Author Topic: Does Lithium answer the FLA problem of adding New batteries with Old  (Read 382 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.
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Ocean

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #2 on: December 27, 2017, 12:55:31 AM »
"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."

Where do you get these "Charge Balancers"???? How are they different than a BMS?

RossW

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #3 on: December 27, 2017, 02:39:04 PM »
Where do you get these "Charge Balancers"???? How are they different than a BMS?

I bought mine directly from the manufacturers.

They are completely different to any sort of BMS in that they are a non-intelligent, continuously operating, voltage-balancing device. They do no monitoring of cell or battery condition, have no LVD, no HVD, no over-current  protection, no temperature monitoring. They do one job, and one job only, which is to try to keep all the cells (regardless if it's a 12V, 24V, 48V, 120V or whatever pack) within a few millivolts of each other.
3600W on 6 tracking arrays.
7200W on 2 fixed array.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
Selectronics SP-PRO 481 5kW inverter
Fronius 6kW AC coupled inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

Ocean

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #4 on: December 27, 2017, 08:24:55 PM »
They sound great.  who's the manufacturer?

mike90045

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #5 on: December 28, 2017, 01:39:32 AM »
Beware the Bandersnatch.  i mean Balancers

Many are of a type that, at a specific voltage, turn on a Bleeder Shunt, and will bypass a couple hundred milliamps around the full battery cell.   But if you are charging with 30A, and are bypassing with 0.6A  ( 600mA) there are still 29.4A going into the full battery, which will rapidly become unhappy.

This assumes the bleeder board has been properly engineered, calibrated and tested, to be more reliable and not a circuit board of lowest bid parts that may puke after 6 months, killing a battery cell and starting a fire.
http://tinyurl.com/LMR-Solar

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RossW

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #6 on: December 28, 2017, 04:06:54 AM »
Beware the Bandersnatch.  i mean Balancers

Many are of a type that, at a specific voltage, turn on a Bleeder Shunt, and

.... and are utter rubbish. I've never had them, would never buy them and certainly would never use them in a solar off-grid situation.

They MIGHT be suitable if you have limited charging current, well controlled charge voltage and regularly available power sufficient to get your batteries charged AND BALANCED.

The ones I specified I emphasised elsewhere, and re-state here to remove ANY ambiguity - CONSTANTLY (that is, ALL THE TIME) are trying to balance the cells. When the battery is charging, the system tries to ensure they're all at the same voltage, shunting power from the cells with the highest voltage to those with lower voltages. When the battery is discharging, the system tries to ensure they're all at the same voltage, shunting power from the cells with the highest voltage to those with lower voltages. When the pack is sitting static with little or no current into or out of it, the system tries to ensure they're all at the same voltage, shunting power from the cells with the highest voltage to those with lower voltages.

They have a common "AC bus" between each unit. There is one unit across each cell. Each unit can be putting power out from its cell into the common bus, or taking power out of the common bus and into its cell, or just sitting idly by and doing nothing.

I trust this is sufficiently clear that nobody thinks it's a fancy zener-diode, because quite simply - they are NOT.
3600W on 6 tracking arrays.
7200W on 2 fixed array.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
Selectronics SP-PRO 481 5kW inverter
Fronius 6kW AC coupled inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

mike90045

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #7 on: December 28, 2017, 03:09:20 PM »
Who's the Mfg of these balancers ?  Can mere mortals buy them ?
http://tinyurl.com/LMR-Solar

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RossW

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Re: Does Lithium answer the FLA problem of adding New batteries with Old
« Reply #8 on: December 28, 2017, 04:02:46 PM »
Who's the Mfg of these balancers ?  Can mere mortals buy them ?

I can't recall their name and I'm not near my office at the moment.
They were a company in China (yes, sneer all you like, some of their stuff is just fine), and I'm most definately a "mere mortal" so clearly the answer is yes!

(I bought 108 of them. I only needed 40, but I'd bought extra lithium cells for a friend when I got mine, and extra balancers for him. It made the importing costs very low per-unit).
3600W on 6 tracking arrays.
7200W on 2 fixed array.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
Selectronics SP-PRO 481 5kW inverter
Fronius 6kW AC coupled inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine