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Re: (ET) What size fuse
At 11:15 AM 1/2/06 -0500, Christopher Zach wrote:
Ok, here is a question for the list: What size and type of crash fuse
should one use for an Elec-trak?
I'm unfamiliar enough with the current draws to ask some basic questions to
I'm curious after blowing up that battery pack the other day. I think
300amp slow blows are not a good idea, and I have two battery strings.
Then again I use the tiller and the blower, and those can pull way over
150 amps for brief spikes.
Question: What are the current draws of all the devices? Accessories and
300A seems way too high. I see forklifts running with 150A fuses and they
can have peak draws of several hundreds of amps.
So what size fuse should I be using? And if I have two batteries should
I use a fuse at the end of the string, two fuses in the middle at half
rating, or three fuses; one in each string, and one on the end?
I'd favour a layered approach.
A - A fuse on each pack.
B - A fuse on the point where the packs combine feeding into the
main DC bus.
C - A fuse block distributing to the various power points, one for
drive, one for PTO (a separate one for each PTO if there is more than one),
one for lift, one for control circuits.
B could be eliminated w/o worry. It's main purpose in some respects is to
provide a simple way of disconnecting the DC Bus.
That structure provides protection to each of the main circuits and
protects the pack separately. If the packs are reasonably balanced in
their ability to source current then the A fuses can be ~1/2 the B fuse and
you get some additional overload protection in case one pack physically
disconnects for some reason.
Now start with a fuse that is rated for about 30% more than the expected DC
current level at each of those points. The final point to consider is the
pulse current (and frequency) from startup etc.. That may require raising
the current rating. My suspicion is that a 150A fuse might well be
sufficient but I'd need more info.
See the second littlefuse link I sent. It deals with the pulse issue.
I'd lean towards sizing the fuses so they had to be replaced every year or
two due to wearout rather than making them large enough to never need
" 'Freedom' has no meaning of itself. There are always restrictions, be
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