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# Wounding a transformator

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#### Tony

##### New Member
Wounding a transformator with a phisics theory [(Vp:Vs)=(Np:Ns)], i'm trying to create a transformator dc converter. The data is Vp=300v, Vs=100v. Since [(Np:Ns)=3], i was wondering how i should wound this transformator. It is Np= 18, and Ns= 6 ? I still confuse about this theory.
Anyone could help me ! Thank You.

you can't convert DC voltage with a transformer. It works with 2 coils. when you apply/unapply a current, the flux (change in magnetic field) induces the current in the other coil. therefore it will only work with AC or pulsed DC (hence the oscillating part of most stun guns, to get the voltage into a form where a transformer will work.

you are correct about the number of turns, it is the same relationship as the voltage on p and s.

if you want to take 300v down to 100v, you would use 3x the number of turns on your secondary as on your primary.

hope that helps

david

But for 300V primary voltage Np=18 work only on extreme great iron core...

Your number of turns is probably incorrect. If you apply 300 volts (Vp) to 18 turns of wire (Np), you have probably created a direct short circuit.

I agree with Gene. I think you'll need 20 times more for example (360).

well as they said the ratio is correnct but not the number of turns. 18 turns is like short circuit, you need to determine the number of turns acording to your current trough the transformer, the type of core you use, the value of the volteges you will have trough the transformer. something like you said 18/6 turns, i dont think that you can use that as a audio power transformer. you got to consider that the wires need to hold the current you calculate considering then Win=Wout, and add to it the current that passes trough the primary due to its inductance. if you REALLY can't find all you need to design a transformer, ill do a search trough my old books.

If you use 18/6 turns you'd better be using a real high frequency.

If you are really tring to make a DC-DC convertor you need to build an oscillator to pulse the DC, send it through a transformer with the appropriate turns ratio. Then you will need to rectify it back to DC, filter and regulate it to the voltage you want.

You could also use a charge pump to step up a DC voltage. This is several caps in parallel, charge them up and switch them all to a series configuration. The voltages all add up.

There are chips out there specifically designed for DC-DC conversion, you can usually get free samples if you have an official business address to send them to.

Hey Tony
If you can supply me with the specs of the core you have maybe i can assist you, send me the lxbxh or a small sketch and if it is silicon steel or ferrite etc

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