BMS requirements 4P8S Lithium set up?

[poiu]

I have 32 CALB 180 cells on the way. I plan to wire them up in parallel, then 8 in series to give 720Ah at 26v. I want to get a BMS just for over voltage and under voltage safety trips.

If there are 4 cells in parallel, will they always balance out at the same voltages? If that is the case I will not need to monitor more than 8 voltages or do I need to monitor all 32?

[smac999]

The 4 in parallel will always be the same. As they are wired together. For the overal bank voltage high or low. You’d only have to measure one voltage.


However each cell can vary high or low. For safty you should be monitoring all 32. And ideally 4 different bms and 4 switches. So if one cell goes bad. Only that string shuts down. Not the whole bank.

[poiu]

Originally Posted by smac999

The 4 in parallel will always be the same. As they are wired together. For the overal bank voltage high or low. You’d only have to measure one voltage.


However each cell can vary high or low. For safty you should be monitoring all 32. And ideally 4 different bms and 4 switches. So if one cell goes bad. Only that string shuts down. Not the whole bank.

That would be a 8S4P set up, which I didn’t want to do because of complexity, power drain from 4 BMSs and cost. I realise it there is a risk from a cell failing, but I have had some years experience with failures with lithium and they have all gone fairly slowly. I don’t feel I need this level of protection.

[Singularity]

I suggest that this short thread parses the pros/cons about paralleling, where ultimately you've got to make your own decision.

https://www.cruisersforum.com/forums...ot-221600.html

FWIW I'd vote to go parallel first, use a single BMS, though obviously a single BMS sensing on 4p is less desirable than 2p or 3p.

And just to confuse things I'll repeat the rumor that perhaps the prismatics coming out of China today may not be as consistent cell to cell than a few years ago, such that maybe one should be less confident that the DIY practices of a few years ago might not be as reliable today.

[GRIT]

You'll only monitor the 8 voltages.

We used CALB 180 cells too, and they were all within a couple thousands of a volt of each other. I can't imagine getting any closer than that.

You cannot monitor every cell, those that are paralleled will, by default, all show the same voltage.

Cheers.
Paul.

[GRIT]

After two years of use, without balancing (though we can with our BMS), I just checked my voltages, and our highest group is at 3.349 and our lowest is 3.346 volts.

I'm pretty happy with our CALB cells. I'm sure you'll be too.

We have them setup as 4P4S, same as you're planning, but at half the voltage.


Cheers.
Paul.

[Fam1949]

Folks,
I am not an expert on these issues, but I am considering buying a hybrid boat - e.g. a Greenline 40 or 45. I have asked the producer about what type of batteries and safety measures they have on their hybrid boats and the answer is:

1- Our batteries are 56V lithium polymer with each 13.3 kW.
2- The cells come from Kokam which is a battery manufature in Korea.
3 - The final battery is built in Slovenia by us.
4- The maximum current before overheating for our battery is 700A but we limited the BMS (battery management software) even to 300A.
5- In the unlikely event of overheating each battery has a thermo sensor and the system will shut down.

What is your opinion? I am afraid of batteries catching fire: am i exagerating this fear?

[PineyWoodsPete]

Originally Posted by Fam1949

Folks,
I am not an expert on these issues, but I am considering buying a hybrid boat - e.g. a Greenline 40 or 45. I have asked the producer about what type of batteries and safety measures they have on their hybrid boats and the answer is:

1- Our batteries are 56V lithium polymer with each 13.3 kW.
2- The cells come from Kokam which is a battery manufature in Korea.
3 - The final battery is built in Slovenia by us.
4- The maximum current before overheating for our battery is 700A but we limited the BMS (battery management software) even to 300A.
5- In the unlikely event of overheating each battery has a thermo sensor and the system will shut down.

What is your opinion? I am afraid of batteries catching fire: am i exagerating this fear?

We have had our '14 Greenline 33 Hybrid (hull #314) for about 18 months with a nominal 48V/11.6kWh LiPo battery bank. Battery performance to date has been flawless with the Victron Quattro 48V/5000W inverter/charger and the 7/5 kW motor-gen. in line with the 165HP diesel. Max float voltage is 54.35V. The BMS has 13 temp monitors - presumably one for each group of 4 cells.
As far as I know there have been two fires in the 33' of the probably 450 or more built to date, and smaller numbers of the 40 (two of same LiPo banks) and larger yachts to 65' - none of which I've heard of any fires in.

I don't know the circumstances of the two 33' fires - in '12 and '17 - except that the the owner of the '17 reported "trouble with the battery" preceding the fire. Don't know the age of that boat, but the 1st model year was '10 and the GL 33 Hybrid was Euro. "Boat of the Year" after introduction, with many in the charter trade.

[Fam1949]

Thanks.
I asked Greenline about those fires and the answer is that The incident in Germany was caused because the BMS was broken and the owner connected the battery directly to the charger.
Then the programmed security obviously did not work anymore.
It was an older models and had no thermos sensor yet.

So I guess the probability to battery fire is now as low as it can possibly be. That’s good news for me who hopes to buy a Greenline 40 (or 45) - but I probably should buy a new one or a very recent model to make sure the technology is up-to-date��