Rectifier ringing snubbers

Prune · 24th September 2004, 08:15 PM

I know this has been mentioned here before:
http://www.hagtech.com/pdf/snubber.pdf

The problem is, how to guesstimate values for the snubber for those that can't measure transformer and diode parasitics because they don't have a scope?

sam9 · 24th September 2004, 08:35 PM

I suspect that the performance difference between "optimum" and "approximate" is not large. Facing the same problem as you I've used C=.01uF and R= 1kR -to- 2KR. I may be totally wrong but I think these values will get one close to ideal under a wide range of circumstances and in any case much better than no snubbing or even C-only snubbing.

Prune · 24th September 2004, 09:13 PM

On a 40 VA transformer, my C was similar to yours, but the R was more like 100 Ohms...

However, now I'm faced with very different iron -- 1.5 kW microwave oven transformer with a rebuilt core (and removed shunts), and I have a feeling it's different enough that these values are useless.

Wouldn't there be any way to perform a measurement to see if given values are helping without an oscilloscope or inductance/capacitance meter?

rcavictim · 24th September 2004, 11:09 PM

Prune,

You can buy an o-scope good enough for what you are wanting to do on ebay for $20. Try Vancouver surplus electronics stores. Is Rendell Parret Electronics still there on 4th ave? I lived there in the 60's to early '70's. There was also The Ham Shack just south of the Granville St. bridge on the east side. Better yet go to a Hamfest. There must be lots of those in the area. Do a google on "Hamfests British Columbia" or "Hamfests Vancouver" to find one.

dmfraser · 24th September 2004, 11:29 PM

Rendell Parret is now RP Electronics and had a shop at 4th and Arbutus. The parking around there is horrid and they do not have anywhere as much surplus as before. They also have a shop near BCIT, near Lougheed Highway and Winnlingdon. I've moved to LA now and since I moved, I heard they may have moved the whole operation to the new site.

The surplus business in Canada has never been the same since Vanguard in Edmonton closed in 1979.

Prune · 25th September 2004, 01:51 AM

Speaking of which, I've been looking at scopes on eBay, but my problem is that I don't know which ones are any good. For example, if I'm dealing with digital audio also, how many MHz do I need? S/PDIF is between 12 and 13 MHz, so would a 20 MHz scope be any good? What sensitivity in mV, and what other features/specs should I look for, or what kind of probes? For example, I've seen a 20 MHz with 5 mV sensitivity and dual trace sell for $100, but I don't know if this is good enough for audio work or whether the price is any good.

Brian Donaldson · 26th September 2004, 01:00 AM

Buying a scope on Ebay is a very good idea, but beware. Get one from someone that says it works as it should, not I don't know how to test it, but it makes this line.

For digital, you may want to look at something 100mhz. Also beware. probes can cost $50 each, so be sure to factor that in on your bidding. I would budget $200 for what I think you need.

martin clark · 26th September 2004, 01:36 AM

Prune - a slightly simpler way of looking at snubbers is to realise that in essence, it's an AC-coupled resistor. All the damping comes from the energy of the ringing being dissipated in the resistor. The cap functions to reduce losses in the resistor at the line frequency - you could use a resistor alone, but imagine the waste heat...!

Obviously, the bigger the cap, the lower the frequency the damping is effective from. 100ohms is about right for the resistor, so you are left guessing the strays to work out how big to make the cap. If you're winding your own secondary on a big core, I'd make the guess conservative and go larger with the caps, assuming the ringing could be at a lower frequency than your previous experience; try 0.047uF maybe.

Prune · 26th September 2004, 04:14 AM

My secondary is the MOT output, 2.1 kV AC RMS, into a bridge rectier. Would the values mentioned above make sense for this situation too?

martin clark · 26th September 2004, 01:06 PM

Help! At those sorts of voltages you're going to *really* need to know what you are doing. Even a small cap will be storing a lot of energy; probably need parts rated in excess of 4KV as well. That said, current is going to be low, so maybe you don;t need snubbers at all.

Sorry, but it's well outside my experience.

24th September 2004, 08:15 PM	#1
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	Rectifier ringing snubbers I know this has been mentioned here before: http://www.hagtech.com/pdf/snubber.pdf The problem is, how to guesstimate values for the snubber for those that can't measure transformer and diode parasitics because they don't have a scope?

