I have been trying to calculate the turns on an multiple output AC transformer.
I have seen many suggestions on Youtube. When I plug in my voltages, they
do not come back the same! One from europe measures the core form and
then comes back with a reference multipler. How ever it is only good for the
length and width of their core. There is no information on how the multiplier
is calculated!

Others use voltage per turn calculated by voltage and turns on the primary (turns ratio).
None of the formulas come out the same as the others! Can any one help me?

Input 120 volts AC, Out puts, 500 volts AC, 55 volts AC and 12 volts AC .
Wanted is turns on the outputs, using 120 turns on input.

 

Hi

Look this over.
Calculations on the left of schematic. (example uses LP of 100u)
Measurement results at bottom of schematic.

 

You will probably need more than ~120-Turns on the Primary
to prevent excessive Idling-Current / Magnetization-Current.
Possibly 3 to 4 times 120-Turns.
This will depend heavily on the Mass of the Core, and the Core-Material.

The Mass of the Core, and the Core-Material will determine
the amount of POWER the Transformer can comfortably transform into another Voltage
without overheating.

Unless You really just want to knock-yourself-out with all the required Math-Formulas,
I would suggest that You purchase a Toroidal-Core-Transformer,
because You can Wind all the Secondaries You want on to it very easily.

To determine how many Turns a Secondary Winding will require for a given Voltage,
all You have to do is power-up the Transformer,
and wind a temporary 10-turn Secondary,
then measure the Voltage on your new Secondary-Winding.
This will tell You how many Volts to expect per-Turn.
It should be very close to 1-Volt per Turn, but it may be
something like ~0.8-Volts-per-Turn, or maybe, 1.2-Volts-per-Turn.

What is the Total-Calculated-Wattage that You expect to pass through your Transformer ?
.
.
.

 

You will probably need more than ~120-Turns on the Primary
to prevent excessive Idling-Current / Magnetization-Current.
Possibly 3 to 4 times 120-Turns.
This will depend heavily on the Mass of the Core, and the Core-Material.

The Mass of the Core, and the Core-Material will determine
the amount of POWER the Transformer can comfortably transform into another Voltage
without overheating.

Unless You really just want to knock-yourself-out with all the required Math-Formulas,
I would suggest that You purchase a Toroidal-Core-Transformer,
because You can Wind all the Secondaries You want on to it very easily.

To determine how many Turns a Secondary Winding will require for a given Voltage,
all You have to do is power-up the Transformer,
and wind a temporary 10-turn Secondary,
then measure the Voltage on your new Secondary-Winding.
This will tell You how many Volts to expect per-Turn.
It should be very close to 1-Volt per Turn, but it may be
something like ~0.8-Volts-per-Turn, or maybe, 1.2-Volts-per-Turn.

What is the Total-Calculated-Wattage that You expect to pass through your Transformer ?
.
.
.

15 VA

 

Here is the Transformer that I suggest that You start with.
HM2454-ND
~$56.oo each,
30-VA,
1.1-Pounds, 0.5kg,
3"-Diameter,
1.5"-Thick,
1.5"-Internal-Hole,
Dual-Voltage-Primary,
12-VAC, 2.5-Amp-Secondary,
Multiple Secondaries may be additionally Hand-Wound.

The High-Voltage-Winding should be added-on first,
then completely covered with Fiber-Glass-Tape after testing,
then the 55-Volt-Winding should be added last,
and also covered with Fiber-Glass-Tape after testing.
.
.
.

 

15 VA

1200 turns will be closer to the mark than 120.
1 turn per volt is a very large transformer, probably about 1.5kVA

You need to keep the flux density (B) below 1.7T
B=V.t/n.Ae
V.t is actually ∫V.dt with the limits of integration from peak negative voltage to peak positive voltage.
Ae is cross sectional area of the core.

 

Hi CP,
Add this transformer PDF to your document's database.
It will give you more detailed information regarding transformer design
E

 

None of the formulas come out the same as the others! Can any one help me?
Input 120 volts AC, Out puts, 500 volts AC, 55 volts AC and 12 volts AC .
Wanted is turns on the outputs, using 120 turns on input.

Generally the very simplest way is to wind on 10 turns and calculate the turns-per-volt-. for a typical EI core, expect ~6T/V for Toroidal, ~2T/V

 

The turns formulas tend to work well as long as the core is operating in the linear portions of the B-H curve, which relates magnetization to the applied magnetic field strength. THAT is why the number of primary turns is important. So with that 120 turn primary, an input of ten volts might provide better results, depending on the core volume, which affects how much a given magnetic flux input causes some level of magnetization.

 

So the first step is to determine the watts for the transformer to deliver. That will determine the core size because the cor transfers the power. Then you can determine the input inductance and amp-turns to put that much power into the core. That will allow determining the number of turns for the primary. Then the voltage ratio will allow determining the urns ratio. But somewhere in there you need to account for the efficiency being less than 100%