Step down Transformer 240v AC to 12v 100amp

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SUMMARY

The discussion centers on the use of a step-down transformer rated at 240V AC input and 12V AC output, with a query about its capability to function as a step-up transformer when connected in reverse. Participants confirm that while transformers can operate bi-directionally, caution is essential due to potential hazards such as overheating and insulation failure. It is advised to limit the input voltage to 12V on the primary side to avoid exceeding the current ratings and risking damage. The importance of consulting the manufacturer for safety and specifications is emphasized.

PREREQUISITES
  • Understanding of transformer operation and principles
  • Knowledge of electrical safety standards
  • Familiarity with voltage and current ratings in transformers
  • Basic concepts of magnetizing current and thermal run-away in electrical components
NEXT STEPS
  • Research transformer design specifications and safety standards
  • Learn about the effects of magnetizing current on transformer performance
  • Investigate the thermal characteristics of transformer cores
  • Explore practical applications and limitations of bi-directional transformers
USEFUL FOR

Electrical engineers, hobbyists working with transformers, and anyone involved in designing or using AC power systems will benefit from this discussion.

  • #31


burnit said:
Gday Phrak,

Supply voltage is 240v AC & the Variac is rated at 10 A as mentioned.

Burnit, given that the transformer VA rating is not exactly known the magnetizing current referred to the 12V winding could be close to 10 Amps. Say the rated 12V current was 150Amps and the magnetizing reactance was 15 (pu) then you're looking at 10 amps already. In other words you're variac might be close to it's ratings just supplying the excitation current. It might get a little warm but things do that when you're running close to rated current.

Can you measure the magnetizing current (that is, the current being drawn by the 12V winding when the 240V winding is open circuit). A true RMS ammeter would be best because the current might have a lot third harmonic and this will cause an ordinary ammeter to slightly under-read. Any measurement would be better than nothing though.
 

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