I bought a 50w travel transformer with the intention of providing isolated power for a 110v relay switching 240v heater circuit. When tested the output was about 230ma and although the power relay in it's DC form is a 2w coil they only list it as 11va@60hz with no power factor given.

However, I found that I had a common connection from the 110 side to the 220 side. So I unwrapped the outer layer of insulation to isolate the windings only to find I had an autoformer, basically two 120v windings in series one side grounded and a center tap. I still isolated the sides because 110 v source was available and I wanted to switch the coil from a small solid state timer driven relay but when testing, the output current had dropped to 5-6ma. The windings are 420ohm and 2nd half is 450ohm.

 

Yes, most travel transformers are autotransformers since they are smaller and isolation is normally not required.

Don't understand your question, what you are trying to do, or why you need isolation?

 

Yes, most travel transformers are autotransformers since they are smaller and isolation is normally not required.

Don't understand your question, what you are trying to do, or why you need isolation?

I probably don't. Just thought it would be better. The power relay is certainly not going to suffer but I was concerned about the ratings of timer since I've noticed some circuits advertise capabilities the components don't support. I see terminals and components not to mention layouts that are suspect. Maybe I'll use dc relay module separate from the timer to drive the power relay. I am attaching the power relay data.

 

I was concerned about the ratings of timer since I've noticed some circuits advertise capabilities the components don't support.

That does not tell us enough to answer your concerns.
What "capabilities the components don't support"?

It seems like you have concerns about things you don't need to concern yourself with.

 

Well the basic question is why does the transformer not provide the current. ?

 

Well the basic question is why does the transformer not provide the current. ?

Sorry, but since I don't really understand what you did to the transformer, I can't answer your question.
Just put the transformer back the way it was originally (if you can).

 

I guess I really don't understand, either. If you aren't getting the current out of the transformer, maybe you broke it or it was bad to begin with. A sketch of what you are trying to do i.e. where the timer is, relay is etc. would help here.

 

I guess I really don't understand, either. If you aren't getting the current out of the transformer, maybe you broke it or it was bad to begin with. A sketch of what you are trying to do i.e. where the timer is, relay is etc. would help here.

The transformer had two leads on one end of a 230v winding with a center tap. The common and 230v end was connected to the euro socket and the common to center tap was connected to the US blades of the transformer. When connected as built you could get about .144ma even though it was rated for 50w but that was more than sufficient for my need. However when I separated the winding at the tap and made it into a 120/120 isolation transformer the current available dropped to less than 10ma, no longer enough to power the relay coil. Hence my question about the load current contributing to the transformer in an additive fashion in some way as when it's plugged in to the 110 side it still produces about 30w at the 240v output while only connected to 1/2 of the winding from the line.

 

The current capability of the 120v winding will be somewhere in the order of 100mA, no matter if the the windings are joined or separated. You have incorrectly read the output current. The current-capability does not change.

 

The current capability of the 120v winding will be somewhere in the order of 100mA, no matter if the the windings are joined or separated. You have incorrectly read the output current. The current-capability does not change.

That was what I was expecting but is not what happened. Although it was rated at 50w I had no requirement for that much so my initial measurement of 144ma didn't bother me. I measured the current on two different meters (Fluke 27 and HP3478A) and also tried it using a load matching the required load to see if the load somehow affected the magnetic saturation but I could only get anything over 10w by using it as an Autoformer. As an isolation transformer it basically did not have any useful power.

Just trying to fathom why this did't work though.

As an aside I've decided to use as autoformer and move on without isolation.

 

50 Watts needs to be a 1kgm transformer The max you can get is 50 watts per kgm

 

They are relying on 25 watts "for free" and 25 watts via the transformer.