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Why are 12v lifepo4's cheaper than individual cells? What's the catch?
#1
G'day 

So I want to put together a 5 kw/hr 48v system with lifepo4 batteries and the all-in-one 5kw  mppt/charger/ups/inverter (ebay item 132735948201)

I'm weighing up between:

- getting 4x 12v ~100a/hr batteries for ~AUD$500 each, cutting open each one, taking out the BMS and using a seperate active balancer across 17 cells (about $200 online) (ebay item 192850425946

- or, getting 17x individual 100ah lifepo4 cells (aliexpress) which are about $210 each.

My question is: why is it cheaper to buy the 12v batteries for their cells (~$2000 for 5kw/hr, which are also already in Australia) compared to the overseas cells which are ~$3500 for 5kw/hr? Seems upside down to me. Is their something I'm not seeing?

It's in my interest to go for the cheaper option (buying 4x 12v batteries, opening them up, ditching their crappy BMS and using an active equalizer) because it's a lot cheaper. Hopefully the 12v batteries don't have many barriers such as epoxy in the way to access the cells.

Would love to hear your thoughts and experiences using cells from pre-built 12v lifepo4 batteries.

Cheers
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#2
Buy one of the 12v 100ah eBay $500 batteries and capacity test it.. then let us know you’ve answered your own question :-)
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#3
Font trash the ecisting bms for active balancers you dont gain anythibgm use a proper installera bms instead.

IF you cant explain here how much you can save with active in wh then its waste Wink

Im mostly using prebuilt 12v LiFePo4. Running 16s of course with Them and have 100kwh
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#4
(02-29-2020, 06:25 AM)daromer Wrote: Font trash the ecisting bms for active balancers you dont gain anythibgm use a proper installera bms instead.

IF you cant explain here how much you can save with active in wh then its waste Wink

Im mostly using prebuilt 12v LiFePo4. Running 16s of course with Them and have 100kwh
Are you using them in a 48v setup?

Would I be able to put 4 of these 12v batteries in series? (Without opening them up.) 
Or would I need to add something to all of them (still without opening them up.)
Or do you think I'd be better off opening them up and using a decent BMS and/or active balancer?

I'm a bit put off by BMS's because they all seem to say 200mA cell-to-cell which seems quite low, compared to active balancers which say 2 to 3 amp.

Thanks!

(02-29-2020, 05:38 AM)slimf Wrote: Buy one of the 12v 100ah eBay $500 batteries and capacity test it.. then let us know you’ve answered your own question :-)
Funny you say that cause I can't find any C rating in the ad.
On the other hand, it still weighs 12kG.
If it was false advertising then I'd probably have a fair chance returning it since it's an Australian seller on eBay.
Not good if it isn't up to its name nonetheless.
Thanks for the heads up.
I'm looking up "cheap ebay lifepo4 100ah" on youtube at the moment and it looks like I should be cautious indeed. (Namely https://www.youtube.com/watch?v=XNyLb-KCQ5A)

I'm so tempted to spend all my money on a 5 or 10kw/hr lithium titanate arrangement hey. Hardly need it though. Although ~$1000/kw/hr isn't so bad considering it should last like 50+ years I guess..
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#5
I’ve seen some photos of so called 100ah 12v drop in replacements with foam packing in them.. lucky to get to half advertised capacity.

Then again, I have two I got for camping fridges and they were 699 delivered and seem to be the real deal. Still expensive thou.
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#6
(02-29-2020, 08:43 AM)slimf Wrote: I’ve seen some photos of so called 100ah 12v drop in replacements with foam packing in them.. lucky to get to half advertised capacity.

Then again, I have two I got for camping fridges and they were 699 delivered and seem to be the real deal. Still expensive thou.
Yeh, I've got my eye on https://www.ebay.com.au/itm/12V-120Ah-Pr...ctupt=true
aswell.

Do you know what I'd have to put between each of these 12v batteries if I had four in series?
The seller said he can sell me 3x $90 each Victron balancer but he hasn't replied the model number yet. I'm really curious to see the specifics of it, cause before today I've never heard of having a parent level of balancers. Very interesting.

Don't suppose you know of any cheap second hand lifepo4 sources/options preferably closer to perth by any chance?

I'd consider using second hand 18650's but im sh!t scared of burning the house down.
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#7
If your wanting a 48v system, I would pull these apart and make a 48v pack of the cells.. and use a real BMS like Batrium
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#8
(02-29-2020, 09:19 AM)slimf Wrote: If your wanting a 48v system, I would pull these apart and make a 48v pack of the cells.. and use a real BMS like Batrium
Good point. I think I might confirm with the seller that they can be pulled apart easily enough and I might as well ask if he sells the cells individually.
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#9
They will all use separate cells inside.. you will need to split the case open, but that shouldn’t be a biggie.

I still think they are to expensive to consider thou. Source real LifePo4 from China or elsewhwreZ
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#10
(02-29-2020, 10:06 AM)slimf Wrote: They will all use separate cells inside.. you will need to split the case open, but that shouldn’t be a biggie.

I still think they are to expensive to consider thou. Source real LifePo4 from China or elsewhwreZ
Best value I've found is this one: https://www.aliexpress.com/item/40005630...web201603_

although after import duty the $699 still works out cheaper
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