Powering The Basic Stamp (BS2) on 240VAC
Hello, I have done several basic stamp projects, using step down transformers to covert 120VAC to 12VDC.· In this project I want to convert 240VAC using only phases A and B in the home (with no neutral) to 12VDC.· All the transformers I see from·places like digikey and mouser are rated at 115/230.· Firstly the 230VAC is lower than the required rating, and secondly these transformers require that the primary side be wired with 2 HOTS and a neutral.· Can someone help me out??
Comments
Most any transformer that would output 6V on the secondary with 120VAC on the primary would give you 12VAC when you supply 240VAC. From there, bridge rectifier, filtering caps and chokes, feed that to a 7805 and you should have what you're looking for.
Don't let the "230" fool you -- 208, 220, 230 and 240 are all pretty much the same, when dealing with this sort of thing. The voltages aren't that precise and tend to refer to a "nominal" value. There are some other strange system voltages that you have to worry about (277/480 Y ...) where using a 230VAC rated transformer would be the wrong approach, but if you're in the range between 208 (120 / 208 Y) and 240, you're golden.
Any three-wire 240VAC plug is going to have L1, L2 and EGC (not neutral) if it's coming from a 120/240V split single phase system. Additionally, European power often doesn't have a neutral.
It's just one of those things people need to do sometimes. Like me and my 42 to 65VDC power supplies ...
You can't always assume the worst, because even low voltages can be very deadly. I work in 48 volts a lot these days and I've made some spectacular mistakes -- far more spectacular than anything someone with a small AC transformer is going to do. But mention 48 volts and people think it's a lot safer than 120 or 240. Except that I've got 10,000 amps of available fault current ...
And good to be here -- I've not done electronics design work for almost 30 years and I'm surprised that some of the cob webs are blowing away as easily as they are.
ie in the UK phase -neutral will give you 230v (used to be 240v)
phase to phase gives you 415v
Regards,
SoulJaH
I get mine from DigiKey with standard (North American) parallel blade for the high voltage side. Simple plug adapters are available to convert to North American 220 and Euro 220 volt inputs.
Cheers,
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Tom Sisk
http://www.siskconsult.com
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The DigiKey part # is T1000-P5P-ND and the catalog section has other voltage outputs.
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Tom Sisk
http://www.siskconsult.com
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You wrote:
Most any transformer that would output 6V on the secondary with 120VAC on the primary would give you 12VAC when you supply 240VAC.
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Please, that's a·VERY·DANGEROUS statement. Let me explain.· If you put 240VAC on the primary winding of a magnetic that is designed for half of that, 120VAC, you will most likely saturate the core. This will make the primary impedance of the transformer drop to a low value causing much higher primary current to be drawn. This will quickly lead to overheating of the core and wire, shorted turns and failure of the transformer in a very unsafe manner.
I just wanted to raise a caution flag so that no one gets·injured.
DF
Post Edited (dexf) : 12/8/2009 8:31:19 PM GMT