# Coil suppression diode damaging contactors?



## JRP3 (Mar 7, 2008)

In his most recent show Jack Rickard mentions that the common practice of using a coil suppression diode on the contactor delays the release time causing pitting and welding and is a bad idea. A little research came up with this from Tyco:


> Even though the use of coil suppression is becoming more significant,
> relays are normally designed without taking the dynamic impact of
> suppressors into account. The optimum switching life (for normally-open
> contacts) is therefore obtained with a totally unsuppressed relay and
> ...


PDF
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf


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## etischer (Jun 16, 2008)

I suppose it's a trade off. Risk damaging the contactor by slowing the release of the contacts, or risk damaging the device that turns the contactor on by inducing a high voltage arc. 

- no diode
The device that turns the contactor on will be exposed to high voltage arc every time the contactor is opened. If this gets welded, you could blow out your motor controller because next time you turn the key the contactor will turn on immediately instead of waiting for precharge to complete. 

-with diode
The contactor should always be switching with no load, so in theory, it should never arc. The exception I guess would be in a real emergency when the throttle is stuck on and you have to shut down.

Maybe you can get the best of both worlds by placing the diode in a different place in the circuit? My main contactor closes when my inverter is healthy and the ignition switch is on. I can put the diode across the inverts "healthy" contacts for protection, and the ignition switch will not slow the contactor opening.


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## piotrsko (Dec 9, 2007)

I dunno, we started putting diodes on relays way back in the 70's military electronics because the capacitors we used before then weren't doing a decent enough job depleting the back emf into the sensitive transistors. I can see the argument about delays, and understand the theory, but cant see where in practice it matters a heck of a lot. Pitting and burning has been a fact of life with high voltage high current contacts since Marconi (actually Tesla)


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## JRP3 (Mar 7, 2008)

etischer said:


> I suppose it's a trade off. Risk damaging the contactor by slowing the release of the contacts, or risk damaging the device that turns the contactor on by inducing a high voltage arc.


You're talking about the precharge resistor, I'm talking about the coil suppression diode that clamps the spike that appears when the coil collapses.


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## JRP3 (Mar 7, 2008)

piotrsko said:


> I can see the argument about delays, and understand the theory, but cant see where in practice it matters a heck of a lot. Pitting and burning has been a fact of life with high voltage high current contacts since Marconi (actually Tesla)


I guess the point is if there is a way to eliminate or reduce that pitting why not use it? The contactor manufacturer gives specific alternatives to a diode:


> Based upon the impact on armature motion and optimizing for normallyopen
> contacts, the best suppression method is to use a silicon transient
> suppressor diode. This suppressor will have the least effect on relay dropout
> dynamics since the relay transient will be allowed to go to a
> ...


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## etischer (Jun 16, 2008)

I'm talking about removing the suppression diode. If the diode on the main contactor coil is removed, my "inverter healthy" contacts may get welded. Next time I turn on my ignition, the contactor will turn on immediately, instead of waiting for my inverter to be "healthy" (precharged). 




JRP3 said:


> You're talking about the precharge resistor, I'm talking about the coil suppression diode that clamps the spike that appears when the coil collapses.


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## etischer (Jun 16, 2008)

JRP3 said:


> I guess the point is if there is a way to eliminate or reduce that pitting why not use it? The contactor manufacturer gives specific alternatives to a diode:



Anything that keeps current flowing in the contactor coil will increase the time it takes for the magnetic field to collapse.


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## JRP3 (Mar 7, 2008)

So are you saying that without coil suppression the contacts on a second contactor might be welded? You're talking about two contactors? I'm confused.
Note that Tyco doesn't say you shouldn't have any suppression, just that a plain diode isn't the way to do it.


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## JRP3 (Mar 7, 2008)

etischer said:


> Anything that keeps current flowing in the contactor coil will increase the time it takes for the magnetic field to collapse.


Yes but to varying degrees. Look at the PDF I linked.


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## etischer (Jun 16, 2008)

JRP3 said:


> So are you saying that without coil suppression the contacts on a second contactor might be welded? You're talking about two contactors? I'm confused.
> Note that Tyco doesn't say you shouldn't have any suppression, just that a plain diode isn't the way to do it.



I have only one contactor. (well two if you include the precharge contactor, but it's not part of what Im talking about)

The main contactor is energized when the ignition switch is on, and my inverter is healthy. The contactor coil is a large inductive load that will fry the wimpy "inverter is healthy" relay contacts in my inverter. The diode protects the relay contacts from damage.


