Lithium mini batteries

[CaptainRivet]

Originally Posted by more

what cable you use to carry 500A load.
you know is very,very stupid pull 100A from 12v battery. or use bigest inverter 2000w on 12v system.
watch from begining to end.couple time again,again also have video of your T-fuse-Fast acting fuse. when use ,why ecc
this for AC but similar is DC only different is arc arestor,and contactor.

Fuse never save life, thats the job of the FI.

For my max load of 600A i use for positive and negative each 6x70sqmm cable, 2 for each inverter, 1 for life dependend equipement and 1 for rest house loads and 1x 95sqmm for the charge bus.
The 2 inverter as main big load are within 1m of the bank, so it really doesn't matter if they are 12V or 24V for this short distance. 24V will be 1 cable with 1 fuse, 12V is 2 cable with 2 fuses.
All connected to each an NH2 200A fuse and that to a sliver plated 99.8% cooper busbar in 9mmx45mm directly connected to the main load fuse NH 3 630A fuse.
Have my reasons to stay 12V...

But thats not the point here, point is how you parallel mosfet BMS and how you rate and install them.

[s/v Jedi]

There will be many with burned out mosfets who don’t even realize it.

[wholybee]

Originally Posted by s/v Jedi

There will be many with burned out mosfets who don’t even realize it.

So you are saying that there are millions of MOSFET BMS's sold, and since they are working and the evidence is lacking that they are unreliable, your position is that they must be broken and the users just don't know about it? That certainly can happen (example below) but overall it's a laughable idea.

Re: Andy's off grid garage failure of a JK BMS FET. The video where the overcurrent cutoff time was set to 5 minutes, and then he applied over the max current for more than 5 minutes?

He gave the BMS a positive review overall. The MOSFETS were rated at 85A each(which to me is questionable), and there were 20 in parallel. So, 10A each at the rated BMS current of 200A. He believes the MOSFET itself was defective and the BMS will still meet it's rated performance without it.

I don't at all think that means a JK BMS will blow MOSFETS like popcorn if run at it's rated current. Or that MOSFETS will blow like popcorn if 600A is distributed between 3 200A JK BMSs. More, I think that the BMS was engineered with enough overhead that it should run at rated current quite easily, and even if there is a defective part or some outstanding even occurs, it will still function at specified ratings.

Andy probably has as many or more JK BMS's than anyone. He has had a few failures, mostly firmware issues from what I have seen. He also subjects them to abusive tests, and I don't see enough evidence from him to suggest that FETS are a problem. As I said before, of course they will fail on occasion. But far less often than a relay.

[s/v Jedi]

Originally Posted by wholybee

So you are saying that there are millions of MOSFET BMS's sold, and since they are working and the evidence is lacking that they are unreliable, your position is that they must be broken and the users just don't know about it? That certainly can happen (example below) but overall it's a laughable idea.

Re: Andy's off grid garage failure of a JK BMS FET. The video where the overcurrent cutoff time was set to 5 minutes, and then he applied over the max current for more than 5 minutes?

He gave the BMS a positive review overall. The MOSFETS were rated at 85A each(which to me is questionable), and there were 20 in parallel. So, 10A each at the rated BMS current of 200A. He believes the MOSFET itself was defective and the BMS will still meet it's rated performance without it.

I don't at all think that means a JK BMS will blow MOSFETS like popcorn if run at it's rated current. Or that MOSFETS will blow like popcorn if 600A is distributed between 3 200A JK BMSs. More, I think that the BMS was engineered with enough overhead that it should run at rated current quite easily, and even if there is a defective part or some outstanding even occurs, it will still function at specified ratings.

Andy probably has as many or more JK BMS's than anyone. He has had a few failures, mostly firmware issues from what I have seen. He also subjects them to abusive tests, and I don't see enough evidence from him to suggest that FETS are a problem. As I said before, of course they will fail on occasion. But far less often than a relay.

No, Iam not saying any of that, you are. I said:

Originally Posted by s/v Jedi

There will be many with burned out mosfets who don’t even realize it.

[Statistical]

Originally Posted by more

what cable you use to carry 500A load.

500A continuous? Probably not on a boat but instantaneous loads due to capacitor inrush, and motor starting can be multiples of continuous load.

you know is very,very stupid pull 100A from 12v battery. or use bigest inverter 2000w on 12v system.

