Lithium Bank Voltage Drop.....

[more]

Originally Posted by CaptainRivet

Which model?

The 24V and 48V smart inverter BMS is explicitly allowed to parallel and even has a master BMS and slave BMS functionality to act as such.

What you have to do but thats for every mosfet BMS that if paralleling (if not explicitly stated different) the current rating is half of each BMS due to uncalibrated mosfets.
Means 200A and a 2nd in parallel is 300A for both, 3 in parallel is 400A and 4 is 500A...more then 4 not more current capabilities but to extend capacity you can parallel as many as you want.
The reason many drop ins limit paralleling to 4 batteries.

read her i now reeding interesting fantasy answer.
https://diysolarforum.com/threads/jk...s.38623/page-4

normaly i put in parallel also more valid last snow vs chinese warranty.
i trust more fish around boat ws chinese company. thanks for nkon.nl i just order 32 Eve LF304 Prismatic 304Ah - LiFePO4 - 3.2V A-Grade for €2,800.05
to door with tax also grab last 8 jkbms 4-8S200A 2A for 72€ pcs from poland

[CaptainRivet]

Originally Posted by more

read her i now reeding interesting fantasy answer.
https://diysolarforum.com/threads/jk...s.38623/page-4

normaly i put in parallel also more valid last snow vs chinese warranty.
i trust more fish around boat ws chinese company. thanks for nkon.nl i just order 32 Eve LF304 Prismatic 304Ah - LiFePO4 - 3.2V A-Grade for €2,800.05
to door with tax also grab last 8 jkbms 4-8S200A 2A for 72€ pcs from poland

My answer is what my buddy is using in their cheaper Lifepo4 powerwalls depending on capacity 1 till 3 JK inverter BMS in 48V. Thats what they extensivly tested and killed several BMS to be 200% safe. They are good quality BMS with constant production quality. The 200A one i wouldn't put more then 150A on one, the rating is a bit optimistic.
On a boat i would put a BMV712 with a disconnect relay as last resort...on 4S with winston i am using only BMV712 and a neey active balancer which is also cell monitor. These are mostly heavy cycled high power system wit 2-3C use, so balancer is needed and for the cell price its worth to go 200% safe. They are so stable that more is not needed.

[s/v Jedi]

All these BMS systems are mediocre for boats. When I see the difference in performance between a MOSFET based BMS and a Solenoid based BMS it is crazy.

So this story with JK BMS … hard to decipher what the Chinese English is actually trying to bring over… but it is about one battery being cut off by the BMS while another is not and now they go wildly out of balance, then when the battery that was cut off is switched back online, it discharges massively into the lower SOC batteries.

BS of course.

They are afraid their MOSFETS blow up. He’s trying to explain to use separate charge and discharge busses and give each battery a diode in the positive conductor to the common discharge busbar to that this can’t happen.

[Montanan]

I would check your connections to the battery terminals that may be where the voltage drop is most severe.

[CaptainRivet]

Originally Posted by s/v Jedi

All these BMS systems are mediocre for boats. When I see the difference in performance between a MOSFET based BMS and a Solenoid based BMS it is crazy.

So this story with JK BMS … hard to decipher what the Chinese English is actually trying to bring over… but it is about one battery being cut off by the BMS while another is not and now they go wildly out of balance, then when the battery that was cut off is switched back online, it discharges massively into the lower SOC batteries.

BS of course.

They are afraid their MOSFETS blow up. He’s trying to explain to use separate charge and discharge busses and give each battery a diode in the positive conductor to the common discharge busbar to that this can’t happen.

Andy from offgrid garage testing this since 3 years with 3 banks in parallel and even 3 different mosfet BMS. In reality they only switch the charge off very close to each other, so load side is always connected to the 3 BMS. At low voltage cutoff they are also close, it’s not happening that one is totally full and the other totally empty…and even if it was like around 100A max for 280AH 1p16S from an empty to full battery.

The issue here is the mosfet BMS have multiple mosfets that share the load but these mosfets are not calibrated means there is always the weakest one that switches first and get the full load for milliseconds. For the rating for 1BMS that fits. But if you put 2 parallel and expect double current capabilities, that’s not the case because there is still one weakest mosfet that gets the full load and if double current which the one mosfet cannot handle anymore and burns through…with 3 in parallel the chances are very very high you have 2 weakest mosfet that share the loads. That's the real issue when paralleling mosfet BMS also the dropins which 99.9% have mosfet BMS inside. And that’s what my buddy tested for their budget powerwall series and told me what is save „rating for paralling these mosfet BMS“.
It’s cheaper to put 2 or 3 of these uncalibrated mosfet BMS into a powerwall, then build one with calibrated mosfets which jk did for mueller energy in Australia.

