Author Topic: Does Lithium answer the FLA problem of adding New batteries with Old  (Read 203 times)

Westbranch

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Note: this was also posted in the FLA section as an answer to the Old/New problem...

LiFe (Power Wall , LG Chem, etc) battery technology....

 I just thought of an issue FLA has in spades and that is B. Bank expansion, ie adding more capacity after say 4 years due to increased/ing loads. with FLA it is a No-No...

 I have not seen this issue addressed to date in the LiFe type batteries literature...

As these systems have essentially a separate additional bank to add with its own BMS etc there, theoretically, should not be any imbalance between banks, because each bank controls its own charge rate over the day, thus the problem of a different charge acceptance may be solved....????

thoughts?
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RossW

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3 years ago I replaced my aging and problematic, pre-owned AGM battery with a 300AH, 52V LiFePO4 pack.
Because it was my first foray into LFP, and the uncertainty around them, I only got 300AH, despite knowing I really needed more.
My intention was to try with 300AH, leaving space to parallel a second cell beside each of the first ones, and if all went well then I would purchase a second set.

A year down the track, the new bank was performing so well, I decided to get a second set, but the original supplier was non-responsive or non-existant. Their website was still up, but they didn't respond to any email or online enquiries, calls to their phone numbers came up as not in service etc.

I spent another 18 months trying to find identical cells, and ended up giving up. Then, a short time ago circumstances came about where I was able to justify more cells (and someone else was going to help pay for them), so myself and someone else purchased a "48V/600AH" pack each, consolidated into one shipment to reduce costs.

The 600AH was made of 16 series blocks each of 3 parallel 200AH cells.

I've now been running this 300AH + 600AH parallel arrangement for 6 weeks. While I have monitoring on the original bank, I haven't yet built another for the new bank, so I routinely check them with a decent DMM. My usual practice is to put the probes across one cell, check it reads around 3.2V, then hit "Relative" and then go down all the other cells. This way, it reads purely the difference between the original (reference) cell, and the cell under test.  Usually they're all within 1mV of each other - not just the new bank, but each of the cells in the old bank too.

I have charge balancers across each cell (original bank) and each block-of-3-cells (new bank), but otherwise I've made no changes to anything in the system.

When I use a DC Clamp meter to check charge and discharge currents, the new bank is generally taking (or supplying) twice the current of the original bank (which is exactly as it should be, but good to see that it works out that way in practice!)

I'd have to say that it's working perfectly at this early stage.
3600W on 6 tracking arrays.
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16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
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