Consumer electronics with RTC annoyances

[Martin Brown]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

This is pretty ludicrous since the newer RTC chips draw under 1uA and
the older ones maybe 10uA including driving an LCD display.

For the cost of a capacitor and a diode to keep the RTC clock powered
for a few minutes of power outage all the devices have to be manually
reset to the correct time each time the powerline glitches. A 3300uF
capacitor ought to be good for nearly an hour or so down time.

At least a traditional mechanical mains powered alarm clock would only
be thrown by however long the power cut lasted. The modern ones are now
out by however long it was to midnight when the power briefly went off.

The powercut last night was 10s long an hour before midnight. Grrrr!

Regards,
Martin Brown

 

[_]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

This is pretty ludicrous since the newer RTC chips draw under 1uA and
the older ones maybe 10uA including driving an LCD display.

For the cost of a capacitor and a diode to keep the RTC clock powered
for a few minutes of power outage all the devices have to be manually
reset to the correct time each time the powerline glitches. A 3300uF
capacitor ought to be good for nearly an hour or so down time.

Howevere, there can be a good reson for not having the machine just start
where it was when the power comes back; lathes for example often are
switched such that if the power stops the machine stops and will *not*
start again when the power returns; as bits of the operator may be in a
different place that they would be were it running. To have the machine do
this is more complicated that just adding a small backup supply to the RTC.

 

[Raveninghorde]

Howevere, there can be a good reson for not having the machine just start
where it was when the power comes back; lathes for example often are
switched such that if the power stops the machine stops and will *not*
start again when the power returns; as bits of the operator may be in a
different place that they would be were it running. To have the machine do
this is more complicated that just adding a small backup supply to the RTC.

We have some portable air con units we use in summer. We had a power
cut which went on to the end of the day. So we pulled the hoses in for
the night and shut the windows.

Next morning one had a damaged compressor and the place was a furnace.
They had switched back on when the power was restored. Not that we
were using the clock option.

Damn things have a battery back up and remember what they were doing
when power is restored.

 

[Jeroen Belleman]

On Mon, 11 Jan 2010 09:46:41 +0000, Martin Brown wrote:


Howevere, there can be a good reson for not having the machine just start
where it was when the power comes back; lathes for example often are
switched such that if the power stops the machine stops and will *not*
start again when the power returns; [...] To have the machine do
this is more complicated that just adding a small backup supply to the RTC.

You must be joking. A single relay with a hold contact will do this
perfectly. RTC, sheesh!

Jeroen Belleman

 

[Jeroen Belleman]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

This is pretty ludicrous since the newer RTC chips draw under 1uA and
the older ones maybe 10uA including driving an LCD display.

I fully agree! Modern electronics is loaded with gadgets many of which
are rendered useless because of some silly oversight.

Take my portable telephone for example: It has a colour screen with
loads of themes and background pictures. It also has very poor
contrast. The only colour scheme that could save the day would be
simple black & white, which, of course, is missing. Grrr.

Jeroen Belleman

 

[_]

On Mon, 11 Jan 2010 09:46:41 +0000, Martin Brown wrote:


Howevere, there can be a good reson for not having the machine just start
where it was when the power comes back; lathes for example often are
switched such that if the power stops the machine stops and will *not*
start again when the power returns; [...] To have the machine do
this is more complicated that just adding a small backup supply to the RTC.

You must be joking. A single relay with a hold contact will do this
perfectly. RTC, sheesh!

That's essentially what is used on lathes etcetera, which in their simpler
forms do not have an RTC - but that was just an example. Perhaps you
missed that acronym in the subject line, and/or the original post.

 

[Martin Brown]

Howevere, there can be a good reson for not having the machine just start
where it was when the power comes back; lathes for example often are
switched such that if the power stops the machine stops and will *not*
start again when the power returns; as bits of the operator may be in a
different place that they would be were it running. To have the machine do
this is more complicated that just adding a small backup supply to the RTC.

Yes. I understand the need to fail safe when the power or any other
essential service is removed. Many of the instruments I work on have
such critical fail interlocks. Typically to protect the water cooled
delicate vacuum interface cone from the 9000K argon plasma.