[UFO]

Manage to get some time to run a quick test....


Sitting at around 13.29V with minimal load (around 10 amps) and about 75% Charged.



Ran a 260Amp load....


Victron BMV: Fluctuates between 12.7V to 12.8V


BMS which are motherboards directly on each battery set vary between 12.9V and 13.1V


Multi-Meter sitting directly on the battery terminals show a steady 13.15V


Batteries are connected by Tin Coated bars - approx 3CM wide x 8MM deep - These do not get warm at all. Cable coming off for 12V and Inverter are VERY Large (Not sure exact size) and do not get warm.



All terminals are secure, tight and clean.

[CaptainRivet]

Originally Posted by UFO

Manage to get some time to run a quick test....


Sitting at around 13.29V with minimal load (around 10 amps) and about 75% Charged.



Ran a 260Amp load....


Victron BMV: Fluctuates between 12.7V to 12.8V


BMS which are motherboards directly on each battery set vary between 12.9V and 13.1V


Multi-Meter sitting directly on the battery terminals show a steady 13.15V


Batteries are connected by Tin Coated bars - approx 3CM wide x 8MM deep - These do not get warm at all. Cable coming off for 12V and Inverter are VERY Large (Not sure exact size) and do not get warm.



All terminals are secure, tight and clean.

That’s exactly what I expected.

Your 8x30mm busbars are good for 288A.
That’s a good calculator: https://www.allumiax.com/bus-bar-size-calculator

260A readings on BMS means effectively 260x1.4=364A on/off several times during a millisecond because it’s an inverter and that’s exactly the fluctuations you see. Means the busbar fit for the average continuous current but not for the peaks, that’s why they don‘t get very hot quickly but you see a voltage drop as fluctuations. It’s ok like that but limit for your 260A..
The fluctuations are bigger if you run the induction cooktop as cos pi is bad so you have a higher phantom load then with eg toaster which is a restrictive load.
But they are by far to small for 600A, that’s why you get that massiv sag.
You either need to limit your inverter or upgrade the busbars.

[more]

Originally Posted by UFO

All terminals are secure, tight and clean.

check under load cell by cell voltage

[Pete7]

Originally Posted by more

check under load cell by cell voltage

Yup, we all have one of those on board

Do you carry one?

Pete

[more]

Originally Posted by Pete7

Yup, we all have one of those on board

Do you carry one?

Pete

yes 3-4 different, this is important toll. for current ac/dc current clamp you need for diagnose alternator,solar for all ?. multimetar UT-139 for example tru RMS voltage cheap and good accuracy in dc is ok. don't need more expensive for electronic, couple cell monitor cheap from hoby shop, uni thermal camera excellent toll for checking conection,lug in reality only way for check connection. engine overheat problem ecc. probe lamp
o yes also solar panel monitor is good easy instrument, he save me hour and hour finding source of malufuction. magnetic field mini detector good for ac curent, be nice have this for DC. batery capacity tester charg/discharg if need but this stay in car

[CaptainRivet]

Originally Posted by more

check under load cell by cell voltage

That's not his problem. Cell voltages are max 30mV at 260A...that shows its in balance and the connection are good.
His busbars are at the limit for 260A as described above and because 4 cell parallel they split the load so its 65A per cell, nothing for a 280AH cell but all 260A go through busbar causing the voltage sag. Keep the 260AH load for 15min and measure every minute the temp of busbar and the cell stud/nut of every cell with a temp gun, same for battery cable and post the temperature. Are all 4 cells having the same temp at the nut after 15min or is the first cell nut hotter then the last of the 4 cells and by how many degrees.
UFO how and where do you connect the main battery cable? How many sqmm is the cable? Post a foto of your battery please.
At the end or middle of the busbar or do you have 2 and go inbetween cell 1+2 and 3+4 which is the right way.
2 fotos of mine how this should look, you must connect the shunt and main fuse like i done, it must be 100% symetrical. Your shunt reading shows you have an issue here too, most likely cable undersized.

[s/v Jedi]

Originally Posted by UFO

Manage to get some time to run a quick test....

Sitting at around 13.29V with minimal load (around 10 amps) and about 75% Charged.

