When is inrush relay necessary?

eem2am · 02:47 PM

Hello,

We are doing a non-PFC SMPS of 330W. (90-265VAC)

The input stage is as follows:-

http://i39.tinypic.com/29bmxci.jpg
(Electrolytic caps are 680uF, 200V

Capacitor Part Number = ESMQ201VSN681MQ30S

cap datasheet
http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/005-snapin/al-smqlug-e-110701.pdf

....How can we evaluate when the inrush is so much that the input electrolytics will be damaged and we therefore need an inrush resistor which is shorted out by a relay?

Also, are NTCs chosen on the basis of their RMS current withstand, as well as cold and hot resistance?

sawreyrw · 08:59 PM

I've never heard of using an NTC thermistor to limit the current to protect the capacitor, but I suppose it is possible. The purpose of the thermistor is to limit the current drawn from the power line, and also to prevent blowing the input fuse.

The thermistor needs to be able to handle the inrush energy and steady state RMS curreent, as well as have the required cold and hot resistances. See: http://www.ametherm.com/inrush-curre...FQhjhwod8Dbr8w

! · 04:45 AM

Not necessary for these caps. Their ripple is rated RMS over a 120Hz period and always with the capability of power-on inrush up to the max spec'd voltage.

dtproff · 28th December 2011, 07:42 AM

NTC thermistors (add heat shrink tube around teh device) are the standard way. Since it doesn't appear that you are busing the envelope on efficiency it should do fine.

We use a 4-10 ohm PTC in the signal path and bypass it with a relay once the line gets up high enough. That is usually 4-10 half cycles. Typically >500W is where I see them most often used. This is all under hardware control since usually nothing is awake downstream.

When using large capacitances, peak line voltage and 90 degree phase angle usually greatly exceeds the bridge rectifier surge rating so that is usually the weak point.

Tony

Kv3audio · 28th December 2011, 08:10 AM

Best thing is to use resistors, 10W or 2x5W, around 47 Ohm

Thats an advice

27th December 2011, 02:43 PM	#1
eem2am diyAudio Member Join Date: Jun 2011	When is inrush relay necessary? Hello, We are doing a non-PFC SMPS of 330W. (90-265VAC) The input stage is as follows:- http://i39.tinypic.com/29bmxci.jpg (Electrolytic caps are 680uF, 200V Capacitor Part Number = ESMQ201VSN681MQ30S cap datasheet http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/005-snapin/al-smqlug-e-110701.pdf ....How can we evaluate when the inrush is so much that the input electrolytics will be damaged and we therefore need an inrush resistor which is shorted out by a relay? Also, are NTCs chosen on the basis of their RMS current withstand, as well as cold and hot resistance? Last edited by eem2am; 27th December 2011 at 02:47 PM. Reason: forgot datasheet

27th December 2011, 08:56 PM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	I've never heard of using an NTC thermistor to limit the current to protect the capacitor, but I suppose it is possible. The purpose of the thermistor is to limit the current drawn from the power line, and also to prevent blowing the input fuse. The thermistor needs to be able to handle the inrush energy and steady state RMS curreent, as well as have the required cold and hot resistances. See: http://www.ametherm.com/inrush-curre...FQhjhwod8Dbr8w Last edited by sawreyrw; 27th December 2011 at 08:59 PM. Reason: Add info on NTC

28th December 2011, 04:42 AM	#3
! diyAudio Member Join Date: Jun 2005 Location: Midwest	Not necessary for these caps. Their ripple is rated RMS over a 120Hz period and always with the capability of power-on inrush up to the max spec'd voltage. Last edited by !; 28th December 2011 at 04:45 AM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
inrush current	doktor	Solid State	123	20th February 2012 02:26 AM
Inrush current limiter and choosing a correct relay	Legis	Power Supplies	5	30th September 2011 06:41 AM
Thermistor or relay for inrush protection	Kees	Solid State	17	14th April 2005 05:14 AM
Inrush Relay Q's..	EchoWars	Solid State	10	7th April 2004 04:33 AM
About Inrush Current	JDeV	Parts	0	2nd December 2002 06:40 AM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

28th December 2011, 07:42 AM	#4
dtproff diyAudio Member Join Date: Oct 2008 Location: Plano, TX, USA	NTC thermistors (add heat shrink tube around teh device) are the standard way. Since it doesn't appear that you are busing the envelope on efficiency it should do fine. We use a 4-10 ohm PTC in the signal path and bypass it with a relay once the line gets up high enough. That is usually 4-10 half cycles. Typically >500W is where I see them most often used. This is all under hardware control since usually nothing is awake downstream. When using large capacitances, peak line voltage and 90 degree phase angle usually greatly exceeds the bridge rectifier surge rating so that is usually the weak point. Tony

28th December 2011, 08:10 AM	#5
Kv3audio diyAudio Member Join Date: Sep 2011	Best thing is to use resistors, 10W or 2x5W, around 47 Ohm Thats an advice

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read