If the windings of the transformers are kept in 'common phase' orientation, is it ok to vertically stack two identical Toroidal transformers?
The transformers are to be wired in series and both will have identical loading.
Any advise would be greatly appreciated 🙂
The transformers are to be wired in series and both will have identical loading.
Any advise would be greatly appreciated 🙂
I never actually did it. Toroids are designed so all magnetic field lines are contained inside the core. Minimal magnetic fields on the outside. If there still are marginal magnetic fields outside the toroid those will be in phase for your 2 transformers.
So no, for power transformers I don't see any problem.
So no, for power transformers I don't see any problem.
This configuration might be slightly disadvantageous from the thermal POV: the area to volume will be decreased because two sides face one another instead of being exposed to the ambient air.
Anyway, be sure to insert a rubber washer between the transformer, to avoid stressing the windings
Anyway, be sure to insert a rubber washer between the transformer, to avoid stressing the windings
The bottom transformer will loose a lot of radiating surface on the top where it actually is facing the other transformer. It is more or less 50% of the total radiating surface and in this case it is a warm surface and not free air.
The upper transformer is resting on the lower and even if the heat loss through the surface facing the bottom is less important rubber washer insulating, unknown chassis material etc etc) I would assume that the upper transfeormer needs to de-rate asswell.
So to play it safe I would guess 50-75% de-rating for the package. 50% means you could go with only one...
And depending on size, make a good fixture with a center bolt (NEVER connect both ends of it to a conducting chassi) will be difficult due to the weight. unless using a very thick bolt...
The upper transformer is resting on the lower and even if the heat loss through the surface facing the bottom is less important rubber washer insulating, unknown chassis material etc etc) I would assume that the upper transfeormer needs to de-rate asswell.
So to play it safe I would guess 50-75% de-rating for the package. 50% means you could go with only one...
And depending on size, make a good fixture with a center bolt (NEVER connect both ends of it to a conducting chassi) will be difficult due to the weight. unless using a very thick bolt...
The radiation area to volume ratio as @Elvee pointed out is different. That is correct.
However when a single toroid transformer is designed for a larger capacity exactly the same happens. There are toroid transformers with a certain height/diameter ratio. And larger transformers with the same diameter and a larger height.
Besides, when stacking 2 transformers, the bottom transformer dissipates the heat to the mounting plate and to the upper transformer. It simply becomes one larger body. With a different volume to area ratio, that is true. Toroid transformers have much less losses anyway.
So I am wondering where the 50%-75% derating claim comes from. I am not denying the heat transfer dissipation is different. But I surely would like to see a more scientific calculation for this derating figure. As it is now I can not assess the value of it in any way.
Given the fact that toroid transformers often are completely potted in aluminium or steel casing and filled with epoxy makes me assume that heat transfer problems cannot be such a big issue.
However when a single toroid transformer is designed for a larger capacity exactly the same happens. There are toroid transformers with a certain height/diameter ratio. And larger transformers with the same diameter and a larger height.
Besides, when stacking 2 transformers, the bottom transformer dissipates the heat to the mounting plate and to the upper transformer. It simply becomes one larger body. With a different volume to area ratio, that is true. Toroid transformers have much less losses anyway.
So I am wondering where the 50%-75% derating claim comes from. I am not denying the heat transfer dissipation is different. But I surely would like to see a more scientific calculation for this derating figure. As it is now I can not assess the value of it in any way.
Given the fact that toroid transformers often are completely potted in aluminium or steel casing and filled with epoxy makes me assume that heat transfer problems cannot be such a big issue.
There is no effect that I have experienced or measured by stacking Two toroid's for mounting, especially if they are running the same frequency..............
Crosstalk, I have not detected any.
Although, I did not measure it for absolute values at barely detectable levels either.
Most HF and HF noise is coupled through its parasitic capacitance in some case across specific higher frequency regions are typically snuffed out to ground by a electro-static shield to earth ground, placed between the primary and secondary winding's.
FWIW 😉
jer 🙂
Crosstalk, I have not detected any.
Although, I did not measure it for absolute values at barely detectable levels either.
Most HF and HF noise is coupled through its parasitic capacitance in some case across specific higher frequency regions are typically snuffed out to ground by a electro-static shield to earth ground, placed between the primary and secondary winding's.
FWIW 😉
jer 🙂
I wrote "slightly disadvantageous", for most applications it will not matter: in an amplifier for example, a certain VA rating is required to avoid droop during loud passages, but the average power taken by the amplifier will be much lower.
In applications where the power is ~the VA rating, for a halogen lamp for example, it could be problematic
In applications where the power is ~the VA rating, for a halogen lamp for example, it could be problematic
Thank you for all your replies 🙂
I am looking at 2x 300 VA transformers that are slightly over-rated for the application and will never be continuously loaded at full capacity.
Because heat rises, I can understand a possible implication, however because of the 'over-rated situation' this probably won't be a problem.
The original question obviously relates to space within a given enclosure.
Thank you all again.
I am looking at 2x 300 VA transformers that are slightly over-rated for the application and will never be continuously loaded at full capacity.
Because heat rises, I can understand a possible implication, however because of the 'over-rated situation' this probably won't be a problem.
The original question obviously relates to space within a given enclosure.
Thank you all again.
One way to get a value is testing. Run DC current through the stack (I2R losses is about 90% of total losses) at capacity and measure temperature increase.
Factor in ambient temperature.
You wont however se the hotspots, where you risk damaging insulation. You only see the average , integrated temp increase of the windings.
I would say that the surfaces facing each other(bottom, top) where no cooling is present is at risk.
I admit that 50% is a bit wild, but guestimating 75% is maybe not so far of the mark.
A toroid is not a plane surface and the rubber washer is not sufficiently thick or flexible to completely cover the gaps. It would be difficult to get a good number of the thermal conduction through to the mounting base.
The surfaces facing each other conduct and radiates into another hot surface. That is the worst condition.
For the air exposed surfaces you can estimate better. You can mabye make an guestimate of the conduction of the base plate. Check if the transformer supplier datasheet states anything about VA rating (remember that transformera VA rating is based on losses/efficiency and temp increase) depending on mounting base.
Here is one Google Fu that seems to be freely downloadable.
https://www.researchgate.net/publication/254057774_Heat-Transfer_Model_for_Toroidal_Transformers
I spoke to my toroid transformer supplier (Tiger Toroids) a few months ago about a transformer for a restricted space and he suggested stacking them as it’s something that’s regularly done. So my take on this is it’s ok.
This is another option if the chassis height allows.
Why didn't I think of that! Good call Chris! With smaller transformers this would fit almost anywhere in a 2U chassis.