Fuses

[croberts]

Hello All

This is more of an FYI than anything else. Recently I referred a forum member to my topic https://www.eevblog.com/forum/projects/bidirectional-current-monitor-fits-anl-fuse-holder/. This is a design I'm testing for a current monitor that installs in an ANL fuse holder that uses an ATO Style fuse. I also use ATO fuses in the power distribution box for my solar powered lighting system. They responded with a warning about melting ATO fuses based on a youtube video they had seen. This of course concerned me so I wrote to Digikey and asked them to contact Littlefuse for a comment. Below is my inquiry to Digikey and comments from Littlefuse. Since fuses are a part of a lot of designs and the application of fuses apparently (according to Littlefuse) misunderstood by many designers I thought you might find this useful. All the best!

My inquiry to Digikey Technical Support
"I am using ATO Style automotive fuses in a 12VDC solar powered LED lighting system in my home. I have ordered 15A and 40A fuses from you made by Littlefuse. I participate in an electronics forum at eevblog.com and a member recently referred me to a youtube video warning that these fuses can get hot and melt without blowing if operated for a prolonged period of time near their rated current (no specific fuse manufacturer was mentioned). Naturally I am very concerned about this and wondered if you would contact Littlefuse and find out if this can happen with their ATO fuses and are they safe to use in my application."

Comment From Littlefuse Apps Engineer
"A note of my own, it is recommended that the fuse be operated at no more than 75% of the nominal current rating, this will assure the fuse will do its job and not melt or open prematurely.  Like the statement below from one of the engineers at Littelfuse that for the fuse to open properly the circuit must be able to withstand a 2X fault current.  Here is a link to some details around choosing a fuse you can share with the customer.  Heat also can affect the fuse as well."

www.digikey.com/Web%20Export/Supplier%20Content/Littelfuse_18/PDF/LF_IntroductiontoCircuitProtection.pdf

Comment from the Littlefuse Product Manager for this product line
"This is a point that many designers fail to understand. A fuse (anybody’s) is just a piece of wire that melts open when the current gets up to a certain threshold. If the current is slightly above or below that threshold, the wire will stay intact for a long time (hours) and often result in melting of surrounding components such as a plastic fuseholder or the fuse itself if it is a plastic design. The designer needs to anticipate the magnitude of the faults his circuit is liable to encounter and use careful judgment in selecting the fuse rating. Hopefully, the faults will be around 2X the fuse rating to allow the fuse to melt open in around 1 second."