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Active inrush current limiting problem spiking to 360KAmps
Active inrush current limiting problem spiking to 360KAmps
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Old 3rd December 2017, 06:30 PM   #1
rhythmsandy is offline rhythmsandy
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Default Active inrush current limiting problem spiking to 360KAmps

I was just trying to simulate the Active inrush current limiting but I see a significant increase in Inrush current as much as 360KAmps. Is there anything wrong with the circuit?
I have an application where I need to put 60VDC with 0.1F capacitance. What values to be chosen for this circuit?
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Old 3rd December 2017, 08:00 PM   #2
nigelwright7557 is online now nigelwright7557  United Kingdom
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Did you mean 40m or 40 millifarads ?
That's a lot of capacitance.
It will present pretty much a short on power up.
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Old 3rd December 2017, 08:31 PM   #3
Ketje is offline Ketje  Belgium
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60V in 100mF is a charge of 6 Coulomb. That is a current of 6A during 1sec. or 6kA in 1msec. and so on ... Mona
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Old 3rd December 2017, 08:52 PM   #4
Mark Johnson is offline Mark Johnson  United States
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Active inrush current limiting problem spiking to 360KAmps
The MOSFET drain current spike at t=1.6 seconds is caused by the "PULSE" voltage source in the SPICE simulation. If you want to get rid of the spike, change your circuit design to include slow ramp-up when the power is turned ON, and also slow ramp-down when the power is turned OFF.
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Old 4th December 2017, 05:13 AM   #5
PRR is online now PRR  United States
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9V/360,000A is 0.000,025 Ohms.

The MOSFET channel and diode, even in a SPICE model, do not have so few Ohms.

I'm guessing it is a device capacitance, modeled with NO series resistance, caught between the near infinite cap and near infinite pulse source.

In real-life you could not possibly build it with so few Ohms. 0.001 Ohms would be hard. Also you do not have an infinitely powerful pulse source. And even if that is a 60,000uFd cap, it has a few milli-Ohms of ESR.

It's not "real". But it does suggest trouble in a real world.
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Old 6th December 2017, 11:18 AM   #6
AndrewT is offline AndrewT  Scotland
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Yes, PRR has addressed the resistances. They RULE.

Try using a Power NTC just like the manufacturers show for their products. Current limiting is just what they are made for.
We even have them on 240Vac supplies to charge capacitors direct online to ~400V in fractions of a second in all our mains SMPS
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Old 9th December 2017, 02:59 AM   #7
rhythmsandy is offline rhythmsandy
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How do you do it andrew.

Look at the example I have purchased the largest NTC Ametherm manufactures

https://www.ametherm.com/datasheetspdf/MS3210015.pdf

But as per the calculation provided by the Ametherm

Transformer Inrush Current | Ametherm

The inrush for 0.1F will be quite large many Joules beyond the rated Joule value for the NTC.

I agree to use Resistor but the resistor at primary just like in place of NTC but My doubt is that will the NTC withstand the inrush of 5KVA or 7KVA for a Class H amplifier with 0.1F capacitance?
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Old 9th December 2017, 05:41 AM   #8
PRR is online now PRR  United States
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Quote:
Originally Posted by rhythmsandy View Post
....My doubt is that will the NTC withstand the inrush of 5KVA or 7KVA for a Class H amplifier with 0.1F capacitance?
KVA? Or KA??

I would not expect 7,000 Amps from a domestic wall outlet.

It is not impossible. US 20A breakers and fuseboxes are rated to break 10KA or 22KA, for situations with a very minimum of line impedance. When the house is right next to the transformer and the subcircuit receptacle is right next to the fusebox. Even 10 feet of our standard 20A wire would hold bolt-fault current to 7,000A.

(At my house the very most I could pull is 700 (hundred) amps into a dead-short. But my street-line is at the other extreme: way long.)
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Old 9th December 2017, 10:43 AM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by rhythmsandy View Post
How do you do it andrew.

Look at the example I have purchased the largest NTC Ametherm manufactures

https://www.ametherm.com/datasheetspdf/MS3210015.pdf

But as per the calculation provided by the Ametherm

Transformer Inrush Current | Ametherm

The inrush for 0.1F will be quite large many Joules beyond the rated Joule value for the NTC.

I agree to use Resistor but the resistor at primary just like in place of NTC but My doubt is that will the NTC withstand the inrush of 5KVA or 7KVA for a Class H amplifier with 0.1F capacitance?
60V and 100mF is only 180Joules.
Inrush Current Calculators | Ametherm
look at this page and you'll see 22 NTC power Thermistors that meet or exceed that
MegaSurge - Inrush Current Limiters | Ametherm

But I do wish these USA based companies would learn that F= Farad
Quote:
by 1873, the farad had become a unit of capacitance.[4] In 1881 at the International Congress of Electricians in Paris, the name farad was officially used for the unit of electrical capacitance
and f = femto
Quote:
Adopted by the 11th General Conference on Weights and Measures, it was added in 1964 to the SI
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Last edited by AndrewT; 9th December 2017 at 10:51 AM.
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