That is an overly broad dubious statement. Pretty much anyone with a starter is pulling >100A from a battery. 2kW inverter on a 12V system is fine.

[Statistical]

Originally Posted by wholybee

As I said before, of course they will fail on occasion. But far less often than a relay.

The failure mode is different though. Nobody is using multiple contactors in parallel on a boat. If the contactor fails it isn't going to lead to a cascade of failures in the other components.

Your house AC has a contactor and given enough time there is a good chance it fail. When that happens your AC just won't turn on.

Note BMS (mosfet based or contactor based) should not be the primary overcurrent protection both have the potential to fail on meaning the BMS can't stop the flow of current. It is why the battery should be fused and fused with one that has significant AIC (i.e. Class T fuse).

[wholybee]

Originally Posted by s/v Jedi

No, Iam not saying any of that, you are. I said:

Originally Posted by s/v Jedi

There will be many with burned out mosfets who don’t even realize it.

Said in response to my assertion that MOSFET BMS's are reliable, and my asking where are the failed ones are.

[Statistical]

Originally Posted by wholybee

Said in response to my assertion that MOSFET BMS's are reliable, and my asking where are the failed ones are.

Mosfet based BMS are generally reliable. It gets a bit more iffy when people start pushing the limits of what they are capable of. One 200A battery drawing 50 to 100A loads is fine. Putting four in parallel and routinely drawing close to 800A due to say electric propulsion you are probably asking for problems.

[more]

Originally Posted by Statistical

Pretty much anyone with a starter is pulling >100A from a battery. 2kW inverter on a 12V system is fine.

and how long from 10 second to max 120 second .who use starter motor 1 hour continuous.

[CaptainRivet]

Originally Posted by wholybee

So you are saying that there are millions of MOSFET BMS's sold, and since they are working and the evidence is lacking that they are unreliable, your position is that they must be broken and the users just don't know about it? That certainly can happen (example below) but overall it's a laughable idea.

Re: Andy's off grid garage failure of a JK BMS FET. The video where the overcurrent cutoff time was set to 5 minutes, and then he applied over the max current for more than 5 minutes?

He gave the BMS a positive review overall. The MOSFETS were rated at 85A each(which to me is questionable), and there were 20 in parallel. So, 10A each at the rated BMS current of 200A. He believes the MOSFET itself was defective and the BMS will still meet it's rated performance without it.

I don't at all think that means a JK BMS will blow MOSFETS like popcorn if run at it's rated current. Or that MOSFETS will blow like popcorn if 600A is distributed between 3 200A JK BMSs. More, I think that the BMS was engineered with enough overhead that it should run at rated current quite easily, and even if there is a defective part or some outstanding even occurs, it will still function at specified ratings.

Andy probably has as many or more JK BMS's than anyone. He has had a few failures, mostly firmware issues from what I have seen. He also subjects them to abusive tests, and I don't see enough evidence from him to suggest that FETS are a problem. As I said before, of course they will fail on occasion. But far less often than a relay.

No they are neither unrelaible, nor they are unsafe.

BUT why if their are 20 mosfets in parallel, each a 85A rating and the BMS is just rated for 200A????

Because they are uncalibrated mosfets, so not all switching at the same time!!! Thats why!

2nd JK states NOT to parallel them!!!

Ratings from a Chinese company with no official subsidiary in europe have to be taken with a grain of salt! Jk is good constant quality but need to be derated.

Andy is Youtube channel and he has 1 or 2 of the same model, maddie has 24 JK BMS in parallel runing her mono with E-engine and 24 batteries parallel (and killed 3 completely) ...my buddy is CEO of an NPO building powerwalls and commercial EVs with a proffessional R&D lab and he killed over 50 JK BMS to figure out when using them which model and which combo in his budget powerwall series what currents and rating he can securely offer based in Austria and have to offer garauntee for his products that contain JK BMS. I posted the result and that is inline with what also JK R&D recommends.
Take 75% of cont rating for real rating, so the 200A BMS a 150A fuse. if paralleling them use for each 125A superfast fuse for the 200A model.
Other ratings accordingly with same ratio.

Like this you can operate them safe and relaible.

And yes i agree with Jedi there are a lot other chinese BMS out there i would highly doubt their ratings especially the surge capabilities they stating. And yes many mosfet BMS out there will have some burned mosfets but still working from eg owner connecting big inverters without a precharge resisitor and resulting surge killed some mosfets....
Especially earlier typical 5$ BMS in cheap chinese surprise boxes...

