I think this is only a partial understanding of the situation. There are two factors to consider when sizing wire (1) Voltage Drop (that is mostly an efficiency and system design concern, is relative to distance, and is what your above example shows) (2) Ampacity, this is the safety issue, and this is independent of distance to the best of my understanding. This is what the NEC cares most about (there primary wiring charts dont actually consider voltage drop IIRC)The NEC current rating for conductors is extremely conservative, accounting for variables which don't exactly cross reference to use in battery based applications due to the short runs typically associated with them, but a useful guide none the less.
When used in conjunction with a voltage drop calculator it can be seen that over a short distance, voltage drop is extremely low, in the example below a #3 AWG with 200A at 12V over a 1 foot run is only 0.032V, so keeping runs short allows for smaller gauge. Being that current is inversely proportional to voltage, at higher nominal voltages, the voltage drop will be further reduced.
I think this is only a partial understanding of the situation. There are two factors to consider when sizing wire (1) Voltage Drop (that is mostly an efficiency and system design concern, is relative to distance, and is what your above example shows) (2) Ampacity, this is the safety issue, and this is independent of distance. This is what the NEC cares most about (there primary wiring charts dont actually consider voltage drop IIRC)
Its important to understand both factors, especially the second. And to understand that most "voltage drop calculators" only consider voltage drop and not ampacity. Calculators or charts that do consider ampacity will ask about the insulation rating of the wire (or state assumptions about it).
The longer board is usually the 150 amp 8s version, the other is the 150 amp 4s version.The longer board is the JBD 150A BMS. They have updated the versions over time, but the basic layout has remained. The smaller ones are 100A or 120A units unless something has changed. Perhaps the vendor did not have the correct picture associated with the 150A BMS.
I'm using three 10AWG wires each to B- and C- and a single 10AWG to B+
Do you have a link to that? Anything above 6 gauge is difficult to find, but I can recommend the Bntechgo 6 gauge tinned wire for the 150A JBD since you really need the flexibility for the two connections that are 180 degrees apart.I have found some #2 Silicone wire on the internet. Takes 2 months to get here. I’ll probably buy some as I think that would be the preferred setup, but for now I need something to start laying out the insides.
I haven't tried this, but they do claim to have larger gauge.silicone insulated wire above 6 gauge is hard for me to find too. any tips for sources welcome
can confirm that BNTECHGO silicone jacket tinned strands copper cables are pretty nice.
for now i am experimenting a bit with combining the silicone BNTECHGO wire with selterm tinned copper lugs. got a spool of the 8awg.
View attachment 71610
here’s four 8awg conductors crimped into 1 gauge 1/4 inch lugs.
what do y’all think?
ideally could find a source of thicker silicone jacketed cable but this is what i’ve got for now.
considering this to handle some areas in upcoming 300Ah cell build. terminal stress is something i want to minimize.
That is the exact supplier I bought the 6 AWG from. Here is some #2.Do you have a link to that? Anything above 6 gauge is difficult to find, but I can recommend the Bntechgo 6 gauge tinned wire for the 150A JBD since you really need the flexibility for the two connections that are 180 degrees apart.
Two of these fit very well in a 2 gauge Ancor lug, different brands of lugs will fit differently. The Ancor brand lugs have thicker walls and better tin plating in my experience.
I thought about this, but I couldnt guaranteed a good crimp, as the wire “gauge“ vs the lug size was just too varied. I’m building for a mobile (boat) application, so I don’t want to solder it either. I bought some 1/8” x 1” copper bar to bake a buss bar with 3-4 indiviually crimped #6 lugs bolted on, top/bottom. Also easily replaced with the #2 AWG wire when I receive.silicone insulated wire above 6 gauge is hard for me to find too. any tips for sources welcome
can confirm that BNTECHGO silicone jacket tinned strands copper cables are pretty nice.
for now i am experimenting a bit with combining the silicone BNTECHGO wire with selterm tinned copper lugs. got a spool of the 8awg.
View attachment 71610
here’s four 8awg conductors crimped into 1 gauge 1/4 inch lugs.
what do y’all think?
ideally could find a source of thicker silicone jacketed cable but this is what i’ve got for now.
considering this to handle some areas in upcoming 300Ah cell build. terminal stress is something i want to minimize.
indeedI thought about this, but I couldnt guaranteed a good crimp, as the wire “gauge“ vs the lug size was just too varied.
I’m doing the same. Starting with#6…indeed
got some of the 6awg silicone type and will continue with that for now
thanks for linking the #2 wire
cheers
interesting idea, thank you for mentioningThinking outside the box.
Why not just bend and drill a copper busbar to join the mechanical lugs to a single cable.
I have the exact same setup with welded studs (LF280K) and have tested with #1ga and #4ga welding cable. My testing was done at 140a in a closed Basen plastic case. The short #4ga cell interconnects got to mid 80 degree F temps but the longer single #4 run from both main negative > bms and neg BMS > basen case terminal were at ~ 107 degrees. Additionally the main positive was ~ 110 as it was about 4 inches longer.I am building 2 12v 280ah 4s batteries each with a jbd 150a bms that will be connected in parallel. Each bms has two screw terminals for the B- and two for the C- connections. I am not counting on using the full capacity of the bms but seems reasonable to design the wire for 150a since that's the advertised capacity of the bms. From pictures of other installs I've seen it seems its considered best to use both B- and C- terminals with the two wires then going to a single terminal ring connector for each. So my question is what gauge wire to use if there are two wires for the B- and two for the C- connections with given the the rated capacity of the bms is 150a? The maximum draw I expect from the two batteries in parallel would be 100-200 amps if I run the microwave or air conditioner in my rv (but not at the same time!).
the cable needs to be below the maximum amperage allowed for its situation. Current causes voltage drop causes heat. The ability of the cable to dissipate heat, and the allowable temperature determines it's maximum rated current.The NEC current rating for conductors is extremely conservative, accounting for variables which don't exactly cross reference to use in battery based applications due to the short runs typically associated with them, but a useful guide none the less.
When used in conjunction with a voltage drop calculator it can be seen that over a short distance, voltage drop is extremely low, in the example below a #3 AWG with 200A at 12V over a 1 foot run is only 0.032V, so keeping runs short allows for smaller gauge. Being that current is inversely proportional to voltage, at higher nominal voltages, the voltage drop will be further reduced.
As a general rule it best to use the highest gauge possible and keep the runs as short as possible particularly in low voltage applications.
View attachment 59468
This is a very nice succinct explanation of a sometimes complicated and often misunderstood area of system design/wire sizing! I admire those who can convey a concept succinctly and clearly.the cable needs to be below the maximum amperage allowed for its situation. Current causes voltage drop causes heat. The ability of the cable to dissipate heat, and the allowable temperature determines it's maximum rated current.
the total voltage drop only becomes the determining factor for longer runs than this.
150 amps / .8 fuse headroom = 187.5 fault amps
2x 6 awg is equivalent to 1x 3 awg.
3 awg pure copper with 105C insulation is rated for 180 fault amps.
With a 180 amp fuse you would be pushing it to the razor's edge.
2x 4 awg of the same specs would give some breathing room.