Hello.
I have an old wired doorbell that has an 18V DC power supply. The actually transformer has been (I think) channelled into the wall, or underfloor boards in the attic. i.e. hard to get to.
A new fancy doorbell requires connection to a 8V AC power supply.
Is there a simple way to do this? i.e. 18V DV in, 8V AC out?
Thanks.
Not really, far easier to get a matching power supply.
I doubt it!
Presumably the new door bell came with a power supply? Just graft it to the existing wiring if you don't want to redecorate.
Tim
Apologies, missed this bit.
Think you'll just need to look harder. ;-)
I'd be most surprised if the transformer has been channelled into a wall. Usually they're next to the main fuse box.
Tim
But all that finding it gives you is an 18 volt DC power supply.
A 50Hz oscillator could do it if suitably rated. Many 8v ac devices are also happy on 12v dc, so a regulator could also work.
NT
18v would be unusual for a door bell. Did you measure the voltage from the power supply with no load? The sort used for this likely has very poor regulation since it doesn't much matter. Real doorbells will work over a wide range of voltage.
If it's an electronic device it will run off DC. So if no internal transformer, it will accept DC too. The DC will go through its internal rectifier OK. If so a simple regulator will give you the DC voltage you want. Exactly what that is, I'm not sure. As a nominal 8v AC supply depends on how it is rectified etc for the final DC voltage. Can this device be run off batteries? That would tell you what it needs, DC wise.
You will probably find that the new bell only requires 8V AC because it converts it internally to whatever DC voltage it requires to operate, possibly by no more than a rectifier and smoothing circuit. You could try connecting a 7.5V DC supply to it to see if it works (and change the polarity if it doesn't). If it does, and you want to be bothered, you could try one of these:
And select the voltage output which you have checked works ok. Whatever you do, don't connect up the 18V DC supply directly to the new bell.
No.
I'd guess 18v with no load, nominal 12v supply but 8v and transformer humming in protest when the solenoid is being powered continuously.
That is an unusual requirement. Most modern stuff uses a DC switched mode PSU (or even batteries) rather than an iron transformer and AC.
You need to know how much current the new device will draw and what its absolute maximum voltage rating is. It might be possible to put a well heatsinked 5W 10v Zener diode in series to drop the excess voltage. eg
It only has to survive a few seconds of intermittent use.
Somewhat grubby solution and it might not work if the thing draws too much current when going ding dong or if the psu regulation is ropey. (as seems likely from the OPs description)
I agree with that, although I'd want at least three buck converters for that price.
Just to be certain, if the OP could tell us the make and model of his new doorbell it would help.
There is no /simple/ way to convert. Best buy a transformer - it seems that 8V AC is quite a common doorbell voltage. For something that's connected to the mains and left unattended for years, I wouldn't fiddle about.
Cheers
If the power so low enough and audio amplifier fed from a 50Hz oscillator is one way.
Would you *seriously* fit that yourself rather than use a bell transformer designed for continuous use? It's not simple, not certified, certainly not as reliable and awkward to explain to the insurance company when the firemen have left.
Cheers
GHiven that I was an audio circuit designer for may years, probably ';-)
I thught he needed AC from DC?
A 'bell transformer' only works from AC..
It all depends on why it needs an AC supply. If its then rectifying the
8V AC to get a 12V DC supply you may find that the first component in the doorbell is a bridge rectifier followed by a smoothing capacitor.If this is the arrangement you could feed in DC - and possibly the 18V you already have. Assumptions: a bridge rectifier as the first component and 18V is the no load voltage that possibly would drop under load
Do you have a photo of the innards of the doorbell showing any components that may related to a power supply?
This.
Tim
Not if you rip out the old transformer and connect the new power supply/bell transformer to the old transformer's supply and connect the output to the existing bell wires.
Tim
the audio amp can be the oscillator.
I'd use a voltage regulator.
it is
what's that got to do with anything?
no less reliable than any electronics. If you're competent you can do it to mil spec.
no it's not. Insurance doesn't exclude electronics, and it's trivial to make it not a fire risk.
The only thing that might need ac is some small bells that work the wacker at 50Hz.
NT
Do you know it will work with DC?
A mains transformer designed specifically for continuous use is more reliable than a bunch of electronics. Why would you even argue the point?
And this might well be one. The Amazon reviews of a Friedland 8V AC doorbell suggest a 'Brrrrrrrrh!' sound.
Like this, perhaps...
Or if it's a simple electromechanical 'ding - dong' type using a solenoid actuator then there is a difference between AC and DC solenoids, just as AC and DC relays are different.
Wind your neck in, bellend.
Cheers
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