Electronics > Projects, Designs, and Technical Stuff
60Hz Transformer Core Loss
james_s:
IIRC at no load the core losses will be higher. As you put some load on the transformer that draws some of the flux out of the core. It would not surprise me if the core is saturating with no load at all, especially if your line voltage happens to be a tad on the high side. Try connecting a resistive load of at least 10% or so of the transformer's VA rating and see if the losses drop.
duak:
I believe james_s is right on the money. I understand that microwave oven transformers are generally designed for full load and can saturate at no load.
I got a bunch of vacuum tube telco exchange equipment in the early 70s and found the quality of the components to be top notch. Wasn't this stuff designed for 20 years of 24/7? The power transformers ran remarkably cool compared to, say, consumer audio or TV stuff of similar vintage.
I haven't bought any new Hammond stuff since the 90s. Their potted toroidal transformers easily met their specs. I hope the trademarked product names like Imperator doesn't mean the end is nigh. (Anyone remember jumping the shark?).
lifted from wiki: Avē Imperātor, moritūrī tē salūtant ("Hail, Emperor, those who are about to die salute you") is a well-known Latin phrase quoted in Suetonius, De vita Caesarum.
H713:
Lots of cheap transformers are running right on the edge of core saturation, and at 124 VAC you might be pushing it slightly farther into saturation. Not ideal, but it's probably fine if it doesn't get too hot. I will agree that the current you're reading is pretty high for being just magnetizing current on a transformer that size- I read about 350 mA on a "750 VA" (it weighs 50 pounds... by my calculations it's more like a 2400 VA transformer).
I've had good luck with Hammond tube output transformers. Price is a bit high, but the fit and finish has been fine.
I have not heard good things about their power transformers. A lot of them seem to run ridiculously hot even when running at less than 50% load.
For Toroids, I have had good experiences with Antek for the price.
trobbins:
If the magnetising current waveform is peaking due to onset of saturation, then even more doubtful that the current measurement is representative (especially given a reported sensitivity of 0.1A, although my plugin monitor has a mA resolution), and doubtful about the PF value as well.
H713:
--- Quote from: trobbins on July 18, 2020, 11:55:29 am ---If the magnetising current waveform is peaking due to onset of saturation, then even more doubtful that the current measurement is representative (especially given a reported sensitivity of 0.1A, although my plugin monitor has a mA resolution), and doubtful about the PF value as well.
--- End quote ---
Agreed, it would be nice to get a scope waveform of the primary current. Of course, this would require a differential probe or current transformer.
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