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Old 5th January 2013, 07:00 PM   #11
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Quote:
Originally Posted by bobodioulasso View Post
The big transformer inrush current is the main issue to deal with.
Soft charge is secondary.
When you say transformer inrush current, are you referring to the current it requires to build up the flux in the core? Does that require controlling current on the primary rather than the secondary?
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Old 5th January 2013, 08:37 PM   #12
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Yes, primary surge is huge and will blow the fuse. (if only)
A soft start is needed in the primary. A thermistor shunted by a relay for instance.
Capacitor charging is usually not an issue except for an extravagant amount of capacitance.
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Old 5th January 2013, 09:22 PM   #13
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Quote:
Originally Posted by bobodioulasso View Post
Yes, primary surge is huge and will blow the fuse. (if only)
A soft start is needed in the primary. A thermistor shunted by a relay for instance.
Capacitor charging is usually not an issue except for an extravagant amount of capacitance.
Well I suppose if you're taking care of the primary inrush, the cap charging is taken care of by default.

I guess I'm going to use a resistor/relay combo on the primary then.

Thanks!
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Old 6th January 2013, 05:06 PM   #14
sbrads is offline sbrads  United Kingdom
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I don't know if you can still get them but old TVs etc used to have a mains series NTC resistor that was a few tens of ohms at ambient to reduce startup surge and as it warmed up it dropped in resistance to let full power flow.
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Old 6th January 2013, 05:22 PM   #15
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Thermistors are still in production. I thought of using them, but they only work when cool. If an accidental power cycle takes place after the unit is warm, they don't do the job intended. Bypassing them with the relay is a possibility to let them cool after their initial surge, but it seems that a power resistor would do the same thing.

Thanks for all the suggestions guys.
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Old 6th January 2013, 07:56 PM   #16
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A good softstart (primary of the transformer) will solve your problem anyway.

And at the same time reduces the surge on the power line in to the amp.

A real win-win-situation.

Then You won't need any bypassrelay or fet on the secondary either.
Cleaner, more efficient and power when you need it where you need it.
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