Step down Transformer 240v AC to 12v 100amp

Click For Summary
A step-down transformer rated for 240V AC to 12V can technically be used as a step-up transformer by applying 12V to the primary side, resulting in 240V output from the secondary. However, caution is advised as the transformer’s coils and insulation may not be designed to handle reverse operation, posing risks of overheating and electrical hazards. The primary winding is designed for reflected load current and magnetization current, which could exceed safe levels if not properly managed. Users are encouraged to consult with professionals and consider the transformer’s specifications to avoid potential damage or safety issues. Overall, while transformers can be reversed, it is essential to adhere to voltage and current limitations to ensure safe operation.
  • #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.
 

Similar threads

Power supply for testing: Variac or isolation transformer first?
  • · Replies 6 ·
Replies
6
Views
3K
12V DC Motor in Light Fixture with Dimmer & 12V DC to 110V AC Inverter
  • · Replies 21 ·
Replies
21
Views
2K
Understanding an Inverter Simulation
  • · Replies 26 ·
Replies
26
Views
4K
Asymmetrical grounding of a 3 phase motor being run on a 1 phase supply
  • · Replies 7 ·
Replies
7
Views
3K
"Ground" and "Center Tapped" Power Transformer Secondary in guitar amp
  • · Replies 6 ·
Replies
6
Views
4K
US Split-Phase to EU Heat Pump Not Working
  • · Replies 1 ·
Replies
1
Views
2K
Step down transformers used in residential AC Mains distribution
  • · Replies 2 ·
Replies
2
Views
1K
How to Make a 24V Transformer Output 24V?
  • · Replies 18 ·
Replies
18
Views
4K
Resistive heating power AC vs rectified AC/DC
  • · Replies 10 ·
Replies
10
Views
4K
2 different AC voltages on 1 circuit
  • · Replies 2 ·
Replies
2
Views
2K