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## etischer (Jun 16, 2008)

JRP3 said:


> Yes but to varying degrees. Look at the PDF I linked.




Ahh, so a diode and a zener seem to be a win - win solution.


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## JRP3 (Mar 7, 2008)

Yes, though they do say


> the best suppression method is to use a silicon transient suppressor diode.


 However I haven't yet found one.


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## Weisheimer (May 11, 2009)

JRP3 said:


> Yes, though they do say However I haven't yet found one.


Check out Transorb devices.

They are included with the Zilla and you can get them there or from DigiKey

Here is a sample link though I'm not sure that this is the same exact one as the part that Zilla specs.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1.5KE30CALFCT-ND

Cheers
Mark


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## jackbauer (Jan 12, 2008)

I've used diodes on a coil or relay only when its being controlled by a semiconductor device eg a transistor. If its being controlled via another relay or a switch why bother in the first place?


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## JRP3 (Mar 7, 2008)

To protect the controller. From Alltrax:


> DIODE is a protection device across the
> contactor coil. The contactor coil is a magnetic
> device. When the contactor is turned off, the
> magnetic field collapses causing a “voltage
> ...


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## Dave Koller (Nov 15, 2008)

Interesting - as both of my SW-200's came with a resistor/diode across the coils - and they slam open - Maybe faster without - BUT if my relay that controls them STICKS its contacts from the back EMF, then what ?

here is specs for SW's suppresson..

Not so worried here....... 

without suppression 10ms
with diode suppression 100ms
with diode and resistor 30ms (what I have )


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## JRP3 (Mar 7, 2008)

I think this is the TVS diode specified for the Zilla http://www.digchip.com/datasheets/parts/datasheet/333/NTE4933.php


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## Dave Koller (Nov 15, 2008)

Whoops forgot the other part of the contactor equation :

"Rare Earth Magnets molded into the top cover which produce magnetic fields which act on the main contact arcing, thereby extinguishing the arc outwards."

Magnetic blowouts ...

Hence some difference in speeds compared to those in the pdf from Tyco..


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## EV-Eric (Jun 21, 2009)

JRP3 said:


> In his most recent show Jack Rickard mentions that the common practice of using a coil suppression diode on the contactor delays the release time causing pitting and welding and is a bad idea.


Could someone explain exactly when the contactor is turned "off" that causes this damage? (Think before you answer it's a trick question!)


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## JRP3 (Mar 7, 2008)

EV-Eric said:


> Could someone explain exactly when the contactor is turned "off" that causes this damage? (Think before you answer it's a trick question!)


Are you suggesting that it's only a problem under load?


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## etischer (Jun 16, 2008)

EV-Eric said:


> Could someone explain exactly when the contactor is turned "off" that causes this damage? (Think before you answer it's a trick question!)


A contactor coil is a huge inductor. 

Inductors want to keep current constant, much like a capacitor keeps voltage constant. 

If a coil consumes 1 amp, and you open the circuit, the coil wants to keep that 1 amp flowing. If there is very high resistance (open circuit), the coil will produce a very high voltage trying to maintain 1 amp. You can usually see a spark jumping an air gap. This high voltage arcing damages the contacts in the relays and switches used to control the contactor.

In the article the JRP3 linked, a standard automotive relay with a 12v coil produces 750v when de-energized without suppression.


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## EV-Eric (Jun 21, 2009)

JRP3 said:


> Are you suggesting that it's only a problem under load?


 
Yep you got it! 





etischer said:


> If a coil consumes 1 amp, and you open the circuit, the coil wants to keep that 1 amp flowing. If there is very high resistance (open circuit), the coil will produce a very high voltage trying to maintain 1 amp. You can usually see a spark jumping an air gap. This high voltage arcing damages the contacts in the relays and switches used to control the contactor.


I think your mixing the coil current with the actual current being switch which typically comes from the traction battery pack.


Unless it's normal to switch off you power relay (contactor) while under a load like, accelerating from a stop or going down the freeway there should be no high current(100s of amps) load while turning OFF the power relay (contactor).

Now for safety and reliability one needs to install (diode, transient suppressor) as required by the unit controlling the power relay. You also need to make sure the power relay (contacts) are rated for more then the current draw (more then your fuse is rated for is a good start) since in an emergency you need to count on the relay opening the contacts and not arching permanently closed


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## JRP3 (Mar 7, 2008)

In an emergency situation the last thing you want is to delay the contact opening, so a plain diode seems like a really bad idea. TSV or diode plus Zener for the win.


