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Need help constructing a transformer!!! Answered

Here are my specs and anticipations for my homemade transformer:

Im looking for my transformer to produce a voltage of 400vAC out of a standard 115vAC wall socket.
If ive done my math, and this is where I would like do correctig if noticed I need a turns ratio of 1.2 : 3.5. That is 1.2 to 3.5 or 115 turns of primary and 350 tunrs of secondary. 115 X 3.5 = 402.5vAC respectivley.

I have access to a fero-core so thats not a problem. Im using 22-20 gauge wire for the primary and 18-16 gauge wire for the secondary. If you find my wires to be of incorrect gauge please let me know. I realise 18-16 is rather large for a coil but I was trying to keep safety in mind do to the high voltage.

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PKM
PKM

10 years ago

I don't entirely follow your numbers.  To convert voltage A to voltage B you need  B/A turn ratio- in this case, 400/115 ~= 3.48.  You can round this to 3.5 to account for losses and inefficiency, so you need 7 turns on the secondary to 2 turns on the primary.

I don't know how you got from 400/115 (ratio of 1.15 : 4) to 1.2 : 3.5, or from 1.5 : 3.5 to 115 to 350 (a ratio of 1.15 : 3.05). 115 turns on the primary to 350 on the secondary would give you 350V, or thereabouts.  

If you are going to have the same number of turns on the primary as the primary voltage, the number of turns on the secondary will equal its voltage as well, so you could do 115 to 400 turns, or 230 to 800 or 46 to 160 (actually that might be too few) or any number that maintains that 1 : 3.5 ratio.

Gauge-wise, the ratio of current is the inverse of the ratio of voltages.  Current in the output will be current in the input divided by 3.5.  Work out how much current your load will draw at 400V, gauge the secondary to handle that current, then multiply by 3.5 and gauge the primary to handle that much.

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Goodhart
Goodhart

10 years ago

Well, since the "higher voltage" will be at a reduced amperage, the safety involved will depend on insulation efficiency as well as on wire gauge.