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Chinese Xiaoxing BMS with Calb cells
#1
I finally got delivery of all my parts from china, partly due to me been busy, and partly due to delivery times :-)

So I have 4 x 100ah CALB cells, which I've top balanced over the last couple of days. and a Bluetooth\USB enabled BMS. All of which are wired up and working quite nicely with my old 12v UPS.

So now time to start fine tuning. I'm using the android app and the default settings are


Overvoltage: 3.75v
Overvoltage Release: 3.6v
UnderVoltage: 2.7
UnderVoltage Release: 3.0
Discharge Overcurrent 30.0a
Cycle Capacity : 16ah
Nominal Capicity : 20ah

Open Balance - open
Balance Mode - charge balance

Balance turn-on 3.4v
Balance Precision 0.015v

Hardware Overcurrent protection 70a
Hardware short circuit protection 445a


Okay so straight away the nominal capacity is 100ah, but I'm thinking of charging 20-80 so does the Cycle Capacity need to be 60ah?

The BMS is a 20amp model so it makes sense to change the Discharge Overcurrent to 20amp??

Both the undervoltage settings are as high as they can go which is a little disappointing, however I can change the Overvoltage to 3.6v and 3.5v ?



While on the subject I vaguely remember someone logging data with a Pi Zero connected to either the Bluetooth or USB, can anyone point me to the project, ideally I want to log BMS information along with a sonoff POW before and after the UPS to see what sort of efficiency I'm getting.

The sonoff units can also then be used to control the load and charging to preserver the battery.
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#2
You're probably talking about my project, and a few others.

I'm using a Raspberry Pi 3 using 2x USB/Bluetooth dongles to communicate with currently 6 BMSs.

Member "Solloh" has reportedly cleaned up and updates my code, but I haven't checked it out yet:
https://secondlifestorage.com/showthread...1#pid66091
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#3
Thanks for that, that looks like the stuff I was thinking of.

Next problem, looks like the ups is only charging at 13.8v to 14.0 at 0.3A so isn't giving the batteries much charge.
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#4
Isn't 13.8V~14.0V about 80% charge for LiFePO4, what you were aiming for?
Perhaps if you post which UPS you're using, someone might be able to suggest settings/modifications to set higher charge voltages.
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#5
The UPS is Cit UPS-650B it's old, was cheap and I had it lying around, so it got used.

The BMS reported 68% charge, and never really shifted
I suspect the 0.3A didn't really help. I'm going to run them down to a something like 20% and try charging from there see if it makes a difference.
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#6
14V is float voltage for most UPS systems. The BMS base their SOC on voltage.

LiFe is generally pretty full at 3.4-3.5V per cell. I bet they have a rather linear SOC vs Voltage curve and therefore dont think the cells are full untill they have reached 3.65V. LA chargers work a bit different with Bulk and float settings and most of the UPSs out there you cant change those settings.
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#7
(08-28-2020, 03:37 PM)daromer Wrote: 14V is float voltage for most UPS systems. The BMS base their SOC on voltage.

LiFe is generally pretty full at 3.4-3.5V per cell. I bet they have a rather linear SOC vs Voltage curve and therefore dont think the cells are full untill they have reached 3.65V. LA chargers work a bit different with Bulk and float settings and most of the UPSs out there you cant change those settings.

Sorry I'm a little confused by that, are you saying the batteries are pretty well charged but the BMS thinks they aren't, or that the UPS thinks they are charged, so goes to a 0.3amp trickle when infact they could do with a little more.
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#8
The ups you picked was for Lead acid batteries and you did add Lithium batteries right?
Unless you hacked the code the UPS still think it have Lead acid batteries and will charge them like that. Therefore the voltage is like it is Smile

The BMS is as i said a cheaper variant and most of them base their SOC on rather linear voltage curve vs SOC. They often trade their SOC value based on Voltage. So 14V might be 68% meanwhile 14.6 is 100% and 3.0 is 10%.. Or whatever...

So at 14V yo uhave 3.5V per cell and max on LiFe is generally 3.65 that is 14.6. So the BMS wont ever get to 100% unless the charger goes above 14V.

La Charger depending on UPS may top to 14.5 for a short while and then go down to idle at 13.5-14V for the rest of the time.



As me and other said before LiFePo4 is pretty well charged above 3.45V.

Note that im guessing a bit so dont take all my numbers above. I havent read up on that UPS as an example.
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#9
(08-28-2020, 06:22 PM)daromer Wrote: The ups you picked was for Lead acid batteries and you did add Lithium batteries right?
Unless you hacked the code the UPS still think it have Lead acid batteries and will charge them like that. Therefore the voltage is like it is Smile 

The BMS is as i said a cheaper variant and most of them base their SOC on rather linear voltage curve vs SOC.  They often trade their SOC value based on Voltage. So 14V might be 68% meanwhile 14.6 is 100% and 3.0 is 10%.. Or whatever...

So at 14V yo uhave 3.5V per cell and max on LiFe is generally 3.65 that is 14.6.  So the BMS wont ever get to 100% unless the charger goes above 14V.

La Charger depending on UPS may top to 14.5 for a short while and then go down to idle at 13.5-14V for the rest of the time.



As me and other said before LiFePo4 is pretty well charged above 3.45V.

Note that im guessing a bit so dont take all my numbers above. I havent read up on that UPS as an example.
Thanks for the explanation. I'm currently running the battery down ready to start a recharge in the morning, it may well work in my favour and give me longer battery life. I don't think it is worth the effort of trying to trick\hack the UPS to behave more lifepo4 than lead acid. So if it doesn't charge properly my options are either us it as an inverter only, and find a better charger or even a charger\inverter.
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#10
I would say if it doesn't go above 14V thats pretty fair and good top voltage Smile

If you can monitor the voltage during charging do that. Some UPS systems do a bump where it goes to 14.5 or even 15+v before settling.

Testing is a good way of knowing how it behaves and if that suits you.
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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