Properly Sizing DC Busbars?

[Jammer]

Originally Posted by er9

do we size it according to max amperage of all the charge sources feeding it or max draw amperage for all the devices that would draw from it? neither?

One way to do it is to calculate the maximum possible current for each busbar segment (between terminals) and then size the busbar based on the largest of the currents.


Busbars tend to overheat from continuous loads not intermittent ones and so I wouldn't necessarily size it for the full current draw of the bow thruster (for example) or the starting motor for the engine.

[chowdan]

This is exactly right. I sized mine based on maximum loads that will be running for 5minutrs or longer. I felt this time window(windlass specifically) would be long enough to add significant heat to the bus bars.

Originally Posted by Jammer

One way to do it is to calculate the maximum possible current for each busbar segment (between terminals) and then size the busbar based on the largest of the currents.


Busbars tend to overheat from continuous loads not intermittent ones and so I wouldn't necessarily size it for the full current draw of the bow thruster (for example) or the starting motor for the engine.

[er9]

Originally Posted by s/v Jedi

You only need to look at the connected battery banks. If you have one bank then the busbar must be at least rated for the value of it’s fuse. If you have multiple banks, sum their fuses.

You basically choose between 250A and 500+A. That’s where most busbars go from one size to the next. A 300/400A battery fuse puts you into the expensive category.

BTW, buy a bigger busbar rather than two. Each stud can have up to 4 terminals but see my recent thread about that as stud height limits that number when they are all bug sizes. I would limit it to 2 per stud for the big ones (3/0 and 4/0) then add at most one 2/0 or 1/0 plus a small one. This allows washer and nut to fit on there comfortably.

Got it thanks. definately looks like im buying 650's. Blue Sea has a 650 x 8 stud bars. should give me room for expansion.

[er9]

much thanks for all the input.

[Manateeman]

Good to see you are going with Blue Sea Systems. I recently bought three 500 amp BEP bars and wondered why they were so much thinner and lighter.
Both companies are sister corporations.
Blue Sea Systems measurers from end to end. BEP measures from the middle to the end. Copper costs money. I’ve built a lot of boats and the experts on electrical systems on the forum really impress me. Ask and you will get great advice. Good luck with your project. BEP has some advantages but overall...
I’ll stick with Blue Sea Systems.
Happy trails to you
Captain Mark and his “Tesla coil testing “ manatees.

[er9]

Originally Posted by Manateeman

Good to see you are going with Blue Sea Systems. I recently bought three 500 amp BEP bars and wondered why they were so much thinner and lighter.
Both companies are sister corporations.
Blue Sea Systems measurers from end to end. BEP measures from the middle to the end. Copper costs money. I’ve built a lot of boats and the experts on electrical systems on the forum really impress me. Ask and you will get great advice. Good luck with your project. BEP has some advantages but overall...
I’ll stick with Blue Sea Systems.
Happy trails to you
Captain Mark and his “Tesla coil testing “ manatees.

Huh thats interesting...thats what Mainesail appears to have on his website. i didn't recognize that they weren't Blue Sea. it wasnt a conscious decision on my part to go with Blue Sea. i didn't realize they were different.

i honestly dont understand how measuring from one location or another affects performance other than i would think it equates to a thicker piece of copper as you pointed out, meaning it can absorb more heat? something i need to look into. i want to be able to dump pretty much whatever i want onto my busbars and not have to worry about them.

wow! the blue sea 600 AMP power bus bar weighs almost three pounds. 600 amp continuous load indefinately.

[NPCampbell]

Originally Posted by er9

I just realized i dont actually know how to choose the proper Amperage busbar for my DC positive and negative loads.

i want to feed all my charge sources to a single positive busbar and have one, possibly two negative busbars to consolidate my grounds.

do we size it according to max amperage of all the charge sources feeding it or max draw amperage for all the devices that would draw from it? neither?

As the posters above have detailed, you base it off max draw. A 1000 amp charge source will feed 0 amps to the bus bar if there is nothing drawing from it.

Originally Posted by er9

any harm in grossly over-sizing a busbar since its essentially just a pass-through? i can see how under-sizing might be an issue but over-sizing?

Maybe. Larger bus bars can have larger terminals on them. If your devices have low current draw and smaller gauge wire, it gets tougher to find larger ring/spade lug terminals that crimp onto smaller gauge wire.