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In Reply to: Re: Are my transformers hot !!?? posted by budm on April 24, 2007 at 12:29:58:
Thanks good point, I had them made locally, will contact the manufacturer and enquire, but generally, should I expect EI's to run hotter than Toroids - any ideas?
Follow Ups:
Toroids are more efficient and have wider bandwidth, so they will have less power loss than an equivalent-capacity E-I core transformer. They should run a little cooler. Any transformer can be overloaded, though. Do your E-I core devices buzz or hum? Are you keeping the currents well below the rated maxima for each winding?
They are impressively quite, I can hear them if I get my ear close, but very soft.. Current through them is low (should be), as they are idling, no music playing. Playing music does not get them hotter, or has not at the levels I listern at.I'm going to tackle ventilation, as I could make some improvements there.
Would I expect better performance from toroids for audio?
There is a lot of debate about whether toroids are better or worse than E-I core transformers for audio.Toroids are more efficient and have a wider bandwidth. Thus, they are smaller for a given application and can respond more quickly. The wider bandwidth may not be a good thing if they pass RF noise more effectively than the equivalent E-I core designs.
Charles Hansen of Ayre has posted several times on his choice of the E-I core designs in part to improve isolation from RF noise. Other designers have told me the same thing.
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 (from appliances that cause waveform distortion, such as hair dryers) and to hum loudly while the "DC" is present.
The wider bandwidth of toroids makes the Paul Speltz ZERO autotransformer a good device for coupling low-impedance speakers to modest amplifiers. Their smaller size allows more powerful amplifiers to be compact.
You should definitely look into the ventilation, as restricted air flow will kill most electronic components, not just transformers. If you are sure your current demands are low, then the transformers may be getting hot due to core losses. This might be an advantage if it results in better isolation from RF noise.
< < 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.
Hi.Since the core built up a torroid iron is gapless (vs gapped EI core), very little magnetic flux leakout, therefore low low leakage inductance.
But it is not a all blessing. On the momnet of switching on the power iron, the low primary winding DCR is so low plus low low leakage inductance will generate a hugh incoming current surge.
So for torroids, it is always good practice to get a surge current limiter upstream of the primary winding. If not, at leasst a slow-blow fuse.
Plus it is next to zero DC offset tolerance, which is not at all a healthy feature for push-pull O/P transformers where DC offset is so common due to not perfectly matched O/P power tubes.
Plus EMI/RFI flash-over from the primary to the seocnding winding is much more ready in toroidals.
c-J
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