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Modelling of a DC Contactor

 

The goal is to model a dc contactor for a precharge circuit. Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?
 
 

So, a SWITCH in LTspice?

What else specifically do you need to model?

Contact bounce, coil inductance and resistance, drop-out voltage )or current) vs. pick-up?

All doable with normal circuit elements.

 

Dave

 

From: LTspice@groups.io <LTspice@groups.io> On Behalf Of Nara962 via groups.io
Sent: Tuesday, July 16, 2024 12:12 PM
To: LTspice@groups.io
Subject: EXTERNAL: [LTspice] Modelling of a DC Contactor

 

The goal is to model a dc contactor for a precharge circuit. Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?

 
 

A contactor is basically a relay.
There are relay models in this groups files with parameters that can easily be modified to model this contactor.
 

Nara962 asked:
Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?
 
That entirely depends on what you are trying to simulate with it.
 
It is a simple relay, right?  So, it has a coil, and two contacts that open and close.
 
The coil part can be modeled as a resistor and coil in series.  The datasheet gives you the resistance, but nothing about the inductance, so you may be on your own with that, and a wild guess may have to suffice.
 
The simplest way to model the contacts is with a current- or voltage-controlled switch.  The current-controlled switch is the "CSW" symbol (which is actually a W-element in netlist form).  The voltage-controlled one is the "SW" symbol (which is actually a S-element in netlist form).  Both types of controlled switches depend on a .MODEL definition on your schematic.  This version is rather basic with no mechanical delay and no contact bounce.  If those do not matter to you, then they should suffice.
 
including contact bounce, mechanical delay, and hysteresis require a more complex model, which you are welcome to try.  Or, search through the group's Files for "relay" and see what pops up.  It's a lot.
 
Andy
 
 

I will look through the files, thank you!
 

Dave,
 
I reckon a switch should be the way moving forward. The datasheet does not seem to be rich in information.
 
I would like to go through the exercise of designing a precharge circuit. Nothing specific needs to be modelled - enough details for an accurate result (nothing specific).
 
What are your thoughts?
 
 
On Tue, Jul 16, 2024 at 01:17 PM, Bell, Dave wrote:

So, a SWITCH in LTspice?

What else specifically do you need to model?

Contact bounce, coil inductance and resistance, drop-out voltage )or current) vs. pick-up?

All doable with normal circuit elements.

 

Dave

 

From: LTspice@groups.io <LTspice@groups.io> On Behalf Of Nara962 via groups.io
Sent: Tuesday, July 16, 2024 12:12 PM
To: LTspice@groups.io
Subject: EXTERNAL: [LTspice] Modelling of a DC Contactor

 

The goal is to model a dc contactor for a precharge circuit. Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?

 

 
 

I (may) understand your question better, now.

Are you trying to implement a precharge circuit that passes a limited current “around” the contactor, with a delay before closing the main contacts?

 

 

From: LTspice@groups.io <LTspice@groups.io> On Behalf Of Nara962 via groups.io
Sent: Tuesday, July 16, 2024 2:47 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Modelling of a DC Contactor

 

Dave,

 

I reckon a switch should be the way moving forward. The datasheet does not seem to be rich in information.

 

I would like to go through the exercise of designing a precharge circuit. Nothing specific needs to be modelled - enough details for an accurate result (nothing specific).

 

What are your thoughts?

 

 

On Tue, Jul 16, 2024 at 01:17 PM, Bell, Dave wrote:

So, a SWITCH in LTspice?

What else specifically do you need to model?

Contact bounce, coil inductance and resistance, drop-out voltage )or current) vs. pick-up?

All doable with normal circuit elements.

 

Dave

 

From: LTspice@groups.io <LTspice@groups.io> On Behalf Of Nara962 via groups.io
Sent: Tuesday, July 16, 2024 12:12 PM
To: LTspice@groups.io
Subject: EXTERNAL: [LTspice] Modelling of a DC Contactor

 

The goal is to model a dc contactor for a precharge circuit. Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?

 

 
 

On Tue, Jul 16, 2024 at 03:55 PM, Bell, Dave wrote:
Are you trying to implement a precharge circuit that passes a limited current “around” the contactor, with a delay before closing the main contacts?
Nothing specific, any representation in a spice model that can leverage datasheet parameters would be worth investigating.
 

Contactor is an old school term for a relay whose contacts are capable of handling large currents. The contact resistance is smaller than a "signal" relay.
 

Nara962,
 
The upper limit of your coil inductance can be determined by creating a series R/L circuit pulsed at coil voltage given in the datasheet and permitted to flyback into a diode.
The resistance is the coil resistance given in the datasheet.
Adjust the L to obtain a current that results in the reaching the dropout voltage across the resistance within the given dropout time.
Adjust L downward, somewhat to account for the time of mechanical movement.
 
Also note that the dropout time is highly sensitive to the flyback voltage.
A relay who's coil is snubbed by a single diode will take the longest to drop out.
A relay who's coil is snubbed by a series diode-zener arrangement that permits the coil to flyback to lets say 25V, will drop out considerably faster than a coil that is snubbed to 1V by a single diode.
The higher the flyback voltage the quicker the inductive energy will dissipate.
Higher flyback also reduces the dropout bounce due to swifter armature movement.
 
As for bounce modeling; try a random number generation like V=round(rand(time*10000)) input to a schmitt, who's output is anded with a pulse to control the bounce time which is anded with the contact simulation switch drive signal.
 
See message where Andy I explains more about the use of the rand function.
A relay symbol and more may be found in https://groups.io/g/LTspice/files/Temp/Relay%20circuit.zip
 
All for now.

 
Sent: Tuesday, July 16, 2024 at 3:12 PM
From: "Nara962 via groups.io" <ee.thgxq@...>
To: LTspice@groups.io
Subject: [LTspice] Modelling of a DC Contactor
The goal is to model a dc contactor for a precharge circuit. Should this be designed as a voltage-dependent voltage source that closes the contactor? Or can this be done in a more representative model of the real life behavior?
 

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