The actual electricity is always cheaper by a factor of 300.
Bill
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10 years ago
Door Bell Transformer
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10 years ago
What is the quiescent current draw then on a tiny little transformer, Harry?
Bill
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10 years ago
300 times I reckon.
Bill
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10 years ago
Which is often irrelevant. A mains powered torch might be cheaper to run too, but not so handy. ;-)
Tim
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10 years ago
My mains powered torch is very useful. It comes on when the mains goes off. Its probably cheaper to run on batteries for the amount of on time it gets.
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10 years ago
But that really is the whole point. Of course you have to use batteries of some sort on portable equipment which may be used anywhere. Like a torch. But most doorbells are fixed.
I do admire those who carry around a cordless one with them around the house or into the garden etc. I have enough problems finding the remote for the telly.
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10 years ago
Dunno, two or three watts =26Kwh/year? = 3.60/year? For the DIN rail mounted ones. I think the older transformers used a lot more, maybe ten watts
So how long the life and what cost would a battery be? You really want one that lasts as power used would be negligable. (No standby losses.) So it's a matter of the type of battery. Rechargeable?
The lithium ones in fire alarms last seven years, maybe more, maybe this would be the ones to gofor.
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10 years ago
Not the issue, there are no standby losses with a battery. Could be rechargeable too.
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10 years ago
Irrelevant.
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10 years ago
My DIN rail one (powering an illuminated bellpush) draws 27mA
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10 years ago
So around 6.5VA - but what's the power factor?
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10 years ago
Something that size which consumed 10 watts would get pretty hot.
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10 years ago
That is 6.5 watts. Do you know what the bulb is rated at? It could be reduced considerably by using an LED.
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10 years ago
I've vaguely considered that, it uses a tiny wire-ended bulb, rather than a festoon one, any worry from back-EMF spikes from the solenoid?
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10 years ago
LEDs - especially under-run ones - are pretty good at short term overloads.
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10 years ago
Might be less so under reverse voltage?
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10 years ago
Actually it's 6.5VA - I doubt the power factor is anywhere close to 1.
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10 years ago
A zener should fix that on dc, 2 zeners on ac
NT
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10 years ago
I've ordered twenty white LEDs from china (1/3 the price of two from the UK inc P&P) plan to fit a resistor and two LEDs (in inverse parallel to reduce flicker) in the bellpush.
Might struggle to to also squeeze two zeners in the bellpush itself, plenty of room in the bell itself, but wouldn't inverse parallel zener pair there just suck current all the time, defeating the lower consumption purpose? a varistor across the bell instead perhaps?
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10 years ago
At each kickback one LED will conduct the current the bell was taking briefly. Its half a solution so far.
2 zeners need to be in series, back to backIf you really cant get the zeners into the bellpush, its also an option to fit a pair across the bell and another pair across the supply.
NT