Transformers and Bmax

[Prune]

Say I want to modify a transformer because it's running too close to saturation. The Bmax formula only uses parameters for one winding. So if I increase the number of turns to decrease Bmax, does that mean that Bmax is reduced by the same amount regardless of whether I add 10% more turns to one winding, or 10% to both windings?

Also, I want to ask how the load affects this. Since a bridge rectifier into a Pi filter means power is drawn only at the peaks of waveforms to recharge the filter capacitors, does that make the saturation issue worse, or it doesn't make a difference?

One more thing. Since I can't take the core appart, I assume it doesn't matter how the extra turns are added, as long as they turn in the same direction as the original windings, no?

[Sch3mat1c]

Saturation depends entirely on the driving winding, the secondary load factors out as far as the core is concerned.

Say you have no load, it might draw 1A inductive and possibly saturation currents. Add a load to the secondary and it might be drawing 6A, 5A of which is actual power being passed; the 1A remains. You can overload it to 51A and the 1A will still be there, the other 50A being transformed properly - winding resistance aside!

To keep the same voltage output, you have to increase secondary by 10% if you increase primary by 10%. Simple turns ratio stuff. If you increase (or decrease) secondary turns alone, you will only change the voltage produced, not the field. If you change primary turns, you will change B as well as secondary V.

For your case, if you have some extra space say between the windings (like, where the shunts used to be), wind on some whatever gauge wire inbetween and connect it in series with the primary, with an ammeter. If current draw is higher, you got it backwards. Think buck winding: if it's backwards, you subtracted 10% and it's more like 80V. It might be best at 100V right now. You want it up to 120V...

Tim

[Prune]

If the core saturates, is the output waveform not distorted? Does the output voltage remain the same? If so, what's the problem with letting the core saturate?

[Prune]

For example, at http://www.allaboutcircuits.com/vol_2/chpt_9/11.html it says that the secondary waveform will be distorted. So it seems to me that if the core is saturating, output voltage can be lower than the turns ratio would suggest.

Therefore, if by adding 10% more turns to the primary I bring my transformer away from saturation, output voltage will decrease not quite 10%.

What's wrong with this reasoning?

[Sch3mat1c]

Originally posted by Prune
Therefore, if by adding 10% more turns to the primary I bring my transformer away from saturation, output voltage will decrease not quite 10%.

What's wrong with this reasoning?

Nothing at all, spot on. Saturation is, by definition, a nonlinear region.

Tim