BAE A123 packs for a 48V system?

Ahoy there friends. Long time lurker, and now really looking to get into my first project what with the whole California PG&E fiasco in full swing right now.

I'm super hesitant to go for traditional LiIon due to its volatility, so LFP has been my aim, but those bad boys seem to be relatively expensive. That changed when recently I came across some 36V 12S8P BAE A123 26650 used packs for ~110/kwh. This voltage is obviously a little wonky for the 48V architecture that I was intending to aim for, but the price really made my brain wander withhow I could get it to workthe actual use cases that I was going for.

Given that I want the cells to have a long life, I was gonna shoot for probably 40-50% DoD on my ideal system (open to alternative suggestions). With these cells, I got it in my head that they could be stacked in a 2SNP configuration for 72V nominal, but then just charge to the top end limitof a 48V system, which is ~54V. 54V/72V = 75%, which is totally in the realm of a reasonable top end DoD limit.

Can anyone tell me what I'm missing, and if I'm completely off base?

kpeters000 said:

Ahoy there friends. Long time lurker, and now really looking to get into my first project what with the whole California PG&E fiasco in full swing right now.

I'm super hesitant to go for traditional LiIon due to its volatility, so LFP has been my aim, but those bad boys seem to be relatively expensive. That changed when recently I came across some 36V 12S8P BAE A123 26650 used packs for ~110/kwh. This voltage is obviously a little wonky for the 48V architecture that I was intending to aim for, but the price really made my brain wander withhow I could get it to workthe actual use cases that I was going for.

Given that I want the cells to have a long life, I was gonna shoot for probably 40-50% DoD on my ideal system (open to alternative suggestions). With these cells, I got it in my head that they could be stacked in a 2SNP configuration for 72V nominal, but then just charge to the top end limitof a 48V system, which is ~54V. 54V/72V = 75%, which is totally in the realm of a reasonable top end DoD limit.

Can anyone tell me what I'm missing, and if I'm completely off base?

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For what's it worth - your thoughts are perfectly rational, but of course you're leaving capacity on the table that you might regret later on. There may be some inverters that would let you capture the higher voltage. And of course the obvious question is why notbreak down the original packs apart and assemble the cells into your own packs?

kpeters000 said:

Ahoy there friends. Long time lurker, and now really looking to get into my first project what with the whole California PG&E fiasco in full swing right now.

I'm super hesitant to go for traditional LiIon due to its volatility, so LFP has been my aim, but those bad boys seem to be relatively expensive. That changed when recently I came across some 36V 12S8P BAE A123 26650 used packs for ~110/kwh. This voltage is obviously a little wonky for the 48V architecture that I was intending to aim for, but the price really made my brain wander withhow I could get it to workthe actual use cases that I was going for.

Given that I want the cells to have a long life, I was gonna shoot for probably 40-50% DoD on my ideal system (open to alternative suggestions). With these cells, I got it in my head that they could be stacked in a 2SNP configuration for 72V nominal, but then just charge to the top end limitof a 48V system, which is ~54V. 54V/72V = 75%, which is totally in the realm of a reasonable top end DoD limit.

Can anyone tell me what I'm missing, and if I'm completely off base?

Click to expand...

if i understand that Will not so work with lifepo4
they Need to be charged to 3,45/3,55 or you aren t charging cc CV.


never tried to charge only
so low you should get crappy Ah

54/24 (12sx2) gives 2,25 v and at that voltage cells are going in starve/die mode

They are setup in what would be equivalent to a 36v lead acid system (10s lithium-ion / 12s LiFePO4).

Truthfully my experience with the BAE System A123 modules was hit/miss as in those modules appear to be pretty beat up / end of life. I would he hesitant spending money on those because I saw anywhere between 30-50% capacity loss / degradation. Some people got luckier than others, but I think there are better options for batteries.

I probably paid a lot more than I should have for these things which sours the taste even more I would only consider buying if the price was heavily in your favor. $100/kWh sounds great until you realize the module only had 60-70% of it's capacity left. All I am trying to say is proceed with caution and insist on a capacity test.

Oh wow I didn't even realize I was messaging you! Hhaha I was looking at your pack breakdown videos, which I was also considering after OffGridInTheCity's response. Definitely a bit of a buzzkill to hear your poor experience with their capacity. It seems after all that, you ended up going with the Fiat Li-ion cells. What made you lean that direction? What has been your experience with Li-ion vs your initial foray into LFP?

kpeters000 said:

Oh wow I didn't even realize I was messaging you! Hhaha I was looking at your pack breakdown videos, which I was also considering after OffGridInTheCity's response. Definitely a bit of a buzzkill to hear your poor experience with their capacity. It seems after all that, you ended up going with the Fiat Li-ion cells. What made you lean that direction? What has been your experience with Li-ion vs your initial foray into LFP?

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Price, availability, and quality those are the three driving factors in my decision making.

Most modern electric cars use lithium-ion type chemistry. Its just more available and in abundance for less money and work. Cells out of a production EV tend to be very good in quality and consistency.

About $100/kWh I got good cells out of a low mileage salvaged car, and everything has remained consistent and in balance which is a nice change of pace after working with salvaged laptop cells which are all over the place in quality, capacity, and health.

From my research, if I wanted LiFePO4 is a similar quantity and capacity, I would have to spend a lot more money as I would most likely have to import large prismatic cells. This also does not guarantee me consistency or quality, sometimes the import vendors are hit/miss as well. While expected cycle life is greater, so is the cost of admission.

I also find that LiFePO4 discharge curves are a bit harder to work with in that the discharge curve is very flat, then drops off fast. Monitoring SoC of Lithium-Ion by voltage is a lot easier, with LiFePO4 you really need an SoC monitor. Not the end of the world either way, both are fine, I just tend to prefer working with Lithium Ion its 100% personal preference, not a technical pro or con.

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Regarding my initial foray into LFP The only reason I even started buying LiFePO4 cells was because that chemistry fits very well into a 12 volt system. I was going to build some portables for 12v gear so I didnt have to keep using a DC-DC converter. If I was building 24v, 36, or 48v system, one could easily achieve those voltages ranges with li-ion in a 7s, 10s, or 14s configuration.

My Fiat modules being 5s each, I build a 15s 48v system which works perfectly as many charge controllers, inverters, and equipment can often times support that higher input voltage (66v on Victron Inverters). The higher input voltage can actually be a advantage in some instances. Point being, if your design/equipment allows, you dont have to stick with the convention in terms of voltages.

I think its important to note that I am not against LiFePO4, I really wanted some good cells and those modules to work out, but it didnt. Its just harder to find good LiFePO4 at a reasonable price. Its just difficult to justify for me when I have many options for good quality of li-ion available to me without any hassle of import or shipping.

I also bought some of A123 cells 200 of them, and was also planning to build a small power pack similar to a goal zero 40ah range. But the case I was going to use I could only fit 30ah. It was going to be too large and heavy for a powerpack.

I decided to make jumpstart packs instead 4s6p 10ah range. So far I made 4 of them. Recently I was building a 3s16p li-on pack and noticed the size was similar to the 10 ah lifepo4 pack. below is the picture of both of them together. Lifepo4 10ah, li-ion 31ah in the same footprint.

The a123 cells take up alot of space for the limited AH they produce. They are excellent for running my 12 volt 30 amp tire inflator. As far as jump pack, I only had to use it in anger 1 time to try and jumpstart my van dead battery and it failed to crank it over, but in defense of jump pack my 27ah fullriveragm also wouldnt jumpstart it , start battery was completely dead.

I wouldnt recommend them for a small powerpack or even a powerwall.