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Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
One Way i saw it done was to use a small circuit to switch some resistors in series with the transformer and then after the core was slightly magnitised a relay would then swith the resistors out of the circuit , and as the core was slightly magnitised when resistors are switched out inrush current is reduced .
Any idea if that would work ?
You coluld use a NTC thermistor with a inital high resistance to limit inrush and then as it heats up resistance drops .
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
I just deleted a bunch of off-topic posts from this thread. Everyone involved should take some time to read the rules again.
For the soft-start I would use something like this . Be sure to dimension the series capacitor for the relay current. Or just try with different values until the voltage across the relay coil is close to the rated voltage after the delay. 0.47uF will give a relay current of around 30mA at 50Hz.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
A small AC relay, SPST Arranged with a resistor in series, such that it could not pull in, however, if pushed in by hand, it would hold. This is connected across your variac input.
Wrapped around the relay coil, is several turns of wire, This extra coil is sized to soft start the variac. When the power is switched on, the heavy current times the inrush current will provide the amp turns necessary to pull in the relay. The contacts then short out this coil and the relay will hold in via the voltage winding. It only works if the polarity of the coils is cumulative, that is the fields add.
Variarions of this fiddle involve making the hold circuit DC.
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Wireing my Variac
