A small but strange phenomenon

[Kes]

In our kitchen we have three appliances incorporating electrical digital clocks. We also have, but not in the kitchen, overhead power supplies. On the occasions when we lose power for a while the clocks have to be reset and more or less synchronised, which is a pain.

Yesterday, in a thunderstorm, there were a few lights on, the TV, and me foolishly pottering about on my pc. There was a fairly close lightning strike which resulted in a transient loss of power. Lights and tv off momentarily, and of course the pc straight into reboot. But the clocks on the appliances kept the correct time, despite the interruption.

What is it that enables the leds (or whatever they are) to retain their settings over a small but discrete loss of power? What and where is the remanence inside the circuits? I suspect it's something to do with capacitors, but that's just a guess.

 

[sm1thson]

I suspect it's something to do with capacitors, but that's just a guess.

you guess correctly, think of the capacitors as small rechargeable batteries, it helps that clock circuits and LEDs dont use much power. to keep the PC running you would need a ridiculously sized capacitor, a lead acid battery is smaller for the amount of charge held which is what is used in a UPS backup power supply.

 

[Kes]

Ta, I wish that Bosch had included small battery or backup in their clocks so they didn't have to be reset after a power outage of more than a few secs. And auto GMT/BST switching, it must cost pennies to provide that.

 

[breezer]

it may cost pennies but they dont have to set the clocks do they.

FWIW when i was working for HP we were told the marketing dept were arguing over a new design that cost 1p yes one single penny.

the reason they were arguing was that the would have to supply millions of them which equals to thousands of pounds they would have to pay for.

so that is probably the reason timers on cookers need to be reset.
1, they dont have to do it
2 the cost of fitting the extras when you make millions of them

 

[2scoops0406]

Not as good as where I worked once, was in a IT to business meeting, business argued successfully (despite being told the consequences) that there was no point in spending the extra 30p per NIC card for Wake on LAN (WOL). I few years later, the business wanted the Workstations to power down after a certain period of inactivity (fine) but if updates needed to be applied then the workstations would be need to be woken from their slumber (oh dear.....)

Ha Ha (repeat to fade).

 

[Lectrician]

BT did a cost saving exercise on their master NTE5a line jacks.

They used to have brass inserts and machine screws to secure the front to the backbox.

By removing this brass insert and changing to self tapping type screws in a plastic 'tunnel', they saved a few pence per NTE.

However, they had many complaints from engineers who where attending faults and finding they where having to replace not just the front plate of the NTE, but also the rear box as the new fronts could not be used with the old backs. They also had problems with flush fitting the NTE's, and fitting to non-standard back boxes such as those in trunking etc.

The outcome? They enlarged the fixing holes, and supplied an additional two screws in each box - two machine screws and two self tappers.

The cost? The NTE's now cost more than they previously did.