Wire gauge for JBD 150a bms

smoothJoey

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It was a pleasure to help you.
Would be glad to answer any followups you might have.
 

Dzl

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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 to the best of my understanding. 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).
 
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Dtfeld

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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).

I've considered both along with the "bendability", abrasion resistance of the insulation, and ultimately the availability of the wire. I am looking for #2 AWG silicone wire and will double or triple that up is I can find some. For now, a 3x #6AWG silicone is what is readily available. Fine stranded battery cable is also available, but not a "bendable".

For the internals of the battery with very short lengths, probably about 12-15" total, the voltage drop is pretty manageable with the 3x#6 (about .6%). Moving to 2x #2 AWG or 3x #2AWG cuts that down to a pretty negligible amount considering the over all system.

The Ampacity for a given heat rise is critical and is the most critical factor, and I think the 3x#6 will handle the max 200A load, and I will be running the system well under that.

Regardless, a little testing will be in order.
 
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shadowsteve

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I configured my pack cells as 2x2 (4s 150A) and used #2 for the cell interconnects as pos lead to the binding post. The neg leads are 2x #4 from the cells to BMS and then to the binding post. I have two spots where the #2 is a pretty tight bend (off the pos end and middle cell connection) but I'm fine with it. I used welding cable as anything fancy is hard to get in my locale. It's up and running but not heavily used, that'll come this winter (RV install)
 

Dtfeld

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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.
 

Just John

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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+
The longer board is usually the 150 amp 8s version, the other is the 150 amp 4s version.
 

Just John

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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.
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.
 

curiouscarbon

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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.

1636303978632.jpeg

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.
 

Just John

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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.
I haven't tried this, but they do claim to have larger gauge.

 

Dtfeld

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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.
That is the exact supplier I bought the 6 AWG from. Here is some #2.

—> https://www.ebay.com/itm/183777607534?hash=item2ac9ffbf6e:g:XdMAAOSw5kJctZ-z
 

Dtfeld

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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.
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.
 

curiouscarbon

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I thought about this, but I couldnt guaranteed a good crimp, as the wire “gauge“ vs the lug size was just too varied.
indeed

got some of the 6awg silicone type and will continue with that for now

thanks for linking the #2 wire

cheers
 

curiouscarbon

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random note about 4x 8awg test.

ensured all the copper conductors were able to reach to the end of the interior of the lug.

crimped it probably too much.

1636930076596.jpeg
1636930087032.jpeg
1636930097630.jpeg

will update if/when get to the 6awg silicone stuff.

used this device to crimp:
“TEMCo TH0020 Lug Crimper Tool for 10 AWG - 400 MCM”
1636930474200.jpeg
 

smoothJoey

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Thinking outside the box.
Why not just bend and drill a copper busbar to join the mechanical lugs to a single cable.
 

EcoRV

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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!).
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.

For test #2 i used a second run of #4ga on both sides of the BMS and then a single #1 Utraflex welding cable from the main positive to the Basen case terminal. (the reason for the different wires was purely due to space logistics in the tight Basen 280ah case). On the second 140a test none of the wires got above ~85 degrees F while the internal on BMS temp got to 122 degrees F.

The reason i am sharing this is that I could never find any actual testing data of #4ga cell interconnects so like other i used #1ga, so my testing revealed there is no need for the #1ga cell interconnects.

For those worried about the internal BMS temps in my setup. The max i can pull with my inverter is ~ 300a with an average sustained high of 150a which would be spread across 5 LF280K's so i am looking at ~ 30-60a max draw from each 280.

I hope this helps others in the future.
E00703F5-21F6-4158-8FB1-F941A178FD46.jpeg
 
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squowse

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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
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.
 
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Dzl

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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.
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.
 

w28

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I got a JBD 150A BMS from Current Connected here. I wanted the 150A BMS so I could potentially pull up to 150 A to power a 1500 watt inverter (at 12v)…( at least I think 150A should be adequate for that.)

I also purchased “Y” cables from Current Connected (sold as an accessory) to hook up the BMS to my batteries and to my load. The Y cables are 6 AWG.

However, I’m confused as to whether the two 6 AWG cables are big enough to safely carry 150A? This Blue Sea chart makes it look like 3 AWG (or 2 x 6 AWG) would be safe for 180A (so fine for 150A). But this thread makes it seem like 2x6AWG are just barely adequate, so I should increase the wire size to 2x4AWG. And this other Blue Sea chart seems to recommend at least 1 AWG for 150A?

Basically if I want to use this BMS to safely provide power up to the capacity of the BMS do I need to use 2x4AWG cables in parallel instead of the 2x6 AWG cables?

Also, do I understand correctly that to find the correct fuse size to protect the wires, I need to divide the max amp rating for the wire by 0.8? I thought you wanted your fuse to give up well before your wires… so you would want a fuse rated LESS than the rating of the wires. I was planning on using a dc circuit breaker (blue sea), but only seem to be able to find 150A or 200A, so it seems my options are limited there. I’m not opposed to using a fuse if that’s a better idea.

Thanks for any input or advice you can provide to this newbie!



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.

 
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