What is this weird heat-wire glass fuse? PJ698B-3 Airfryer

[cybermaus]

Casual inspection makes it a normal fuse. It is also designated as a F2 on the PCB
And it has very normal F 250mA/250V specs

But it seems to be some rheostat-like wire-wound resistor wire?
I am wondering what the function is, it is a secondary fuse, placed behind the normal fuse (labeled F1)
The markings on one side are F 250mA/250V. But the F is inside some weird L.
And the other side has 239. Might just be a production batch number. But given the weird "rheostat" like winding, it could also mean something

It is also blown. You can see the blowout in the middle in the larger image.
I am wondering if I should replace it with a "normal" fuse of the same specs.

It comes from a Tefal Airfryer. With 250mA it is obviously not the main heat fuse. And there is little in the way of other functions, this is one of the first generation of air fryers. It rotates, there is a fan, but not even a heat contol nor timer. (there is a separate clock, when it beeps you are supposed to open the lid, and that stops the heat. The heat is not stopped at all by the device itself.


Apart from having some desire to fix the airfryer, I am also wondering what this fuse is supposed to do.
With heat wire, is it supposed to combine a function of fuse and PTC-resistor?
Surely it is not supposed to be a poly-fuse, I may not know what it is, but I do know this one is not going to reset itself.

[cybermaus]

Best I can find myself, (but still open to the opinion of others) it is a fuse with inrush protection.

Among other, I found this text:
(I guess in this case, it is cheap capacitor inrush protection)

Code: [Select]

"This slow-blow fuse from RS PRO is designed for electrical devices which need a high inrush
 of current to start. It allows for an initial surge of power without blowing the circuit and is commonly
 used in equipment that runs on a motor." https://cl-en.rs-online.com/product/rs-pro/6109850/70823846/

A bit weird though that mine has a F marking for fast fuses.


Also I found this similar looking fuse specs, that shows a 1 Ohm cold resistance, and a 1.4 Watt nominal current dissipation.
https://4donline.ihs.com/images/VipMasterIC/IC/LFSI/LFSI-S-A0012939319/LFSI-S-A0012939319-1.pdf?hkey=6D3A4C79FDBF58556ACFDE234799DDF0

[tooki]

Casual inspection makes it a normal fuse. It is also designated as a F2 on the PCB
And it has very normal F 250mA/250V specs

But it seems to be some rheostat-like wire-wound resistor wire?
I am wondering what the function is, it is a secondary fuse, placed behind the normal fuse (labeled F1)
The markings on one side are F 250mA/250V. But the F is inside some weird L.
And the other side has 239. Might just be a production batch number. But given the weird "rheostat" like winding, it could also mean something

The L with F inside is the simplified Littelfuse logo they put on components. And the “239” means it’s a 239 Series fuse.

https://www.littelfuse.com/products/fuses/cartridge-fuses/5x20mm-fuses/239.aspx

The coiling around a mandrel is simply one way of controlling the blow characteristics. It’s a slow-blow fuse.

[cybermaus]

Well, I guess you are right, with data sheet and all, thanks.
It also makes more sense.

But that means F and T as standard for Fast and Timed (=slow) fuses is a little undermined
When Little Fuse puts such a stylized brand indicator F in front of a slow-blow range.

Anyway, I figured out that the reason it blew was because it drives the fan, and the fan motor had worn out brushes.
I mean, I did realize one should always try and find the cause of the blown fuse, before replacing it, but the fan motor looked OK on casual inspection.
The fan motor brushes are non-replaceable. So this airfryer is .. ahem .. fried.

[tooki]

Well, I guess you are right, with data sheet and all, thanks.
It also makes more sense.

But that means F and T as standard for Fast and Timed (=slow) fuses is a little undermined
When Little Fuse puts such a stylized brand indicator F in front of a slow-blow range.

But they put their logo on everything, and it’s not just an F, it’s a stylized “LF” where the F is clearly a different size from the actual text.

FYI, I think I read somewhere that T and F actually came from the German “flink” (quick) and “träge” (sluggish), and that it’s just a coincidence that the abbreviations also work in English. I believe they work in Dutch, too?

Anyway, I figured out that the reason it blew was because it drives the fan, and the fan motor had worn out brushes.
I mean, I did realize one should always try and find the cause of the blown fuse, before replacing it, but the fan motor looked OK on casual inspection.
The fan motor brushes are non-replaceable. So this airfryer is .. ahem .. fried.

How about a replacement motor or fan assembly?

[cybermaus]

FYI, I think I read somewhere that T and F actually came from the German “flink” (quick) and “träge” (sluggish), and that it’s just a coincidence that the abbreviations also work in English. I believe they work in Dutch, too?

Correct, or at least, I hear the same.
In Dutch, the T works (traag), but the F does not (snel).
Except, almost no-one realizes F does not work, because F=Fast is such a common angelism, no one notices. So F=Fast and T=Traag feels completely native Dutch

How about a replacement motor or fan assembly?

Sort of. we had another old broken one with a broken heater element, so indeed, we now have one working one.
(or at least, my brother does)

[CaptDon]

'F' is also a style of fuse and among the 'F' size of fuse the letter F does not indicate fast but rather the dimensions of the body.