24th September 2004, 11:09 PM	#4
rcavictim diyAudio Member Join Date: Jun 2004 Location: Cool end of a soldering iron NW of Toronto	Prune, You can buy an o-scope good enough for what you are wanting to do on ebay for $20. Try Vancouver surplus electronics stores. Is Rendell Parret Electronics still there on 4th ave? I lived there in the 60's to early '70's. There was also The Ham Shack just south of the Granville St. bridge on the east side. Better yet go to a Hamfest. There must be lots of those in the area. Do a google on "Hamfests British Columbia" or "Hamfests Vancouver" to find one. __________________ I.Q.Test. Have you ever purchased a recreational snowmobile?

24th September 2004, 11:29 PM	#5
dmfraser diyAudio Member Join Date: Dec 2003 Location: Orange County, CA	Rendell Parret Rendell Parret is now RP Electronics and had a shop at 4th and Arbutus. The parking around there is horrid and they do not have anywhere as much surplus as before. They also have a shop near BCIT, near Lougheed Highway and Winnlingdon. I've moved to LA now and since I moved, I heard they may have moved the whole operation to the new site. The surplus business in Canada has never been the same since Vanguard in Edmonton closed in 1979. __________________ Dan Fraser

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
Rectifier switching / choke ringing noise	zigzagflux	Tubes / Valves	13	12th October 2007 04:18 PM
ADC without pre-ringing	jzagaja	Digital Source	3	3rd July 2007 08:22 AM
Anybody heard about Tarzian Silicon Rectifier for Tube Rectifier Replacement?	zxx123	Tubes / Valves	4	21st February 2005 04:02 AM
PSU Ringing	Kashmire	Pass Labs	1	11th January 2005 08:31 PM
Acoustic ringing?	grataku	Solid State	1	15th March 2001 04:55 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

24th September 2004, 08:35 PM	#2
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	I suspect that the performance difference between "optimum" and "approximate" is not large. Facing the same problem as you I've used C=.01uF and R= 1kR -to- 2KR. I may be totally wrong but I think these values will get one close to ideal under a wide range of circumstances and in any case much better than no snubbing or even C-only snubbing.

24th September 2004, 09:13 PM	#3
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	On a 40 VA transformer, my C was similar to yours, but the R was more like 100 Ohms... However, now I'm faced with very different iron -- 1.5 kW microwave oven transformer with a rebuilt core (and removed shunts), and I have a feeling it's different enough that these values are useless. Wouldn't there be any way to perform a measurement to see if given values are helping without an oscilloscope or inductance/capacitance meter?

25th September 2004, 01:51 AM	#6
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	Speaking of which, I've been looking at scopes on eBay, but my problem is that I don't know which ones are any good. For example, if I'm dealing with digital audio also, how many MHz do I need? S/PDIF is between 12 and 13 MHz, so would a 20 MHz scope be any good? What sensitivity in mV, and what other features/specs should I look for, or what kind of probes? For example, I've seen a 20 MHz with 5 mV sensitivity and dual trace sell for $100, but I don't know if this is good enough for audio work or whether the price is any good.

26th September 2004, 01:00 AM	#7
Brian Donaldson diyAudio Member Join Date: Jan 2003 Location: Texas, Love it or leave it	Buying a scope on Ebay is a very good idea, but beware. Get one from someone that says it works as it should, not I don't know how to test it, but it makes this line. For digital, you may want to look at something 100mhz. Also beware. probes can cost $50 each, so be sure to factor that in on your bidding. I would budget $200 for what I think you need.

26th September 2004, 01:36 AM	#8
martin clark diyAudio Member Join Date: Jul 2003 Location: Bath, UK	Prune - a slightly simpler way of looking at snubbers is to realise that in essence, it's an AC-coupled resistor. All the damping comes from the energy of the ringing being dissipated in the resistor. The cap functions to reduce losses in the resistor at the line frequency - you could use a resistor alone, but imagine the waste heat...! Obviously, the bigger the cap, the lower the frequency the damping is effective from. 100ohms is about right for the resistor, so you are left guessing the strays to work out how big to make the cap. If you're winding your own secondary on a big core, I'd make the guess conservative and go larger with the caps, assuming the ringing could be at a lower frequency than your previous experience; try 0.047uF maybe.

26th September 2004, 04:14 AM	#9
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	My secondary is the MOT output, 2.1 kV AC RMS, into a bridge rectier. Would the values mentioned above make sense for this situation too?

26th September 2004, 01:06 PM	#10
martin clark diyAudio Member Join Date: Jul 2003 Location: Bath, UK	Help! At those sorts of voltages you're going to really need to know what you are doing. Even a small cap will be storing a lot of energy; probably need parts rated in excess of 4KV as well. That said, current is going to be low, so maybe you don;t need snubbers at all. Sorry, but it's well outside my experience.

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