Have knocked up a fan speed controller ... where temp control speed ...
and hence cooling.

The temp sensor is a Thermistor - the cct board is inside a metal case,
I'm thinking that it might not be responsive enough if the thermistor is
inside the case.........

I could arrange to glue it to inside of case lid, or even onto outside
of case lid ........ anybody done any thermistor based projects ... just
wondered what is normal.