Re: (ET) Fuse fireball--warning - Fuse time curves

[JBR <reinharj frontiernet net>]

Hi All,
When I was in the Air Force, they listed all kinds of specifications for 
repair parts that I had never paid attention to before:

In the case of fuses and circuit breakers, the interesting part was how 
long - 
usually in seconds, but often MORE -  it would take various amounts of 
current to trip a breaker or melt a fuse.

The numbers were interesting - longer than you might expect for either 
fast or 
slow blow fuses or breakers.

For instance, a fuse rated 10 amps might carry 20 amps for 60 seconds, 15 
amps 
for 5 minutes, 12 amps for 20 minutes, 11 amps for an hour, and 10 amps 
almost continuously.

I kinda made up the above numbers just to give an idea - I probably 
exaggerated - but I was QUITE surprised when I first read the rating 
curves.

So, I would suggest anyone designing (or even replacing) fuses or circuit 
breakers into high current battery powered systems would get and STUDY 
these 
time curves.

John
E20's, E-15, Comuta-Cars, B&D cordless mowers, etc

On Sunday 01 January 2006 05:06 pm, Chris Zach wrote:
> 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
>
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