Dear Byron,
Today I have installed a "720k" wired door chime that I purchased from my local Screwfix a couple of weeks ago.
I am writing to let you know that I have completely discarded the useless so-called bell wire you provided, which has a single strand no thicker than a human hair...in favour of "proper" bell wire which I must have purchased in the 1970's.
Can I suggest you have made a cost-saving too far!
David
Shuddagottafriedland.
Owain
Remember those smart arrays of black & white bellpushes outside blocks of flats, each with a festoon bulb illuminating the name Friedland?
I suppost that was to confuse the cold callers.
Crikey, they still make 'em.
I wonder if the festoon lamp that often drew too mutch current and made the bell buzz is now an LED, or is that too sensable?
ah yes I have a door intercom like this. I'm told this wire is easier to hide. However making it grey would seem to not be a good idea if this was the reason.
Brian
It says it costs ?9. Bit steep for what it is.
According to 192.com there are 81 people in the UK with that surname.
The old lamps are still available
I don't see any mention of new pushes being LED.
Owain
LED would need zeners to avoid being fried by mechanical bells
NT
Not in practice. I've been using a LED for years. Two basic bells wired in parallel so quite a bit of spiking. Remember the LED is shorted out when the bell is ringing.
Won't the big spike often be when the push is released?
Andy
Yup. I'm not sure how Dave's have survived.
NT
Depends on the design of the bell. Universal types, which can run off AC or DC, had a switching circuit. I have one of each. ;-)
The LED in question is very much under-run. Less than 10 mA.
It's the spikes that I wonder how it's survived. Mechanical bells are inductive, open the switch and the bell gets electrically aggressive. Perhaps one has a big cap across it or something.
NT
Yes - but it's excess current which kills an LED, and they can take a short pulse which would kill them long term.
Doing a quick calc, you'd need about 60v to give double the continuous rating of this LED and resistor combination. Which isn't far away from what I'd expect to see. ;-) But anyway, it's worked just fine for many years.
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