Metal Covered Fuses ?

[macspring]

What the reason that Audi used the metal covered fuses in some applications in our S cars, rather than normal plastic fuses ?

Just curious.

Thanks.

[UrS4boy]

Thermal Fuse info

What the reason that Audi used the metal covered fuses in some applications in our S cars, rather than normal plastic fuses ? Just curious. Thanks.

Those are not just go/no go fuses. They are thermal fuses and are capable of flowing more than their rated current for a short period of time to allow for initial current in rush/transcient voltage/current spikes. Inside there is a bi-metal spring that heats up as it passes current. If the current is too high for too long, the heat bends the bi-metal spring away from the contacts and the circuit goes open until the spring cools off. Then the current flows again. If the flow is lower than it was, then things carry on fine. If the current is too high for too long again, then the circuit opens again. In short, it is a forgiving/multi-event reusable fuse not an absolute go/no go fuse.

The bad part is they can age and either fail closed or fail open, with bad consequences either way.

Visit this website for more UrS thermal fuse info: https://plus.google.com/photos/+Jame...209?banner=pwa

[macspring]

13 minutes before your reply, on a Friday, pretty good.

Are they all the one part number ?

Are there a few with different ampage ratings ?

[UrS4boy]

Are there a few with different ampage ratings ?

All of them 12 Amp, 15 Amp, 20 Amp and 30 Amp can be replaced by regular spade connectors if need be.

Red 12 Amp



Green 30 Amp/Yellow 20 Amp





Blue 15 Amp

[bluequattro]

I tracked these as a fail on my urs4 a few years back.
Dumped me on a busy dual carriageway on wrong side of a bridge, in the dark.

[UrS4boy]

I tracked these as a fail on my urs4 a few years back.
Dumped me on a busy dual carriageway on wrong side of a bridge, in the dark.

Some UrS4 folks have just replaced their above ECU thermal fuses with spade fuses just like the factory did with the UrS6.

[bluequattro]

I did that. Never let me down after that

[macspring]

Thanks Dave for the additional information, much appreciated.