Transformers, well, in theory the iron loss is proportional to weight, and a function of flux density and frequency. What makes small transformers inefficient is a combination of the fact that only a part of the iron is aligned to the magnetic field, because the core is stamped from a sheet. Distribution transformers are built up from separate strips of grain-aligned electric steel. They operate at 1.7 T and higher, where the amorphous sheet E-I cores typically are no higher than 1.2 T.
Automatically this means more turns of a smaller wire. it's also a squared function, double the flux density, halve the turns, 1/4th the resistance, 4 times the VA's.
Perhaps the real reason small transformers are inefficient is because they can be, proportionally they have 1000 times more cooling surface area, compared to a 100MVA Tx.
thanks for the comments
my question is, if small transformers are less efficient, how do inverters that use them in the final stage (60 hz) reach overall efficiencies of ~90%?
it would seem to me that perhaps the transformers used in inverters must be more efficient than their off the shelf counterparts.
if they were 80% efficient, then the rest of the circuit, controls, cooling fans, etc would have to be at the very least 100% efficient for an average of 90% overall. (and we all know nothing in the real world is 100% efficient)
the reality would seem that the electronics would be closer to maybe 95% efficient and the transformer to be 85% for it to average out at 90%? that is if the losses are about evenly shared between the electronics and the final stage transformer? it would seem to me that the losses would be weighted toward the transformer instead of the electronics in reality, so would it not follow that the transformer would have to be much closer to 90% for the total of the inverter to achieve 90% efficiency?
i have two sets of transformers out of inverters, they are both EI cores but are built up that way, out of seperate pieces interweved to form the E section and the I section rather than the more common stamped complete E section with its complimentary I stampings.
perhaps the inverter transformer cores are made to a higher standard and therefore achieve higher efficiency?
just trying to get an understanding of these efficiencies,, there is not much written about transformers in this kva rating that i have found.
if it is true that inverter transformers are built to a higher standard and achieve higher efficiencies it would appear to me that old inverters/ups transformers might be useful for power conversion/transmission of diy'er windgenerators.
thoughts?
bob g[ Parent ]
I have used a 450va rated transformers from an APC ups as a 600 watt oil cooled battery charger, it didn't burn up, also the no load current draw was 1 amp from a 12 volt lead acid, when operating as an inverter. now that I think of it, that is really good, considering the iron core weighed a few pounds. I would not be surprised if the iron is of a much better grade than it was 10 years ago.[ Parent ]
