eXnOf
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Power model A+ with doorbell tranformer

Tue Jun 14, 2016 8:22 am

Currently, I am building a smart doorbell that sits on top of my current traditional one. The idea is to close the traditional doorbell's circuit using a relay, but share the existing power source for both devices. My field of expertise is in programming, not electronics... so it's kind of a hurdle for me. :?

The problem I am facing is getting my Raspberry Pi A+ powered using the available circuit for the current doorbell. The latter is powered through the following transformer: http://www.ecataleg.be/nl/product/413091. I read that I could be using a UBEC to step down the voltage, but I'm wondering if this is going to be a stable enough power supply, certainly when my traditional doorbell is going to consume power on the same circuit.

Anyone has experience with this? Some pointers, maybe? Much appreciated! :D

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Burngate
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Re: Power model A+ with doorbell tranformer

Tue Jun 14, 2016 10:51 am

That bell transformer appears to have AC outputs, and so would be unsuitable as a supply for a ubec (which generally requires a DC input)
http://media.ecataleg.be/2012/11/20121113_70991_1.pdf

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penguintutor
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Re: Power model A+ with doorbell tranformer

Tue Jun 14, 2016 1:31 pm

I'm not aware of anything you can buy that will do what you want. It is possible to make one, but would need a bit of electronics.

As the transformer is AC and the Raspberry Pi is DC then you will need a bridge rectifier circuit. You would need to connect a bridge rectifier to the 8V output of the transformer providing a rectified DC output, also connect a large capacitor across the output to provide smoothing. You can then feed the DC from the bridge rectifier into a BEC / Buck convertor or through a voltage regulator such as a 7805.

drgeoff
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Re: Power model A+ with doorbell tranformer

Tue Jun 14, 2016 3:57 pm

A bell transformer may not be suitable for continuously powering even a RPi A+. Bells are typically only run for a few seconds with minutes or hours between those few seconds.

eXnOf
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Re: Power model A+ with doorbell tranformer

Sun Jun 19, 2016 7:42 pm

Thanks for the replies you guys, but I must admit it sounds awfully complicated to me. It seems I have some more studying to do. ;)

Maybe I need to rethink the entire thing and create a solution that is entirely DC-powered, ditching the existing doorbell. New challenge ahead! :)

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Burngate
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Re: Power model A+ with doorbell tranformer

Mon Jun 20, 2016 9:03 am

Depending on its type, you may find the existing doorbell will work with DC. Some just need power of some sort, while others require AC to make a buzz

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