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## etischer (Jun 16, 2008)

JRP3 said:


> In an emergency situation the last thing you want is to delay the contact opening, so a plain diode seems like a really bad idea. TSV or diode plus Zener for the win.


It's going to be tough to find a zener that can handle the current required for an EV sized contactor coil. 

There is a trade off, the faster you want the contact to open the higher the voltage spike you will have. First priority should be quenching the voltage spike so it is within the rating of your contacts. 

The Kilovac EV-200 has the diode built in so I'm sure Tyco has taken it's effects into account. Might be worth checking to see if your contactor has supression before going through the hassle, the work might already be done for you =)


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## JRP3 (Mar 7, 2008)

This is mostly theoretical for me as the Curtis AC instructions say to remove all diodes and resistors from the contactor as they are handled by the controller. I'm using a Kilovac LEV200 that does not have the economizer.


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## PTCruisin (Nov 19, 2009)

I'm sitting here looking at the specs. for the Kilovac EV200AAANA contactors that I plan on using and it states that the built-in coil economizer will suppress the back EMF to zero volts. I assume that means that whatever component (transistor, mechanical switch, or relay) used to switch the coil current will not see a back EMF. Does anyone have experience with these contactors? I was not planning on putting reversed biased diodes on these contactors.


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## major (Apr 4, 2008)

PTCruisin said:


> I'm sitting here looking at the specs. for the Kilovac EV200AAANA contactors that I plan on using and it states that the built-in coil economizer will suppress the back EMF to zero volts. I assume that means that whatever component (transistor, mechanical switch, or relay) used to switch the coil current will not see a back EMF. Does anyone have experience with these contactors? I was not planning on putting reversed biased diodes on these contactors.


Hi PTC,

Yeah I've used a lot of them. I have never used a coil diode with them and never had a problem. I did not look it up just now, but I think you are instructed not to use a diode in the spec sheet.

major


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## PTCruisin (Nov 19, 2009)

major said:


> Hi PTC,
> 
> Yeah I've used a lot of them. I have never used a coil diode with them and never had a problem. I did not look it up just now, but I think you are instructed not to use a diode in the spec sheet.
> 
> major


Thanks major, for confirming that.


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## Dave Koller (Nov 15, 2008)

On the Tyco:

http://www.alliedelec.com/Images/Products/Datasheets/BM/TYCO-ELECTRONICS/433-0016.PDF

Kilovac EV200AAANA


EV200: 
A = Normally Open 
A = 9-36VDC (_*1=requires external coil economizer*_)(?????)
A = 15.3 in (390 mm) B = 6.0 in (152 mm)
Coil Terminal Connector:
N = None
A = Bottom Mount & Male 10mm x M8 Terminals


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## Coulomb (Apr 22, 2009)

PTCruisin said:


> I assume that means that whatever component (transistor, mechanical switch, or relay) used to switch the coil current will not see a back EMF.


I've had one of their economisers apart; there is a surprising amount of componentry inside:

http://www.aeva.asn.au/forums/forum_posts.asp?TID=142&KW=economiser&PID=14109#14109

So yes, I'd say you'll see very little spike coming back after that lot's been at it. Certainly, you would not use a diode or anything else in addition to all that circuitry.


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## Dave Koller (Nov 15, 2008)

Coulomb said:


> I've had one of their economisers apart; there is a surprising amount of componentry inside:
> 
> http://www.aeva.asn.au/forums/forum_posts.asp?TID=142&KW=economiser&PID=14109#14109
> 
> So yes, I'd say you'll see very little spike coming back after that lot's been at it. Certainly, you would not use a diode or anything else in addition to all that circuitry.


Sounds interesting - BUT I get an 
[h1]Access Denied[/h1]
to that link - LOL members only?


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## JRP3 (Mar 7, 2008)

Dave Koller said:


> On the Tyco:
> 
> http://www.alliedelec.com/Images/Products/Datasheets/BM/TYCO-ELECTRONICS/433-0016.PDF
> 
> ...


I guess they offer it with and without the economizer, "1" denoting without the economizer.


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## Dave Koller (Nov 15, 2008)

JRP3 said:


> I guess they offer it with and without the economizer, "1" denoting without the economizer.


