diy solar

diy solar

A faster & better way to top balance?

What does crowbar mean in this context?

If power supply terminal voltage is higher than programmed output, higher than over-voltage limit, it will pull down with transistors to correct the over-voltage. i.e. short battery to ground. Some HP and other brand supplies say to use a diode when charging batteries.
 
Actually a few condos and apartments may have 208 volts as the complex has 3-phase power but each unit operates on just two of the legs.
I have a condo with this set up. Dryer and range operate at about 10% lower power. Cannot access all three phases.
 
Actually a few condos and apartments may have 208 volts as the complex has 3-phase power but each unit operates on just two of the legs.
I have a condo with this set up. Dryer and range operate at about 10% lower power. Cannot access all three phases.

But ya got two, so if you try hard enough you can generate the 3rd (with some arrangement of transformers).
Or, talk to your neighbors and stuff a wire through the wall.
 
Seems a bit extreme - just to make rechargeable batteries for my electric wheelchair...

Anyway, this thread seems to have gone all the way to Cuba and back.

End of Hijack.

:cool:
Thanks guys.
 
Let's try this another way.
The big LFP cells we deal with are "tedious" to Top Balance because they hold a LOT of AH.
Take a 200AH LFP cell. It can discharge 200A (1.0C) and take 100A to charge (.5C)
From 0%SOC (2.50v) to 100% 3.65v would take 2 hours at 100A, 4 hours at 50A and so on.
To TOP BALANCE, all cells are placed in PARALLEL ! NOT Series.
They are then charged to 3.650V with as many amps as possible but NOT exceeding the cell Limits. This continues until the amps taken falls below 1.5A (this is considered as saturated). Technical spec says cutoff can occur at 0.05C, for a 200AH cell that is 10A.
Once all the cells have reached 3.65 & saturated, then they should be left connected in parallel while they settle for the next couple of hours. Typically the cells will drop to around 2.550 within 1 hour and 3.500+ within two hours. This is NORMAL for LFP.
Once settled, then configure that battery pack into Series Config with BMS and fuse and your ready to go (casing etc of course being done too).

Shortcuts & rushing usually do NOT end well, Patience Testing happens in this process. BE PATIENT ! Very patient !! smoke'm if ya gottem LOL.

One "shortcut" that is safe:
You can Top Charge 4 cells - This is the same as Top Balancing but with 4 cells at a time it will be faster to get the cells up to 3.65. Even after they settle, getting them back to 3.65 will be Much Quicker. Do the cells in "lots" of 4 cells, once you have 8 cells Top Charged, then do a Top Balance with all 8 cells in parallel, (it will be quicker) and then assemble the battery packs per standard.

I have built several packs and suffered many of the hard lessons and costs that go with that... some pretty $$ One of the reasons I wrote the Luyuan Tech LifePo4 Assembly guide (link in my signature). I gave up playing & bought a TekPower TP1540E bench Power Supply that can output up to 15V @ 40A and charging the cells at 3.65V/40A goes fairly well. The CC ( Constant Current) get's the charge to 90% and CV (Constant Voltage) takes it the rest of the way as the amps decrease as the cells saturate.

BMS' with Passive Balancing do not do much for Large Capacity cells, that is NOT their target, they can only handle small capacity cells as it only burns off Hi Voltage from cells and is very slow. At this time, very few BMS' have Active Balancing which is suitable for Large Capacity LFP cells. Active Balancers do work and QNBBM, Heltec are Known Good devices that work as designed but they are not that cheap either.

Bulk Commodity ESS grade cells CAN deviate up to 1,v per AH of capacity when reaching above 90% SOC. That's 200mv for a 200AH cell. Top Charging & Balancing can resolve "some" of that and smooth things out.

Matched, Batched & Binned cells (cost more) will behave identically to each other through their entire voltage & load cycles (just like in EV's) and they will not generally deviate more than 30mv and will often settle in at below 10mv difference.

Example of Bulk versus "properly" Matched EVE-280 Bulk = $92, Matched = $125 (and THAT is a deal, typically it is 50% above Bulk Cost) due to the 3 full cycles of Charge/Discharge at various C-Rates with measurements logged every 10 minutes.

FYI: Many Chinese Vendors rely on the fact that the Translator Software is partly borked and inaccurate... (the excuse)
Many say they sell "Matched" cells BUT what they mean to say, is they are Voltage & IR (Internal Resistance) matched so they are identical when shipped. THIS IS NOT MATCHED ! This is Voltage & IR Matched at the storage voltage NOT through operational Test Cycles which is what Proper Matching IS.

Several links in my signature will help you, so grab the downloads etc.
Hope it helps, Good Luck.
Steve
That was a great explanation ! Thank you
 
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