Kendrick Digifire 7 fuse

[Ulysses]

Hi all, has anyone ever had to change the fuse in their Digifire 7 dew controller? After a useful email from Jim at Kendrick in the US I identified that the 7amp fuse had blown. I've been looking for a replacement with little success. Any advice gratefully received. Cheers, Paul

[Markjlynch]

Hi Ulysses, did you manage to find a solution to the blown fuse? Mine just popped last night too!

seems these are longer than most (at 33mm) than I see advertised on the Internet (though perhaps not very thoroughly)!

Thanks for any help.

Mark

[Steep]

You can buy 7 amp fuses from RS-Online or CPC in various forms, possibly from Maplins too.

[Ulysses]

Hi, I managed to find replacement ones at Maplins in the end. They are 6.3 amps though but I have used the unit a few times now and they seem to work. A pack of 10 cost a couple of quid, so not bad really, Paul

[Markjlynch]

Thanks for that Ulysses

[Carbon Brush]

A 6.3amps fuse as replacement for 7amps will be fine.

Fuses are not precise items.

In fact you get huge variance in blow characteristics simply by changing manufacturer and keeping the same time characteristics.

The on/off switching characteristic of dew heaters controls means that fuses get fatigued and can fail early.

Each time the heater turns on, a high current flows and the fuse wire heats a little and sags.

After a second or two, the power turns off and the fuse wire cools, returning to size.

Eventually, after thousands of cycles, the wire fails for mechanical reasons.

Another contributory cause of failure is low cost manufacture. If the wire is not sealed inside, then moist air exchanges with the outside. The fuse wire corrodes a little and with the temperature cycling described above, new metal is repeatedly exposed.

As the remaining wire is now thinner, the fuse rated is effectively reduced. This effect takes years to show usually.

If you use a fuse described as 'slow blow' or 'time delay' or 'surge resisting' then these are better for withstanding the on/off switching without failure.

They will still blow in the event of a short circuit in the wiring.

A better solution is to us resettable circuit breakers or PTC thermistors, but that another big subject.

Hope this helps, David.

[Ulysses]

Thanks David, interesting stuff. It's a good job I've got a few spares then! Paul