Boater, aiming to build safe and stable 12V consumer Powerbank for boat.

[Jobba]

Hi all !

I am planning to build a 12V power bank for my boat, my initial plan is 8 x 3.2V 280AH Lifepo4 cells, that should give me 560 AH at 12V.
I wish to have high BMS capacity and a safe and stable setup.

* would like to have some input of which BMS to use ?
* would it be better to build 2 power bank with 4 cells in each rater to fit all 8 in one bank ?
* does the BMS need to have active cell balancing ?

Please come with recommendations and maybe links to suitable equipment

Regards:
Jobba

 

[chrisski]

What is the max watts? That would drive a BMS recommendation.

IMO two batteries set up 4S2P is better than One battery 2p4s. Two is better than one for redundancy if one goes down.

Balancing in a BMS is nice, but a BMS likely only turns it on at a voltage slightly under charging which means it’s batteries won’t balance all that much. I have a BMS with a balancer, but not a separate active balancer and after one year, my batteries are fine. Just top balance first.

 

[Jobba]

What is the max watts? That would drive a BMS recommendation.

IMO two batteries set up 4S2P is better than One battery 2p4s. Two is better than one for redundancy if one goes down.

Balancing in a BMS is nice, but a BMS likely only turns it on at a voltage slightly under charging which means it’s batteries won’t balance all that much. I have a BMS with a balancer, but not a separate active balancer and after one year, my batteries are fine. Just top balance first.

I have a 4000w 12v->230v inverter, so let us say with other stuff running of 12v plus the inverter, i might have 4500w draw maximum.
would a separate active balancer be an idea, does not seem to be expencive, and if this keeps the cells in a better condition/lifetime it seems like a good idea ?

 

[chrisski]

I have a 4000w 12v->230v inverter, so let us say with other stuff running of 12v plus the inverter, i might have 4500w draw maximum.
would a separate active balancer be an idea, does not seem to be expencive, and if this keeps the cells in a better condition/lifetime it seems like a good idea ?

IMO, I believe active balancers are good if the batteries will spend most of their time at a high state of charge. This will basically keep them top balanced.

If the batteries are not at a high state of charge, then it could misbalance them and once topped off they drift. I believe this is why BMSs tend not to turn on balancing until a set voltage, like 3.45 per cell and also limit balancing to only when charging.

Someone who uses active balancers will disagree with me.

4000 watt loads on a 12 volt system is well outside my league. My calculations had 4/0 for a 12 volt 2000 watt inverter running full out. I’ve since upgraded to 24 volts and 3000 watts and used the same 4/0 for that. For 4000 watt continuously I would use a 48 volt system.

 

[Jobba]

IMO, I believe active balancers are good if the batteries will spend most of their time at a high state of charge. This will basically keep them top balanced.

If the batteries are not at a high state of charge, then it could misbalance them and once topped off they drift. I believe this is why BMSs tend not to turn on balancing until a set voltage, like 3.45 per cell and also limit balancing to only when charging.

Someone who uses active balancers will disagree with me.

4000 watt loads on a 12 volt system is well outside my league. My calculations had 4/0 for a 12 volt 2000 watt inverter running full out. I’ve since upgraded to 24 volts and 3000 watts and used the same 4/0 for that. For 4000 watt continuously I would use a 48 volt system.

The maximum of 4500 watt is "worst case scenario" and will if so only be for a period of 30 sec (ex. Using coffee machine while cooking), but still i would like to dimension the system to have the possibility.

* As of now it seems like the best idea would be to build 2 12v battery's with 200A BMS, giving me a total of 400A maximum continuous draw.
* Would it be best to look for a BMS and Active Balancer separately or a BMS with integrated active balancing ?
* Any other stuff i would need or that would be beneficial to have ?

Regards:
Jobba

 

[chrisski]

This chart I think shows for 400 amps of current, 1/4” x 1” or 1.5” copper bus bar for 400+ amps

Electrical: Busbar - DC Copper Busbar Ampacities

The following tables have been provided by the Alliance for Telecommunications Industry Solutions (ATIS), T1 Committee, and represent ampacities for busbar sizes and arrangements typically found in the telecommunications industry.

www.copper.org

 

[mikefitz]

Use quality cells and you wont need an active balancer. There are in general not required and if faulty may destroy your battery. Consider two 4 cell batteries each with its own BMS , then connect in parallel. This gives redundancy and a high output current with lower stress on the BMS.
4000 watts of inverter at 12v needs serious cables and interconnection hardware. It is possible but every cable termination and connection needs to be of a high standard. It may be worth evaluating you actual 230v needs and considering a lower power inverter, or changing to a 24 volt system with a DC to DC converter for the 12v stuff.

For marine installs I specify Victron equipment, chargers, inverters, battery monitoring and display is easily integrated together as a complete system.

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.pdf

Mike

 

[Jobba]

Ok, so i have decided to build 2 12V packs with 4x280AH Lifepo4 cells, from what i have found out the JK-B2A8S20P seems to be a good BMS with active balancing.
So what i am planning to order is:
* 8 x LF280K Lifepo4 cells
* 2 x JK-B2A8S20P BMS with active balancing

Anything else i would need to build a safe package ?
Regards:
Jobba

 

[Jobba]

Use quality cells and you wont need an active balancer. There are in general not required and if faulty may destroy your battery. Consider two 4 cell batteries each with its own BMS , then connect in parallel. This gives redundancy and a high output current with lower stress on the BMS.
4000 watts of inverter at 12v needs serious cables and interconnection hardware. It is possible but every cable termination and connection needs to be of a high standard. It may be worth evaluating you actual 230v needs and considering a lower power inverter, or changing to a 24 volt system with a DC to DC converter for the 12v stuff.

