Problem with travel transformer

[thebadtall]

Hello ! how are you?

here 's my problem :

I have a travel transformer, 100W wich converts 220vac to 110vac and the opposite.

I use it to supply a tube preamp at 150VDC.

When I connect the transformer to mains, it heats a lot and then stop working. It has not ntc, but the tape of the transformer has melted and it smells horrible, like fresh paint !

However, when I connect back to back a 12v and a 20v transfomer, i have no problem at all...

Any ideas why ?

thank you !


( And summer isnt over yet ! )

 

[zsolt1]

hi,
when a transformer over heats operating without load in the secondary winding(s) it can mean 2 things:
1 the magnetization current is to high ->......->.......-> ....-> primary winding trouble
2 secondary winding has short circuited turns (actually the short circuited winding is the load and produces heat...)
or... the magnetic core is compromised by rust, meaning that the magnetic core itself is a big short circuited turn, driving a high current load thru its laminations that are in contact vith eachother
As you describe the situation your transformer is burnt and you need to by an other one or rewind this one ...

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Ps : transformers can overheat when they are externally overloaded ( by your amp for example ... )

 

[thebadtall]

the transformer is 100W, the preamp draws no more than 5w so is not overloaded.... but the transformer was very cheap, and so... its shorted as you mentioned.
it has no rust. It costed around 7 eur
thank you

 

[Raza]

the transformer is 100W, the preamp draws no more than 5w so is not overloaded.... but the transformer was very cheap, and so... its shorted as you mentioned.

Yes it seems that there is shortened winding. Do a test, just simply connect to mains without connecting any load to it and see if heats same way, if YES, the trafo is short circuited and if the answer is NO then there is some thing wrong with the connected load, drawing over current and causing over heating. ( a very simple and quick test without ant any tools)

 

[thebadtall]

yes it heats without load. and either with very low load.. it experienced an overload some days ago and burned the fuse

 

[jeffrey samuel]

it is better that you rewind the secondary and try to put new copper in the secondary that will deal your issue

 

[thebadtall]

I will buy a new one , as it cost around €7
does not worth to rewind
thank you...

 

[jeffrey samuel]

that is also a solution in a different form

 

[thebadtall]

My initial concern was if there was something different in travel transformers, but all in all this cheap equipment is not at all reliable
it is marked as 100W and weights about 500gr, where as any real 100va transformer is a few kilograms

 

[Raza]

There is a bit difference in VA and WATTS.
" In AC, the product of current and voltage is called the apparent power of a load, and is measured in volt amperes (VA). The watt is the unit of true power which is the product of current, voltage, and power factor of a load ". In resistive loads the power factor is 1 as the Voltage and the Current are in phase.

 

[thebadtall]

i know, they are not identical, but I apply a low load of less than 5w so its insignificant.
by my previous post i mean that this transformer is a cheap chinese junk !

 

[jeffrey samuel]

some chinese product are junks as you say but not all some of the rarest products are chinese

 

[tpetar]

High power transformeless 220V to 110V with triacs :

 

[thebadtall]

hello tpetar. you finally show up!! how are you?
bad you post this now as i ordered a very large amount of components and id like to include those!..next time!
this circuit is DC ? what is the coil for?

 

[tpetar]

Hi, I'm nice, thanks,

Its 220V AC to 110V AC.

Coil is load.

 

[thebadtall]

and i can replace the coil with the amplifier?
also can i modify it for lower or higher voltage?

 

[tpetar]

There is explanation in text how this works in second picture is whole page of project, this is used for 220V to 110V, for other transformeless voltages you have other designs.

 

[szhighstar]

There is explanation in text how this works in second picture is whole page of project, this is used for 220V to 110V, for other transformeless voltages you have other designs.

H friends,I am Chinese engineer in magnetics component industry, yes, some false parts are from China, I suggest to look for official factory from China,many factories in China pay attention for quality, if you select transformer from official factory,you do not worry about quality, all transfomers and chokes and inductors must be 100% test, including HI-POT/Inductance/leakage inductance/DCR/ turns ratio/capacitance/SRF and so on, from IQC to IPQC and OQC, have full quality system.

 

[FvM]

A point hasn't been mentioned yet, travel transformers are usually auto-transformers, providing no isolation between 220 and 110 V side. I don't know how you exactly connected it, but if you grounded the output, fatal damage won't be surprizing.

 

[thebadtall]

i measured the secondary to primary and it is not connected. both are not grounded.
i connected the secondary to rectification bridge and 200v electroclytic capacitor