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Old 22nd Mar 2023, 10:42 pm   #39
kalee20
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Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,059
Default Re: Transformers in parallel?

Quote:
Originally Posted by mhennessy View Post
Trying to reduce the ripple by using large smoothing capacitors might seem like a good idea on the face of it, but the reduced ripple means that the conduction angle is reduced - therefore there is less time to "top up" the capacitors, so you have to draw more current from the transformer.

This image shows the relationship between ripple voltage and conduction angle:

https://www.markhennessy.co.uk/artic...tion_angle.gif
It's true that upping the smoothing capacitor reduces the conduction angle and the peak current gets higher, but it's not without limit! The transformer (and rectifier) resistance ultimately limit the charging current, and the capacitor voltage never reaches the AC peak, as per your linked diagram.

Once you go round the 'knee' in Schade's curves, the peak current and charging-pulse duration hardly change with increase of C. The ripple of course does decrease without limit, but once it's a small fraction of the voltages under consideration, the transformer resistance dominates the situation and it makes no difference to the transformer, once steady-state conditions have established, whether the OP has his several tens of thousands of microfarads, or a hundred million farads. (This latter extreme would of course take a lot longer to reach steady-state, but once there, the transformer wouldn't notice the difference).

See attached sketch.
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