RE: "not all fuses react to inrush current the same way"

Posted by 1973shovel (A) on May 8, 2017 at 07:03:47

In Reply to: RE: Thanks for the feedback, Mike posted by Mike B. on May 7, 2017 at 10:58:40:

And that was the intent of my original post, to try and get a better understanding of "why".

I once posted an observation on the Asylum about the element of a 0.25A fast-blo glass fuse glowing bright orange when I first apply 24 VDC to one of my phono stages, which has a quiescent current draw of about 30mA. It does it every time I've switched the power on. The glow lasts for about a second and then looks normal, and yet the fuse has never opened (i.e. "blown").

According to Neolith in his reply to my post, ceramic fuses contain silica. Pure speculation on my part, but I wonder if that silica doesn't allow the resulting heat of a "glowing orange" fuse element to dissipate as quickly as an element in the open air of a glass fuse would, causing the fuse to blow. Still, you'd think that if that were the case, manufacturers like Buss, etc. would take that into account when assigning their fuses over-current protection ratings.

My Nelson Pass First Watt F1J (not a DIY amp) has thermistors in the power supply, and I've never had its fuse open, so your point regarding inrush current is well taken. The schematic calls for a "4A slow", and I got curious while typing this to see if the fuse was glass or ceramic. It turns out it's a 2.5A slow blow glass fuse, 1.5A under spec, and yet has never blown. I guess those thermistors do their job!

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - More on (or is that moron?) fuses - 1973shovel 06:03:00 05/04/17 (24)

That has been my experience - rickmcinnis@dogwoodfabrics.com 10:46:53 05/10/17 (7)

I hate to sound like the little kid in the back seat - 1973shovel 09:41:22 05/11/17 (6)

I would like to know, too - rickmcinnis@dogwoodfabrics.com 15:56:27 05/11/17 (5)

As we speculated further down - 1973shovel 22:40:52 05/11/17 (4)

Heat generated.... - Lew 10:03:32 05/13/17 (3)

But my question wasn't about boutique fuses, Lew - 1973shovel 10:34:18 05/13/17 (2)

If that's so, I agree... - Lew 15:57:29 05/13/17 (1)

No reason to be sorry, Lew - 1973shovel 16:20:42 05/13/17 (0)

RE: More on (or is that moron?) fuses - Lew 17:18:29 05/04/17 (9)

Since you use the ACME fuses.... - mitch2 05:05:38 05/06/17 (3)

I think I did buy some of those - Lew 12:20:16 05/08/17 (2)

RE: I think I did buy some of those - throwback 06:09:40 05/09/17 (1)

Hoping you would say that... - Lew 10:03:30 05/09/17 (0)

RE: More on (or is that moron?) fuses - Tweaker456 20:02:08 05/04/17 (4)

Haha. Yes, "sole" was at the soul of my message - Lew 08:38:46 05/05/17 (3)

RE: Haha. Yes, "sole" was at the soul of my message - Tweaker456 12:06:29 05/06/17 (2)

RE: Haha. Yes, "sole" was at the soul of my message - throwback 16:34:47 05/07/17 (1)

I need no assistance with that ritual - Lew 12:15:17 05/08/17 (0)

RE: More on (or is that moron?) fuses - Mike B. 14:12:33 05/04/17 (3)

Thanks for the feedback, Mike - 1973shovel 04:27:10 05/06/17 (2)

RE: Thanks for the feedback, Mike - Mike B. 10:58:40 05/07/17 (1)

RE: "not all fuses react to inrush current the same way" - 1973shovel 07:03:47 05/08/17 (0)

RE: More on (or is that moron?) fuses - mitch2 11:32:05 05/04/17 (0)

RE: More on (or is that moron?) fuses - neolith 09:20:23 05/04/17 (0)

Follow Ups

RE: "not all fuses react to inrush current the same way" - 1973shovel 07:03:47 05/08/17 (0)

RE: "not all fuses react to inrush current the same way"

Post a Message!