Question about battery bank bus bar sizing

[myersfamilyhome]

So I have my 32 304ah cells (2 banks of 16), the hardware they sent with the cells (nuts, studs, and bars@90*20*2mm), and I have my 2 Daly 48v/300a BMS. Are these bars enough to supply the 300a max draw on the cells without significant resistance? Does each bus bar going from cell to cell need to be able to carry the full 300a since they are in series?

If my calculations are correct using the below formula, and I'm looking to use common copper c110 flatbar, it seems the minimum size I need would be 3/16"*2" (this should give me just under 300a). Since both banks are being paralleled I rarely think my bank will be drawing 580a of draw).
4.7625mm*50.8mm=241.935mmsq*1.2=290.322a

It seems the bus bars sent are only rated for 48a

 

[FilterGuy]

I had not seen that formula before so I don't know its validity. I generally just use look up tables.

The chart I usually use for BB ampacity starts at 1/8" thick, but I found this table on BB ampacity. Unfortunately, they are in inches so I used 1/6" x 3/4" which is pretty close to 2mm x 20mm.



(They are using 1 for the skin effect so the numbers are the same for DC.)
30deg rise is more than I would want so let's call it 100A.

The busbars can be sized to the max load on the system. With two parallel banks, that is a total of 200A and at the lower end of the battery voltage that works out to 48 * 200 = 9600W at the higher end of the battery voltage that is 57.6 x 200 = 11,520W.

What is the max wattage you expect on your system?

Since both banks are being paralleled I rarely think my bank will be drawing 580a of draw

I am guessing that is an understatement. 580A X 48 = 27,840W... That is defiantly a 'plus sized' load!!!. Unless you have a crazy big system you would not draw anything close to that... Furthermore, if you are drawing that much then you probably need a bigger battery. That would drain them in 304Ahx2/580A=1.05hours. Also, that is nearly a 1C discharge rate. What are your cells rated for?

 

[myersfamilyhome]

I had not seen that formula before so I don't know its validity. I generally just use look up tables.

The chart I usually use for BB ampacity starts at 1/8" thick, but I found this table on BB ampacity. Unfortunately, they are in inches so I used 1/6" x 3/4" which is pretty close to 2mm x 20mm.

View attachment 74504

(They are using 1 for the skin effect so the numbers are the same for DC.)
30deg rise is more than I would want so let's call it 100A.

The busbars can be sized to the max load on the system. With two parallel banks, that is a total of 200A and at the lower end of the battery voltage that works out to 48 * 200 = 9600W at the higher end of the battery voltage that is 57.6 x 200 = 11,520W.

What is the max wattage you expect on your system?


I am guessing that is an understatement. 580A X 48 = 27,840W... That is defiantly a 'plus sized' load!!!. Unless you have a crazy big system you would not draw anything close to that... Furthermore, if you are drawing that much then you probably need a bigger battery. That would drain them in 304Ahx2/580A=1.05hours. Also, that is nearly a 1C discharge rate. What are your cells rated for?

I'm completely offgrid and building a farm. I'm just preparing for the worst case load at one time. When you look at loads of things like 2 AC's, deep freeze, refrigerator, clothes dryer, stove, microwave, deep well submersible pump, and hot water heater alone not including the smaller loads that run all the time, it adds up. Several of these are 240v. In a perfect storm there could be all of these that put load on the system at the same time.

As far as the formula goes I found it as an electrical standard used by many electricians.

My grade a cells are rated at 1C charge/discharge rating with a 2C discharge rating at a max of 30sec.

 

[myersfamilyhome]

If you lookup on Google "copper bus bar ampacity formula" it will show it as well.
It's different for other metals