For marine installs I specify Victron equipment, chargers, inverters, battery monitoring and display is easily integrated together as a complete system.

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.pdf

Mike

Most of the equiment in my boat is Victron, and i have decided to build 2 batteries with separate BMS, does i understand correct that you would recommend a BMS without active balancing ?

 

[Jobba]

Questions about assembly and layout:
* If i need to make cables with crimped/soldered terminals is it important that the cables is same length ?
* What would be sufficient cable AWG/mm2 ?
* Is there any display available that the battery`s can be connected to show battery/cell details ?
* It seems like the LF280K is one of the most popular cell to use, any reason for that other than the physical size of the cell ?


Regards:
Jobba

 

[740GLE]

Same length per battery is ideal but the system won’t fail if one is slightly longer than the next. You just don’t want one with 2x conductor length or something crazy.

I’d say 2/0 should be minimum with 4/0 ideal.

How are you planning on charging these cells? Are you heart set in 12v?

 

[Jobba]

Same length per battery is ideal but the system won’t fail if one is slightly longer than the next. You just don’t want one with 2x conductor length or something crazy.

I’d say 2/0 should be minimum with 4/0 ideal.

How are you planning on charging these cells? Are you heart set in 12v?

Good, so minor difference is not a problem.
When it comes to charging the batterys my plan was 12V, since the boat alternators is 12v i guess that that is the easiest ?

 

[Goboatingnow]

My own LFp boat project is to create 3x100Ah LFp batteries. These will not only replace the domestic but akso the LA starter battery.

The bms are my own design and thd system is designed to degrade to 2x or 1x LFp battery

The removal of any lead simplifies the charging regime considerably.

Each battery has a separate bms , and active capacitor balancer along with their own disconnects etc. the bms is designed to facilitate engine starting current as it adjusts its current limits on an ignition key signal.

 

[Jobba]

My own LFp boat project is to create 3x100Ah LFp batteries. These will not only replace the domestic but akso the LA starter battery.

The bms are my own design and thd system is designed to degrade to 2x or 1x LFp battery

The removal of any lead simplifies the charging regime considerably.

Each battery has a separate bms , and active capacitor balancer along with their own disconnects etc. the bms is designed to facilitate engine starting current as it adjusts its current limits on an ignition key signal.

The starter on my engine is 12V 3,6Kw, that requires 300A draw from the battery package for 10 seconds, would this high current draw damage/degrade the battery cell`s or BMS in any way ?, if not i could convert the entire 12V setup in the boat to Lifepo4 batterys, wich would simplify things a bit.

 

[12VoltInstalls]

Two is better than one for redundancy if one goes down.

That’s thinking like a boater!

 

[Jobba]

That’s thinking like a boater!

I will always have redundency, as i also have a 7.5Kw generator with separate start battery..

 

[12VoltInstalls]

Questions about assembly and layout:
* If i need to make cables with crimped/soldered terminals is it important that the cables is same length ?

Not so much of a concern with LiFePo
But do not solder them especially in a boat! Crimp and seal them properly.

* What would be sufficient cable AWG/mm2 ?

Chrisski has that mentioned above.
But personally I would not run a 4500W inverter. I would run a 2000W for general daily power and either cook with propane or use a separate dedicated inverter for the electric stove. But again- I would use a propane appliance. Plus with propane on board tankless hot water heater makes sense to me. 30# cylinder lasts forever

* Is there any display available that the battery`s can be connected to show battery/cell details ?

Many. Even little 100A shunt versions for $15 are out there.

* It seems like the LF280K is one of the most popular cell to use, any reason for that other than the physical size of the cell

That however is not in my wheelhouse to answer.

 

[12VoltInstalls]

I will always have redundency, as i also have a 7.5Kw generator with separate start battery..

It’s virtually no cost on the grand scale of things and little to no real estate difference to make two batteries. A bit for cables and what? $100 for BMS?

 

[Goboatingnow]

The starter on my engine is 12V 3,6Kw, that requires 300A draw from the battery package for 10 seconds, would this high current draw damage/degrade the battery cell`s or BMS in any way ?, if not i could convert the entire 12V setup in the boat to Lifepo4 batterys, wich would simplify things a bit.

No thete is no problem with LFp starting engines. The primary issue is most bms are not set up to support high current short time transfers it needs a specialised bms thst can manage the start current. The lithium is a. Ideal starter battery

 

[Jobba]

It’s virtually no cost on the grand scale of things and little to no real estate difference to make two batteries. A bit for cables and what? $100 for BMS?

Hi ! Thanks for replies.
As previously stated i have decided to build 2 batteries with separate 200A BMS, but if i also will be able to use the Lifepo4 battery bank`s to start engines from and use thrusters etc. i am considering to add a third battery into the build, that will if so give a total of 840 Ah with 600A available as max current draw for starting and use of thrusters etc.

Any concerns i need to take into considerations regarding this ?

Regards:
Jobba