Inductor saturation tester, alternative route to dump the excess energy ?

[BravoV]

Thanks for sharing this ! 
Damn, I'm impressed, you built it just in few hours ?    I just introduced you to this circuit yesterday, did you etch the board using film transfer ?

Scope captures:
1. 200uH inductor wound on improper core (high permeability ferrite toroid)
2. 1mH inductor wound on the same core
3. Inductor from #2 with the core broken and glued back together. The inductance fell to 32uH.
4. Murata 32101C (100uH 1.4A)

Great results ! 

On the gap matters, especially I love to salvage those big beads and turning them into power inductor, those glued core can be further "enhanced" by widening the gap like this, sometimes hundred fold increase. 

The wide air gap at the left one is created using cut-off rotating wheel.

Modifications:
1. AC terminated the trigger input (makes it easy to just throw in a square wave without worrying about overheating the termination or having to use a big one).
3. RC (1k/22nF) snubber keeps the inductor from ringing horribly when the diodes shut off.

Mind post this mods in circuit picture here please, as a noob I'm not very sure how to visualize it in circuit.

About the snubber values, did you go through calculating them or just slap in what ever R & C you could find ? 

[c4757p]

Thanks for sharing this ! 
Damn, I'm impressed, you built it just in few hours ?    I just introduced you to this circuit yesterday, did you etch the board using film transfer ?

Even faster: toner on magazine pages!

Modifications:
1. AC terminated the trigger input (makes it easy to just throw in a square wave without worrying about overheating the termination or having to use a big one).
3. RC (1k/22nF) snubber keeps the inductor from ringing horribly when the diodes shut off.

Mind post this mods in circuit picture here please, as a noob I'm not very sure how to visualize it in circuit.

About the snubber values, did you go through calculating them or just slap in what ever R & C you could find ? 

The termination is C2 and R2. During the edges of the input waveform, the capacitor allows current to flow into the termination resistor, but then tapers off between edges. It rounds the waveform significantly, but does prevent reflection. C2 and R2 are visible in the first photo, right next to the left BNC jack.

The snubber is R1 and C6. And yes, I pretty much slapped in any R/C, after verifying that they wouldn't introduce too much error. There's not much to calculate, as the proper values will depend on the inductor being tested. It didn't really matter, though, pretty much anything clamped off the violent ringing significantly. R1 and C6 are visible in the third photo: C6 is the green film cap, and R1 is the brown resistor directly under the large diode.

Your gapped toroids are much more "proper" than mine! I just put the toroid in a bag and smacked it with pliers

[Jay_Diddy_B]

Hi c4757p and the group,

You have done a nice job implementing the Inductor saturation tester in thru-hole. !!! 

I had a quick look at your schematic. D2 should be a Schottky diode like D3

I am pleased that it worked for you. Did you have any trouble at all?

Jay_Diddy_B

[BravoV]

Your gapped toroids are much more "proper" than mine! I just put the toroid in a bag and smacked it with pliers

LOL ... thats the Neanderthal's way of breaking ferrite core. 

I guess that leaves lots of other unusable small pieces, and ended up with a ugly core with tons of chipped surface, just becareful on those rough surface, they may scratch the copper wire.

My method is to wrap the core with some soft cloth, the secure half of it in a vise, while using plier or even better using vise grip to clamp the other half, then blow the vise grip with a small hammer. That will ended up splitting the toroid core into two pieces without any chipped surface and nice & smooth join.

To glue it back in one piece seamlessly, I use PC-Fahrenheit epoxy, and capable of yielding a really tight gap. Sort of controllable gap creation, and the increase at the core saturation is like only few times rather than wildly hit & miss results that sometimes ended up with too low core permeability to be usable.


Interesting experiment, while running with this circuit, try heat up the core like blowing it with warm air from hair dryer, sometimes you can get interesting results when the core is heated up or cooled down. 

[c4757p]

Jay_Diddy_B, D2 is indeed a Schottky - thanks for pointing out that I have the wrong symbol in my library. I'll have to fix that.

Nope, no problems at all. It worked perfectly on the first try. I did "cheat" a bit by double-checking in SPICE where all the critical current paths were, but they were all the obvious ones anyway, so nothing gained from cheating as usual

BravoV, clearly from the pathetic etch job, I've been having a Neanderthal kind of day! The surface is quite chipped, but I don't really care. The inductor was wrapped sparsely enough that it could have been done with bare copper wire anyway. I used cyanoacrylate to reassemble it.

I didn't think of heating the core. It makes sense that it would have an effect, though. Definitely something to experiment with.

[BravoV]

I didn't think of heating the core. It makes sense that it would have an effect, though. Definitely something to experiment with.