However, I was talking here about white/brown consumer appliances where
the main purpose of the RTC is to *display* the time and switch an oven
on at the appointed hour. An alarm clock that resets to midnight after a
power cut whilst retaining the alarm time is neither use nor ornament.

It is perfectly sensible to disable any dangerous functions and abandon
work in progress, but it is extremely annoying to have to reset the time
on multiple appliances if the power glitches even for a few seconds.

Regards,
Martin Brown

 

[Nobody]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

This is pretty ludicrous since the newer RTC chips draw under 1uA and
the older ones maybe 10uA including driving an LCD display.

For the cost of a capacitor and a diode to keep the RTC clock powered
for a few minutes of power outage all the devices have to be manually
reset to the correct time each time the powerline glitches. A 3300uF
capacitor ought to be good for nearly an hour or so down time.

You may also need an oscillator, as the mains frequency is often used as a
timebase. Although, in the case of a brief "glitch", having the clock lose
a couple of seconds would still be preferable to a 00:00 reset.

 

[Nico Coesel]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

The powercut last night was 10s long an hour before midnight. Grrrr!

We have a perfect solution: don't bother to adjust.

 

[GregS]

Increasingly home consumer electronics has an RTC built in to display
the time in some fashion. Ovens, microwaves, alarm clocks and teamakers
being obvious examples. Alas most of them do not survive even a couple
of seconds of mains interruption without resetting to midnight.

This is pretty ludicrous since the newer RTC chips draw under 1uA and
the older ones maybe 10uA including driving an LCD display.

For the cost of a capacitor and a diode to keep the RTC clock powered
for a few minutes of power outage all the devices have to be manually
reset to the correct time each time the powerline glitches. A 3300uF
capacitor ought to be good for nearly an hour or so down time.

At least a traditional mechanical mains powered alarm clock would only
be thrown by however long the power cut lasted. The modern ones are now
out by however long it was to midnight when the power briefly went off.

The powercut last night was 10s long an hour before midnight. Grrrr!

Needless problems to reset the clocks. The only thing that comes back on that I know of, is
some TV sets. They will remember. Most other appliances have fail safes.

Just bought a new alarm clock. My trusty battery portable clock bit the dust.
I still have a Sony Dream machine that I bought well over 10 years ago.
I consider it unusable because of the display system is terrible to
read, but it did have the built in 4 hour rechargable battery susyem that still works.
I checked it out yesterday. The new Emerson from Target
was $20. Has radio, projector, comes preprogrammed for EST, with
year, month, DST, etc. I hate to change 9 volt batteries in most clocks, and they drain
even though they are not needed, and can easily top the price of the clock after
a few years. The Emerson has a 3 volt Lithium that should last over 5 years,
but also enables a separate alarm even if the power is off. A lot for $20.

I'm still waiting for the day when refridgerators have clocks so you can set the proper
defrost time of day.

greg

 

[GregS]

I don't see the problem, because the clock would control just like the microwave
counterpart. I'm used to combo microwave/Turbo Ovens. They came on the market
about 1980 but they did not catch on at that time, mostly because
of cost. I use and own 3 turbo ovens and thet are all very different. I also
have two microwaves in the kitchen one being the combo unit.
I can use all at the same time, plus the regular gas oven/range.
I don't recall any mechanical timer microwave having a start button.
All would come on after power failure. Using those rotating mechanical
timers is still superior to most anything else for speed. They still are used on some
commercial turbo ovens and such.


I like to argue, all ovens are convection, until the food temperature equals the oven temperture.
I use the Turbo Oven terminology because thats what the fan opperated ovens were first called.

greg

 

[Martin Brown]

We have a perfect solution: don't bother to adjust.

A fair proportion of ovens will not operate at all until their clock has
been adjusted (setting to 00:01 will do). My parents is like that.

