Limiting Inrush??

Deltat · 30th March 2006, 03:34 PM

Will the following circuit work to limit the inrush current from my 625VA transformer?

Kurt

ifrythings · 30th March 2006, 03:50 PM

The circuit will help with the inrush of current but why not just use a NTC?

edl · 30th March 2006, 04:07 PM

Quote:

Originally posted by ifrythings
The circuit will help with the inrush of current but why not just use a NTC?

Because it haven't got time to getting colder when you reswitch the amp fast (or in case of a short blackout), and the toroidal transformer will kick the fuse because of the inrush current. Some manufacturers using NTC for this purpouse, but it's a slightly incorrect solution.

Best regards,

Deltat · 30th March 2006, 05:30 PM

i really wanted to go with an NTC but im also affraid that since this is going to power a switching amp that it may not ever really get hot and lower its resistance.

richie00boy · 30th March 2006, 06:12 PM

Yes both good points. NTC are no good IMO. Your circuit is good, I would use a bigger amount of reistance though. Try it and see, it's easy enough to change the resistor.

edl · 31st March 2006, 09:53 AM

Here the AC-mains is 230V, and I'm using 47ohm/20-25W wirewound resistor. Anyway many amplifier-factory using this value.
On the margin: yes, your circut will work, as Richie said.

Deltat · 31st March 2006, 11:57 AM

I haven no delay circuitry, will what ever delay there is on the AC/DC conterter board be enough?

peranders · 31st March 2006, 12:09 PM

By this you mean

If you don't have any problems with the inrush current, then you don't have a problem.

AndrewT · 31st March 2006, 01:18 PM

Hi,
try using a much smaller fuse once you have it up and running.
Aim for T6A or T8A. It might work with T5A if you up the resistor to 15r or 22r.

You want that mains fuse as small as possible to provide effective protection.

testlab · 31st March 2006, 01:33 PM

Check this out http://www.edn.com/article/CA198898.html

30th March 2006, 06:12 PM	#5
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Yes both good points. NTC are no good IMO. Your circuit is good, I would use a bigger amount of reistance though. Try it and see, it's easy enough to change the resistor. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

31st March 2006, 12:09 PM	#8
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	By this you mean If you don't have any problems with the inrush current, then you don't have a problem. __________________ /Per-Anders (my first name) or P-A as my friends call me

31st March 2006, 01:18 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, try using a much smaller fuse once you have it up and running. Aim for T6A or T8A. It might work with T5A if you up the resistor to 15r or 22r. You want that mains fuse as small as possible to provide effective protection. __________________ regards Andrew T.

31st March 2006, 01:33 PM	#10
testlab diyAudio Member Join Date: Dec 2005 Location: Grand Rapids MI	Check this out http://www.edn.com/article/CA198898.html __________________ It's not whether you win or lose, it's how you lay the blame.

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30th March 2006, 03:50 PM	#2
ifrythings diyAudio Member Join Date: Oct 2005	The circuit will help with the inrush of current but why not just use a NTC?

30th March 2006, 05:30 PM	#4
Deltat diyAudio Member Join Date: Oct 2004 Location: St. Louis, MO	i really wanted to go with an NTC but im also affraid that since this is going to power a switching amp that it may not ever really get hot and lower its resistance.

31st March 2006, 09:53 AM	#6
edl diyAudio Member Join Date: Oct 2004	Here the AC-mains is 230V, and I'm using 47ohm/20-25W wirewound resistor. Anyway many amplifier-factory using this value. On the margin: yes, your circut will work, as Richie said.

31st March 2006, 11:57 AM	#7
Deltat diyAudio Member Join Date: Oct 2004 Location: St. Louis, MO	I haven no delay circuitry, will what ever delay there is on the AC/DC conterter board be enough?

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