# Load sharing transformers of equal voltage

#### supernut

Suppose parallel 5VAC 1A of equal voltage load sharing transformer.

How much we get voltage, ampre, and % load sharing at output?

Thank you

#### ximikas

Hi. Try to connect few those transformers, you think identical, primaries to mains, secondaries in opposite phase ,and measure voltage difference when both no load , and when both have rated load connected, each its own. Can't draw schematic at a moment, what i mean. Voltages may differ withload , regardless of same rated voltage/power ,so 100 percent of sharing / doubling not real in practice. Maybe 1,5-1,8 times.

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#### supernut

I don't have 2 Transformers on hand. I think calculation can show result but I failed in math. Sadly

#### ximikas

Before calculating anything, you need to measure all first, this will give you approximate result . Secondary winding resistance is most important i think.

#### newvirus2008

If you're looking to use the transformers to share a DC load current, the best way to do it would be to parallel them after the rectifier(s).

#### Ian Finch

Paid Member
This is not a good idea. Assuming the phase of each transformer's windings is connected the same, the voltage across each transformer's output winding must also be the same because electrically, they will be sharing the same circuit nodes. The AC current supplied by each transformer though, is uncontrolled and likely, it will switch between the transformers according to their temperature rise - hence the conductance of each transfomer's output winding.
In reality , one transformer will always have slightly more conductance than the other, meaning it will supply most if not all the current. Both transformers will likely fail if the load current remains at >40% of their ratings.

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#### supernut

suppose we need 5VAC 2A but we have 2 transformers of 5VAC 1.5A each. How to attain 2A

#### Ian Finch

Paid Member
There is no proper way to do that, so if the load is a constant 2A, get a bigger transformer - preferably one with a single winding rated at 3 or more amps. If the 2A load is only periodic, you may be fine with using just a 1,5A transformer. Is this actually a solid state class A amplifier, class AB or something other than an audio amp?

If you actually need this supply for DC output, you could try rectifying to DC first, as newvirus2008 suggests, using separate rectifiers for each transformer, then fit some low value, 5W power resistors inline before joining the DC supplies together, in order to dissipate the likely voltage differences. Better still, if you intend to power a stereo amplifier, build it according to dual mono construction.

Note: there's an error in #8. I should have typed >140%, not >40%.

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#### supernut

Low value resistor how much sir? I order 2 secondary 6.3ac 0.4Afor 2 sets but when electrician told me he only need 1 set of 6.3VAC 0.6A

Yes final what he want is DC.

Then after rectifie each sections how much 2 5-watt resistor value?

Thank you

#### supernut

Can i use 2 of 6VAC to same bridge rectifiers diode to get 0.8A

#### TonyTecson

that should work.....

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#### supernut

Thank you so How about Low 5-watt R? No need? If need how much the R vslue Thank you

#### ximikas

Resistor depends on how much different transformers are. Try with 1 ohm, and measure voltage drop on each resistor, when maximal load is connected to diode bridge dc output. If you get very similar voltages, you may decrease resistor, or even omit it.

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#### TonyTecson

if using identical transformers like you said, no need for equalizing resistors methinks..

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#### supernut

Thank you all of you guys.