650A cell busbars?

[jakobmagnusson]

Hi,
I'm building a LiFePO4 battery bank using EVE LF304 in a 2P4S configuration in my boat which should handle normal day to day consumption but also my large bowthruster which takes 650 A 5-120 seconds. The batteries can handle that peak discharge but the busbars are only rated at 325 A (made from "Nikkel welding strip" with 2x20 mm area). See picture (yeloow busbars are between paralell cells, should be ok with standard 325 A busbars(?), the green ones are in the series which needs to take full discharge 650 A.

Do you have knowledge or experience of such system? A few questions I have:

Is it possible to use double busbars? If not, why not?

Does all busbar (serial and paralell) need to be identical in a system like this?

Where can I buy busbars on internet which have a 650 A rating?

Or how do I make my own? What material? Dimensioning?

Appreciate your input if you have the knowledge and/or experience.

Thanks,
Jakob Magnusson
Stockholm,
Sweden

 

[chrisski]

I follow this chart for bus bar ampacity

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

Is it possible to use double busbars? If not, why not?

Yes, but getting thicker busbars to secure to terminals is difficult especially if studs come installed batteries. The studs installed in a-battery limit busbar thickness to less than the stud. You will still have two sets of busbars on nearly all studs.

Does all busbar (serial and paralell) need to be identical in a system like this?

Each cell needs bus bars just as thick. Busbar length does not need to be the same. IME, the 2P4S battery you picture the
-horizontal busbars connecting cells are the same length
-the vertical us are connecting the cells is longer
-the main + and main - connecting the battery to the main bus bar is longest.

Where can I buy busbars on internet which have a 650 A rating?

Good luck. Will probably need to be custom cut, or multiple stacked.

Or how do I make my own? What material? Dimensioning?

not easy to build, but what you’re asking for may not be available. I buy copper 110 flat and cut to size and drill. If you have access to metal working tools like a drill press it’s much easier and accurate. I don’t.

Copper is a bit expensive to learn how to cut, probably $5 per inch, so getting it right the first time is important.

Double check the charts. 1/4” busbar x 2 1/2” handles the amperage you’re asking for. That wide busbar must be checked prior to ensure it won’t touch other busbars. This has been an issue with wider busbars on smaller sized 25ah cells I worked with.
======
I’ve got issues with using a battery with that much discharge, mostly having a BMS to handle that current. Most BMSs will cut out at that current. I’d want that much current spread amongst 4 batteries; no more than 200 amps per battery.

 

[MrSparkle]

The value 650A of the bow thruster. Is that the nominal value or the very max surge value? (Electric motors surges several times their nominal.)

What BMS are you using for your battery bank?

 

[Drunkin Solar]

Might be best for your very high amperage requirements to go with multiple separate packs each with their own BMS and parallel each of those packs onto a 1000 amp bus bar. Your proposed cell arrangement will not be capable of your draw even thought you "could" maybe push those cells that hard. I'd recommend you get at least double the amount of cells and make four separate packs.
That should put you into a more realistic scenario.

Edit: It boggles my mind that such a important function on a boat requires that kind of current to run... but I'm way out of my league on that.
With that said and further thought I feel my proposed solution above is still underwhelming for your requirements even with each pack having a 300 amp BMS. Much more thought is needed to make this work reliably.

 

[jakobmagnusson]

Thanks for great feedback!

I follow this chart for bus bar ampacity

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

Is it continous or bursts?

Yes, but getting thicker busbars to secure to terminals is difficult especially if studs come installed batteries. The studs installed in a-battery limit busbar thickness to less than the stud. You will still have two sets of busbars on nearly all studs.

Forgot to mention that these batteries have two threade holes instead of a stud. So I assume it's just to have longer bolts then.

Each cell needs bus bars just as thick. Busbar length does not need to be the same. IME, the 2P4S battery you picture the
-horizontal busbars connecting cells are the same length
-the vertical us are connecting the cells is longer
-the main + and main - connecting the battery to the main bus bar is longest.

Why does they need to have the same thicknes (and area I assume)? The length also impacts resistance.

Good luck. Will probably need to be custom cut, or multiple stacked.

not easy to build, but what you’re asking for may not be available. I buy copper 110 flat and cut to size and drill. If you have access to metal working tools like a drill press it’s much easier and accurate. I don’t.

Copper is a bit expensive to learn how to cut, probably $5 per inch, so getting it right the first time is important.

Double check the charts. 1/4” busbar x 2 1/2” handles the amperage you’re asking for. That wide busbar must be checked prior to ensure it won’t touch other busbars. This has been an issue with wider busbars on smaller sized 25ah cells I worked with.

Again, is this for continous or bursts (max 120 seconds, but probbaly never longer than 30 s)

======
I’ve got issues with using a battery with that much discharge, mostly having a BMS to handle that current. Most BMSs will cut out at that current. I’d want that much current spread amongst 4 batteries; no more than 200 amps per battery.

The thruster will be connected directly to the battery with abreaker and fuse. The thruster control electronics is managed by the BMS which indirectly controls the thruster motor.

 

[jakobmagnusson]

Might be best for your very high amperage requirements to go with multiple separate packs each with their own BMS and parallel each of those packs onto a 1000 amp bus bar. Your proposed cell arrangement will not be capable of your draw even thought you "could" maybe push those cells that hard. I'd recommend you get at least double the amount of cells and make four separate packs.
That should put you into a more realistic scenario.

Edit: It boggles my mind that such a important function on a boat requires that kind of current to run... but I'm way out of my league on that.
With that said and further thought I feel my proposed solution above is still underwhelming for your requirements even with each pack having a 300 amp BMS. Much more thought is needed to make this work reliably.

Thanks! You have point that this is on the limit.. I have a fallback scenario to run the thruster on a separate AGM-lead battery, which is charged by a DCDC charger from the LFP bank...

 

[jakobmagnusson]

The value 650A of the bow thruster. Is that the nominal value or the very max surge value? (Electric motors surges several times their nominal.)

What BMS are you using for your battery bank?

It's the nominal value. It is using a 500A MEGA fuse today.

I will use a HLPata BMS4S: https://www.hlpdata.se/index.php/en/

The thruster is connected directly to the battery (with fuse and switch), only the thruster controller electronics is controlled by BMS, so if the system is shut down the thruster motor is not possible to use.

 

[mikewalls]

I live on a Mainship 34 Trawler that has a bow and stern thruster. I am in US so I try to follow ABYC. (American boating and yachting council) when building my system. They prefer Class T fuses for Large LI-ion or AGM banks. This article has lots of details when it comes to fusing your batteries for high current situations. https://marinehowto.com/battery-banks-over-current-protection/ A Bow thruster typically have a starting surge then level off but pull more continue current. Looks like a 300 amp class T would get you 1125 amps to start the thruster and then 600 amps to run for 30-40 seconds before it would blow. FYI i have Daly truck starting BMS on order to do some testing with my thrusters. Supposed to handle 2000 amp surge.

 

[mikewalls]

I bought these on Amazon for parts of my battery build. Not sure what the amp hour rating would be but they also have thicker ones.