Ran a 260Amp load....

Victron BMV: Fluctuates between 12.7V to 12.8V

BMS which are motherboards directly on each battery set vary between 12.9V and 13.1V

Multi-Meter sitting directly on the battery terminals show a steady 13.15V

Batteries are connected by Tin Coated bars - approx 3CM wide x 8MM deep - These do not get warm at all. Cable coming off for 12V and Inverter are VERY Large (Not sure exact size) and do not get warm.

All terminals are secure, tight and clean.

This confirms my initial suspicions that we are talking about voltage drop, not voltage sag in the cells.

I am not sure if the cell terminals are available to measure against or only the 12V terminals. Let me read back before continuing… okay, it is Eve cells so terminals are accessible and there is a 4p4s configuration.

Measure each 4p cell block voltage under load.

[CaptainRivet]

Originally Posted by s/v Jedi

This confirms my initial suspicions that we are talking about voltage drop, not voltage sag in the cells.

I am not sure if the cell terminals are available to measure against or only the 12V terminals. Let me read back before continuing… okay, it is Eve cells so terminals are accessible and there is a 4p4s configuration.

Measure each 4p cell block voltage under load.

I spent 5 weeks troubleshooting mine 4P4S with the exact same symptoms…and fixed all so I can pull nearly 100min 600A as max possible stress test.

Forget Multi-Meter and measure voltages, it’s too slow to see what’s going on.
Best friend is your BMS with cell voltages, an IR temp gun and first 260A load then 400A for at least 10min straight…the temps will exactly tell you what’s going on between the cells and where your contact or Undimensioned cables problems are, the only way in 4P4S and in general best and quickest way to find where your issues are. It’s not heating up extremely but the IR temp gun tells you where differences are. Eg I bet a bottle of champagne that with 400A you will see the following: measured on the nut of the cell=>cell 1 is at 35 degrees, cell 2 at 32, cell 3 and 30 and 4 is at 28 degrees…the same cell 13 till 16. that’s because you connected one battery cable at the end of the busbar as main positive and negative terminal. Will cause imbalance over time and make the cells fluctuate because cell 1 carries a much higher load then cell 4. that’s because a) busbars are underdimensioned and b) the distance from cell 1 to 4 run through the busbar is >30cm and that creates a higher resistance means cell4 even resistance matched has now a higher resistance then cell1.

[more]

Originally Posted by CaptainRivet

I spent 5 weeks troubleshooting mine 4P4S with the exact same symptoms…and fixed all so I can pull nearly 100min 600A as max possible stress test.

Forget Multi-Meter and measure voltages, it’s too slow to see what’s going on.
Best friend is your BMS with cell voltages, an IR temp gun and first 260A load then 400A for at least 10min straight…the temps will exactly tell you what’s going on between the cells and where your contact or Undimensioned cables problems are, the only way in 4P4S and in general best and quickest way to find where your issues are. It’s not heating up extremely but the IR temp gun tells you where differences are.

more easy cheap uni-t show problem in second,minute.
https://youtu.be/ciZhLaU6HyM?si=hztogv-413P-qAfN&t=404
also you can return investment in first customer.

[s/v Jedi]

Originally Posted by CaptainRivet

I spent 5 weeks troubleshooting mine 4P4S with the exact same symptoms…and fixed all so I can pull nearly 100min 600A as max possible stress test.

Forget Multi-Meter and measure voltages, it’s too slow to see what’s going on.
Best friend is your BMS with cell voltages, an IR temp gun and first 260A load then 400A for at least 10min straight…the temps will exactly tell you what’s going on between the cells and where your contact or Undimensioned cables problems are, the only way in 4P4S and in general best and quickest way to find where your issues are. It’s not heating up extremely but the IR temp gun tells you where differences are. Eg I bet a bottle of champagne that with 400A you will see the following: measured on the nut of the cell=>cell 1 is at 35 degrees, cell 2 at 32, cell 3 and 30 and 4 is at 28 degrees…the same cell 13 till 16. that’s because you connected one battery cable at the end of the busbar as main positive and negative terminal. Will cause imbalance over time and make the cells fluctuate because cell 1 carries a much higher load then cell 4. that’s because a) busbars are underdimensioned and b) the distance from cell 1 to 4 run through the busbar is >30cm and that creates a higher resistance means cell4 even resistance matched has now a higher resistance then cell1.

Wow… I actually agree with you!