What is this weird heat-wire glass fuse? PJ698B-3 Airfryer - Page 1
Forum section: electronics / projects

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 22, 2024, 02:20:33 pm
content: Casual inspection makes it a normal fuse. It is also designated as a F2 on the PCBAnd it has very normal F 250mA/250V specsBut 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 somethingIt 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.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 22, 2024, 02:49:56 pm
content: 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:"This slow-blow fuse from RS PRO is designed for electrical devices which need a high inrushof current to start. It allows for an initial surge of power without blowing the circuit and is commonlyused 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

author: tooki
author_rank: Super Contributor
timestamp: June 22, 2024, 03:10:31 pm
content: Quote from: cybermaus on June 22, 2024, 02:20:33 pmThe 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.aspxThe coiling around a mandrel is simply one way of controlling the blow characteristics. It’s a slow-blow fuse.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 22, 2024, 04:33:26 pm
content: 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 underminedWhen 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.

author: tooki
author_rank: Super Contributor
timestamp: June 22, 2024, 06:36:29 pm
content: Quote from: cybermaus on June 22, 2024, 04:33:26 pmBut 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?Quote from: cybermaus on June 22, 2024, 04:33:26 pmHow about a replacement motor or fan assembly?

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 22, 2024, 06:49:29 pm
content: Quote from: tooki on June 22, 2024, 06:36:29 pmCorrect, 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 DutchQuote from: tooki on June 22, 2024, 06:36:29 pmSort 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)

author: CaptDon
author_rank: Super Contributor
timestamp: June 22, 2024, 08:34:01 pm
content: '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.