On 19/07/2020 23:52, Brian Reay wrote:
Cursitor Doom wrote:
On Sun, 19 Jul 2020 18:47:51 +0100, Harry Bloomfield, Esq.
wrote:

Brian Gaff (Sofa) wrote on 19/07/2020 :
I was thinking, how are the three adjustments done? Could they merely be
using a triac already in the control box. If so that might be affected by
your other triac.

They usually use a simple parallel series arrangement. I have one which
works like that, but includes a timeout system.

Indeed. By using 3 different elements within the one blanket, they
have eliminated the necessity for any form of temperature control at
all. It's all done by just a simple switch; nice 'n' cheap!


Before disposing of an old electric blanket, I looked inside the
controller. As you say, it was a simple switch to select the €˜elements.
It didnt have any obvious overheat detection in the controller. There
could have been a simple thermal switch €˜buried in the blanket.

There is a fuseable link inside the little controller which blows if the
thing starts to draw unexpectedly high current or after about 5 years
whichever occurs sooner. They die much quicker if you use them on
maximum a lot the internal switch contacts are very cheap and cheerful.

The resistive load tends to fail open circuit eventually.

Weve had several over the years, all the same brand from memory. Weve
varied between single temp/setting ones and variable ones - the latter have
always ( from memory) had cables between the blanket and controller
suggesting multiple elements.

It is usually a single cable with 3 to 5 way multicore cable with a flat
connector on the blanket. Some do have temperature feedback.

--
Regards,
Martin Brown