12V bus bar question

[Mike Lewis]

Currently I have two 12V lithium batteries connected in parallel to form the 12V system in my trailer. These are the Battle Born batteries that can output 100 amps, 200 amps for a short period. The connections are made with a heavy-duty terminal stud on the negative side and a Blue Sea battery switch on the positive side.


I intend to revamp my 12V system so that I can add up to two more 12V lithium batteries over time. I intend to replace the terminal stud and switch with bus bars (the battery switch will be connected to the positive bus bar). What amperage rating would I need for these bus bars? I do not intend to use more than maybe 110 amps at any one time to run a microwave via the inverter.

[Brian B-P]

The Battle Born BMS will allow up to 200 amps, and even more for a fraction of a second. Unless you have a common fuse or fuses for each battery limiting current to a lower value, it appears that you need the bus bar to handle 200 amps multiplied by the number of batteries, to handle the current potentially resulting from a wire or equipment fault.

[Vermilye]

Originally Posted by Brian B-P

The Battle Born BMS will allow up to 200 amps, and even more for a fraction of a second. Unless you have a common fuse or fuses for each battery limiting current to a lower value, it appears that you need the bus bar to handle 200 amps multiplied by the number of batteries, to handle the current potentially resulting from a wire or equipment fault.

2X. While your maximum planned draw is only 125 amps, a fault could draw far more.

[Mike Lewis]

Blue Sea has (expensive) bus bars that will handle 600 amps continuous. If I use 100 A fuses at each battery positive terminal will this work?

[tdf-texas]

Originally Posted by Mike Lewis

Blue Sea has (expensive) bus bars that will handle 600 amps continuous. If I use 100 A fuses at each battery positive terminal will this work?

100 amp fuses might be a little small considering they should be sized for the battery fault current. Maybe one of these for each battery mounted as close to the battery terminals as possible.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Here's a thread showing how I mounted one on my batteries. A short section of copper buss bar makes it easy.
https://www.escapeforum.org/forums/f...les-19164.html

[Steve S.]

In my current camper, I used the blue sea bus bars with ~200A fuses for each battery. Using the bus bars, they can easily incorporate additional batteries if need be.

[Centex]

Originally Posted by tdf-texas

100 amp fuses might be a little small considering they should be sized for the battery fault current.

I thought that a fuse should be sized according to the ampacity of the wiring (or connected devices, if less than wire ampacity) it protects, which might in turn be sized according to the load the circuit is designed to carry (perhaps less than the battery fault current)

Correction of my misimpression (with explanation) would be appreciated!

[Vermilye]

Originally Posted by Centex

I thought that a fuse should be sized according to the ampacity of the wiring (or connected devices, if less than wire ampacity) it protects, which might in turn be sized according to the load the circuit is designed to carry (perhaps less than the battery fault current)

Correction of my misimpression (with explanation) would be appreciated!

In general, fuse size is determined by the wire size, but there are exceptions. Many device manufacturers specify fuse size & type. The installer is expected to choose wire size that is at least large enough for the specified fuse.

In the specific case, we are looking at 600 amp buss bars. If the maximum battery draw is less than that, I'd fuse for the battery draw, not the buss bars.

Again, in general, you fuse for the weakest link.

[Centex]

Originally Posted by Vermilye

In general, fuse size is determined by the wire size, but there are exceptions. Many device manufacturers specify fuse size & type. The installer is expected to choose wire size that is at least large enough for the specified fuse.

In the specific case, we are looking at 600 amp buss bars. If the maximum battery draw is less than that, I'd fuse for the battery draw, not the buss bars.

Again, in general, you fuse for the weakest link.

^Emphasis added by me, and with that 'fair enuf'. Perhaps the following exposition is what you intended to convey in your much more concise statement, Jon: "If the maximum battery draw is less than that, I'd fuse for the battery draw, not the buss bars", in which case I apologize for the waste of words....

Noting OP Mike's original question and anticipated demand of inverter support for a microwave, and even allowing for conversion (in)efficiencies and some 'inrush current' higher than the microwave's (15A? 20A?) assumed () nominal plug-in circuit requirements, I'm struggling to understand the need for a DC system (including the busbar) rated for 600 amps?

Isn't it reasonable, if not even prudent, to work from the loads back to the power source in designing an efficient system? In that approach the battery bank may well be sized in consideration of amp hours, not its potential amp output.

In such cases, wouldn't it be reasonable to size the wiring and appurtenances between the battery bank and the loads according to the load demand, and protect those wires and appurtenances accordingly?

I'm trying to not let the original question and most efficient solution be derailed by mention of an available 600 amp rated busbar, an appurtenance which may be convenient for several reasons (e.g. number of lugs) other than it's ultimate rated capacity.

It strikes me that neither the battery bank's potential amp output nor the busbar's rated capacity may be good reasons to 'drive' the overall solution for this "specific case". Might it be prudent to step-back, look at the overall system requirements rather than the maximum potential of any given component, and size wiring and protective devices accordingly?

[Greg A]

One resource Mike, is to sign up on the Battleborn website for a design consultation. I heard back in 12 hours and have a direct line into a fella who is helping me with all the Battleborn pieces and requirements of the new system I’m installing.
I bought the Gopower 2000w inverter, and every video and wire/fuse chart gave me different recommendations. Went to Gopower support and within minutes they recommended 2/0 cables and 300 amp class T fuse specifically for that inverter.

[Brian B-P]

It would certainly be possible to use a bus bar with substantially lower capacity than the total possible output of all connected batteries (as long as it is comfortably greater than the highest operating demand), but that assumes that current through it is limited by something. If you don't want to put a fuse between each battery and the bus bar, it seems to me that the overcurrent limitation is the sum of the battery BMS limits.

If this were a lead-acid system there would be no BMS and a terminal-mounted fuse on each battery would make sense - if those were only 100 A each then a 400 A (to allow for the eventual 4 batteries in parallel) bus capacity would seem appropriate.

How expensive could a good bus bar be compared to thousands of dollars of batteries?

Of course wiring and overcurrent protection downstream of the bus bar (such as Greg's 2/0 cable and 300 A fuse) would be determined by expected demand, not by total battery current capability.

[Mike Lewis]

Originally Posted by Greg A

One resource Mike, is to sign up on the Battleborn website for a design consultation. I heard back in 12 hours and have a direct line into a fella who is helping me with all the Battleborn pieces and requirements of the new system I’m installing.
I bought the Gopower 2000w inverter, and every video and wire/fuse chart gave me different recommendations. Went to Gopower support and within minutes they recommended 2/0 cables and 300 amp class T fuse specifically for that inverter.

Thanks for that info; I'll look into it. I decided to buy the 600A bus bars anyway as their physical size and form factor fit my plans. I'll figure out how to fuse the batteries later.

BTW- if anyone is interested in that model bus bar, Powerwerx is selling them for $70.99, well below the $100+ price I've seen from other sellers. It's Blue Sea 2104 PowerBar 600A BusBar.