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Author Topic: Correct type of transformer for powering Arduino off AC?  (Read 703 times)
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I have completed a prototype Arduino Sous Vide cooker that I am now trying to get ready to put in an enclosure (laying out PCBs etc).  Currently, I have to power the Arduino board, an always-on 120v AC pump, and an SSR relay controlled heating element.  In my prototype, this requires three power outlets! One for the Arduino's wall wart, one for the pump, and one for the relay/heating element.  Putting the pump in parallel with the relay is trivial, but  I want to put in a transformer and rectifier to run the arduino in parallel with them as well so that I can run all the components off one wall plug.  I tried looking at Mouser and Digikey for a suitable 120v to 12v transformer, but there are many different varieties and I am not sure what type is appropriate for this task.  They also seem to be a lot more expensive than I expected.  I would like to keep the option open of replacing the 120v pump with a 12v DC pump running off the same transformer and rectifier in the future.

I'm considering just gutting a wall wart and using its parts.  Is that a reasonable solution to such a problem?
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IRL
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A small caged switching supply would be appreciate.

Radionics has them in professional quality, there are also some on eBay.

Some weeks ago I ordered some (not on eBay) from a power LEDs vendor, it made "pop" after 2 minutes, bridge rectifier had a visible hole, replaced with diode. After 2 weeks, it actually failed in a moment when I just looked at the installation, completely "dead", I guess the switching IC.

I am getting some 12v/1A one's from eBay in a few days.

However, professional caged supplies won't have such issues. They can be a bit expensive, though, depends...

If you are lucky and get a good one from eBay, it will work the same as any professional supply, you just won't have the same approval/guarantee which you maybe need if you do a commercial installation.
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yea the cheapest one I see on digikey is about 14 bucks

http://search.digikey.com/us/en/products/VOF-6-12/102-2213-ND/2441888

course you could get a wall wart from the thrift store and pop it open (sometimes they have a screw in them, sometimes they will pop apart with a little pressure from a vice)
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Thanks for the suggestions.  Looks like I'll be heading to the thrift store to find a wall wart to take apart.
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Same Panasonic adjustable resistor, same color AC compensation capacitor,
same color low voltage electrolytics,

as the components in that caged supply from LED vendor that costed 6 dollar.

Maybe the components are rated for 120 volts, not for 240.

I'd even say, the same IC, same LED, and same optocoupler.
Mine was a 5v/50W caged supply, bigger transformer.
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Taking the guts from a wall wart is a good idea (I've done it myself). But if that doesn't work out these guys have a large selection of inexpensive power supplies: http://www.mpja.com/Power-Supplies/departments/1/
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Quote
course you could get a wall wart from the thrift store and pop it open (sometimes they have a screw in them, sometimes they will pop apart with a little pressure from a vice)
Why would you want to take it apart? 

Don
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Why? Sometimes its fun to play with transformers by say putting 16volts on a 120 to 9v tranformer backwards and getting 240 to play with lol which can go to like 330v dc to charge a hv capacitor quite cheaply
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Have you thought of using the power supply unit from inside an old PC (or powered PC periferal)? Plenty of stable 5v and 12v outputs at quite high currents. Old AT PSUs are preferable as there's not the momentary 'power on' switch in those as there is in an ATX PSU. Most have a switch on the rear (120 or 240 volts) that you can set to suit your mains supply voltage. Also, they have a cooling fan built in.

The outputs from these units are +12v YELLOW, +5v RED and (common) Ground BLACK. If you're using an ATX PSU, to start it, short the green lead to ground momentarily.
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Quote
course you could get a wall wart from the thrift store and pop it open (sometimes they have a screw in them, sometimes they will pop apart with a little pressure from a vice)
Why would you want to take it apart?  

Don

sometimes having the full deal will not fit in an enclosure, pop it open, remove wires and bam! instant open frame supply. Obviously people should be wary of dealing with items connected or potentially connected to mains, but since the op seems to be somewhat confident about it ...
« Last Edit: March 12, 2012, 11:21:41 pm by Osgeld » Logged


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