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Have just built an amp, using 2 x 300VA EI transformers, they get hot, not playing music, probably about 70 Celsius, in a relatively well ventilated case. Not much hotter playing music.I plan to ventilate better, and maybe use fans, I hear they run hotter than toroids, should I expect this heat when idling, is it excessive, what should I aim for temp wise?
They look very impressive!!!!!
Amp is SS class A/B..
Any comments!
Follow Ups:
What is brand and model of the transormer? Does it run hot even without anything hooked up to the secondary windings?
Haven't tried that yet, have only tried with everything connected, I'll try, good point!
The maker of the trnasforme should be able to give you the temperature rise spec of the transformer at full load, it is part of the UL spec.
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?
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.
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.
Hi.Is it finger burning hot or what?
It's approx 65-70 degrees celsius.. makes good music, so I'm wondering if its normal..
Hi.The insulation varnish of the magnet wires used for the windings are normally from 155C (PU varnish) & up to 200C (PE varnish).
The 'weakest' thermal part of a transformer is the interwinding insulation sheets. Old transformers used sort of kraft papers which can go up to 105C. Nowadays, polyester (mylar) sheets are commonly used to replace old kraft papers & can go up to 130C.
So it should be safe for a max steady operation temp of 65-70C.
Yes, torroidal power irons are more efficient than EI. But given same VA loading, torroidal power irons are usually made smaller. Their smaller sizes kinda offset the higher efficiency.
I spoke to the transformer supplier, he said they were safe to 180 degrees celsius, I imagine many things surrounding them would ignite before they got there! I'm still going to look at my ventilation and do some checks as I'm suspicious everythings not as it should be..
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