Re: Underfloor Heating In Conservatory problems

On Fri, 07 Apr 2006 13:55:24 +0100, Palindr?me <me9@xxxxxxxxxxx>
wrote:

Selectively losing the clock setting but not the other settings is an
interesting one. It could be that only the clock is maintained by the
battery backup and the rest stored in non-volatile ram. There are
battery charging circuits that are rendered totally ineffective by
brownouts. So you could be right. But this would need the brown out to
be maintained for many hours, if not days, and the OP might have
reported that the lights were often dim. But I suspect that it is more
likely that it is caused by transients or noise.

Having designed a few products with uninterruptable real-time clocks,
the clock issue is to me not so mysterious. All other settings are
probably held in Flash memory these days, which is not at all
succeptible to power outage. But the clock is changing all the time,
so its setting is typically held only in volatile registers inside a
RTC chip (which may be part of the embedded processor chip). Those
registers will get corrupted if power to them is interrupted for a
very short time.

In some circuits, the RTC is kept running by a small battery
(rechargeable or not) in the event of a power fail, or even a special
capacitor designed for such a purpose. But in order to work reliably,
many RTC chips must be supplied with a "power down" signal a few uS
before its Vcc is removed so that it switches off all its circuits
except the oscillator and time counters & registers. Without that
signal, the RTC will get corrupted if power is removed even though it
has a good battery supply on its maintainance power input pin.

A "brown out" can result in Vcc to the chip falling below the
necessary value to keep the chip working without triggering the "power
down" logic signal (which may be derived from an "early warning"
circuit monitoring the raw mains input).

One of the tests I do on new designs is to supply them via a variac,
and see what happens when I *slowly* turn down the input voltage.
There are often some very interesting phenomena that has required a
circuit addition to cope with on more than one occasion. More than
one commercially available switch-mode power supply has gone up in
smoke when subjected to such a test. I also use a mains fault
generator that can create all sorts of nasty transients, but by far
the most headaches occur with the simple brownout test.

As we all, I think, agree, the OP needs an electrical expert. Though we
might possibly disagree over who is going to have the right expertise..;)

I'll stick my neck out and say that based on the information given,
even a modestly qualified independent electrician will most likely
find something fundamentally wrong with the way the conservatory has
been wired.

I hope the OP keeps us informed of the outcome.

--
Cynic

.

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