center-tapped full wave vs. single winding bridge rectifier

[pula58]

It seems like if you abandon the common center-tapped power supply transformer scheme with full wave rectifcation that you could have only a single HV winding and have half the wire (inside the PT). But wait, now the single winding is being used every half cycle whereas in the center-tapped PT each winding is only used for half the cycle. So the power dissipated in the windings (from IR losses) in the single (non-center tapped) PT winding would be twice that of the center tapped PT given the same wire gauge. Thus, you would probably have to increase the wire gauge of the single-winding PT. So...and I think you see where I am headed on this, if the wire gauge of the single-winding PT has to be increased, does the total amount of winding wire end-up being the same in terms of the sheer amount (mass)of copper wire?

[martin manning]

In a first-order analysis, yes. The average current in the single FWB winding doubles with respect to a FW, but the length is cut in half. For the power dissipated I^2 R to be the same R must be 1/4 as much. R is proportional to L/A, so with L reduced by half A must be doubled. Since mass is proportional to volume AL, the mass is the same.

[pula58]

I think I get what you're saying Martin. The total amount (mass) of wire would be the same.

Then it seems like the foilliwng is true:
comparing single HV winding with a bridge vs. Center tapped winding with a full wave rectifier: There is no advantage in terms of the size/mass of the transformer.

[martin manning]

The above talks about the mass of the wire only, but the mass of the core should be about equal too since the flux density is proportional to the number of Ampere-turns, which is the same either way. There is a likely a cost advantage in using a shorter length of heavier wire, and there is often no separate winding or tap for the bias supply in a FWB arrangement.

[katopan]

I don't know how it turned out by weight, but single winding with the higher current rating takes up less room in the winding window. The first PT I wound was 225V for a 10W amp. I was reusing the existing primary and rewinding the secondaries. When I calculated up the wire size and layers there was no way I could fit a 225-0-225V HT secondary, but 0-225V with thicker wire fit no problem. That's how I wound it and was forced to use a bridge recto for that amp.