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Old 8th Jan 2021, 6:24 pm   #13
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: Home made transformer

Quote:
Originally Posted by Diabolical Artificer View Post
using an unknown tfmr core of laminations is always a gamble as you have no BH curves...
True. Although, if you design for 1.3T flux density, you're unlikely to have any problems.

Or: Wind a test winding of a couple of hundred turns, doesn't matter too much as long as you know the number. Apply a low voltage, measure the current drawn. Keep increasing the voltage and measuring the current until the current starts to increase disproportionately (the thing will probably start humming quite loudly then too). Reduce the voltage to 85% of this 'knee' voltage, divide by the turns, and you have your volts-per-turn figure.

The other points: Handling the wire like you're wearing kid gloves is important. Kinks are a no-no, unless it's a trial winding only, which will be run under supervision. Sizes below 40SWG (0.125mm) are tricky to handle and you really need a shaft through the wire reel centre, on smoothly turning bearings, with a spring-loaded snatch-absorbing arm and pulley, to avoid breakages. Finally, wind evenly, so that each layer is filled - you don't want turns of wire from a late layer slipping down to an earlier layer, or else you'll have many turns-worth of volts which the thin enamel will have to withstand.

Testing: if you have an audio amplifier, feed it with 100Hz sinewave and use it to drive your transformer, into a suitable winding, so that it's running at about double the voltage. If it survives this, it's good to go.
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