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Author Topic: Transformer wanted  (Read 1283 times)

funtimefrankie

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Transformer wanted
« on: April 01, 2011, 08:20:53 pm »

I'm after a transformer for my central heating, It's mains 240 volt down to 24 volt, it says 12VA, is this half an amp output?,
or what does 12VA mean?

Any suppliers recomended?

Ta Frank
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john s 2

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Re: Transformer wanted
« Reply #1 on: April 01, 2011, 08:48:56 pm »

Im taking a guess that the Transformer you require is for your Combi Boiler. 24 v is often used as output for
the wall thermostat and to drive relays etc. It is rare for the transformer to fail. There may be a very
small fuse on the board. Two ways of fixing things come to mind. My local specialist Boiler Bits sells recon
cards at a lot less than new price. A Scrap merchant or your local Council tip should have Boilers in for
recycling possibly yeilding the correct card or a transformer. Or of course there  is Maplins . Nice to know
that im not the only one who likes to repair things. I have 7 Combis in use. Often these types of Boilers are
scrapped because the plumber shakes his head. He of course wants the job of fitting a new one. Before the
brickbats come not all are dishonest, Yes im also aware of rules on gas. But work on the electrics and
water side should be ok. John.   
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funtimefrankie

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Re: Transformer wanted
« Reply #2 on: April 01, 2011, 08:56:22 pm »

It's not a combi, it's a vintage glowworm. The transformer powers the gas valve. I've it out next to me and the primary winding is dis.
We are running on a US robotics plug-in power supply out of my "don't throw that away box" at the moment, it's 18 volt but seems to be Ok for the time being,
Anyway its now warm again, the house that is
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flashtwo

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Re: Transformer wanted
« Reply #3 on: April 01, 2011, 09:32:59 pm »

Hi,

Try Rapid Electronics, since they have a better range than Maplins:-

http://www.rapidonline.com/Electrical-Power/Transformers/Power-Transformers/Control-Panel-Transformers/400342

I use Rapid for the more uncommon components that Maplins don'tstock.

Ian
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flashtwo

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PMK

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Re: Transformer wanted
« Reply #5 on: April 01, 2011, 11:44:47 pm »

12VA is just another way of writing 12 V*A (volts times amps), which is just another way of expressing Watts. In order to calculate the amperage on the secondary, you simply divide Watts by Volts. In your case you only have to divide 12 Watts by 24 Volts, which, as you correctly said, is 0.5 Amp (or 500 milliamps).
Flashtwo beat me to it with his suggestion to check the Rapid site, but it's not clear if your transformer is of the PCB-mount type. In which case you might otherwise grab a grok of this link on the ESR site, http://www.esr.co.uk/electronics/products/frame_transformers.htm , then click "Encapsulated", then scroll down to part number 300-935. Price = 8.48 plus 2.50 shipping, plus the dreaded VAT.

Good luck.
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funtimefrankie

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Re: Transformer wanted
« Reply #6 on: April 02, 2011, 04:09:53 pm »

Thanks for the info, it's a chassis mount, so I've gone with one from Rapid.
Just another point it has two 24 v outputs, do I just use one or can they be looped together, ie the 0v together and the two 24v together, or just use one output?
Thanks
Frank
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PMK

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Re: Transformer wanted
« Reply #7 on: April 02, 2011, 06:00:21 pm »

The two separate 24v outputs will be out of phase with each other with respect to 0v. Some form of ac/dc rectification will already be there on your boiler's circuit board, so your best bet is to use the transformer 0v and just one of the 24v outputs.
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funtimefrankie

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Re: Transformer wanted
« Reply #8 on: April 02, 2011, 07:00:27 pm »

Thanks
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funtimefrankie

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Re: Transformer wanted
« Reply #9 on: April 05, 2011, 05:39:49 pm »

All fitted and working. Rapid, link above, recommended for fast service :-))
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