Yep - so most people are getting it and DO NOT need a diode ! Trouble is if you want to remove it I think it might be hard and a lot may not realize they have it !


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## JRP3 (Mar 7, 2008)

Indeed. When I was having contactor issues I tried swapping one in not realizing the economizer wouldn't work with the Curtis 1238 AC. I then removed the economizer, not that hard, just take off the cover and cut the two wires, but it still wouldn't work because it was a 12-24 volt coil and the Curtis needs exactly 24 volt coil. So don't use one of those if you have the AC system from HPEVS


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## frodus (Apr 12, 2008)

Talked to HPGC today is that the curtis has a built in PWM output for the Contactor. Its a % of full pack voltage. They set it for 24V output. The EV200 will not work with a PWM signal. If you take the economizer off, the coil is expecting a different voltage than 24V, I think its 12V and 24V is pretty much the lowest you should set the PWM, as the coil is not made for such high inrush.

The right thing to do, is order an LEV200 for 24V and be done with it. Its easy to resell the EV200's if you already got one (as I did).


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## frodus (Apr 12, 2008)

JRP3 said:


> This is mostly theoretical for me as the Curtis AC instructions say to remove all diodes and resistors from the contactor as they are handled by the controller. I'm using a Kilovac LEV200 that does not have the economizer.


Correct. The settings in the manual seem to confirm that. It does its own coil economizing.


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## JRP3 (Mar 7, 2008)

frodus said:


> Talked to HPGC today is that the curtis has a built in PWM output for the Contactor. Its a % of full pack voltage. They set it for 24V output.


Yes this is where my problems started. The PWM made the contactor buzz quite a bit and I thought something was wrong with the controller. Turned out it was just a noisy contactor, which Brian seemed to think was normal, Bill thought it was a bit much and sent me another contactor which was much quieter though still has a slight buzz.


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## frodus (Apr 12, 2008)

You could get a 48V coil contactor and adjust the PWM higher, it should get rid of that.


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## JRP3 (Mar 7, 2008)

It's not that loud, and not worth spending $500 on the programmer or control software and another $100 on a contactor


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## Coulomb (Apr 22, 2009)

Dave Koller said:


> Sounds interesting - BUT I get an
> [h1]Access Denied[/h1]
> to that link - LOL members only?


Huh, it should be available to all. It's an Australian web site, so it might have been doing maintenance in the dead of night Australian time, which is probably morning US west coast time.


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## Dave Koller (Nov 15, 2008)

Coulomb said:


> Huh, it should be available to all. It's an Australian web site, so it might have been doing maintenance in the dead of night Australian time, which is probably morning US west coast time.


Here is what I got today...


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## Coulomb (Apr 22, 2009)

Dave Koller said:


> Sounds interesting - BUT I get an
> [h1]Access Denied[/h1]
> to that link - LOL members only?


It was in the "Ebay finds", which is in the For Sale forum, which has special access rules. Something about spam, I think.

Anyway:

========================

Mine arrived today, thanks Johny. 

The economiser is surprisingly complex: 










I count 3 chips, 3-4 tiny transistors, 1 medium transistor (just at my finger tip), and a host of small stuff.


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## Dave Koller (Nov 15, 2008)

LOL Well that is not a resistor/diode 

Rather complex little board..


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## Linghunt (Oct 20, 2010)




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## Linghunt (Oct 20, 2010)

I have blow out 3 of the PCB's so far, got 26 more to go. PCB releases smoke after 20 seconds. Running 30A at 400VDC, and do not apply load till after the contacts are closed. Plan on running 90A and fails at 30A.

Will Call Manufacturer in morning... Note the different Rev of the PCB.

-Linghunt


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## etischer (Jun 16, 2008)

What voltage are you applying to the contactors coil?

Are you sure you have the polarity correct?

I assume you are not using a diode since the contactor has an economizer built in?





Linghunt said:


> I have blow out 3 of the PCB's so far, got 26 more to go. PCB releases smoke after 20 seconds. Running 30A at 400VDC, and do not apply load till after the contacts are closed. Plan on running 90A and fails at 30A.
> 
> Will Call Manufacturer in morning... Note the different Rev of the PCB.
> 
> -Linghunt


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## Linghunt (Oct 20, 2010)

24 VDC fused at 5A. (3.8A inrush current). Yes, the Black is Common Bus and Red wire is the 24VDC. 

Relay works just fine until the load is applied to the to the Contacts. We tested these relays last X-mas to verify specification, with 100A DC current through them and 600 VDC. The isolation of the contacts to the coil and circuit is my concern.

