Replacement transformer for Christmas decoration

Daniel112

I'm trying to find a replacement transformer for an old Christmas decoration. The original transformer gets very hot when plugged in so needs to be replaced. It's at least 15 years old at this stage anyway. I'm hoping that someone can point me to a replacement that I can buy online. I've searched for TDC Power which is an American company and as far as I can tell they no longer manufacture this model (They don't sell direct to consumers regardless). I also had a quick look on Amazon and only found a lot of Chinese transformers that don't 100% match what is on the original label. I've been trying to find an exact match in case the product is damaged with a replacement transformer but if someone knows of a replacement that will do the job that would be great!

cml387

Any bog standard 12Vac 1 amp will do:

https://uk.rs-online.com/web/p/ac-dc-adapters/1391775

The problem you may have is the connector. Does it plug in to the Christmas decorations?

10-10-20

That's a 12v AC 1A double-isolated transformer. Double-isolation is indicated by the image of the square inside the larger square.

Those are tricky to find. Most of the ones on Amazon are marked as AC in the text, but are DC in the images.

The likes of this should do it, except they aren't fully robust from an electrical safety standpoint in that the wires aren't very well secured; but it is double-isolated:

https://www.amazon.de/-/en/Isolicht-Universal-Transformer-Suitable-34078/dp/B01F2AYCO2/ref%3Dsr_1_25?crid=191CP7DHIFBW1

This is another option and is fully sealed for outdoor use and that would imply double-isolation:

https://www.amazon.de/-/en/ledscom-Transformer-Power-Supply-2-Wire/dp/B005JXH28G/ref%3Dsr_1_41_mod_primary_new?crid=191CP7DHIFBW1

10-10-20

Oh and Premier UK might be able to help:

https://www.premierdec.com/Support

10-10-20

https://www.boards.ie/discussion/comment/120059981#Comment_120059981

Yeah, that's a good one. It's double-isolated too.

kirk.

https://www.boards.ie/discussion/comment/120059998#Comment_120059998

I thought that symbol was double -insulated not isolated ?

As in doesn't require earthing

hawkwing

is this what you need 1.5VA Plug-in Adaptor For Premier Water Spinners – McD's Garden & Home (mcds.ie)

10-10-20

https://www.boards.ie/discussion/comment/120060057#Comment_120060057

Ha! It is. I learned it wrong, but same implication.

It also implies that there should be inherent isolation from the input to the output so that no one fault in the electrical device can allow the incoming mains to pass through to the output. Many cheaper USB chargers fail on this aspect and have killed people and also become the subject of YouTube videos (example: https://www.youtube.com/watch?v=wWAA3Z4cfCg).

Some older transformers had major issues with isolation in that a fault on the primary coil could short directly into the secondary coil within the same physical loop. Hence they regulated transformers so that the primary and secondary are now physically isolated from each other within sleeving and no one fault can cause the mains to cross over to the output.

kirk.

https://www.boards.ie/discussion/comment/120060155#Comment_120060155

Off the top of my head I don't think it relates to electrical isolation of the transformer sec from primary

Think basically it means it doesn't need earthing and you won't get a shock touching the body of the transformer itself

Open to correction if I have that wrong

10-10-20

https://www.boards.ie/discussion/comment/120060244#Comment_120060244

https://jestineyong.com/double-insulated-smps/

OT, but here's an interesting article on double-insulation on an SMPS PSU. Class-II (double-insulated) requires that physical gap between the hot and LV side, crossed only by a class Y cap.

A class Y cap's failure-mode is to default to open circuit and not closed (short) hence maintaining that physical barrier to protect the user from mains voltage on the LV side in the event of a failure.

kirk.

Think we're talking about 2 different things

SELV and Double Insulation

I don't see the connection in the article between the Y capacitor and double insulation

10-10-20

It's the subject of much debate but SELV does mandate double-insulation, but double-insulation in it's own right is the physical separation of the primary and secondary side and mandates insulation at transformers, armature/stator cores and the elimination of earthing (unless specially required for the primary side) or a metal chassis surrounding the device.

With either transformer or SMPS based PSU's the primary side is isolated from the secondary using physical separation and there is no external earthing or metal chassis. It's also isolated from earth on the secondary side (if earth is used).

That physical isolation is the gap in the PCB tracks and the air-gap above which is only bridged by an EMI filter which is a mandated class-Y cap.

The way I understand is is that you can't have "double-insulation" in a transformer based PSU if you don't isolate the primary and secondary, and in an SMPS PSU you need that track gap and possibly an air-gap between the HV and the LV.

Lenar3556

I think you are confusing the principles of isolating transformers and the SELV directive with the double insulated symbol which is a different matter entirely.

Many applicances are ‘double insulated’ by virtue of their having supplementary insulation between the user and live components contained therein. They don’t require a safety earth connection. They are usually encased in plastic. Many double insulated applicances are directly connected to 230V and there would be no transformers involved at all. My wife’s hair dryer for example is double insulated.

10-10-20

I'm fully aware of class II devices which are double-insulated and do not have a transformer. But this is a discussion about a transformer based power supply and how the double-box logo both indicates that the transformer is fully enclosed in plastic and also has fully isolated primary windings from the secondary. That's the point of double-insulation on power supplies - it's not just to avoid the IR and continuity parts of the PAT test!

How that carries over to SMPS based PSU's has confused the point, and that's my fault.

carltonleon

Having the same issue myself and apologies for hijacking your thread a little, but trying to find an replacement transformer for an indoor Christimas decoration which is over 20 years old

cml387

The same power supply I linked to in my previous mail will work fine but again you need to check that the connnector end that plugs into the decoration is compatible.

kirk.

https://www.boards.ie/discussion/comment/120062846#Comment_120062846

I saw online a reference to double insulation on transformer windings.

Bell trafos are mostly marked with a double insulated symbol. Would that refer to the windings then ?

It would seem odd otherwise a double insulated symbol on a bell trafo

Class II plug in power supplies only refer to the basic insulation and the case as the double insulation as a far as I can find

10-10-20

https://www.boards.ie/discussion/comment/120063811#Comment_120063811

Yes, it indicates that the primary and secondary coil are separated/insulated from each other, but obviously linked though the core - which is also insulated - AND that the device is encased in plastic or another material which isn't tied to earth.

Otherwise you have a failure mode where a fault on either coil (such as overheating and delamination) can cause a short with the alternate coil and transfer mains voltage out down the 8v AC wire to the bell/button.

Good link here illustrating the confusion:

https://www.eevblog.com/forum/projects/transformers-used-in-class-2-double-insulated-mains-powered-devices/

10-10-20

By-the-by - if you look at an audio transformer you'll see that these are "close-coupled" so that both the primary and secondary windings are tight against each other to enhance the audio properties rather than provide unnecessary safety. That's how mains transformers were all initially built in the dark-days and that brought about the double-insulated requirement to provide necessary isolation.

I think it's true to say that the "Double-insulation" symbol came over in the 70's from transformers into household devices as a way of describing the isolation steps taken within the device.

kirk.

Thanks I'll have a read of that sometime

One thing I learnt it pays to buy a quality bell trafo like an ABB, they're not all the same in terms of build quality and protection