cupoftea
Advanced Member level 6
Hi,
Just investigating bringing a product from a friend in India. It is a 30W audio product, with a 30W offline flyback at the front end. It has no input fuse, but instead a “PCB fuse track” of length 5mm, width 0.2mm, 2oz copper, and a 1mm round SMD pad (wetted with solder) at each end , to prevent any arc from continuing up the tracking, further than the fuse. The fuse trace is covered in solder resist. In a progressively increased inrush test, it was shown to blow out before a 10A “Official” fuse in series with it…so it must be lower rated than 10A. The PCB fuse track blew out without fire, smoke , shrapnel, or persistent arcing. The product is pretty well enclosed totally in an earthed metal enclosure, so there is no way for shrapnel to blow out.
What are the regulatory bodies (EN) like with this sort of thing? There is the option to have an external fuse (customer replaceable) with it. That fuse could be low rated say 1A, since customer could replace it.
The problem with customer replaceable fuses, is that the customer can put a much higher current rated fuse into it….but for this case, at least we have the PCB track fuse to act as a second safety net.
There is a 50R NTC at the front end , and a 47uF, 400V capacitor just after the diode bridge. As you know, if there is much occurrence of “hot NTC inrush”, then a normal fuse would eventually nuisance trip due to frequently occurring “hot inrush” events. Also, mains transients will , if often enough, eventually result in an “official” fuse blowing out. This is why the PCB track fuse has a use. It stops the scrapping of good product which has simply suffered a nuisance tripped fuse.
As you know, a PCB fuse track is more resilient to repeated overcurrent surges, since it is contiguous with the rest of the copper tracking. Whereas an “official” fuse has terminals, which feature bond wires to the fuse element. Repeated overcurrent surges can eventually break the bond wires. This is why PCB track fuses have their place.
Just investigating bringing a product from a friend in India. It is a 30W audio product, with a 30W offline flyback at the front end. It has no input fuse, but instead a “PCB fuse track” of length 5mm, width 0.2mm, 2oz copper, and a 1mm round SMD pad (wetted with solder) at each end , to prevent any arc from continuing up the tracking, further than the fuse. The fuse trace is covered in solder resist. In a progressively increased inrush test, it was shown to blow out before a 10A “Official” fuse in series with it…so it must be lower rated than 10A. The PCB fuse track blew out without fire, smoke , shrapnel, or persistent arcing. The product is pretty well enclosed totally in an earthed metal enclosure, so there is no way for shrapnel to blow out.
What are the regulatory bodies (EN) like with this sort of thing? There is the option to have an external fuse (customer replaceable) with it. That fuse could be low rated say 1A, since customer could replace it.
The problem with customer replaceable fuses, is that the customer can put a much higher current rated fuse into it….but for this case, at least we have the PCB track fuse to act as a second safety net.
There is a 50R NTC at the front end , and a 47uF, 400V capacitor just after the diode bridge. As you know, if there is much occurrence of “hot NTC inrush”, then a normal fuse would eventually nuisance trip due to frequently occurring “hot inrush” events. Also, mains transients will , if often enough, eventually result in an “official” fuse blowing out. This is why the PCB track fuse has a use. It stops the scrapping of good product which has simply suffered a nuisance tripped fuse.
As you know, a PCB fuse track is more resilient to repeated overcurrent surges, since it is contiguous with the rest of the copper tracking. Whereas an “official” fuse has terminals, which feature bond wires to the fuse element. Repeated overcurrent surges can eventually break the bond wires. This is why PCB track fuses have their place.
