On 08/04/2008, Jinx <joecolquitt@clear.net.nz> wrote:
> The thermal fuse in our deep fryer is open. Looking around, the
>  recommended cooking temperature for a fryer is around 175C
>  (350F). Presumably the fuse would have been rated higher than
>  that. How much, I don't know. The fuse would be there to guard
>  against something like a thermostat failure

That is correct.

>  The fuse is marked Microtemp 4377A BKAUL
>
>  I wonder though, if the cooking is always supervised, whether a
>  thermal fuse is absolutely necessary. Prudent, obviously

Not just prudent. I would say essential. I used to work for a company
and did lots of development work on Deep Fat Fryers. My advice would
be to fit the same as was originally fitted. You have to be careful
with selecting a value. The temperature where the fuse is fitted can
be some way off the temperature of the oil, depending on the type of
construction of the fryer. The ones I worked on had a die cast
aluminium bowl, with an electric element attached to the bottom, and a
variable thermostat attached to the front. The thermostat was rated at
something like 156C for an oil temperature of 190C.

If you put a fuse of too low a temperature, there could be occasions
where it gets too hot and will fail again. The other problem could be
if the fuse is too high, then the oil may get too hot and you risk
having a fire. If you were in the room, I would hope that the
billowing smoke will warn you to turn it off before it does catch
light :-)

When you replace the fuse, make sure that you use the same mounting
method. That could have an effect on the temperature that it sees.

For the ultimate deep fryer, a micro controller is the way to go. We
built a test rig with an old laptop controlling a fryer using a NTC
device as the temperature sensor. After playing with the control
system for a few weeks, we had the ultimate chip fryer. It even had
funky safety features such as detecting that the oil was too low by
looking at the rate of heating, and then switching off. The idea was
to refine the control, and then implement it in a PIC for production.
However, the cost was too high at the time.


>  One source, RS, has several fuses in that temperature range, and
>  15mA to 15A current (fryer is 1800W).  But you have to buy a
>  pack of 5. Won't be doing that, will look elsewhere if I do put a
>  new one in

Please put a new one in! Yours and your households safety deserve it.

>  So, no real question that sticks out, just musing for comments

-- 
Philip Stubbs
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist