darryl

01-07-2012, 08:03 PM

I expect a few here at least will know about this-

I have not been able to find much about the relationship between transformer core size and power capability. I'm talking about the typical EI core steel lamination transformer core construction.

I have a formula that suggests that multiplying the core area (in sq cm) by itself will give a good representation of the power capability of the transformer. In other words, a transformer with a core 2.5 cm wide and stacked 6 cm high gives an area of 15 sq cm, which should be good for about 225 watts. I can find examples of power transformers from audio amplifiers which are quite close in core area, but are a factor of two apart in total weight. Offhand, the heavier of the two would seem to be capable of more power, but not according to the formula. Magnetic path length is longer on the larger transformer and winding area is larger, though the same distance around the core.

How does magnetic path length enter into the equation? I understand that a longer center leg gives more length to wind the wire onto, so you could decrease losses by using a larger gauge of wire, or by keeping more of the wire closer to the core for a shorter length overall, thus reducing copper losses. Also, I have read that the optimum height of the stack of laminations is equal to the width of the center leg. But if you double the height of the stack, for instance, you are doubling the amount of core area, doubling the power capability, but only increasing the length of the wire by 50%. At the same time you are reducing the number of turns required, so it would actually seem like you would be improving the efficiency by making the height of the lam stack more than the width of the center leg.

Turns per volt seems to be closely related to core area, but how does magnetic path length relate to turns ratio?

I understand that transformers are designed differently depending on use- intermittent use under full load gets you maximum power for core area, continuous use under mainly part power lets you minimize the magnetizing current for lower operating temperature, but costs in the ultimate power producing capability, etc. My questions relate to the latter type of use.

I'm leaning towards mating the lamination stacks from two or three transformers into one stack, thus making one higher powered transformer of the same low profile.

I have not been able to find much about the relationship between transformer core size and power capability. I'm talking about the typical EI core steel lamination transformer core construction.

I have a formula that suggests that multiplying the core area (in sq cm) by itself will give a good representation of the power capability of the transformer. In other words, a transformer with a core 2.5 cm wide and stacked 6 cm high gives an area of 15 sq cm, which should be good for about 225 watts. I can find examples of power transformers from audio amplifiers which are quite close in core area, but are a factor of two apart in total weight. Offhand, the heavier of the two would seem to be capable of more power, but not according to the formula. Magnetic path length is longer on the larger transformer and winding area is larger, though the same distance around the core.

How does magnetic path length enter into the equation? I understand that a longer center leg gives more length to wind the wire onto, so you could decrease losses by using a larger gauge of wire, or by keeping more of the wire closer to the core for a shorter length overall, thus reducing copper losses. Also, I have read that the optimum height of the stack of laminations is equal to the width of the center leg. But if you double the height of the stack, for instance, you are doubling the amount of core area, doubling the power capability, but only increasing the length of the wire by 50%. At the same time you are reducing the number of turns required, so it would actually seem like you would be improving the efficiency by making the height of the lam stack more than the width of the center leg.

Turns per volt seems to be closely related to core area, but how does magnetic path length relate to turns ratio?

I understand that transformers are designed differently depending on use- intermittent use under full load gets you maximum power for core area, continuous use under mainly part power lets you minimize the magnetizing current for lower operating temperature, but costs in the ultimate power producing capability, etc. My questions relate to the latter type of use.

I'm leaning towards mating the lamination stacks from two or three transformers into one stack, thus making one higher powered transformer of the same low profile.