Transformer help

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  • #1
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What should be the maximum and minimum primary voltage of output transformer with 10 turns of 22 SWG primary winding and 500 turns of 34 SWG Secondary winding?
 

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  • #2
vk6kro
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Depends on the iron core, but as a rough guide take 5 turns per volt.
10 turns 2 volts
500 turns 100 volts
 
  • #3
negitron
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It depends on the core AND the supply frequency. You can put more volts per turn on a given piece of iron with a higher frequency.

Assuming 60 Hz, this can be determined experimentally, if you have a Variac. You'll need two meters, one to monitor the input voltage, and one to monitor the input current. SLOOOOOOWLY ramp up the voltage with the Variac, keeping a close eye on the current. When the core begins to saturate, you'll see the start of a sudden, sharp rise in excitation current. At that point, STOP, dial the voltage back a bit and note the voltage. That's your absolute max. There is no practical min, although efficiency will suffer at too low a drive voltage.

You can also roughly calculate your volts per turn figure if you know the core dimensions and permeability. If it's a laminated core power transformer, assuming silicon steel alloy is a safe bet. In that case simply divide 38 (for 60 Hz; for 50 Hz use 45) by the core cross-sectional area (in square cm) to obtain a rough figure.
 
  • #4
uart
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You can also roughly calculate your volts per turn figure if you know the core dimensions and permeability. If it's a laminated core power transformer, assuming silicon steel alloy is a safe bet. In that case simply divide 38 (for 60 Hz; for 50 Hz use 45) by the core cross-sectional area (in square cm) to obtain a rough figure.

Actually that will give you the number of turns per volt (for a nominal 1T peak steady state flux density). If you want volts per turn you'll have to take the reciprocal of this.
 
  • #5
negitron
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If you want volts per turn you'll have to take the reciprocal of this.

Right. My error. Oddly, I had it right to start but then I "corrected" it.
 
  • #6
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Thanks for the quick replies! I am using two ferrite EE cores, dimensions 60x35x8mm size each. The input to the primary is the current-amplified output of a darlington pair (SL-100 and 2N3055)
 

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