The core heating experiment is really useful especially when you have a really tight margin on the core saturation point at your swicher circuit. Highly recommended to try it especially when the circuit might exposed to wide temperature fluctuation range.

For one off project using random ferrite cores or enthusiast like me that love to play with switcher + salvaging inductors, this circuit is a really handy tool to get a unknown inductor saturation profiles.

[mazurov]

Just ordered my variant of the board at OSH Park, hopefully will get it before Christmas.

[BravoV]

Looks pretty small, thanks for sharing, can't wait to see the real circuit in work.

Btw, I see you have the trigger output and assuming you have your own modded circuit from the original design maybe ?

[mazurov]

@BravoV, I used your schematic. The only thing I added was a jumper to turn off current limit. I also used compl.pairs instead of single transistors so I won't mix them - there are two distinctive packages. I'm going to try 2N2369A (and 2N2501) in the inverter so  also added pads to Q4 to accommodate a TO-18.

The board will be attached directly to the scope's vertical input.

[BravoV]

I can see you're also interested with the experiment to shorten propagation time at the inverting stage, great to hear that, please share the results too.

Fun experiments, cold (normal room temp) vs hot inductor, and the most weirdest effects I found are using magnet on the inductor with various distances to the inductor. 

Btw, its not my circuit, credit should goes to Jay_Diddy_B. 

[mazurov]

Here is my build (see pictures). Works very well. Now I need to figure out how to get more current into the inductor (in this circuit current levels at about 20A).

The inductor used in the scope screenshot is secondary winding of Coilcraft DA2032-AL flyback transformer, ~1mH on ferrtite. The sense resistor is 50 mOhm.

[Jay_Diddy_B]

mazurov,

Congratulations !!

The circuit board looks great. The results you see are the expect results.

Excellent !!

Jay_Diddy_B

[mazurov]

JDB,

Thank you for designing this!

To all - the PCB can be ordered at OSH Park -> http://oshpark.com/shared_projects/BzgNwX3Y . It seems that Gerbers can also be downloaded from there so if you don't like OSH Park you can fab the board elsewhere. Compl.transistors are FMB3946, all other parts are as per JDB's docs.

Oleg.

[BravoV]

Oleg, thanks for sharing, that is beautifully built & made, it looks so tiny ! 

Also its cute to see that TO-18 transistor (Is that 2N2369A ?) soldered among that two big caps.

Geezz... 20A is not enough ?  Whats the max supply voltage rail for the inductor did you use at that 20 A ? Please keep us updated on your quest for > 20A current setting.

[mazurov]

First screenshot shows max.current achieved with some pretty large iron powder core inductor at 30V. Second screensot shows what is happening when I increase pulse width. Note that the rep.rate was decreased 10 times since P-FET started melting solder. I can't go past 30V since caps are 35V and they are also quite warm.

The Rsense is 50 mOhm, to get the current multiple the voltage by 20.

I don't know what causes that, seems to be the P-FET. I'll get a bigger one and try again (D2PAK footprints were used here for a reason :-)). It also appears that 2x4700uF bank is an overkill. I'll build another unit capable of higher voltage and try again.

[BravoV]

About your example here, since it is not clear on the "knee", how do you determine the saturation point ?



Since the 2 x 4700uF are overkill, at what inductor current did you max out ? That 20 A ? (assuming it was max at 30 V)

Keep us updated on your new build, it will be interested to watch. 

[Jay_Diddy_B]

BravoV and the group,

Read this application note from Micrometals: Iron Powder Cores for Switchmode Power Supply Inductors

It can be found here:

http://www.micrometals.com/appnotes_index.html

This will be more than you will ever want to know about inductors

Micrometals is one of the leading manufacturers of powered iron cores. 

Jay_Diddy_B

[Ghydda]

About your example here, since it is not clear on the "knee", how do you determine the saturation point ?

The saturation point is where you decide it is.
And as in all electronics, there is no single point, it's always a range/region/area. Some are bigger than others.
It's somewhere between where the curve leaves one asymptote and joins the other asymptote. Take your pick. It all depends on what the application requires.

[mazurov]

Saturation point is not that interesting by itself. What is interesting is inductance change.  When core gets  saturated it is not contributing to the inductance anymore , i.e., the inductor becomes "coreless", its inductance decreases (often substantially) and if, for example, this inductor is a part of DC-DC converter, the output ripple will grow.

Ghydda's picture illustrates that. The straight line on the left shows the region where the core is not saturated. From zero current to the point where current curve stops following this line the inductance of the part is the one any old inductance meter will show you. Past  this current inductance starts decreasing and the curve will eventually start following the right side straight line when core "disappears".