Need 12 volt ac to 24 volt ac transformer

snipped-for-privacy@the.farm wrote in news:gjou23dncnb7ne7u2qcfuaf6nk031r1at7@

4ax.com:

Where are you getting your 12V? You could use a voltage doubler to get around 24 volts dc from your 12 volts ac...

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Assuming that you don't need isolation, just use a tranny with either two

12v secondaries, or one centre tapped 24v secondary, as an auto transformer. Connect the two windings in series ( if it's a centre tapped 24v winding, they already are anyway ), then connect your 12v AC across one of the windings. 24v will then appear across the pair of windings, so one leg will be common to both input and output. The primary would be unused, but it would be a good idea to just tie its ends together with a light load - say a 10k resistor. you could connect a line voltage neon indicator across it as well, just to show that it's powered.

Arfa

On Wed, 25 Apr 2007 14:18:20 GMT, snipped-for-privacy@the.farm put finger to keyboard and composed:

Here's a voltage doubling rectifier:

D1 o-----|--|>|-----|-----o +16V | _|_ +

12VAC | --- C1 rms | | o----- )---------+-----o 0V | _|_ + | --- C2 | D2 | |--|

OR you could get one of those 220 to 110 travel adaptors and wire the

110 side to 12 VAC and get 24 VAC out the other side.

- Tim -

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Its for a 12 volt ac pathway lighting system (300 watt ac transformer). 2 or 3 of the lights I want to use are 24 volts.

That sounds the the perfect idea.

Thanks

They may have too much winding resistance. And of course, must be true transformers, not those triac things that are for hair dryers. ;)

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I rather think not, as the power rating of such an item is highly unlikely to be anywhere near the 300 watts or so that you require. At 24 volts, that equates to more than 12 amps ...

Arfa

300 Watts? He said 500ma right? 24V x .5A = 12W (roughly)

- Tim -

A real converter is just a transformer. We always use 'em backwards to step up voltages for our toys. I know that some newer ones may use semi's to do the job, but I did not suggest that type be used.

- Tim -

You also didn't warn him that if he chose the wrong type it would go up in flames.

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Michael A. Terrell
Central Florida

Yep 500 ma (actually the transformer supplied say 800 ma) for some 24 volt rice lights. I purchased some converters on ebay for 6.75 (doubt they are anything more than transformers) 50 watts each plenty for my app.

Thanks

Indeed. I think I mis-understood his second post where he was talking about the actual lamps that he intended to use and the - quote - " (300 watt ac transformer) " I wrongly assumed that as he was talking about 12v and 24v lamps, and that the 12v ones had a 300 watt transformer to power them, we must have been talking halogens at 20 or 50 watts apiece. If the (few) 24v ones only require 500mA, then a transformer-based 'power converter', as you suggest, would certainly do the job. Sorry for any confusion.

Arfa

Most decent transformer manufacturers supply transformers with 2 primaries &

2 secondaries to make the transformer as versatile as possible.

The primaries (which you don't need for what you want to do) can be in series for 230V and parallel for 115V, the secondaries can also be used in the same way so get 12V secondaries and wire them in series and use them as a 12V to 24V auto transformer.

Radio Shack.