BYD 24 volt Questions of Capacitance

[thealaskan]

I have 4 LV2424's in split phase, 2 in each. I have a separate charge controller from my solar panels. I have 4 BYD 24 volt plug and play units with which have separate BMS's in parallel.
I have had issue with the 24/7 daylight that the LV's, (I think would not go into grid charge because of the panels sending voltage signal.) So I put a separate charge controller in.
Because I've been looking at the past records now, prior to the CC, I've been noticing a fall in capacitance.
Where as 26.8 volts may be held for hours in the past, has turned into 26.5 volts for minutes after charge.
Settings are 27.5/23.5 30amp User no lithium available in settings.

Should the pack's degrade this quick?

Bought a Battgo tester, did 2 so far checked ok like the BMS was doing its job.

Do the Battery's have to be wired in parallel prior to the BMS's?

Is the BMS for charging puposes only?

 

[thealaskan]

The BMS has a 28 volt disconnect to protect the battery's from over charging, according to paperwork I've seen.
If the setting to top off is set to 27.5 volts, and kicks out leaving the battery's at 26.8 volt for a minute.
What caused the chargers to kick off when the battery's are not fully charged? Or is this capacitance?

Changing amp charge to 10 amps thinking that the BMS is acting like a resistor, choking voltage to battery's.

 

[thealaskan]

Test #1 7/23/20 settings 27.5/23.5 at 10 amps, charge stopped at 26.3 volts leaving battery's at 25.8 volts.

 

[thealaskan]

Test #2 7/24/20 same settings, thought maybe I had a power outage, and that's why it did not go to full charge. (whole house UPS) Battery's charged to 26.4 v this time leaving them at 26.0 v and holding for a longer duration after. Capacitance increase 4%. Packs must be out of balance?

 

[thealaskan]

Test 3 software failed to log again, going backwards to service pack 4 on windows 7 computer, looking for different reliable logging/monitoring options.

 

[Maast]

Do you have the ability to look at your individual cell voltages? Just the bulk voltage is mostly useless. Whats probably happening is that your BMS is going into protect mode because one or more of your cells is going over (on the charge) or under (on the discharge) voltage. BTW the BYDs need a VERY robust balancer.

This might be happening because one or more of the cells is badly under capacity and reaching its charge/discharge limits before all the others in the module.

If you do find that one of the cells is under capacity you can add a Headway to the undercapacity cell and do a charge/discharge test again, if it's better but not good add another and that'll almost certainly fix the problem.

 

[thealaskan]

Do you have the ability to look at your individual cell voltages

No these are byd full packs not broke open yet?

Whats probably happening is that your BMS is going into protect mode because one or more of your cells is going over (on the charge) or under (on the discharge) voltage. BTW the BYDs need a VERY robust balancer.

I have 4 plug and play units in parallel which I got from 2 suppliers.

This might be happening because one or more of the cells is badly under capacity and reaching its charge/discharge limits before all the others in the module.

kind of thought that doing a charging amp rate test now, trying to determine where to start.

cells is under capacity you can add a Headway

What is a Headway?

 

[Maast]

What is a Headway?

These cylindrical 8AH LIFEPO4 batteries, these guys are sold out but they're pretty common. Any smallish LFP battery will do, I like these because they're stupid robust and the formfactor makes them easy to work with in tight spaces.

Twelve - HEADWAY 3.2V 8AH LIFEPO4 LITHIUM BATTERIES 38120HP

This is for a set of 12 tested Headway 3.2 cells. Estimated good for ~80% of max capacity. Free Shipping to the 48 states. Connect 4 of them in series to make a 200A rated 12volt pack. (We do not include(or sale separately) bus bars or screws for this product) 38120HP LIFEPO4 3.2V 8AH...

www.batteryclearinghouse.com

 

[thealaskan]

If you do find that one of the cells is under capacity you can add a Headway to the undercapacity cell and do a charge/discharge test again, if it's better but not good add another and that'll almost certainly fix the problem.

Do you know of any Byd cells available for packs? Never had one apart yet, and never seen one. If its not available, and if I have a issue I might just build New.

 

[Maast]

I ended up with 13 BYD modules and with the sheer amount of futzing and fiddling I'm having to do to have a functioning battery pack if I were to do it again I'd go with the new 280AH batts from Deligreen (ones with blue centers) hands down. It'd cost more but they'd be new and I wouldnt have to continually fight the badly imbalanced cells and having to strip down heavy-ass modules.
Having said that, if you really want more modules take a look at here:

BYD LiFePO4 24 volt Battery Pack - Freight Shipping - Bulk Rate

BYD LiFePO4 24 volt Battery Pack Restocked from new shipment. These commercial battery packs are a great value for the money. Each lot that comes in are slightly different. Tested from 3kWh to 4kWh per unit. Flat Rate $297 shipping in US for a pallet within 48 states with lift-gate service...

www.batteryclearinghouse.com

The shipping is $300 whether you get 1 or 16.

