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COIL INRUSH CURRENT

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Thu Jun 14, 2018 4:07 am Post subject: COIL INRUSH CURRENT

Below is a quote from a VansAirforce post.  Why is the inrush current higher than steady state current?  Inductors oppose any change in current.  Why doesn't that opposition limit the inrush current?  I am not questioning the accuracy of the measurements, just trying to understand the laws of physics.

 	  Quote: 	
		  All of this is for the four-post starter solenoid (ACS 11-03162):

Without flyback diode: -510V peak pulse

Current through flyback diode: 6.3A decaying over about 40 ms

Coil inrush current: 7.3A

Coil steady state current: 3.6A

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_________________
Joe Gores

charlesdavis(at)iuncapped
Guest

Posted: Thu Jun 14, 2018 4:51 am Post subject: COIL INRUSH CURRENT

From what I understand, once there is an iron core inside the coil, the 

current through the coil will decrease, if the coil is energised for a 

longish period without the iron, it will overheat - have seen this many 

times with solenoids controlling gas in refrigeration systems where the 

coil housing melts to destruction if not fitted onto the solenoid properly



Charles

On 14-Jun-18 2:08 PM, user9253 wrote:

 	  Quote: 	
		   



 Below is a quote from a VansAirforce post.  Why is the inrush current higher than steady state current?  Inductors oppose any change in current.  Why doesn't that opposition limit the inrush current?  I am not questioning the accuracy of the measurements, just trying to understand the laws of physics.



> All of this is for the four-post starter solenoid (ACS 11-03162):

> Without flyback diode: -510V peak pulse

> Current through flyback diode: 6.3A decaying over about 40 ms

> Coil inrush current: 7.3A

> Coil steady state current: 3.6A



 --------

 Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=480876#480876






	




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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 14, 2018 5:55 am Post subject: COIL INRUSH CURRENT

At 07:08 AM 6/14/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

 Below is a quote from a VansAirforce post.  Why is the inrush current higher than steady state current?  Inductors oppose any change in current.  Why doesn't that opposition limit the inrush current?  I am not questioning the accuracy of the measurements, just trying to understand the laws of physics.

 > All of this is for the four-post starter solenoid (ACS 11-03162):

 > Without flyback diode: -510V peak pulse

 > Current through flyback diode: 6.3A decaying over about 40 ms

 > Coil inrush current: 7.3A

 > Coil steady state current: 3.6A 	

   It's probably vagaries of semantics and

   test setup. This is why it's important to

   publish schematics of test setups, screen

   shots of traces and showing all the

   steps in the math. 

   We KNOW that unlike the charging profile

   for a capacitor (infinite onset current

   flow) the inductor has a zero onset 

   current flow.  The begs explanation

   for the author's definition of 'inrush'

   current.

   I'm guessing that the 7.3A figure was

   measured at the greatest stabilized

   current observed after application of power.

   This would be the t=L/R plot coming

   asymptotic to I=E/R several time constants

   after switch closure. Not what we normally

   refer to as inrush current. I'm guessing

   that the 'steady state' value is due to

   coil heating up after an extended period

   of power on.

   Here's what the numbers look like for

   a continuous duty battery contactor:

 https://goo.gl/gvX4mu 

 https://goo.gl/cpzthL 

   The starter contactor may well present

   a higher ratio of cold to hot because it's

   an intermittent duty device suffering a

   greater copper temperature rise than the

   battery contactor.

   The 6.3A figure for diode current is

   probably taken after a short but stabilized

   contactor coil current of that same value.

   The initial discharge of a capacitor is

   the same as the voltage to which the capacitor

   is charged. Discharge of the inductor yields

   and initial current flow equal to that which

   was flowing in the inductor . . . i.e. the

   contactor was de=energized at 6.3A. Hence

   catch diode current would peak at 6.3A

   and decay along the t=L/R plot.

   Without seeing the test setup and plots, it's just

   guessing . . . 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 14, 2018 6:04 am Post subject: COIL INRUSH CURRENT

At 07:50 AM 6/14/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Charles Davis <charlesdavis(at)iuncapped.co.za>



  From what I understand, once there is an iron core inside the coil, the current through the coil will decrease, if the coil is energised for a longish period without the iron, it will overheat - have seen this many times with solenoids controlling gas in refrigeration systems where the coil housing melts to destruction if not fitted onto the solenoid properly

 	


   Adding a core material does INCREASE the

   inductance of a coil. The time constant

   for charging an inductance is t(seconds)=

   L(henries)/R(ohms).



   Adding the core increases L but the resistance

   is unchanged. Hence, t= goes up. I.e. time to

   charge the coil is longer. Keep in mind that

   the values of t are on the order of tens of

   milliseconds.



   Heating is purely a function of the DC resistance

   of the coil and the applied voltage which

   has nothing to do with the magnitude

   of inductance. The time constant for heating

   is about 1000 times longer than for current

   rise. I.e. measured in minutes.



   The classic definition of 'inrush' is that

   current which flows the instant power is applied

   to the device. For capacitors, inrush is very

   large, for inductors it is zero.   



 

 

   Bob . . .

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yellowduckduo(at)gmail.co
Guest

Posted: Thu Jun 14, 2018 6:25 am Post subject: COIL INRUSH CURRENT

If we are thinking of similar "longish periods" perhaps the iron core is 

just conducting heat away perhaps assisted by the refrigerant flow.

Ken



On 14/06/2018 8:50 AM, Charles Davis wrote:

 	  Quote: 	
		   

 <charlesdavis(at)iuncapped.co.za>



 From what I understand, once there is an iron core inside the coil, 

 the current through the coil will decrease, if the coil is energised 

 for a longish period without the iron, it will overheat - have seen 

 this many times with solenoids controlling gas in refrigeration 

 systems where the coil housing melts to destruction if not fitted onto 

 the solenoid properly



 Charles

 On 14-Jun-18 2:08 PM, user9253 wrote:

> 

>

> Below is a quote from a VansAirforce post.  Why is the inrush current 

> higher than steady state current?  Inductors oppose any change in 

> current.  Why doesn't that opposition limit the inrush current?  I am 

> not questioning the accuracy of the measurements, just trying to 

> understand the laws of physics.

>

>> All of this is for the four-post starter solenoid (ACS 11-03162):

>> Without flyback diode: -510V peak pulse

>> Current through flyback diode: 6.3A decaying over about 40 ms

>> Coil inrush current: 7.3A

>> Coil steady state current: 3.6A

>

> --------

> Joe Gores

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p=480876#480876

>

>

 ---

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