When working wig a transformer that is drawing power from a 120 volt outlet. If it is a 24 volt 20vac transformer how do I figure out the maximum power I can draw from it without burning it out and how do I figure out what a circuits resistance should be so that most of the power is going brought th circuit and not the transformers internal resistance.

 

If it is a 24 volt 20vac transformer

Your transformer is either 24 VAC or 20 VAC at the secondary. The transformer should have a power rating (watts) or a current rating(amps) associated with it. To get current from the power rating, divide power by the voltage. That figure (current) is the limit the transformer can supply - i.e., 24 volts and 1.5 amps.

For your application, use Ohm's law.

 

Hi, your origional post was here
http://forum.allaboutcircuits.com/showthread.php?t=50060
Its generally a good idea not to double post.

Relating to your question, it probably overloaded because you shorted the guitar string across the secondary. Heating elements are coiled because this increases resistance, (among other reasons), and the resistance prevents the current from overloading the transformer.

 

transformers will be rated in VA, or a secondary ampere rating. You can expect some temperature rise in a transfomer running at it's maximum rating, and from that point upwards, the temperature will increase and eventually disrupt operation.

The best prevention of over drawing a transformer is through fusing.