 

[Ampster]

It'd cost more but they'd be new

I guess the cost comparison would depend on how many you purchased because that flat freight rate is almost $100 per kWh for one module. The module cost is somewhere between $70 to $100 per kWh depending on capacity of modules. After spending years nursing Leaf modules of varying capacity having the reliability of a new larger pack had significant value to me. The new pack cost less than $125 per kWh delivered to my door.

 

[thealaskan]

The shipping is $300 whether you get 1 or 16

Its about $450 to me per pallet, 2 per from the 2 California suppliers.

I'd go with the new 280AH batts from Deligreen (ones with blue centers)

I think I found them

EVE 280AH 105AH 90AH 50AH LiFePO4 Battery LF280AH

3.2V Rated LiFePO4 for Electric vehicle RV Car

www.deligreenpower.com

last time I got stuff from china it only took a couple days Ill request a quote.

 

[thealaskan]

I guess the cost comparison would depend on how many you purchased because that flat freight rate is almost $100 per kWh for one module.

I ended up with 13 BYD modules and with the sheer amount of futzing and fiddling I'm having to do to have a functioning battery pack

As I noted a couple months ago, looking for the sweet spot in charge.
Went back 3 computers ago, win 7 got constant readings, and with net search found no lipo4 battery should be charged at over 20a.

 

[Ampster]

found no lipo4 battery should be charged at over 20a.

I assume you mean LiFePO4 (LFP) not Lipo. My LFPs I charge at 60 Amps because that is all my solar can put out. Mine are the 280 Ahr cells mentioned in an earlier post. According to the specs they can be charged at least at 280 Amps which is 1C.

 

[Maast]

I guess the cost comparison would depend on how many you purchased because that flat freight rate is almost $100 per kWh for one module.

Yeah, unless you get 5+ modules shipping is pretty spendy but after that it gets downright cheap by 10 or more modules.

 

[thealaskan]

I assume you mean LiFePO4 (LFP) not Lipo. My LFPs I charge at 60 Amps because that is all my solar can put out. Mine are the 280 Ahr cells mentioned in an earlier post. According to the specs they can be charged at least at 280 Amps which is 1C.

Ill go back through my browser history, see if I can find it, should of kept it. It was a university that was studying chemical breakdown in the battery.

Yes I typed it wrong sorry.

still have got nothing back from Deligreens.

 

[Ampster]

It was a university that was studying chemical breakdown in the battery.

If you want some good University research on Lithium batteries Google, Professor Jeff Dahn from Dalhousie University. He has done extensive research into factors affecting life cycles of Lithium batteries. That sounds like who or what you may be referring to. The context and chemistry would probably be helpful because not all chemistries are alike. Much of his conclusions were around the electrolyte composition to retard the growth of dendrites.
I do not think his earlier research focused on LFP. Increases in the cost and politically correct consumption of Cobalt has caused interest in LFP to increase. He has had a major consulting gig with Tesla who is reportedly trying to reduce the Cobalt content in their batteries. We will know more in a few days when the Tesla Battery Day news is out.

 

[thealaskan]

life cycles of Lithium batteries

I've noticed in mine, since I've been running a constant 20 amp charge rate they have came up .3v, on the top end.
I must have cell issues because the top end is not constant, the highs have been 26.5v with a average of 26.3v.
New to me was 26.9v.

 

[Ampster]

I must have cell issues because the top end is not constant, the highs have been 26.5v with a average of 26.3v.
New to me was 26.9v.

What is the constant voltage setting of your charger? That would be a clue. It should not change over time unless a cell was hitting the HVC and cutting off charging before the pack hit that preset voltage. Do you know if that is what occurred?. That would be a cell issue but it is easily resolved. Over time, if the BMS is shunting that cell, capacity will be bled off until the other cells catch up and the average will increase. Otherwise if you can identify that cell you can put a power resistor on it and bleed off more capacity manually than your BMS can do.
NOTE: Further reading of this thread reminded me that he has 4 packs and I don't know the configuration or have enough data to even reach the conclusion above.

 

[thealaskan]

What is the constant voltage setting of your charger? That would be a clue. It should not change over time unless a cell was hitting the HVC and cutting off charging before the pack hit that preset voltage. Do you know if that is what occurred?. That would be a cell issue but it is easily resolved. Over time, if the BMS is shunting that cell, capacity will be bled off until the other cells catch up and the average will increase. Otherwise if you can identify that cell you can put a power resistor on it and bleed off more capacity manually than your BMS can do.

I'm using the lv2424's auto charge rate, settings are 27.5v/24v, stop and start. Amps can be set between 2 and 60. Charger hits the numbers, the battery's are coming up to 26.7v, when the charger kicks out, but only holding for a max of 1 minute.
they are the BYD 24v plug and plays.