Advice sought - isolation transformer inrush current limiting

[Karl W4KRL]

Mark,

 

This is due to remanent flux in the transformer core. If the first half cycle of the line tries to magnetize the core in the same polarity, it will saturate the core and draw high current. One possible approach is to put a resistor in series with the line and cut out the resistor after the transformer core resets. An incandescent bulb, say 75W if you can find one, would be a good resistor.

 

That said, try an SL22 10008 NTC.

https://www.ametherm.com/inrush-current/transformer-inrush-current.html?gclid=CjwKCAjw_47YBRBxEiwAYuKdw6_IzT-R5wYlOv0eMMWHP5owpuxpxYzNUo4YC3SoXzx-6Xj7CdVNiBoCnDsQAvD_BwE

 

Karl W4KRL

 

From: Tacos <tacos-bounces+karl.w4krl=gmail.com at amrad.org> On Behalf Of Mark Whittington
Sent: Tuesday, May 22, 2018 6:57 AM
To: Tacos <tacos at amrad.org>
Subject: Advice sought - isolation transformer inrush current limiting

 

I've got a 1KW isolation transformer that usually trips the 15A breaker at the breaker box when I turn it on, load or no.  I'm considering installing a pair of NTC thermistors on the input side of the transformer, but I've no idea how to size them or if there might be a better option.

 

Any advice would be appreciated.

 

Cheers.

 

-Mark

 

 

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