Fuse wire size to blow at 2 Amps? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 04, 2013, 09:37:23 am
content: Here in the UK 5 Amp fuse wire is commonly available, but I need to create a 3 inch long high voltage fuse that will open at circa two Amps. How do I work out the wire material and diameter please? A glass bodied fuse is no good as it would either explode messily, or plasma would maintain conduction as it's too short. Voltage is 5kV.

author: Rerouter
author_rank: Super Contributor
timestamp: December 04, 2013, 09:47:27 am
content: For 5KV you really want a spring fuse, you get a spring good for 3-4x the fail current, and tack the correct value fuse wire about 1cm long to the end, then tension it and away you go, ensuring your spring is tensioned over a bigger distance than an arc could be sustained at.when the wire fails, the spring quickly extinguishes the arc as a hobbyist HV fuse, the spring side should be on the cold side, and the fusable link on the hot side, probably in a clear perspex tube or similar so its obvious once its popped.

author: Psi
author_rank: Super Contributor
timestamp: December 04, 2013, 09:49:51 am
content: Since you want to build this rather than buy something im going to assume this is a DIY home project of some sort.You could probably build a working solution with a mousetrap and some typical fuse-wire.The fuse-wire melting fires the trap which breaks the connection and moves the contacts far enough apart to break any arc.

author: Rerouter
author_rank: Super Contributor
timestamp: December 04, 2013, 09:53:04 am
content: psi i have to say that fuse firing on a slow shutter speed would make a nice lightning rainbow shape

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 04, 2013, 09:55:54 am
content: The way I am doing it is similar, albeit the 5 amp wire I am using is too heavy. I have a ceramic tube with a long, soft tension spring inside. External to the tube is the 3 inch fuse wire, anchored to a ceramic pillar. When the wire parts the spring retracts into the tube, making an even longer path than the 3 inch gap. Thanks for the lateral thinking

author: owl_uk
author_rank: Contributor
timestamp: December 04, 2013, 11:02:27 am
content: The way fuse wire is specified is quite complicated. E.g. 5AMP fuse wire does not melt instantly when 5.001 amps passes through it. Usually a time until it blows is given for various currents, e.g. a UK 3 amp plug fuse:0.02–80 s at 9 A, < 0.1 s at 20 A and < 0.03 s at 30 A.So you can potentially use 3 times the rated current for over a minute. There's a bit more on the UK rules here:http://en.wikipedia.org/wiki/BS_1363I expect there are similar international standards

author: ConKbot
author_rank: Super Contributor
timestamp: December 04, 2013, 05:33:59 pm
content: http://www.powerstream.com/wire-fusing-currents.htmas a starting point. As they say, insulation and other stuff can change the fusing current, so I'd conduct some empirical testing. Maybe a fiberglass fill in a tube with the aforementioned spring-loaded fuse setup with some 30 awg wire wrapping wire could get the fusing current low enough to trip at a reasonable current?Also, where is this 10Kw coming from? pole pig?

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 04, 2013, 05:37:34 pm
content: Big single phase 5kV transformer drawing about 1.2 Amps, for an RF welder. Was three phase, now single phase with home brew HV supply. Will check out the link, thanks.