[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: (ET) Fuse fireball--warning

- The interrupt rating. This is the maximum current the fuse can safely disrupt. This is usually much higher than the rated current. If you exceed this you potentially run into arcing as you would exceeding the voltage rating.
*Nod* I think this is where I got nailed. Those auto fuses probably have a low AIR rating since cars have all that sheet metal to act as a current limit. Straight BB600's can source several thousand amps.
What's interesting is I *KNOW* this. My solar shed is powered by a bank of eight 12-370 AGM batteries in 4 banks of 24 volts. I knew that each of those batteries can source 2,000 amps, so the main fuse off the pack is a 125 volt rated, 80 amp, 10,000 AIR *DC* fuse. Expensive, but the only thing that will work with 4 gauge wires.
John mentioned time to blow rating for fuses. That can be an issue if you are close to the rating but I think you probably ran into the voltage rating given the description above.
Yes. That is why the forklift fuse (which is AIR rated to 5,000 amps and is DC rated) didn't blow in time. It's probably a slow blow.
So I'm placing an order for real fuses. Which brings up a question: What size fuse should I use? I'll ask that in another thread.
But I think the standard Elec-trak fuse (that link) is not going to work in a real disaster. Maybe if you use T105 batteries (which have a rather low short circuit current) but *NOT* if you use AGM or NiCD batteries. 

Beware.
Chris
Little fuse has a good discussion on this http://www.littelfuse.com/data/Product_Catalogs/AUTOFUSEOLOGY.pdf and especially http://www.littelfuse.com/data/Product_Selection_Guides/Fuseology.pdf
A rather more obscure but important note from the second reference is an X amp fuse has different requirements depending on the standard it is rated under. (see page 6) 

For instance take a 100A fuse
Under UL/CSA 284-14 it must not fail for at least 4 hours at 110A , take no more than 60 minutes (yes minutes) at 135A and no more than 2 minutes at 200A.
Under IEC type F, it must not fail for at least 60 minutes at 150A at must fail within 2 minutes at 210A. 

Note that not only are the standards different but they are mutually 
exclusive.
I would suggest sticking with tried and true EV fuses and stay away from automotive fuses for tractors. Somewhere I've got a link with some tests Littlefuse did on standard automotive blade fuses for 42V Vehicle testing. The difference between using standard blade fuses and properly rated fuses is rather dramatic. 

Robert
" 'Freedom' has no meaning of itself. There are always restrictions, be they legal, genetic, or physical. If you don't believe me, try to chew a radio signal. " -- Kelvin Throop, III 
http://www.aeolusdevelopment.com/


_______________________________________________
Elec-trak mailing list
Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak