The "Power-Inductor Checker": A tester for power-inductors
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- čas přidán 11. 09. 2024
- This is a (pre-kickstarter campaign) explanation of a nice addition to your test- and measurement equipment.
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It test the linearity and onsetting saturation of any inductor up to 60A DC-current.
With an oscilloscope (analog or digital) you can determine the inductance of any inductor not only at low currents but especially at the rated current or even overcurrents.
Original circuit and further explanation:
elm-chan.org/wo...
Files will be published at start of kickstarter campaign.
I worked in the switchmode power supply indusry in the 1980's and 90's, we would have given our eyeteeth for something like this.
I think you can use the math function of the scope to plot dA/dt, might make it clearer where it becomes less linear and if you want to calculate inductance at a specific point it would be easier than using cursors.
Also you could have taken the voltage at the banana jacks out to the scope to show that it doesn't droop too much to affect the measurement. Not sure if you can do a custom equation on that scope for L = V.dt/dA where V would be one channel and A the other.
Good idea. I will test this if the math-function allows for displaying that.
(Would be a little bit of overkill for a single measurement but for a demonstration or for volume-measurements that would be great)
In the manual the limitations for 10% and 1% accuracy due to voltage-droop will be stated.
I will in the final promotion-video for the kickstarter-campaign implement your ideas :-)
4 years later, you could use a NE556 instead of the two NE555. A schematic on kainkalabs would be nice, but the ELM schematic is good enough as a starting point.
Anyhow, a nice idea!
I am using the CMOS.Version of the 555 to get a larger range of frequencies. 2 CMOS 555 are cheaper than 1 CMOS 556.
@@KainkaLabs Ah! OK, I made a bad assumption.
Hi, is this available to buy? If not are the gerbers available so I can make one? Thank you
The project is stuck since a few years. The last modifications of the PCB were made by an intern and are not yet checked by me. The project is stil in the pipeline but on the priority list it´s around number 10 :-)
I can send you the KiCad-Files so you can create your own Gerbers.
@@KainkaLabs Hi that would be great, I'll send an email to your website contact email address.
Is info@ak-modul-bus.de correct?
@@KainkaLabs any update sir?
Yeah I would like to purchase this as a kit
I built something similar years ago, but unfortunately my circuit did not have enough power to saturate the "beefier" coils and I think my capacitor bank was not much smaller than yours. Although I could not reach more than 20 Amps, 60 Amps like in your device would have been great.
I also wanted to calculate the saturation region with a micro controller. Since there are way faster adcs nowadays I might revive the circuit. Afaik there are no automatic power inductor checkers available on the market.
Hi KainkaLabs! I found your video very interesting.
Please, can you send me or share the schematic?
Thank you in advance.
22:19 I don’t quite get how the vector on the scope read 64kA/s because the cursor says you have 53.5us and 2.3A so that gives you 2.3A per 53.5uS if we scale that up to 1s there are 18,691 53.5uS in 1s so if we multiply 2.3A by 18,691 that gives us 42.99kA ? What have I done wrong here ? Great tutorial though
The curve is nonlinear as you can see. The slope (or rise rate) is also non-constant. That´s like the difference between average values and momentary values. E.g. if are in an accelerating car there is a huge difference between momentary speed and average speed. Same is here.
@@KainkaLabs ahh I see… I thought the calculated value was simple a projection of the X and Y coordinates as indicated by the 2 labels on the LHS
if DUT inductor built for FLYBACK rated for 300 Volt then can we chk its saturation current over 10V supply voltage(prototype kit has 0-10V for capasitor charging voltage)?
Of course this can be tested with the inductor checker. The saturation current is reached with any test-voltage because the current rises with time. And so it´s just a matter of how long the voltage is applied to the coil before the circuit resets.