[s/v Jedi]

Originally Posted by wholybee

Said in response to my assertion that MOSFET BMS's are reliable, and my asking where are the failed ones are.

*zucht*

When a BMS is bad, you would know it, wouldn’t you?! I’m talking about bad mosfets in a BMS that still works except at reduced maximum capacity because of one or more burned out mosfets… which will only get known about when maximum power is needed. Hopefully that isn’t during an emergency…

A BMS that is not in the high power circuit at all and simply controls the Blue Sea RBS doesn’t have any of these weaknesses.

[Pete7]

Originally Posted by more

and how long from 10 second to max 120 second .who use starter motor 1 hour continuous.

However, you also said "or use bigest inverter 2000w on 12v system".

Why not? This is exactly what I have been doing. Is there something wrong with this? you have me really worried now. What is your statement based on and what was your experience of running a 2kW inverter from 12v?

How can I make a cup of tea this morning when we only have electric cooking? Would it be safer to use one of those little disposable camping stove inside? I could try the BBQ but might take a while. Don't think memsahib will be very happy without her coffee. What should I do

[CaptainRivet]

Originally Posted by Pete7

However, you also said "or use bigest inverter 2000w on 12v system".

Why not? This is exactly what I have been doing. Is there something wrong with this? you have me really worried now. What is your statement based on and what was your experience of running a 2kW inverter from 12v?

How can I make a cup of tea this morning when we only have electric cooking? Would it be safer to use one of those little disposable camping stove inside? I could try the BBQ but might take a while. Don't think memsahib will be very happy without her coffee. What should I do

Use your 2kw inverter and be happy, no issue. Gas definitely not saver.
The tricky thing of a starter is its surge of 4 till if bad even 5 times of constant use everytime you use it, not its constant draw and you simply cannot avoid the surge and its value.

What he most likely means is a battery starting the engine can also handle a 2kw inverter but that’s a different story as the issue with inverter is they draw continuous power over a longer time, your LFP is capable of delivering both constant and peak, the lead not.
An inverter only have a big surge when you had it disconnected via the disconnect switch so the capacitors didn‘t stay charged but you can avoid this by using an resistor or right away have a precharge circuit connected if you switch off often…no danger for cells or BMS.

[CaptainRivet]

Originally Posted by Statistical

Note BMS (mosfet based or contactor based) should not be the primary overcurrent protection both have the potential to fail on meaning the BMS can't stop the flow of current. It is why the battery should be fused and fused with one that has significant AIC (i.e. Class T fuse).

You are mixing here overcurrent, reverse polarity, BMS short circuit protection and short circuit protection.
Overcurrent means your loads are simply to high=too much current draw and that’s the job of the BMS to control that and shut it off.
Reverse polarity means you connect BMS the wrong way plus to minus and its job of the BMS switches off/not on.
BMS short circuit protection means its own device fuse (which can be a real fuse or in mosfet BMS the mosfet act as fuse switch) against internal short of BMS or from the BMS upwards means output by a cable or device.
Short circuit protection is the job of your your main battery fuse and/or the charge/load circuit fuse, means the input side of the BMS if mosfet and that fuse must have the AIC of the shorted battery bank, with LFP with min. 30kA your are on the safe side, huge banks over 12kw should use min 50kA. Nearly all contractor or mosfet will survive that means is even able to do the job.

And just be aware there are 3 kinds of BMS out there, mosfet and contactor ones which simply shut off the load or charge on the high side means are in the current flow. And there are no current carrying BMS that simply switch charge and load at the source means on the low current side and if your sources are off high quality that remote ports are tested by R&D eg in case of Victron 7/24/365 for more then 10 years. And that’s the safest as a) tested to work for >10years by the manufacturer and b) these SSD or low current relays are much less prone to fail then the big ones which have all kinds of problems and tend to melt close when failing.
Means you are not switching 1 contractor/paralleled mosfet but several independent sources and instead eg switching all off in an overcurrent situation can simply switch off the biggest load but let the rest run as you are within current spec now. That’s the way Electrodacus BMS works and the reason I chose it.

[Pete7]

Originally Posted by CaptainRivet

Use your 2kw inverter and be happy, no issue. Gas definitely not saver.

Thanks, I fully intend to However, the intent was to challenge a poor statement that he wanted to be taken as good advice when clearly it was nonsense.

Pete