BMS recommendation for high load DIY system

[yabert]

Despite the thin documentation the software looks great. I would need eight K9 units = 1,400 USD plus the Core @ 254. Total 1700 bucks

You don't have to use 8 K9 unit.
A single one will work if you connect your cells in parallel.
In fact, four 100Ah cells in parallel will simply become a single 400Ah cell. OEM do this inside EV batteries
In a boat, it can be a good idea to have two batteries, but clearly not an obligation.
If I had 54 100Ah cells, I would probably build a giant 1300Ah 4S battery with a single BMS and use the $$ saved on BMS to buy a regular 12V LFP battery or two.

 

[boatsparky]

I would probably build a giant 1300Ah 4S battery with a single BMS and use the $$ saved on BMS to buy a regular 12V LFP battery or two.

I like that kind of thinking. Could build one big bank, one "reserve" for backup. Or just two big redundant banks. Comments have been made that EV engineers do not set up monitoring for each cell, so it makes sense. If one bank goes bad, take jumpers off and probe to find the bad cell(s). Remove four and get it working again?

 

[mikefitz]

EV engineers do not set up monitoring for each cell,

It's very different engineering to a DIY battery for marine application.
It's a boat there levels of vibration and shock will stress the battery construction. I sugest constructing 12 volt batteries, 2P4S, each with a 200 amp fet based BMS with Bluetooth and serial communication.
Connect up the batteries to a buss bar systen with a isolator and Class T fuse between each battery and buss bar.
Short term overload of a 200A BMS is around 500 amps so worst case two batteries on line could power the winch.
The battery box for each 200Ah battery idealy needs to offer weather proof and fire resistance.
Suitable BMS,

4S 200A BMS Lifepo4 Battery 3S 12V Li-Ion Battery Smart Balance Protection Board With Bluetooth Uart - LLT POWER ELECTRONIC

Features and Characteristics : Characteristics : this is a smart BMS with Bluetooth and PC communication which will be used to protect and monitor your battery status visible from the computer and your android APP phone .which can support UART or UART and RS485 communication .the charge and...

www.lithiumbatterypcb.com

 

[yabert]

If one bank goes bad, take jumpers off and probe to find the bad cell(s). Remove four and get it working again?

Exactly.
Exemple: if you measured the 4 cells of your battery at 3V, 3V, 3V and 1V.
When some busbars will be removed, some cells at 1V will come back at 3V and you can find cell or cells at 1V or even at 0V.

I have recover, in 2015, some cells from a 160V battery who was drop at 4V for months.
Some recovered cells still work today.

 

[yabert]

It's a boat there levels of vibration and shock will stress the battery construction.

I'm always surprised to see this.
It's not like if a Cybertruck or Rivian pickup or a F150 Lightning battery doing off road had an easy life.

Do you suggest that a boat battery should always be on rubber mount?

 

[boatsparky]

It's very different engineering to a DIY battery for marine application.
It's a boat there levels of vibration and shock will stress the battery construction. I sugest constructing 12 volt batteries, 2P4S, each with a 200 amp fet based BMS with Bluetooth and serial communication.
Connect up the batteries to a buss bar systen with a isolator and Class T fuse between each battery and buss bar.
Short term overload of a 200A BMS is around 500 amps so worst case two batteries on line could power the winch.
The battery box for each 200Ah battery idealy needs to offer weather proof and fire resistance.
Suitable BMS,

4S 200A BMS Lifepo4 Battery 3S 12V Li-Ion Battery Smart Balance Protection Board With Bluetooth Uart - LLT POWER ELECTRONIC

Features and Characteristics : Characteristics : this is a smart BMS with Bluetooth and PC communication which will be used to protect and monitor your battery status visible from the computer and your android APP phone .which can support UART or UART and RS485 communication .the charge and...

www.lithiumbatterypcb.com

View attachment 242320

I just drew out this 4s5p that I was considering before reading your post. It is a low budget build with only two BMS. Each BMS controls a 600a contactor. 20 cells per 500 ah bank. Either bank should be able to carry the big load, especially considering I try to never operate my windlass unless the engine is running (200a alternator).

 

[boatsparky]

My marine application is relatively gentle (heavy sailboat), yet has a "mission critical" aspect of it. *The batteries power navigation and autopilot. I think the go-fast type powerboats would need some cushioning?

That said I definitely will be bolting the enclosure down solidly. Not fun to have a live 1000amp arc welder flying around inside a boat or van

 

[yabert]

Either bank should be able to carry the big load, especially considering I try to never operate my windlass unless the engine is running (200a alternator).

Each of those 500Ah battery will supply 1000A and over without problem.
Those GBS 100Ah cells was rated 3C continuous discharge and 10C peak.
So, in your case, 1500A continuous and 5000A peak... clearly, the weakest link is now the windlass brushes

 

[HarryN]

I'm always surprised to see this.
It's not like if a Cybertruck or Rivian pickup or a F150 Lightning battery doing off road had an easy life.

Do you suggest that a boat battery should always be on rubber mount?

I always mount batteries in any mobile application so there is at least 1/8 inch of EPDM under them. Ideally more.

If nothing else, it helps to protect the case from rubbing against a hard surface, and dampens the more extreme spikes.

 

[boatsparky]

I always mount batteries in any mobile application so there is at least 1/8 inch of EPDM under them. Ideally more.

If nothing else, it helps to protect the case from rubbing against a hard surface, and dampens the more extreme spikes.

That sounds like good design. I am including provision in my battery box to have 3/8 (10mm) closed cell foam all around. Also working on the top security method, keep the batteries from falling out if capsized.

On my old lead acid batteries I used stainless all-thread holding UHMW a plastic plate, backed by aluminum angle to make it rigid. I would think EV should also have this to allow for a roll-over incident.

 

[dmeter]

The difficulty is that I have a very high amperage draw windlass (160 amps continuous, short duration peak over 1000 amps)
I think the only option is a BMS that can drive an external contactor to take that load.
Does anyone have a recommendation on BMS? I prefer one that has alarm output as well.
Thanks

windlass (160 amps continuous, short duration peak over 1000 amps)
who tell you this data,do you know how any dc brushed motor work.
what you have 2000W(max factory tested before engine burn isolation or something) hi theoretical rare work close 1600W 120-150A
120A on source 130 to 200A on motor on windlasse by dropping in voltage in motor widings This is heat of motor if you ever touch dc motor of marine windlasse. this is best scenario usually is worst because testing is in lab condition. if you pull 1000A in battery this be in windlass motor 2500A and motor be melted. windlasses use between 35-200 amps or little more under load,you know when is wind and you want windlass pull your boat,windlass produce heavy sound. in real world do you think your producer of motor in your windlasse don't know this

your engine starter have by law resistor in series or NTC ord PTC Themistors. ask this exact data also for windlass.


for example see my bowthruster motor data on boat check 7000W power 24v system pull max 540A but your math say 24 x 540A = 12960 where is inrush 10 why he say 7000W

Specifications​

Thrust (kgf)	160
Power (kW)	7
Internal tunnel diameter (mm)	250
Weight (kg)	38
Voltage (V)	24
Current consumption (A)	540
Continuous operating time (min)	4,5
Ignition protected	No
Proportional	No
Retractable	No
Extended runtime	No