actual content, working together to further each other's knowledge and skills, just ignore the stuff you don't like.

Of course make corrections where you see **substantive** errors of fact, but without getting personal or attacking credibility ad hominem,

would be much more productive than telling others what and how to post stylistically.

And yes this seems paradoxical, in order for the forum to preserve a community for productive friendly discussions, we must be rigorous in our **intolerance of (unfriendly) intolerance**!

That cannot just be left to the mods, laissez faire rules,

so best to just ignore the stuff you don't like, especially petty "violations of your standards" in obviously understood terminology.

[Belezar]

This may have been posted here already, and I’m not going to read through 7000 posts to see, but I think it’s a shame that this run on post was done this way. There is a ton of good info here, but in this format it is extremely hard to search. And it started 8 years ago. Technology has changed so much since then. Why do I care? I just bought a boat with a LI house bank. I get that it’s your own little community but still...

[CatNewBee]

Originally Posted by Belezar

This may have been posted here already, and I’m not going to read through 7000 posts to see, but I think it’s a shame that this run on post was done this way. There is a ton of good info here, but in this format it is extremely hard to search. And it started 8 years ago. Technology has changed so much since then. Why do I care? I just bought a boat with a LI house bank. I get that it’s your own little community but still...

And what dou you want to say then?
Do you have a specific question?

Maybe you start by describing what you've got, what cells, battery size, bms used, etc...

[Cdn]

Question for the experts. If I have a 1200amph Lithium bank charged by Balmar alternator (I am aware it will take a while and will supplementing a large solar system), can I use my electric appliances while charging via alternator? Ie, if my bank is at 80% and I run my AC, will my alternator charge the batteries while my batteries run the AC?

[exMaggieDrum]

Originally Posted by Cdn

Question for the experts. If I have a 1200amph Lithium bank charged by Balmar alternator (I am aware it will take a while and will supplementing a large solar system), can I use my electric appliances while charging via alternator? Ie, if my bank is at 80% and I run my AC, will my alternator charge the batteries while my batteries run the AC?

If the alternator can put out more amps than the AC plus all other electric consumers like lights, radio, etc., then the net plus remaining charge amps can be used to recharge the battery. Chargers only see the net amps available. If you are running AC off of your batteries your alternator has to be putting out a lot more than the AC uses.



Most AC's use a LOT of power. So your alternator should be a pretty heavy duty beast, as the engine driving it. If you have massive solar then that goes in to the "net" amps available for charging. IME people who use batteries to run AC usually have to replace batteries all the time. Even without AC you need a hefty alternator to recharge highly discharged batteries in the 1200Ah range.



But it all depends on how much solar you have and how big your alternator is and how well regulated your alternator is so that it doesn't run too hard and too hot so that it burns out.

[john61ct]

This really has nothing to do with LFP

X: amps output by sources
Y: amps used by loads

If X > Y, there are (X-Y) amps available for charging and bank SoC will tend to rise

If X < Y, then the bank will be depleted at a rate of (Y-X) amps

[john61ct]

Originally Posted by Belezar

This may have been posted here already, and I’m not going to read through 7000 posts to see, but I think it’s a shame that this run on post was done this way. There is a ton of good info here, but in this format it is extremely hard to search. And it started 8 years ago. Technology has changed so much since then. Why do I care? I just bought a boat with a LI house bank. I get that it’s your own little community but still...

What an entitled attitude.

This thread is an **amazing** resource, provided **free of charge** to you by this website and its community.

There are very strong reasons it's all in one thread, one being, now you don't have to search through thousands of smaller fragmented ones.

If you have a specific question, go ahead and post it, here or in your own fresh new thread, it's FREE!

If you want to educate yourself, read it. But don't whine that some volunteer hasn't nicely compiled a well-organized summary to make life easier for you, **for free**.

Maybe, as a contribution to the community, in return for all this very valuable information, you can be that volunteer!

[Cdn]

Originally Posted by exMaggieDrum

If the alternator can put out more amps than the AC plus all other electric consumers like lights, radio, etc., then the net plus remaining charge amps can be used to recharge the battery. Chargers only see the net amps available. If you are running AC off of your batteries your alternator has to be putting out a lot more than the AC uses.



Most AC's use a LOT of power. So your alternator should be a pretty heavy duty beast, as the engine driving it. If you have massive solar then that goes in to the "net" amps available for charging. IME people who use batteries to run AC usually have to replace batteries all the time. Even without AC you need a hefty alternator to recharge highly discharged batteries in the 1200Ah range.



But it all depends on how much solar you have and how big your alternator is and how well regulated your alternator is so that it doesn't run too hard and too hot so that it burns out.

Thanks for the response.

I thought Lithium batteries could be discharges and recharged between 90% and 10% with out much damage and could be cycled about 5000 times?

The amp draw of a small 6000 BTU cabin AC is only about 7 amps. With an alternator providing 150 amps hot (Balmar XT), I was assuming it would charge batteries while the batteries were also providing power to the AC? Am I missing something?

[newhaul]

Originally Posted by Cdn

Thanks for the response.

I thought Lithium batteries could be discharges and recharged between 90% and 10% with out much damage and could be cycled about 5000 times?

The amp draw of a small 6000 BTU cabin AC is only about 7 amps. With an alternator providing 150 amps hot (Balmar XT), I was assuming it would charge batteries while the batteries were also providing power to the AC? Am I missing something?

yes you are missing one little part of the whole setup .
The 7 amps drawn by the AC is at 120 volts Ac or about 840 watts when running off of your inverter ( you need a minimum 2000 watts out of an inverter to start it )
that comes out to about 65 amps at 12v nom. So yes it should still charge as long as your refer isn't running at the same time.