(ET) Fuse fireball--warning

[Chris Zach <czach computer org>]

Well, that was interesting.

I've been using the Saft BB600's in 360 volt battery blocks to power my 
Elec-trak. I installed a set of 30 of them in the rear utility box as an 
extra power supply. As is custom I installed a 300 amp 48 volt fuse (DC 
rated) from a Cushman golf cart between the two strings of 15 batteries.

I recently bought some automotive master fuses, 100 and 120 amp rated. 
Mainly because I want a slightly lower fuse rating. These fuses are 
rated to clear 120 amps at 32 volts.

Hah.

While measuring the fit, I did something exceptionally stupid: I shorted 
the fuse across the front of the pack. Instant dead short.

The fuse exploded. What was left of it did *not* clear. Instead it 
became a plasma arc that was slowly consuming the fuse and the battery 
connector bar. I was suprised the aft fuse did not blow, then I kicked 
the fuse with my foot to put it out. On the second try it cleared.

Damage: One of my cells had the screw top and nickel plated bar melted. 
Several others had a bit of darkness. The 300 amp fuse in the back did 
not blow.

This bothers me. For one thing, the auto fuses are completely useless. 
Instead of clearing they arced and caused a plasma fire. For another a 
300 amp fuse seems to be too big for these batteries. And another: The 
interconnect melted. Not sure if that was because the fuse touched on 
that bolt and overheated the stainless bolt or what.

Anyone got any good main fuse recommendations? The old fashioned fusable 
link is probably suicide. Untill I work this out, I'm going to install 
200 amp sand packed fuses.

Oh and remember, all of this was one string at a mere 36 volts. Imagine 
what a 300 volt string would do...

Chris