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transorbs

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jj(at)sdf.lonestar.org
Guest

Posted: Tue Jul 21, 2009 3:25 pm Post subject: transorbs

Howdy folks,

In my work we use 30v transorbs similar the ones that have been discussed on this list for years.  We use them to limit relay contact arcing when switching inductive loads such as mag locks and electric strikes.  We have hundreds in the field and until yesterday I would have said they never go bad - but yesterday I had a service call and sure enough a transorb had shorted.  In our applications the coil currents range from 125ma to maybe an amp or so.  I don't know why it failed, maybe a manufacturing defect, but the point becomes that they CAN fail.

 

So I'm thinking, if I have one of these things across the coil on my master contactor and it shorts - bad things happen.  Not only would I loose electric power but the un-fused master switch wiring would be overloaded.  I'm thinking maybe a 30v transorb across the master switch - not the contactor coil may be a better choice if you are going to use them at all.  It would still protect the switch, it would still allow about 15v reverse voltage to collapse the field in the coil (12v system - use a 45v transorb in a 24v system) and in a failure mode you would just be unable to shut off the power.

 

Anyway, I just wanted to bring attention to an admittedly remote failure mode and a possible re-configuration that would have a much more favorable result if a failure did occur. 



Joel

  [quote][b]

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mprather(at)spro.net
Guest

Posted: Tue Jul 21, 2009 4:44 pm Post subject: transorbs

Interesting.



I could imagine that Bob might like to look at the shorted device - if

it's still around.



I wonder what short circuit current such a transorb might support before

itself becoming a fuse (going open circuit)..  If the switch and wiring

can handle it, this may not be a terribly serious issue.  A bit smokey

perhaps...

Matt-



 	  Quote: 	
		   Howdy folks,

 In my work we use 30v transorbs similar the ones that have been discussed

 on

 this list for years.  We use them to limit relay contact arcing when

 switching inductive loads such as mag locks and electric strikes.  We have

 hundreds in the field and until yesterday I would have said they never go

 bad - but yesterday I had a service call and sure enough a transorb had

 shorted.  In our applications the coil currents range from 125ma to maybe

 an

 amp or so.  I don't know why it failed, maybe a manufacturing defect, but

 the point becomes that they CAN fail.



 So I'm thinking, if I have one of these things across the coil on my

 master

 contactor and it shorts - bad things happen.  Not only would I loose

 electric power but the un-fused master switch wiring would be overloaded.

 I'm thinking maybe a 30v transorb across the master switch - not the

 contactor coil may be a better choice if you are going to use them at all.

 It would still protect the switch, it would still allow about 15v reverse

 voltage to collapse the field in the coil (12v system - use a 45v transorb

 in a 24v system) and in a failure mode you would just be unable to shut

 off

 the power.



 Anyway, I just wanted to bring attention to an admittedly remote failure

 mode and a possible re-configuration that would have a much more favorable

 result if a failure did occur.



 Joel

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jj(at)sdf.lonestar.org
Guest

Posted: Tue Jul 21, 2009 6:11 pm Post subject: transorbs

Yes I still have it and I'd be happy to send it to Bob if he wants to take a look.  It's in heat shrink with lead wires sticking out.  I haven't molested it yet - just checked it with a meter.  A transorb is basicaly two zeners back to back and one in this is shorted. It measures a standard diode drop one way and open the other.  

 

Joel



On Tue, Jul 21, 2009 at 8:39 PM, Matt Prather <mprather(at)spro.net (mprather(at)spro.net)> wrote:

[quote] --> AeroElectric-List message posted by: "Matt Prather" <mprather(at)spro.net (mprather(at)spro.net)>

 

 Interesting.

 

 I could imagine that Bob might like to look at the shorted device - if

 it's still around.

 

 I wonder what short circuit current such a transorb might support before

 itself becoming a fuse (going open circuit)..  If the switch and wiring

 can handle it, this may not be a terribly serious issue.  A bit smokey

 perhaps...

 

 

 Matt-

 



 > Howdy folks,

 > In my work we use 30v transorbs similar the ones that have been discussed

 > on

 > this list for years.  We use them to limit relay contact arcing when

 > switching inductive loads such as mag locks and electric strikes.  We have

 > hundreds in the field and until yesterday I would have said they never go

 > bad - but yesterday I had a service call and sure enough a transorb had

 > shorted.  In our applications the coil currents range from 125ma to maybe

 > an

 > amp or so.  I don't know why it failed, maybe a manufacturing defect, but

 > the point becomes that they CAN fail.

 >

 > So I'm thinking, if I have one of these things across the coil on my

 > master

 > contactor and it shorts - bad things happen.  Not only would I loose

 > electric power but the un-fused master switch wiring would be overloaded.

 > I'm thinking maybe a 30v transorb across the master switch - not the

 > contactor coil may be a better choice if you are going to use them at all.

 > It would still protect the switch, it would still allow about 15v reverse

 > voltage to collapse the field in the coil (12v system - use a 45v transorb

 > in a 24v system) and in a failure mode you would just be unable to shut

 > off

 > the power.

