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

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 start.

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 drive.

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 replacement.

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/