@@KainkaLabs That's wonderful. I have various ferrite core and don't have any data sheet.so I will use this cheaker to measure switching inductor/transformer .I think another modification u can do.incorporate half bridge MOSFET arrangement obviously u have to use high side bootstrap circuit if u use 2 n channel MOSFET.dual polarity +-10v to charge dual capasitor bank.my objective to plot BH curve. But above method BH curve may not be completely ploted.becuz capasitor may get discharged at 0to positive X of BH curve
@@KainkaLabs to get BH curve somehow we have to control capacitor discharge current 0to max value then max value to 0 then 0 to negative max value then negative max value to 0 such as sine wave .so need more charge to store and MOSFET should be control in active region.
Hallo, kann man die Platine mittlerweile erwerben ? Oder den geänderten Plan ansichtig werden ?
Eine Antwort wäre nett gewesen, schade.
Hi. Could you share the schematics?
elm-chan.org/works/lchk/lchk_sch.png
Thanks, very interesting video. I don't suppose I could get a look at the current version of your schematics?
It´s nearly identical to the one from elm-chan.org
I have changed the semiconductors to more easily available ones, added some protection diodes and the 2 LEDs, made three timing-ranges instead of two etc.
ATM there are still a few additional components for battery-supply, trigger-output etc. which will be left out because they make no sense.
Just wait for 2 or 3 weeks until I have prepared the kickstarter-campaign.
There everything will be published.
Thanks! I'm doing a presentation this Thursday for the local makerspace, OlyMEGA, and I'm putting together a slightly modified version of the elm-chan circuit. I'm using some scavenged parts including two low ESR 4,700uF Al electro and four 22uF really low ESR ceramic capacitors. My current sense resistor is two paralleled 0.02 ohm 1% that were current sense resistors in a Lithium Ion pack, and the MOSFET is pulled from a dead car booster amp.
I think I'll make the first 555 timer have selectable slower clock speeds so I don't need such a high current power supply for high current inductors.
Are those solid polymer Al electrolytics on your PCB?
Hi Steve,
no they are normal (low-ESR) Al-electrolytics. The polymer ones have a lower capacitance to volume ratio and are much more expensive.
At my first homemade version of the elm-chan circuit the first 555 timer didn´t oscillate!
I had to add a capacitor or resistor at one point, but ATM I don´t have have our modified circuit available from my home and can´t remember where exactly I have placed that component.
Will be back in the office/lab only on Monday which is too late for you to send you the modified circuit.
So first check with an oscilloscope if you get very short pulses with around 50Hz repetition rate at the output pin 3 of the first 555-timer.
They are hard to see/catch/trigger with an "old" low-bandwidth analog scope, but are no problem with a DSO or fast analog scope.
You don´t have to worry about the high currents because nothing can break in this circuit and the inductor also won´t be damaged.
For measuring at not too high currents just start with the *slowest* time-setting of the 2nd 555-timer (with C5=470p and VR1 set to maximum resistance) and then slowly turn VR1 to lower resistance until you see the rising current on your oscilloscope.
The repetition rate of 50 Hz coming from the first 555-timer is of course of no importance.
Nevertheless you could quickly get to very high currents especially with low-inductance values in the µH-range (because the current rise is inverse proportion to the inductance) when you increase the on-time with VR1.
So the critical spec is the max. peak-current capability of Q1 which should really be 60...100A
But if you want to measure at let´s say a maximum of 1 amp, then your oscilloscope should have a high sensitivity because with a 10 mohms shunt-resistor you only get 10mV voltage at 1 amp current.
(Then you could of course use a 100 mohms shunt-resistor which is OK for "low" currents in the single-digit amps range.)
One more hint: A viewer recommended a series resistor to the freewheeling diode D1 for faster energy-decay of the inductor when the MOSFET is switched off.
He was basically right with the idea but his explanation was so totally wrong even after a lengthy discussion and proving the right physics behind that with LTSpice simulations, that I finally deleted the discussion here for just not misleading viewers into wrong physics.
To make a long story short just add a resistor in the range between 10...100 Ohms in series to D1.
Have you already built up the circuit and played around with it?
For a safer working of the first 555-timer add a 100 Ohms resistor between pin 7 (Discharge) pin 6 (Threshold).
In the original circuit pin 7 is directly connected to the RC-combination of R1 and C6 and pin 2 (trigger).
All these connections stay as they are except for pin 7.