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Discussion Starter · #1 ·
I was very impressed with Doug Teggins build of the above. I checked the ebay web site Antek for the transformer and all the transformers appear to be USA and 115 volt mains input. Also they are for CNC machines but I guess this is ok.
My question is if I get one of these transformers (only 2x15volts) available at present, how do I convert if for 220 volt input
RH
 

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Hi Roberth1
Not sure why you want to import from US? (assuming youre in the UK?). P & P on something that heavy must be enormous and then there's the risk of HM Customs charging you import duty!

Have you considerd UK sppliers such as Rapid or RS

and perhaps even Maplins

Good luck anyway
 

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QUOTE (Brian @ 7 Mar 2007, 17:47) <{POST_SNAPBACK}>Not sure why you want to import from US? (assuming youre in the UK?). P & P on something that heavy must be enormous and then there's the risk of HM Customs charging you import duty!
Import duty is based on value not weight
I had a parcel that was over 25kg, a duty query was raised, but when I supplied the invoice the item was released to me, and all within 10 days
Providing the import is less than £100 no duty should apply
 

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Discussion Starter · #6 ·
Thanks to evryone for responding to my query.
Thanks Brian for your links I have found a transformer there which is 300VA and has 2x15volt outputs, I guess 2x15volts for output will be ok Doug.
The transfomer has two primary windings each at 115 volts so I guess I join the 0V terminal of one winding to the 115V terminal of the second winding and then connect the mains across the final 0V terminal and final 115V terminal putting the two windings in series.

Doug when you say you used house wiring did you use 1.5mm wire or 2.5mm wire and did the metal case come from the French site as well as the other items

Thanks
Robert
 

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QUOTE Doug when you say you used house wiring did you use 1.5mm wire or 2.5mm wire and did the metal case come from the French site as well as the other items
Can't see any reference to this at all??

However there is a serious side to all this - You're dealing with 230 volt ac mains power which will kill you.
Therefore there is the requirement to ensure the transformer/s are cased and if a metal case is used an effective earth is provided to the casing.

Use 0.75mm or 1.00mm flex for all mains wiring with core colours of Brown (Live); Blue (Neutral) and Green/Yellow (Earth) from the mains plug to the transformers connections. Keep low voltage outputs well away from any 230v supplies and cables. Also try and use different coloured wires for the low voltage side e.g. Red/Black or Yellow/Pink etc. This will prevent any miss understanding of which wiring is carrying the 230 volts. The use of a mains DPDT On/Off rocker switch inserted between the incoming mains cable and the transformers primary wiring is useful, especially if the rocker has a neon "Mains power on" indicator. such as these Maplins Rocker Switches

Where the mains enters a metal case you will either need to grip the cable via a grommet and this also prevents the metal of the case chaffing the cable, like these Maplins cable grommets or fit a Euro plug (Chassis plug) and a suitable Euro socket onto the lead, like these plugs Maplins Euro Chassis Plug and matching line socket Maplins Euro Sockets (Plugs have pins and are not live until a mating socket attaches power and of course Sockets have recpticals)
 

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Discussion Starter · #8 ·
QUOTE (Brian @ 8 Mar 2007, 11:10) <{POST_SNAPBACK}>Can't see any reference to this at all??


Brian thanks for responding so quickly. In about the 6th or 7th photo down Doug mentins using rigded house wiring to help keep the components in place and it looks to be like solid core cable like you get inside either 1mm or 2.5mm cable for houses. It is red/black on Doug's box but will under the new regs have changed to brown and blue. I just wondered which size he had used
Robert
 

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All the parts were bought from Conrad. You can see their UK store here: http://www1.uk.conrad.com. You can probably find equivalent items at the shops already listed. Toroidal transformers are also available locally, but you pay 2 or 3 times as much for them here.

The wire on the low voltage side was solid core 1.5mm² - I just had that lying around.

I've had the power supply running for a year now and it works fine. Virtually no heat comes out and all circuits are fine. None of my electronic devices (Lenz, Arnold etc.) had suffered in any way.
 

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Another safety point about torroidal transformers. Make sure that the bolt which secures the transformer to the case does not form a continuous circuit with ANYTHING. If it does, it will act as a "shorting turn" and VERY BAD things will happen. Basically make sure there are no wires attached to the top end of the securing bolt.

I would also recommend fitting a fuse on the mains side. I know that you need a particular type of fuse because of the start up current of a torroidal transformer, but I can't remember which kind and I'm not going to guess. I'm hoping Brian might help out?

David
 

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Just in case anyone is put off from building this, there is a fuse on the mains side in the plan. The main on/off switch is rated for mains use. There is also a mains indicator light. If you follow the way I built it, there is a mains socket with the earth connected to the metal box and the toroidal transformer is bolted to the bottom and insulated on the top with the bolt nowhere near anything else.
 

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QUOTE (dwb @ 8 Mar 2007, 18:28) <{POST_SNAPBACK}>I would also recommend fitting a fuse on the mains side. I know that you need a particular type of fuse because of the start up current of a torroidal transformer, but I can't remember which kind and I'm not going to guess. I'm hoping Brian might help out?

David

Hi David,

It's an "anti-surge" type you need. A 300vA transformer will require something in the region of 1.5 > 2.0a (or follow the transformer manufactures recommendations).

Some high current transformers used for low voltage display lighting also use a thermistor on the mains input side to give a certain amount of "soft start".

Hope this helps.
 

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Thanks Brian. The words "in rush" current were lurking about my memory....

David
 
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