iron core saturation

[MacIntoshCZ]

Hello there,
where do you think the core is saturated? Thanks

Its hard to determine where i should place cursors.

 

[kubeek]

Circtuit? what are you measuring there?

 

[MacIntoshCZ]

VCC is 11,2V, current sense resistor is 1,5R., core area is aprox 70mm2, turns = 10
If you consider those values i got as results:
L = VCC*time/(Ursense/Rsense) = 11,2*2,6*10E-6/(2,83/1,5) = 15,5uH
Bs = L*(Ursense/Rsense)/(Turns*Area) = 15,57*10E-6*(2,83/1,5)/(10*70*10E-6) = 42mT

42mT is really low value.

 

[MacIntoshCZ]

Circtuit? what are you measuring there?

Měřím na R4, Prostě snímám napětí rezistoru, přepočítávám na proud.
Measuring on R4. But there is no need for showing circuit.

 

[kubeek]

There is no saturation in that screenshot. If there were, the rate of rise of current would start increasing instead of decreasing. This looks like a normal response of RL circuit, where the current increases exponentially up to Vcc/(Rsense +Rinductor)

 

[MacIntoshCZ]

Its not as clear as measuring on ferrite coil. My R4 is gonna smell horribly if i increase it a little bit

 

[kubeek]

The B/H graph is a completely different thing to what you are measuring. If there was saturation the graph would look like this

The pulse is quite short, you can let it run for say 100us and the resistor will be fine, just repeat the pulse only every second or so. You will see the graph tapers off at 11.2V.

 

[kubeek]

Green is core with no saturation, blue is with saturation. You can see how the current starts rapidly increasing at one point.

 

[MacIntoshCZ]

thanks for info, I changed R4 from 1R5 to 0.1R. Still looks linear.
Now its different story.
Now 1Tesla without saturation

 

[MacIntoshCZ]

I need better device. Just few pulses. This takes like 20W. Looks like task for MCU.
Or even better - just lower frequency to something like 100Hz

 

[kubeek]

How about an 555 oscillator at 1Hz triggering a monostable 555 one-shot with small duration like 100us, then a gate driver, for example IR2113.

 

[MacIntoshCZ]

How about an 555 oscillator at 1Hz triggering a monostable 555 one-shot with small duration like 100us, then a gate driver, for example IR2113.

I am actually using ir2153. I chose 6,8M Resistor for R_off (biggest i found) CT is 10nF, Now i have 15Hz aprox.

 

[MacIntoshCZ]

I am starting to hate emf / emi what else....
I am again suffering with non-saturating coil.
When i connect it to two different powersupplies, 15Hz frequency works but it looks strange.
When i connect it only (that means power part and control part have same vcc) to second PSU (laptop charger) it starts to oscillate on 2khz frequency. i though it has not enough power, I added 15mF (yes mili) cap to VCC. No differents
Those experiments makes me love electronics...

 

[MacIntoshCZ]

Worth mention that current is 82A!!! Its measured on 10miliohm resistor. And it with 10x times probe.
In this case Bsmax is 1,5Tesla. Maybe mosfet do not like high current pulses? =) Also 82A could cause some voltage drops.
I am using if3205

 

[MacIntoshCZ]

Low voltage on power part
thats the reason