I will let you know how it goes. -Linghunt


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## major (Apr 4, 2008)

Linghunt said:


> 24 VDC fused at 5A. (3.8A inrush current). Yes, the Black is Common Bus and Red wire is the 24VDC.
> 
> Relay works just fine until the load is applied to the to the Contacts.


Hi Linghunt,

I use these at 400 Vdc and up to 500 A. With 12 V coil circuits. I have never seen a problem like this. But I am interested to what may be causing it.

Is the 24 V circuit completely isolated from the high voltage? When you say common bus, it makes me think that the 24 V negative might be the same as the high voltage negative.

Is it possible to see your complete circuit?

Regards,

major


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## Linghunt (Oct 20, 2010)

I have a Ground reference to the 24VDC supply at just one point on the common at the 24VDC Supply. 

Do pretty good at keeping my Ground bus, Neutral bus, and Common bus seperate. The High Voltage line going through the Relay is (-) with the anode of the HV supply also referenced to the Ground. There is arcing on the HV line at times, but not yet during this phase of testing.


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## major (Apr 4, 2008)

Linghunt said:


> I have a Ground reference to the 24VDC supply at just one point on the common at the 24VDC Supply.
> 
> Do pretty good at keeping my Ground bus, Neutral bus, and Common bus seperate. The High Voltage line going through the Relay is (-) with the anode of the HV supply also referenced to the Ground. There is arcing on the HV line at times, but not yet during this phase of testing.


That is confusing  Do you have a diagram or schematic? If you don't want to post it, send it PM (or I will send you my email address). I will keep it confidential.

major


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## Linghunt (Oct 20, 2010)

I understand, I tried to be clear, but its complicated. E Tech isolated coil with different 24VDC supply and was able to crank supply up to to 30KW.

The Common reference to the ground is the direction. Adding an isolated additional supply is direction I'm headed. I will post results. Schematic is multiple pages and IP. I'm trying to be careful on what I say, thusly the confusion.


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## Alexander_B (Oct 19, 2010)

just don't tie battery negative to the chassis, then the spark in the contactor won't try to jump to the gnd of the 24v side trough the insulation of the contactor. prevents some other nasty accidents also (accidentally shorting positive of the pack to chassis doesn't harm anything if the negative is insulated as well, to name one.)


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## Linghunt (Oct 20, 2010)

Technician is adding a seperate 24VDC supply that will be isolated so the 24VDC common will not be referenced to the ground. Should have some results in a while. 

Not had this type problem before, but not had to deal with a circuit on a relay coil like that before.


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## Linghunt (Oct 20, 2010)




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## Linghunt (Oct 20, 2010)

We ran the Relays off of a seperate 24VDC Supply and isolated the 120VAC power to the 24VDC Supply. We ran one of the Relays for over an hour with 30KW of power going through it and had no problems. Went to a different relay and were taking a current measurement for coil current and the relay exploded. The Copper bus bent up and scared the crap out of the Technician.

We did blow up a relay early with same effect on the little circuit board.

Pretty strange. Going to verify the Power supplies are not hooked up backwards as we are using 3 High voltage power supplies per Relay.

Might have a Shorted Sputtering target as well. Will update was we figure this out. Will post a scaled down circuit schematic later.


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## Linghunt (Oct 20, 2010)

Final Report:

We did a 100% sort of all the relays, The relays with the PCB that had C8 installed failed, the Current through the Contacts was coupled to the 24VDC coil voltage. 

The Relays without the Capacitor, were fine. The Relay that exploded must have had another flaw, air leak? unknown

I returned all of the parts to the Vendor via the Distrubutor for analysis and refund of $$. Not heard anything back to what they found.

I went with a different Relay (Gigavac). We got a sales sample and tested it hard with success. I ordered a complete set and did not see any problems with any of them. The completed Machine has been been running for almost 6 months now with no issues. 

In my phone calls to various folks, It looks like there were political design issues associated with PCB. but this was hear-say.

Lesson learned: Testing a new component that is critical to a program, test multiple units. don't assume they are the same part even if they have the same part number.


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## Linghunt (Oct 20, 2010)

Update, Gigavac Relays still doing the Job. Not had any issues since. System is completely functional. 

Never did hear back from Kilovac. They did lose a lot of business from me.

-Linghunt


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