| Electronics > Beginners |
| What happens if a transformer that get less voltage then rated for? |
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| FriedMule:
What would happen if lets imagine, you have a 400VA 200V main in to 40V 10A secondary out. And you only supply it with 100V. What would that give? 20V ?A secondary out? |
| Doctorandus_P:
Ratio between input and ouput voltage wil stay the same. So, if you halve the input voltage, the output voltage wil also be halved. The opposite is not true. Most (mains) transformers are driven pretty close to saturation of the core, and if you put more voltage into a transformer winding than it is rated for you are likely to destroy it. Destruction is not instant though, but it wil overheat (too much current) after a short time (can be minutes). Because (usually) transformers are so close to the maximum voltage they can handle, they lose a bit of linearity between input and output voltage. So it is possible that your transformer will output 21V or 22V. Current rating of the transformer wil stay the same. So output will be 20V,10A instead of 40V,10A. Also note that the output voltage is usually specified under full load. Output voltage will be a few percent higher for "big" transformers under a light or no load, and for small transformers this can be upto about 20%. |
| Electro Detective:
Are you limiting the input voltage with a variac ? please explain the conditions |
| FriedMule:
My idea was to get a 600VA 240V in 2 x 30 out transformer but then I read about flux, saturation and heat. That gave me the idea to use a 300V in 2 x 37.5V out or if you recalculate it (300V - 70V ) / 1.25 = 240V - 60V |
| Brumby:
My experience is that people with capacity concerns simply upgrade the VA rating. In your example of 600VA 240V in 2 x 30 out I'd go for 750VA (or higher) 240V in 2 x 30 out. But derating a higher voltage transformer is also valid. |
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