robbob2112
Doing more research, mosty harmless
Once my new BMS gets here I will have fresh wire handy, but intended to re-use the existing wire and just cut it down -
The positive is 4 x 8awg and the negative is 3 x 6awg
Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long
very similar cross-sectional area, but the smaller wires with the higher resistance per foot would mean the positive terminal would get a tiny amount hotter than the negative... at least that is what I think initially....
And I am wrong - the negative post will generate more heat than the positive post - @WorldwideDave - this might be your problem in the Chins -- they use the 4 x 8awg reds to try and balance the 3 x 6awg negatives + BMS.... but no matter how you slice it - the negative post will get hotter than the positive unless they get the cable lengths/resistance inside the battery just right.
See the second picture - that is a screw impression where it was between the case lid and a B- screw on the BMS.
It doesn't take much imagination to believe in a RV that could rub through the silicone and be a dead short between the right most B- screw in the BMS picture and the positive output wire ... You still watching this thread @Will Prowse ?
From the IR calculation on the battery that means we really would have 8000amps through the 7.5" or red + 11" of black to the cell. One wire of red and 1 wires of black.
So,
B+ --- 7.5" 6 awg red --- 11" 8 awg black --- B-
Used the artificial idiot to calculate when the wire reaches 200c and when it vaporizes given it is in a confined space. Took into account the cross-sectional area of the wire, length of wire, resistance of wire, Ir of battery, voltage of battery, confined space starting at 25c
Short answer - 0.054 sec to reach 200c
Wire vaporizes in 3.87 sec -- and at this point the wire is 2562c -- gas generated from vaporization of the copper is 156L- so the top will pop off shooting metal and hot gasses everywhere.... then things will cool off depending on if it caused a fire and if it didn't cause a cell vent.
So, with a pinched wire in an RV setup where the battery is strapped down so it had downward force applied to the top cover if a wire happens to be on top of a screw like mine was..... at some point the battery will do a max dump of current... and I suspect it will cause a fire.
Worst case, the cells the wire is laying on have their thin cases melted and they short/vent -- this results in 560L of gas.... 112L of which is hydrogen - which means we have a boom factor...


The positive is 4 x 8awg and the negative is 3 x 6awg
Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long
And I am wrong - the negative post will generate more heat than the positive post - @WorldwideDave - this might be your problem in the Chins -- they use the 4 x 8awg reds to try and balance the 3 x 6awg negatives + BMS.... but no matter how you slice it - the negative post will get hotter than the positive unless they get the cable lengths/resistance inside the battery just right.
See the second picture - that is a screw impression where it was between the case lid and a B- screw on the BMS.
It doesn't take much imagination to believe in a RV that could rub through the silicone and be a dead short between the right most B- screw in the BMS picture and the positive output wire ... You still watching this thread @Will Prowse ?
From the IR calculation on the battery that means we really would have 8000amps through the 7.5" or red + 11" of black to the cell. One wire of red and 1 wires of black.
So,
B+ --- 7.5" 6 awg red --- 11" 8 awg black --- B-
Used the artificial idiot to calculate when the wire reaches 200c and when it vaporizes given it is in a confined space. Took into account the cross-sectional area of the wire, length of wire, resistance of wire, Ir of battery, voltage of battery, confined space starting at 25c
Short answer - 0.054 sec to reach 200c
Wire vaporizes in 3.87 sec -- and at this point the wire is 2562c -- gas generated from vaporization of the copper is 156L- so the top will pop off shooting metal and hot gasses everywhere.... then things will cool off depending on if it caused a fire and if it didn't cause a cell vent.
So, with a pinched wire in an RV setup where the battery is strapped down so it had downward force applied to the top cover if a wire happens to be on top of a screw like mine was..... at some point the battery will do a max dump of current... and I suspect it will cause a fire.
Worst case, the cells the wire is laying on have their thin cases melted and they short/vent -- this results in 560L of gas.... 112L of which is hydrogen - which means we have a boom factor...


Last edited: