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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Big can of worms! posted by Al Sekela on April 25, 2007 at 11:10:21:
<< Another problem with toroidal power transformers is their low primary winding resistance. This allows them to be saturated more easily by "DC" on the AC line >>Yes, toroids saturate more easily than E-I transformers. But is not because a toroid has a lower primary winding resistance than an E-I. It is because there is much less leakage flux. All of the flux generated by the winding stays in the core and saturates it. In contrast, the E-I core has gaps in it where some of the stray flux leaks out. This makes it much harder to saturate the core.
The penalty is that the E-I transformer is less efficient. It will require a higher "excitation current" (current in the primary with no load on the secondary), because the inductance of the primary winding is lower than for a toroid. This means that an E-I will run hotter than an equivalent toroid.
Please note that in general, big toroids will saturate easier (and hum more) in the presence of DC than small toroids because they are wound with large wires that have a low DC resistance. This means higher currents for a given amount of DC offset.
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- One correction - Charles Hansen 11:43:42 04/28/07 (0)
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