Reuse the autotransformer of a 220-110V stepdown

[Hitto]

I would like to reuse the autotransformer of this device, which converts 220 to 110 and claims to be bidirectional.

This transformer has 0-220V inputs and 3 output wires. One goes to a diode in the PCB, the other one is output, the third goes through a relais which then goes to outputs.



It seems to be a common design in these kind of converters but I can post more photos if needed.

Do you guys know if the autotransformer in these step-down can be used for straight 220-110V conversion, bypassing the circuit?

[sam_sam_sam]

Re: Reuse the autotransformer of a 220-110V stepdown

This depends on whether or not it does setup and step down but sense you said that it bidirectional input/output are reversible then I think that you but you would have check how the winding are wired to really know for sure what type you have

[budm]

Re: Reuse the autotransformer of a 220-110V stepdown

What is the make and model of that unit?
Also provide pictures of the whole unit and full PCB top and bottom side.

[Hitto]

Re: Reuse the autotransformer of a 220-110V stepdown

The unit is quite generic and not available currently on eStores for a comparison.
The PCB is marked LLD57/040ASC.

FRONTAL:



REAR:



TRAFO (TRANSFORMER):



They made a mess of wires with identical colours. Howewer the PCB is clearly marked with AC-IN (220V), OUT (110V), OUT (next to 512#).

[Hitto]

Re: Reuse the autotransformer of a 220-110V stepdown

Judging by the connections, but I am not sure about blue wire:

[sam_sam_sam]

Re: Reuse the autotransformer of a 220-110V stepdown

Are the winding interconnected or they isolated from each other

Do you know how to check this ?

Which side is the winding connected to the 110 volt side or the 220 volt side

[R_J]

Re: Reuse the autotransformer of a 220-110V stepdown

The blue wire is likely a low voltage winding that supplies D1 and (35v) filter cap. The other end of the blue winding likely connects to yellow or red. You need to check the resistance of the windings to see how the transformer is wound.

[budm]

Re: Reuse the autotransformer of a 220-110V stepdown

the blue wire is likely a low voltage winding that supplies d1 and (35v) filter cap. The other end of the blue winding likely connects to yellow or red. You need to check the resistance of the windings to see how the transformer is wound.

+1

[budm]

Re: Reuse the autotransformer of a 220-110V stepdown

"The unit is quite generic and not available currently on eStores for a comparison.
The PCB is marked LLD57/040ASC."
Obviously it's not generic autotransformer setup since it has active circuit with relay in it.
How about the external pictures of the box? It should have model number and some marking on the box itself.
Since it has relay (12V winding) and powered by one of transformer winding, then it not just a passive autotransformer setup.
Where do the whites wires go to? Neutral for the in let and neutral for the inlet and nothing else?
Autotransformer for step or step down will have Neutral direct connection between input and output.

[eccerr0r]

Re: Reuse the autotransformer of a 220-110V stepdown

Interesting, this would be the first...auto switching? step up/down transformer that I've seen...

Did it automatically detect input voltage and switch the outputs accordingly? Seems like it should...

I have two step up/down autotransformers, neither of them are auto-switching, I have to flip a jumper to set the input voltage.

Is there a reason not to use the circuit? Or is it for some other purpose or perhaps the circuit is defective?

[Hitto]

Re: Reuse the autotransformer of a 220-110V stepdown

Yes, it automatically switches between 110 and 220VAC.

This is a close-up of the unit:


I was hoping to use the transformer without the circuit as the PCB has too many lifted pads.

[sam_sam_sam]

Re: Reuse the autotransformer of a 220-110V stepdown

I do see any reason could not use this transformer but you have to answer a very simple question how is this transformer wired then you will know how you could use it

[budm]

Re: Reuse the autotransformer of a 220-110V stepdown

He needs to read post #7 to find out how each winding is.

[eccerr0r]

Re: Reuse the autotransformer of a 220-110V stepdown

I would hope that the two white wires on the transformer are actually connected together internally, so either can be used. In an autotransformer, one wire is shared between input and output, which would be the two white wires. Then just ignore the blue wire which is used for the auto switching...

This sort of makes me want to build an autoswitching circuit for my step up/down converters, alas, the chances of me using it for step down is very unlikely.

[budm]

Re: Reuse the autotransformer of a 220-110V stepdown

OP should find out how the Neutral for the Inlet and Outlet are wired up.
BTW, how much power do you need for the load? The unit that you have is rated at only 40W as printed on the unit.

[Hitto]

Re: Reuse the autotransformer of a 220-110V stepdown

40W should be enough as this unit will be used mainly for testing.

I have another one but it is sealed. Planning to open it with wires intact so you guys can check if it is indeed reusable without the circuit.

[eccerr0r]

Re: Reuse the autotransformer of a 220-110V stepdown

If you're not sure, just get another 12VAC transformer and hook it up to any two wires, with the exception of probably the two white wires together. Measure all you want, and that will be easy to find the remaining wires...