Paralleling Audio Transformers

[laatsch55]

Is it possible to parallel toroid transformers to increase current on the seondaries?

 

[Northwinds]

I found this online:

"Parallel connection of transformer windings is permitted in one case only - the windings must have exactly the same voltage output, and must be connected in phase. Different current capacities are not a problem, but it is rare to find a transformer with two windings of the same voltage but different current ratings

Even a 1V difference between winding voltages will cause big problems. A typical winding resistance for a 5A winding might be 0.25 ohm. Should two such windings be connected in parallel, having a voltage difference of 1V, there will be a circulating current limited only by the resistances of the windings. For our example, the total winding resistance is 0.5 ohm, so a circulating current of 2A will flow between the windings, and this is completely wasted power. The transformer will get unexpectedly hot, and the maximum current available is reduced by the value of the circulating current

Should the windings be connected out of phase, the circulating current will be possibly 100A or more, until the transformer melts or the fuse blows. The latter is generally to be preferred
The transformer manufacturer's specifications will indicate if parallel operation is permitted. If you are unsure, measure the voltages carefully, and avoid parallel connection if the voltages differ by more than a couple of hundred millivolts. There will always be a difference, and only the manufacturer's winding tolerances can predict what it will be. With toroidal transformers, the windings are often bifilar, meaning that the two windings are wound onto the transformer core simultaneously. The tolerance of such windings is normally very good, and should cause no problems"

 

[CASSETTE DECK]

Is it possible to parallel toroid transformers to increase current on the seondaries?

I can't see any reason why not if the number of turns is exactly the same on both transformers, both primary and secondary windings. EDIT: More to the point, exactly the same turns ratio, and of course they must be in phase. Any difference will result in losses. There is no significant radiated magnetic field from toroidal transformers.

 

[laatsch55]

Well the ones I'm considering are the same make, model and manufacturer so the chances are good.

Joe, have you ever measured the voltage sag at clipping on a 700?

 

[Gepetto]

Is it possible to parallel toroid transformers to increase current on the seondaries?

I would recommend you consider having a full bridge on each transformer and parallel them on the down stream side of the diode bridge going into the bulk cap.

 

[laatsch55]

I found this online:

"Parallel connection of transformer windings is permitted in one case only - the windings must have exactly the same voltage output, and must be connected in phase. Different current capacities are not a problem, but it is rare to find a transformer with two windings of the same voltage but different current ratings

Even a 1V difference between winding voltages will cause big problems. A typical winding resistance for a 5A winding might be 0.25 ohm. Should two such windings be connected in parallel, having a voltage difference of 1V, there will be a circulating current limited only by the resistances of the windings. For our example, the total winding resistance is 0.5 ohm, so a circulating current of 2A will flow between the windings, and this is completely wasted power. The transformer will get unexpectedly hot, and the maximum current available is reduced by the value of the circulating current

Should the windings be connected out of phase, the circulating current will be possibly 100A or more, until the transformer melts or the fuse blows. The latter is generally to be preferred
The transformer manufacturer's specifications will indicate if parallel operation is permitted. If you are unsure, measure the voltages carefully, and avoid parallel connection if the voltages differ by more than a couple of hundred millivolts. There will always be a difference, and only the manufacturer's winding tolerances can predict what it will be. With toroidal transformers, the windings are often bifilar, meaning that the two windings are wound onto the transformer core simultaneously. The tolerance of such windings is normally very good, and should cause no problems"

Thanks Ron, guess I' could have googled it too. Never thought of it...

 

[Gepetto]

Well the ones I'm considering are the same make, model and manufacturer so the chances are good.

Joe, have you ever measured the voltage sag at clipping on a 700?

Have not Lee, frankly I do not have a load bank big enough to feel safe in doing that Lee.

 

[laatsch55]

I would recommend you consider having a full bridge on each transformer and parallel them on the down stream side of the diode bridge going into the bulk cap.

That's what I was lookin for, that opens up another possibility I was pondering, Thanks Joe, CASSETTE DECK and Sir Ron....

Joe, does that make things a little easier to deal with if the AC phasing isn't perfect? Easier to deal with on the DC side?

 

[laatsch55]

I did it last night, it was pretty cool in the basement last night the added heat was great. Still wasn't close to needing to water cool that 2,000 watt load though.

 

[laatsch55]

I would recommend you consider having a full bridge on each transformer and parallel them on the down stream side of the diode bridge going into the bulk cap.

The next BABB is gonna be a busy F*&^%$# place....

 

[Gepetto]

That's what I was lookin for, that opens up another possibility I was pondering, Thanks Joe, CASSETTE DECK and Sir Ron....

Joe, does that make things a little easier to deal with if the AC phasing isn't perfect? Easier to deal with on the DC side?

Yes, you have no phasing concerns at all if you just connect bridge 1 plus to bridge 2 plus, bridge 1 minus to bridge 2 minus.

It provides diode isolation to prevent backflow. The IR drop of the windings will compensate for small differences in the construction of the transformer.

You will lose slightly less power in the bridge rectifiers as well using 2 of them.

Diode oring of shared and redundant power sources is done all the time.

 

[laatsch55]

Almost too good to be true.....opens up some more possibilities that have benn ruminating. So if power QUALITY can be attainable then the audio portion should not be affected. Yes I knw the PSRR is inherent in the design, but does that account for opposing magnetic fields or if they happen to overlap in a weird pattern.... just throwing things out there Joe...

 

[laatsch55]

OK, consider I built a power supply with 2-toroids and got them to agree to be X-formers and play well with others and the cap committee agreed to keep the faith and there wasn't TOO BIG a difference in what went where.........what can I load it with to take em to saturation and measure some stuff........

 

[laatsch55]

And one last question tonight Sir Joe........ Is voltage sag, when it happens giving you headroom within the SOA or is the increased current through the device making up for that voltage drop. I realize--power in power out--so it's probably not giving much room to fudge up.....

 

[NavLinear]

OK, consider I built a power supply with 2-toroids and got them to agree to be X-formers and play well with others and the cap committee agreed to keep the faith and there wasn't TOO BIG a difference in what went where.........what can I load it with to take em to saturation and measure some stuff........

When I measure a dc supply output I use a resistive load that could handle the calculated power with a little head room on the load maximum wattage spec. Ohms law comes into play here so you'll need to have the right resistance to get the current you want to pull. I'm assuming that you want to max out the VA capacity of the two transformers - this could be fun.

 

[laatsch55]

That's exactly what I want to do.

 

[Gepetto]

And one last question tonight Sir Joe........ Is voltage sag, when it happens giving you headroom within the SOA or is the increased current through the device making up for that voltage drop. I realize--power in power out--so it's probably not giving much room to fudge up.....

SOA is not a straight linear parameter Lee. It factors in the energy being dissipated (power x time) and the current temperature of the junction. I would NOT count on the small amount of power supply sag to give you any comfort that you have attained extra SOA.

 

[laatsch55]

Ok, figured that was about right.........

 

[Web Police]

OOOOOOOOH! your making a Franken WOPL?

 

[laatsch55]

nO, jOHN, JUST A VERy stiff power supply...