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Old 16th February 2010, 10:17 AM   #1
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Default The ultimate Inrush Current Limiter Solution for large Toroidal Transformers

The normal inrush current limiters consist of one or more NTC resistor in series to the primary winding of transformer like this
MS35 OR550 Inrush Current Limiter Data Sheet
or a high power resistor, which is shortet by a relay after few seconds - like the circuit describted here:
Soft-Start Circuit For Power Amps

The first solution I can accept, if I choice the biggest NTC that have 35mm diameter
The second solution I hate, because the resistor always limit the current, if the relais contact don't longer work (transition resistance through wear and tear)

But this solution could be the royal way:
An inrush current limiting based on a controlled premagnetizing of the toroidal core. Premagnetising of the core with unipolar voltage impulses until the remanence reaches the maximum. Then full switch on, and then shorting through the bypass relay to connecting the primary winding directly to the mains connection.

Why use this approach no commercial power amplifier brands?
This technology could be a very fine solution for the large transformers in the Pass Labs power amplifiers. Additional there is the possibility now to use extremly low loss transformers.

read more about this
Transformer softstart Introduction : EMEKO, Michael Konstanzer
and this
System and method for limiting AC inrush current - Patent 7511975

Last edited by tiefbassuebertr; 16th February 2010 at 10:22 AM.
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Old 16th February 2010, 11:25 AM   #2
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Quote:
Originally Posted by tiefbassuebertr View Post
The second solution I hate, because the resistor always limit the current, if the relais contact don't longer work (transition resistance through wear and tear)
I can only speak for myself. My solution will work more than 20 years for a 600 VA transformer, infact my have worked since 1988 = 32 years. It's pretty reliable. The amp is used every day since I have it for the TV sound. More info here
Click the image to open in full size.
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Old 16th February 2010, 12:39 PM   #3
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Quote:
Originally Posted by peranders View Post
...have worked since 1988 = 32 years.
22 not 32, but still good!
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Old 16th February 2010, 01:05 PM   #4
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I was into 22 years but changed my mind since .... the 80's, 90's and 00's = 30 years
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Old 17th February 2010, 11:47 AM   #5
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R1 = 100 ohms but only 5 watts. What happens, if relay contact don't short it?

Independend of this - 600VA don't say about the DC resistance of the primary winding coil

In the attachement you will find the schematic of Emeko's formerly softstart unit (from me created)
Attached Files
File Type: pdf C_tmp_TSR schematic_ckt.pdf (27.2 KB, 716 views)
File Type: pdf TSR Bedienungsanleitung.pdf (184.0 KB, 411 views)
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Old 17th February 2010, 12:14 PM   #6
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Honestly I am amazed at what some people attempt to patent.

The standard inrush protection for high power transmitters was a variation of a series resistor with an RC time constant relay contact to bypass the series resistor and or step from delta to star configuration, what ever it takes. AKA the solution presented by peranders.
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Old 17th February 2010, 05:18 PM   #7
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Quote:
Originally Posted by Robski666 View Post
Honestly I am amazed at what some people attempt to patent.
The standard inrush protection for high power transmitters was a variation of a series resistor with an RC time constant relay contact to bypass the series resistor and or step from delta to star configuration, what ever it takes. AKA the solution presented by peranders.
The mention of the URL
System and method for limiting AC inrush current - Patent 7511975
was a mistake from me - this patent have to do nothing with this subject here, because there are treated a 3-phase main connection and here only a 1-phase main connection !!

Quote:
Originally Posted by peranders, post #2
I can only speak for myself. My solution will work more than 20 years for a 600 VA transformer, infact my have worked since 1988 = 32 years. It's pretty reliable. The amp is used every day since I have it for the TV sound.
By post #5, I had forgotten to mention this URLs:
http://www.emeko.de/uploads/media/01...zesb_tsr-e.pdf
http://www.emeko.de/uploads/media/02-ERT-GR.pdf

Transformer soft start "State of the Art" - best soft start method until this time
http://www.emeko.de/uploads/media/01...TrafoSTART.png

Last edited by tiefbassuebertr; 17th February 2010 at 05:23 PM.
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Old 18th February 2010, 02:10 PM   #8
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Quote:
Originally Posted by tiefbassuebertr View Post
R1 = 100 ohms but only 5 watts. What happens, if relay contact don't short it?
It will burn but the likelihood is rather low. If you still are afraid of that you can take measures.
Quote:
Originally Posted by tiefbassuebertr View Post
Independend of this - 600VA don't say about the DC resistance of the primary winding coil
Yes it does actually if you are in the business. A normal transformer has a range of primary winding resistance.
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Old 19th February 2010, 12:52 PM   #9
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Originally Posted by peranders View Post
It will burn but the likelihood is rather low. If you still are afraid of that you can take measures.
If you substitute your 100 Ohm 5 Watt resistor through a TO220/247 version from Caddock (together with a heatsink and a overheat switch), then I get more familiar with this topology
An additional step to enhance the reliability could be the mechanical relais contacts through a solid state switch solution. But therefore I need triacs or alternistors appropriate to switch on/off large toroidal transformers. Who knows types that match this requirement?

Somewhere here on this forum even MOSFETs have been recommend instead relais contacts - if I recall right.

Here some URLs in this case
http://www.caddock.com/Online_catalo...000_Series.pdf
...::: ams TECHNOLOGIES DE - MP9100 Power Film ResistorsResistance 0,050 Ohm to 100 Ohm, 100 Watts, TO-247 Style :::...
Attached Images
File Type: png Caddock TO220-247.JPG.png (39.6 KB, 1637 views)
File Type: jpg Switch Overheat 85deg.JPG (45.9 KB, 1633 views)
Attached Files
File Type: pdf TPDV625.pdf (70.9 KB, 121 views)

Last edited by tiefbassuebertr; 19th February 2010 at 12:56 PM.
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Old 19th February 2010, 05:38 PM   #10
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Good thinking but hardly necessary.
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