Glass fuse source

[pishta]

Looking for a 635ma 250V glass fuse i think its a 5×20mm, a little smaller than a car type glass fuse. Any USA sources? Amazon and eBay don't seem to show this size. Out of a Realistic (Hitachi) SCT30 deck.

 

[egellings]

Any of the large electronic suppliers in the US should be able to supply those. As examples, Digi-Key, Mouser.

 

[whoaru99]

Looks like 635mA may not be too common a value much of anywhere.

May want to consider 630mA, I would. Find that size even on Amazon if you want, but I'd still consider Digi-Key, Mouser, et al.

 

[alschmucker]

That's a weird one there are 500mA or 1/2 amp on ebay and amazon. Do not know the size you need may have to get as close as you can. If you go with a 1 amp make it fast blow. 635 Ma is a little over 1/2 amp.

 

[Schurkey]

Looking for a 635ma 250V glass fuse i think its a 5×20mm,

There's usually more to it than just the physical size.

For 5mm X 20 mm fuses made by Bussman:
(COMPARE to what came out of the component!)

GDA IEC 5 X 20mm Fuses

High-break, fast-acting ceramic tube fuses. Ratings from 50mA to 6.3 amps.

GDB IEC 5 X 20mm Fuses

Fast-acting glass tube fuses. Ratings from 32mA to 16 amps.

GDC IEC 5 X 20mm Fuses

Time-delay, low-breaking capacity glass tube fuses. Ratings 32mA to 6.3 amps.

S506-R is the RoHS complinat version of the GDC fuse.

GDC IEC 5 X 20mm Fuses

Time-delay, low-breaking capacity glass tube fuses. Ratings 32mA to 6.3 amps.

S506-R is the RoHS compliant version of the GDC fuse.

GMC UL 5 X 20mm Fuses

Medium time-delay glass tube fuses. Ratings from 63mA to 10 amps.

GMD UL 5 X 20mm Fuses

Medium time-delay fuses. Ratings from 125mA to 4 amps.

^^^All the above info was mined from the Bussman web-page about a decade ago.

 

[ubergeeknz]

630mA is the nearest common value.

Given the general imprecision of fuses in general, a 630mA fuse ought to be just fine.

To be honest, 600mA or even 500mA should be fine if that's what you have on hand/can find.

The other main parameter is fast or slow blow. Fast fuses are usually marked F and slow blow T or S, but with a glass fuse you can tell by looking at the filament inside - a single straight thin filament is usually fast and a coiled up "thick" looking filament slow.

 

[egellings]

I'm surprised that a fuse would have its current rating shown to 3 digits like that.

 

[pishta]

I found them locally for .90 a pop in 630ma. It was a single filament fast blow although fast...? It glowed to yellow then burned in about 1 second on a dead short. I put the circuit in service through a DMM across the open fuse holder and I was drawing a whopping 180ma.

 

[ubergeeknz]

Fuse speed is relative to the amount of overcurrent, and, as I alluded to before, one fuse may not behave like another even in the same batch. They're really more fire prevention devices than anything, often what happens in practice is that the components being overloaded will blow first, you know, in order to protect the fuse...

 

[gadget73]

180ma won't pop a 630ma fuse, certainly shouldn't make it glow like that. 1800ma is a different story.

usually where you need a slow blow / time delay fuse is working into something that has a lot of inrush load. Big transformers are a good example of this, the inrush current is extremely high but only for a split second.

 

[Schurkey]

It glowed to yellow then burned in about 1 second on a dead short. I put the circuit in service through a DMM across the open fuse holder and I was drawing a whopping 180ma.

180ma won't pop a 630ma fuse, certainly shouldn't make it glow like that.

The device drew 180ma. The fuse popped when he ran it into a dead short--which would be far in excess of 630ma, assuming the power supply could keep up.




I don't understand why the fuse took that long to blow, when driven into a dead short.

 

[gadget73]

thats why I was confused, if a DMM showed 180ma, its not a dead short and the fuse should not have blown. Unless he purposely shorted it to see if the fuse would open?

direct short should have blown the fuse almost instantly.

 

[whoaru99]

Even considering a dead short, as pointed out in post 9, the speed at which the fuse opens depends on the type of fuse and the available current.

If the power supply could supply lots of current/amps, you'd expect a 630mA fast blow fuse to blow almost instantly. But, if the power supply could source only an amp or two, it's quite plausible there could be a visible delay as the fuse element heats and finally burns.

 

[WaynerN]

good luck

 

[gadget73]

true, on the secondary side current is limited by the transformer and such. On the primary side you get the full whack of whats coming out of the wall.