ChrisOlson wrote: »
The only way I could see that anything could arc in there is if you put in too short of a fuse and the springs didn't hold enough tension to keep the brass button in contact with the end of the fuse.
mtdoc wrote: »
in my case it was 12 gauge wire on the fuse holder and a 30 amp fuse.
ChrisOlson wrote: »
30 amps is pushing AWG 12 pretty hard.
I'm guessing that at 30 amps the contact point between the brass button and fuse head got really hot and melted the holder, and it had nothing to do with what voltage it was running at.
mtdoc wrote: »
It's interesting that these J-Case Fuse holders I'm using now have 8 AWG wire but are rated for 60 amps at 58V - since 60 amps is really pushing it for 8AWG wire.
BB. wrote: »
40 amps through a 14 AWG wired holder is just going to generate a lot of heat--And to blow a 40 amp fuse is going to generate more heat than a 5 amp fuse.
ggunn wrote: »
True dat. Even with 90 degree insulation the non-derated ampacity of #14 Cu is only 25A and the most code compliant OCP you can put on a #14 copper conductor is 15A. (Article 240.4(E)(3)).
Thank you for your response. I hear that there is little concern about movement between cells so solid bar should not be an issue.
I am a little bit confused about your statement that the aluminum flat bar would be the better choice. Is this based only on the facts that it is harder, stronger, and cheaper than copper? Since copper has a lower resistance, if they were equal in price, or in my case I already have 1/8″ x 3/4″ copper, wouldn’t the copper be better? The strength and hardness do not seem like that are very important in this application. Perhaps I am missing something here.
My concern with using just the single 1/8″ x 3/4″ comes from the rated ampacity of such a bar. According to https://www.copper.org/applications/electrical/busbar/busbar_ampacities.html the cross sectional area is 119.4cm and a rated capacity of 215 amps. I have a 400Ah bank with the potential to pull up to >233 amps at any one time based on my 2800 watt inverter as well as the various DC house circuits, I would think that a higher ampacity should be called for.
I seriously doubt that I will ever even come close to that level of output but I would prefer to error on the side of caution when sizing wiring and busbars.
Copper is quite soft and 3mm if a fairly thin flat bar, which needs to be clamped down very well at each terminal with a stainless steel bolt and locking washer. You will no doubt use the copper because you already have it, but a 1/4”-thick aluminium flat bar is more robust. Copper makes a better conductor for the same cross-section, but doubling the cross-section and using aluminium is no issue here. A lot of power distribution cables are aluminium for the same reasons.
I have issues with your source above on the basis that the cross-sectional area of a 1/8” x 3/4” bar is 3mm x 19mm = 57mm2. “119.4cm” is a length and it is non-sensical in this context. Based on the resistivity R = 7μΩ/inch we calculated earlier, at I = 250A the busbars would dissipate P = R x I^2 = 0.44W/inch. If you were going to sustain this kind of current for long periods, a case could be made on the basis that you don’t want them to gradually warm up the cells over time, but it is not going to make any difference whatsoever if you occasionally peak at 250A for short periods. When it comes to a busbar actually “failing”, even a hit at a few thousands of amps wouldn’t be enough to achieve that and it would blow the protection fuse long before the bars would have a chance to heat up.
If you made your busbars out of aluminium, you would not be restricted to a narrow width of 3/4” only and they would in fact have a much bigger cross-section and be able to handle more current for less temperature rise.
If you stack your copper strips, you will need to sand them bright at the connection points and be very careful to achieve good conduction through the joint and it might still not last over time in a marine environment.I once saw a lithium bank that was exhibiting unmanageable cell balance problems just because one cell in one parallel block wasn’t contributing properly: excessive resistance in the connection, and yet it was bolted tight. It came right after sanding all the faces bright and reassembling and this is why I would choose a solid bar rather than trying to use small copper strips. 3/4” is barely wide enough to be attached with M8 bolts.