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
statements of rated electrical life are usually based on this premise. The
successful "breaking" of a DC load requires that the relay contacts move
to open with a reasonably high speed. A typical relay will have an accelerating motion of its armature toward the unenergized rest position during drop-out. The velocity of the armature at
the instant of contact opening will play a significant role in the relay's
ability to avoid "tack welding" by providing adequate force to break any
light welds made during the "make" of a high current resistive load (or one
with a high in-rush current). It is the velocity of the armature that is most
affected by coil suppression. If the suppressor provides a conducting path,
thus allowing the stored energy in the relay's magnetic circuit to decay
slowly, the armature motion will be retarded and the armature may even
temporarily reverse direction. The reversing of direction and re-closing of
the contacts (particularly when combined with inductive loads) often leads
to random, intermittent "tack welding" of the contacts such that the relay
may free itself if operated again or even jarred slightly.
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
predetermined voltage level and then permit current to flow with a low
impedance. This results in the stored energy being quickly dissipated by
the suppressor. Transient suppressor diodes are available as bi-directional
components and permit the relay to be non-polarized when installed
internally. Note that if a uni-directional transient suppressor is used, a
rectifier diode must be placed in series with it to block normal current
flow and it has little advantage over the use of a zener diode. The transient
suppressor should be selected such that its pulse energy rating exceeds
any anticipated transient such as coil turn-off or motor "noise" found in the
application.
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.
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.
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)
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
predetermined voltage level and then permit current to flow with a low
impedance. This results in the stored energy being quickly dissipated by
the suppressor. Transient suppressor diodes are available as bi-directional
components and permit the relay to be non-polarized when installed
internally. Note that if a uni-directional transient suppressor is used, a
rectifier diode must be placed in series with it to block normal current
flow and it has little advantage over the use of a zener diode. The transient
suppressor should be selected such that its pulse energy rating exceeds
any anticipated transient such as coil turn-off or motor "noise" found in the
application.
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.
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?
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
spike” that can damage the controller. The
diode safely clamps this energy.
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 )
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..
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.
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 =)
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.
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.
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.
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.
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.
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
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
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).
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.
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.
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.
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 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.
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.
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.
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.
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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