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CheapoModo: quick and dirty transformer snubber bellringer jig
CheapoModo: quick and dirty transformer snubber bellringer jig
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Old 1st June 2018, 03:21 PM   #251
Parasonic is offline Parasonic  United States
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Just my experience added. Put together the tester circuit on solderless board just to see if I could make it work. It works very well. Will transfer to a soldered board soon. Cx=6800pf and Cs=.1uf. Under test is an Antek AS-1212, a 115/230 - 12-0-12 toroidal.
Great jig Mark.
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Old 1st June 2018, 03:22 PM   #252
Parasonic is offline Parasonic  United States
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Sorry, this was with R= 10R0
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Old 1st June 2018, 05:33 PM   #253
Mark Johnson is online now Mark Johnson  United States
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CheapoModo: quick and dirty transformer snubber bellringer jig
Beautiful! Congratulations on your success with a solderless breadboard, the electronics hobbyist's best friend.
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Old 3rd August 2018, 10:58 AM   #254
Voysto is offline Voysto  France
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Hello and thank you for providing an easy way to find snuber values !

I am now looking to buy a cheap Scope for DIY audio usage (still quite newbe in the hobby).

I dind't read the full 26 pages but what I noted is the need for min 2uS/div and few other specs. I have a budget of roughly 100€ and so shorted list :
- Owon 1022I
- Bitscope Micro
- PicoScope 2204A
- DSO Nano V3
- DS212

Do you have any recommandation on those ?

Thank you in advance

Last edited by Voysto; 3rd August 2018 at 11:27 AM.
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Old 3rd August 2018, 05:10 PM   #255
Mark Johnson is online now Mark Johnson  United States
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CheapoModo: quick and dirty transformer snubber bellringer jig
I've never used any of those scopes myself. Glancing at their sales pages on Amazon, the Owon seems to have the best specifications and that's probably what I'd choose if I were you. It might turn out to be a terrible product, I don't really know, I've never seen or used one. Sorry.
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Old 4th August 2018, 11:39 PM   #256
BenY is offline BenY
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Hot off the press, not tested yet...

But this one was truly made from the parts I has at hand.
I ran out of 0.1uF leaded ceramic caps, substituted with SMD. had no leaded appropriate mosfets.. used an SOT-223 FQT7N10L. As to, R3-900 ohm was substituted with a 1K.

After all this, I made changes to the original design to accept the different parts, and printed it in my kitchen...

Will test it as soon as I have more time, hope it will work...

Very exciting indeed.
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Old 5th August 2018, 01:53 PM   #257
BenY is offline BenY
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First, I would like to thank Mark for this wonderful and helpful instrument...


It was powered up today...and IT WORKS..!!
the pictures are:

The test subject is a 12V 30VA transformer.


Step response on R2, no load.


Transformer response, no dampening.


Transformer with the optimized snubber- 150 ohm resistor.


GREAT!! Thank you very much..


Now I must test to hear if there is a difference in sound ???... will let you know.
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Old 5th August 2018, 02:55 PM   #258
Mark Johnson is online now Mark Johnson  United States
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CheapoModo: quick and dirty transformer snubber bellringer jig
Congratulations BenY! You've got a very clean waveform with good damping. I'm sure the ground plane(s) on your board are partly responsible for the beautiful output.
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Old 27th August 2018, 03:10 PM   #259
HarmonicTHD is offline HarmonicTHD  Switzerland
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Hi.
I am a noob on this so please don’t kill me. I have read through the 26 pages and most I didn’t understand. However I think I understood enough to order the components tonight and start trying. My goal is to design the snubber for a 800Va, 230V single prim., 2x25V Amplimo toroid.

When reading through the pages I saw mentioning that the Cheapomodo is like an LC Meter. Was that meant literally? If yes, could I use my existing LC Meter to determine the leakage inductance and with some math derive the values for Cx, Cs and Rs?(I think I even saw an excel sheet here or in a link to the Quasimodo)

Thanks.
Regards
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Old 27th August 2018, 04:30 PM   #260
Mark Johnson is online now Mark Johnson  United States
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CheapoModo: quick and dirty transformer snubber bellringer jig
I think you'd benefit from reading post #1 in the Quasimodo thread. Quasimodo is the parent of Cheapomodo. Here's a link:

Simple, no-math transformer snubber using Quasimodo test-jig

In particular, the .pdf attachment which discusses Quasimodo (thus also Cheapomodo) pretty thoroughly Link to Quasimodo manual (.pdf) will be hugely beneficial.

You can slap together a Cheapomodo on a solderless breadboard in about an hour; I recall at least one post in this thread that showed a photograph of somebody's Cheapomodo built this way {aha, there it is, Cheapomodo post #107}. Or you can build it on a little piece of Stripboard / Veroboard, or perfboard, or however you like. You can also have a PCBoard made using the Gerber CAD files I attached a while ago.

One reason why Quasimodo was born, is that I had NO SUCCESS trying to measure transformer leakage inductance using standard test gear. I even measured with an expensive Agilent LCR meter; like everything else I tried, the LCR meter gave inconsistent readings. In my opinion, the reason is that transformer leakage inductance varies with frequency, and so you need to measure it at the resonant frequency of the LRC circuit composed of your transformer, your rectifier(s), and your snubber. The frequency at which it will actually operate. But what the helll is that frequency? I didn't know.

And even if you were somehow able to predict the resonant frequency accurately, then measure leakage inductance at that frequency, you'd still have to use the equations in Hagerman's paper (also found in the Cornell Dubilier application note) to compute component values for your snubber. You'd still have to do mathematics.

Quasimodo and Cheapomodo sidestep all of this busywork by measuring the actual RLC circuit itself, at its resonant frequency, and then visually snubbing resonance away to nothing. Merely by twirling a knob. No LCR meter, no searching around for the correct equations to use, no math. Some people, including myself, don't mind math. But lots and lots of people feel otherwise, and the no-math feature of Quasimodo is quite often the strongest part of its appeal.

By all means, go ahead and try to measure transformer secondary leakage inductance using an LCR meter or other conventional equipment. You'll probably have a lot of fun. Then figure out a way to verify your measurement result: see whether your measured value of inductance, predicts a resonant frequency that matches the actual real-life resonant frequency. To measure resonant frequency, you'll probably end up needing a stimulus/response fixture like Cheapomodo
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