On 19 May 12 at group /sci/electronics/repair in article
(N_Cook) wrote:

Bill Proms wrote in message
...
I have 3 Intelli-Time LED alarm clocks around the house, just like
the one he
[...]
I initially bought these due to them keeping time when the power
goes off and auto resetting for DST. There is a problem, however.
Each of the clocks becomes inaccurate over time. If I set them all
manually to the same
time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?


I've always put this down to hash on the mains being interpreted as
extra cycles by the clock monitoring input. The supply companies
contractually have to correct the mains frequency so an exact number
of cycles per day (50/60)x60x60x24, but at any instant can be above or
below the nominal frequency.

Anyhow in continental Europe the 50Hz is very accurate due to the large
high voltage net, which must be synchronized to all generators in all
connected power plants.

I doubt but don`t know if GB is power connected to the continent.
So their frequency shift is possibly much larger due to less coupled
generators.

Same I think in the US where AFAIK not all powerplants are connected to
a great (one?) power net.

On load the generator/turbine set slows down a little, so frequency goes
down. On load dump they accelerate a little (less or more) depending on
the amongth of all coupled generators and the accuracy of the net
controll.

So the frequeny of 50/60Hz line varies, but in continental Europe the
50Hz varies much lesser than in all other countries.



Saludos Wolfgang

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