I have a blown fuse here, 5mm x 20mm. It is marked 250v 315ma. On the inside, it has what looks like a metal film resistor connected in series with (what used to be) the element. Mouser has a fuse with the above specs available, but also with the choice of 'fast acting' and 'time delay'. Pictures in the datasheets are the same for both.
I assume that this is a time delay fuse, hence the resistor?
Thanks for any help. I want to make sure to replace it with the exact match.
-ph
normally, if you look at the board they're in, there is some indication of a "S" , like "SF1" if not,. then look at what remains of the fuse. if the wire is straight, it's a fast blow, if it's got bends in it. It most likely is a slow blow.
In any case, depending on what the device does. I would just put in a slow blow.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Thanks for the reply. In addition to the usual "Replace only with same type and rating" it does have a small marking of:
115V~S315mA 250V 230V~T160mA 250VWould I then assume that in North America (where I am) it would be a slow-blow? Looking at what's left of the fuse itself, the lead might actually be straight. Is a slow-blow the 'safe' bet in any case?
The circuit is a solid-state guitar amp. Most tube-fired guitar amps say "replace only with slo-blo(tm) fuse".
Thanks
-ph
The resistor dampens some of the the current inrush when the device is powered up. SS amps have a rather quick current inrush whereas a tube amp ramps off more slowly hence the need for the slow blow.
"phaeton"
** Correct.But there are lots of ways to skin cats and make slow acting fuses - the ones which incorporate a small resistor are precise, but only come in low amp values.
Other types have a coil spring that pulls a soldered link apart.
Some look just like a normal, straight wire fuse.
Most carry the letter " T " ( for the German word " trage " ) after the amp figure, which BTW is the never fail current.
...... Phil
"Meat Plow"
** Not of any consequence with a 315mA fuse.** Total drivel.
Both types have similar, transformer based PSUs and so have similar inrush surges.
For a given power rating, the tube amp will have a larger PSU and so a worse surge.
The main part of the surge lasts only one cycle of the AC supply frequency - in both cases.
....... Phil
yes, you assumed correctly.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
IEC style fuses (such as the 20x5mm type) should have a 'speed' rating on one of the end caps.
The most popular are T (trage) for 'slow blow' and F(flink) for fast (normal) blow. FF (superfast) types are typically used for semiconductor protection but are rare as are 'M' types.
The cap will probably say T315mA.
It isn't actually a US 'slo-blo' type since US fuse specs aren't the same as the international IEC ones. However if you ask for a T315mA to IEC spec you're covered anyway.
Graham
Hmmm ... S ?
That's a new one on me. Most likely it does mean slow blow but I've never encountered such a marking before. Possibly an Americanisation.
Graham
on one cap the fuse itself says "(SA) 51S" followed by three circles arranged in a triangular pattern. The "(SA)" is stylized, and my guess is it's a manufacturer logo. The other cap has the "250V 315mA" followed by the three circle in tri-pattern. I see no T.
Not sure how I'd take a pic of this, tho. it's pretty small.
Yup, anything that is out of place with you has to be American!
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
They're the same thing - it's just that somebody copyrighted the name "slo-blo" so they can't use it. ;-)
Cheers! Rich
Conceptually the same thing but US slo-blo fuses do in fact have slightly different fusing chracteristics to international IEC T types.
Graham
THere you go again. Using the US as the displaced member of the world.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
What do you expect from a 'Donkey' that rarely gets a glimpse of the world outside of his filthy stall, behind the barn?
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
Thanks for all the help, everyone!
I've got the replacement on the way, and I'm confident that it's the right thing.
-phaeton
And with me.
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