Powering The Basic Stamp (BS2) on 240VAC

SouLJah

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??

allanlane5

What kind of 240 Volt AC plug has ONLY phase A and B, and no neutral? Did you wire this yourself?

SouLJah

This is not a plug I wired up to try to "Jury Rig" something, I'm just trying to find out what reasonably priced transformer I can use to step down 240VAC

Julie in Texas

SouLJah said...
This is not a plug I wired up to try to "Jury Rig" something, I'm just trying to find out what reasonably priced transformer I can use to step down 240VAC

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.

Julie in Texas

allanlane5 said...
What kind of 240 Volt AC plug has ONLY phase A and B, and no neutral? Did you wire this yourself?

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 ...

allanlane5

Fair enough. I sometimes over-react when I read posts that seem to be trying to do something that could (if done sufficiently badly) be incredibly dangerous. We're talking about fire-hazard from over-heating, to shock-hazard from mis-wiring. Perhaps I over-reacted. Thanks for your good answers, Julie.

Julie in Texas

allanlane5 said...
Fair enough. I sometimes over-react when I read posts that seem to be trying to do something that could (if done sufficiently badly) be incredibly dangerous. We're talking about fire-hazard from over-heating, to shock-hazard from mis-wiring. Perhaps I over-reacted. Thanks for your good answers, Julie.

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.

skylight

single phase in the EU uses phase plus neutral
ie in the UK phase -neutral will give you 230v (used to be 240v)
phase to phase gives you 415v

SouLJah

Hey, allanlane5·your reseverations aren't unfounded, most people don't know as little as 6mA through·the heart could be fatal.· Your concern is greatly·appreciated.

Regards,


SoulJaH

stamptrol

To simplify things, many wallwart style power supplies are designed to have input voltages of anywhere from 100 - 240 volts, 50-60 Hz. They are typically switchmode type and are available in any of the usual outputs. I've purchased 5, 12, 24 volts units for various projects, up to several amps.

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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SouLJah

Do you have a part number?

stamptrol

The one on my desk at the moment is from C.U.I. Inc, model HK-H1-A24, its a 24 volt unit.

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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dexf

Julie in Texas:

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.

================

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