# 2 transformers in parallel?

1. ## 2 transformers in parallel?

Is is possible to wire (2 of the same part number) 20A, 18V step-down transformers to increase load handling?
They are center tap transformers, but the intention would be not to tap them at the center but rather both at the 18V secondary taps.
If it is possible are there any precautions?

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2. ## Re: 2 transformers in parallel?

if they are same its possible. you should connect one end of each outputs together and measure the voltage at two remaining ends. if the measured voltage (AC voltage) is near to 0V, you can connect two remaining ends together also. and if the measured voltage is about twice the output voltage, then you should swap first connections.
in general, when one end of each outputs connected to each other, the AC voltage between remaining ends should be about 0V. at this situation you can safely connect remaining ends.

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3. ## Re: 2 transformers in parallel?

Originally Posted by hamed8419215
if they are same its possible. you should connect one end of each outputs together and measure the voltage at two remaining ends. if the measured voltage (AC voltage) is near to 0V, you can connect two remaining ends together also. and if the measured voltage is about twice the output voltage, then you should swap first connections.
in general, when one end of each outputs connected to each other, the AC voltage between remaining ends should be about 0V. at this situation you can safely connect remaining ends.
Thank you.

I wonder. Are there issues with doing this with benchtop power supplies? If both are set to the same voltage, can their grounds be connected and both positive outputs be tapped (in parallel) to split the load between the two?

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4. ## Re: 2 transformers in parallel?

DC power supplies can be generally connected in parallel. But depending on their characteristic, a stable and equal load share may not be achieved due to there low internal resistance. You achieve the best results with individual cables connecting the point of load.

Transformers have an internal impedance that helps to share the load current. But besides having equal open circuit voltage (respectively windings ratio), the internal impedance must be also equal for transformers of equal nominal power, otherwise the transformer with the lower impedance will be overloaded. Under this condition, paralleling of transformers is common practice in power distribution systems. Of course it also work on a lab bench. Using transformers of the same type is the most obvious way to meet the said condition. But it also works for transformers of different size, if they have equal impedance voltage respectively rated percent impedance.

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5. ## Re: 2 transformers in parallel?

For parallel transformers, do not place them too close to each other as it can increase heat and losses. Even if both have same characteristic is it a good idea with a fuse for each winding. If one winding becomes shortcut gives fuses a chance that at least one transformer survive.
Even better protection is to let each winding have its own rectifying bridge before they are connected in parallel.

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