Power supply

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Joined:Fri Jul 27, 2012 4:55 am
Power supply

Post by GoD » Fri Jul 27, 2012 5:30 am

I am looking for a cheap solution to supply power to a PR28V and Leostick from the mains supply (NZ 220-240VAC).
I need to permanently connect it to the mains so a wire in supply of some sort is prefered over a wall wart style supply.

The idea is the start of a home automation project starting with the living room lights, I want to be able to fit all the hardware into the wall by removing the light switch and poking them through the hole. ( no doubt I'll need to remove the flush box, no biggy).

I brought a 230vac - 12vdc electronic transformer/converter used for home LED lighting, I think it fried my PR28V. :(

This is the tranny i used http://www.jaycar.co.nz/productView.asp ... rm=KEYWORD

Can any one confirm this type of power supply is the cause of the dead PR28V? I never tested the PR28V from new so it's possible it's a dud. I have another working PR28V i can use but I'm not going to kill another one by plugging it into this tranny again.

Or, has some body have a better idea of a power supply solution?

Thank you.

Joined:Tue Nov 01, 2011 10:14 am

Re: Power supply

Post by LukeW » Sun Jul 29, 2012 8:48 am

Something like this, for example?

http://www.digikey.com/product-detail/e ... ND/1010427

http://www.digikey.com/product-detail/e ... ND/2441888

There have been a couple of occasions where I have sawed the outer casing off a SMPS plugpack and rewired the input and output to the naked PCB where I've wanted a 240VAC --> 12V DC SMPS which is integrated within an insulated chassis inside a larger project, because that's the cheapest way to do that job. (The latter link above is a slightly more expensive but much more "professional looking" equivalent that does the same job.)

There are many cheap, small mains AC power supplies on the market intended to run 12V household 50W halogen downlights, or high-power (3W or 5W or so) white LEDs.

For running electronics projects or microcontrollers, etc., avoid these. They are designed to be the cheapest thing available that works acceptably within the use case that they're intended and designed for - they're low-voltage AC or DC, badly regulated, without good isolation from the mains and without good ripple characteristics.

Some of these devices I've seen designed for running power LEDs from 240VAC simply consist of some RC impedance in series with the 240VAC line to limit the current, followed by a small bridge rectifier and a capacitor across the DC side of the bridge, because you don't actually have to regulate the voltage from a LED power supply, just limit its current, and the forward voltage drop across the LED just is what it is.

Joined:Thu Dec 01, 2011 7:57 pm

Re: Power supply

Post by bobj » Sun Jul 29, 2012 11:57 am

Measure twice, cut once.
Measure the output of any supply first before onnecting and using it. It just might be the problem, not the PRV28. Also on the next PRV28, test it on another power supply first.

Lastly, please dont consider either of the originally linked AC/DC power supplies safe for stuffing in a wall. Both are definately intended for secure, ventilated and safe enclosures.
Even the jaycar one is probably meant for roof space installation, not in a wall cavity.

I'd strongly suggest a wall wart regulated PSU for the brains of your Home Automation operation (the arduino).

I agree the simple RC type circuit might satisfy an LED, but usually offers no mains isolation to anything and will likely fry anything smarter than an LED, including yourself.


Joined:Fri Jul 27, 2012 4:55 am

Re: Power supply

Post by GoD » Fri Aug 03, 2012 6:19 am

Thanks Luke, yeah you explained well what I was kinda thinking about LED/Halogen PSU's.

Thanks Bob, yeah this PRV28 is definalty dead. :(
I am aware that Home lighting transformers and the like get very warm, I was hoping that the small amount of current being drawn would mean less heat generated by the PSU, but that idea is out the window now anyway.

Before I even came back to read these replies, I brought a 230vac - 5vdc wall wart/plug pack and did just what Luke described. Took it apart, soldered wires to the pcb etc.
These plug packs are fully enclosed and wont get as hot as a lighting transformer. So it shouldn't mind being enclosed in a new box and placed inside the wall.
Also I don't need the PRV28 anymore.

I'm very nearly done, I'll post a new topic in the projects section next week.
I'm going to test it in the wall, then remove it and test it on the bench for a few days before trusting it doesn't set fire to the inside of my wall.
For the record, I know the dangers in high voltages and respect them. Had my hands in many 400v switch boards, it's nothing new to me.

Joined:Fri Sep 21, 2012 7:22 am

Re: Power supply

Post by csconsulting » Tue Sep 25, 2012 7:45 am

The reason your stuff blew up is that those kinds of power supplies dont output DC. Its more of a messy chopped up waveform that when averaged, looks kind of like DC. Kinda.

Your best bet is to use a phone charger wallwart, and like the other members said, saw it apart and use it directly.

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