 >

 > Anyway, I just wanted to bring attention to an admittedly remote failure

 > mode and a possible re-configuration that would have a much more favorable

 > result if a failure did occur.

 >

 > Joel

 >

 

 

 

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[b]

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nuckollsr

Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS

Posted: Wed Jul 22, 2009 8:45 am Post subject: Re: transorbs

Yes I still have it and I'd be happy to send it to Bob if he wants to take a look.ï¿½ It's in heat shrink with lead wires sticking out.ï¿½ I haven't molested it yet - just checked it with a meter.ï¿½ A transorb is basicaly two zeners back to back and one in this is shorted. It measures a standard diode drop one way and open the other.ï¿½ 



    Yes, I'd like to look at it. Please send to Bob Nuckolls,

    P.O. Box 130, Medicine Lodge, KS  67104-0130.



    Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jul 23, 2009 5:49 am Post subject: transorbs

At 06:23 PM 7/21/2009, you wrote:

  	  Quote: 	
		  Howdy folks,

 In my work we use 30v transorbs similar the ones that have been discussed on this list for years.  We use them to limit relay contact arcing when switching inductive loads such as mag locks and electric strikes.  We have hundreds in the field and until yesterday I would have said they never go bad - but yesterday I had a service call and sure enough a transorb had shorted.  In our applications the coil currents range from 125ma to maybe an amp or so.  I don't know why it failed, maybe a manufacturing defect, but the point becomes that they CAN fail. 	


   The transorb is indeed a specialized zener. In the

   zener conduction mode, the potential for dissipating

   a deleterious level of heat is much higher than for

   a diode rectifier.  The energy available from a magnetic

   field collapse is quite low and measured in millijoules.

   Certainly a low risk stress to any power semiconductor.

   The ability of the electrical system to deliver energy

   to the transorb in a voltage transient condition is

   many times higher.



  	  Quote: 	
		  So I'm thinking, if I have one of these things across the coil on my master contactor and it shorts - bad things happen.  Not only would I loose electric power but the un-fused master switch wiring would be overloaded.  I'm thinking maybe a 30v transorb across the master switch - not the contactor coil may be a better choice if you are going to use them at all. It would still protect the switch, it would still allow about 15v reverse voltage to collapse the field in the coil (12v system - use a 45v transorb in a 24v system) and in a failure mode you would just be unable to shut off the power. 	


   But there are OTHER, equally likely failure modes that

   can take the battery contactor out of service. That's

   what the e-bus alternate feed path is all about. The

   optimum location for transient suppression is at the

   contactor coil terminals. 



   Do I correctly deduce from your posting that your

   contactor coils are protected by a single transorb?

   If so, then it has to be wired as shown in -A- below.



 [img]cid:.0[/img]



    In this configuration, the device HAS to be biased in

    the zener conduction mode polarity while coiled power

    IS APPLIED. When the switch opens, the top of the coil

    swings negative . . . and the transorb is now biased

    in the diode conduction mode. This configuration doesn't

    take advantage of the transorb's voltage limiting function

    as a specialized zener. In other words, your transorb

    functionality in the coil release mode is the same as

    for the simple diodes described in:



  http://www.aeroelectric.com/articles/spikecatcher.pdf



    The proper application of uni-polar transorbs or zeners

    for SPIKE mitigation is to place them in series with

    a plain vanilla rectifier as shown in -B-. In this

    case, power that energizes the coil is blocked by the

    diode, but the strong negative swing at switch opening

    time is carried through the diode to the transorb that

    conducts like a ZENER to limit the excursion to more

    attractive levels (and allows the contactor to release

    faster). See:



    If the contactor release time (15mS versus 60 mS)

    is critical the use of transorbs as shown in -B- is

    indicated . . . -OR- you can use a single, bi-directional

    device to keep the wiring complexity down and eliminate

    device polarity concerns.



    If your transorbs are implemented as in -A- then

    they've offered no more functionality than the simple

    rectifier diode would offer. If contactor release time

    is critical, then changing to -B- or changing to

    bi-directional devices is called for. See:



  http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_with_Diode.gif 

  http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_without_Diode.gif

   http://www.aeroelectric.com/Pictures/Curves/CH_w_2x18v_Transorbs.gif 

  http://www.aeroelectric.com/Pictures/Curves/CH_w_120_Ohm.gif

  http://www.aeroelectric.com/Pictures/Curves/CH_w_1n5400.gif



 

  	  Quote: 	
		  Anyway, I just wanted to bring attention to an admittedly remote failure mode and a possible re-configuration that would have a much more favorable result if a failure did occur. 	


    Failures of the plain-vanilla diode are unknown to

    me. They're simply never electrically stressed in

    a manner that puts them at risk for failure. Similarly,

    Transorbs wired as shown in -B- cannot be impressed with

    system transients because they're isolated by the

    series diode.



    I'll suggest that there's more to your failure

    experience than what you've related in your posting.

   

    Bob . . .

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