My main annoyance was actually with a new mains powered *alarm* clock
which makes tea in the morning and it turns out resets its time to
midnight every glitch. This is a distinct step backwards its defunct
analogue predecessor which lasted nearly 26 years. They are a bit
Heath-Robinson (Rube-Goldberg to our US cousins). A slightly older model
gives the impression - more modern ones were angular and the most sought
after one (a semi-antique now) includes a radio.

http://www.telegraph.co.uk/news/uknews/1554206/Teasmade-the-gadget-that-refused-to-die.html

It is hard to boil a litre of water without a mains supply. Shame that
the designers of the modern LCD based one did not make it robust wrt
mains failure - central heating timers seem to manage to get it right!

Regards,
Martin Brown

 

[Martin Brown]

Another annoyance is that they often drift. This is nonsense in a
situation where they can depend on AC line timing keeping them precise
for years.

If they are continuously mains powered then yes. I actually know of some
gear where a GPS has been installed to avoid having to set the clock!
This strikes me as overkill since the unit cannot be operated without
being mounted on extremely rigid foundations. And many are permanently
installed in observatories for their entire working life. The GPS signal
inside a closed metal dome is not always very good - and it can still be
a bit iffy with the dome slit open. Smaller observatories with
fibreglass domes do not experience problems unless they use fancy
exterior aluminium based paint.

I found 3 independent RTCs in one dire design - it allowed for some
interesting and unnecessary synchronisation faults. And they had skimped
(omitted) on the trimmer capacitor so it ran out by 15s/month (pretty
much all of them by a similar amount +/- 5s). Pretty bad in a few
thousand pounds worth of kit that a $5 watch keeps better time

Using a supercap to keep the thing running over a power outage seems
reasonable until some manager decides to start slicing cost out of the
BOM. Since almost nobody would pay extra for that particular feature, it
isn't really worth putting in.

Don't think it even needs a supercap for the current the RTC takes
3300uF and a diode looks like it will do the job for a hour or so.
Annoying that it will void the warrantee to make the thing work
properly. Woken up again last night by misbehaving alarm.

The rapid thaw is playing havoc with the mains supply - short 10s trips
have been all too frequent this week. Normally the supply is fine.

Regards,
Martin Brown

 

[Mark Zenier]

One stove we had when I was a kid had a switched, timed 15 A outlet,
but didn't time cooking or baking. Mom plugged her kitchen radio into
that outlet and knew it was time when the music stopped.

The stove, when I was a kid, was an Hotpoint that was purchased just
soon enough after WW II that it was probably designed in the 1930's.

It had a timed bake feature that used the time of day clock. There were
a couple of extra knobs that adjusted a ring (in red) on the dial of
the clock, to indicate start and end times.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[JosephKK]

Try to buy appliances where the time display is optional? I have a microwave
oven that's designed this way -- it has a blank display if you haven't yet set
the time, which is infinitely better than devices that flash "12:00" or
whatever if you haven't done so. (I've never tried, but presumably it must
display some error message if you try to program it to turn on at a certain
time and the clock isn't set yet. I find it kinda intriguing that microwave
ovens back in the '80s/early '90s tended to be more programmable than the ones
today -- apparently few people ever programmed in delayed starts, multiple
steps, etc.)

---Joel

Actually that was a holdover from the commercial kitchens where they were
originally used. Real commercial ovens have time vs temperature and even
humidity profile programmability in some models.

 

[JosephKK]

Just as a "convenience?" So you don't need a kitchen clock?

Question for old-timers: When regular convection ovens started sporting
clocks, was it so that they could be set to start/stop baking at a giventime
in the future? Or did some come with clocks strictly for the utility value of
the clock itself (and "timed bake" as a feature came later)?

I remember electric ovens from the early 1960s that had the timed bake operation.

 

[JosephKK]

Install a UPS.
Ken

And which UPS do you recommend for the coffee maker or the electric oven?

 

[Martin Brown]

Install a UPS.
Ken

Doesn't help with ovens and teasmades. Only an industrial grade UPS will
tolerate 3kW and 6kW cold resistive heating loads and a massive overkill
for what are minor power glitches. Most PC UPS will die horribly if you
plug a laser printer into them first time the fuser warms up.

Regards,
Martin Brown