HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors?

SnBGC

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even DCFC peak current is lower than WOT, it typically runs long time (tens of minutes) comparing to seconds of WOT. the contactors and box is in an enclosed environment, heat could accumulate over time.
Heat soak is a real thing apparently.
During the summer, I always plug in when parked. I do the thing where I lower my charge setting and open up the schedule so the vehicle won't charge the HVB but it WILL cool the battery if it gets hot.

When I park, I usually see the "It is hot out. Please plug me in" message. The vehicle usually does NOT start cooling right away. I figure that is because the battery is comfortable since it was being cooled while driving around town. But then I park it and it starts to warm up. Warmer and warmer until the A/C compressor comes on and it starts cooling the HVB. Usually takes about 15-30 minutes before it will start cooling.

I have noticed that the car will usually want to cool itself when parked after being driven. If the car just sits all day without being used, it normally doesn't want to cool itself, even in 113F. I assume the reason is because it doesn't generate heat while sitting parked. Although, it could simply be due to the car falling asleep and not realizing it is getting hot. Sometimes I walk by my car after it's been parked in the sun all day and it will start cooling but normally it doesn't do anything except sit there. Unfortunately there isn't an easy way or me to read the actual HVB temp while it's parked so all I can really do is make general observations and then speculate as to what is really happening. (hate having to do that...) 🤔
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RobbertPatrison

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Why would the inverters need to be switched on? They don't appear to be passing power through to the ACCM or PTC. If the vehicle needs to heat or cool the battery while charging then it could simply close that large negative contactor and then the ACCM and PTC would have power available. The motor inverters would remain powered down (if I understand how the system works...)

One question I have is: IF that scenario occurs......(the car wanting to power on the ACCM or PTC while charging)....then does it first shut off the small black negative contactor BEFORE it closes the large negative contactors of can they both be closed at the same time? Is there some sort of diode to prohibit power back feeding through one of those circuits? Is back feeding power even a thing in a DC circuit anyway? 🤔
Even if the front and rear motors are not running, supplying 380V to their inverters will lose some energy. I presume that the entire reason that a separate Charger Contactor exists is to avoid that energy loss. It would have been cheaper and simpler to switch it all with the Main Contactors. Instead, Ford engineers added this extra complication.

Yes, you are correct about switching from just running the Charger Contactor to powering up the HVAC and inverters. To avoid the spark in the Negative Contactor it probably first de-powers the Positive Contactor. So it briefly interrupts the L2 charging. That is likely not a problem.
 
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SnBGC

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There are 4 contacts involved for DCFC 2 for driving which are different set ups. Who knows if that has something to do with it and all 4 generate more heat even at lower amps? Just what one person is seeing, interesting and worth the debate. Can't believe all you read on the net.
I share your basic thinking path.
I see a max of 655A at WOT and a little over 300A while heavy regen. All that current is passing through just the two main HVB contactors so I presume they can get pretty hot. Then imagine stopping for a heavy DCFC session immediately afterwards. Maybe that could push things over the edge?

Obviously we don't drive at WOT for extended periods but it's very possible to have heavy regen for extended periods. Such as Phx-SD for example. Coming down out of the mountains heading into El Cajon is mostly all regen. The SOC actually increases for a good 15-20 miles during that descent. Then DCFC in El Cajon might add in more heat. Just thinking out loud though....
I will be making that trip next month. Might capture some data during that descent and see what it looks like.

I guess it is a good thing our cars don't run the PTC heater to warm the battery before DCFC events. I don't DCFC very often, but when I do it is just enough to make it to my final destination. If my trip requires more than 1 DCFC event than I usually take an ICE vehicle. It is just more convenient for me to do that (even though I HATE pumping and burning fuel).

I took a short trip this past weekend. 295 miles round trip so I had to DCFC to make it home. The first 4 plugs I tried didn't work. Wasted about 20 minutes there. Then I found one machine that did work but only at 30kW. At that point, not much else I could do but sit there for another 20 minutes to get enough juice to make it home. 45 minutes in total to get 12% added to my car! Not a pleasant experience. :(

On the bright side..... I guess my contactors were happy since only 31 kW was pumping through those 4 connections. 👍

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977198106


Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983
 

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Shayne

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I share your basic thinking path.
I see a max of 655A at WOT and a little over 300A while heavy regen. All that current is passing through just the two main HVB contactors so I presume they can get pretty hot. Then imagine stopping for a heavy DCFC session immediately afterwards. Maybe that could push things over the edge?

Obviously we don't drive at WOT for extended periods but it's very possible to have heavy regen for extended periods. Such as Phx-SD for example. Coming down out of the mountains heading into El Cajon is mostly all regen. The SOC actually increases for a good 15-20 miles during that descent. Then DCFC in El Cajon might add in more heat. Just thinking out loud though....
I will be making that trip next month. Might capture some data during that descent and see what it looks like.

I guess it is a good thing our cars don't run the PTC heater to warm the battery before DCFC events. I don't DCFC very often, but when I do it is just enough to make it to my final destination. If my trip requires more than 1 DCFC event than I usually take an ICE vehicle. It is just more convenient for me to do that (even though I HATE pumping and burning fuel).

I took a short trip this past weekend. 295 miles round trip so I had to DCFC to make it home. The first 4 plugs I tried didn't work. Wasted about 20 minutes there. Then I found one machine that did work but only at 30kW. At that point, not much else I could do but sit there for another 20 minutes to get enough juice to make it home. 45 minutes in total to get 12% added to my car! Not a pleasant experience. :(

On the bright side..... I guess my contactors were happy since only 31 kW was pumping through those 4 connections. 👍
If the two 50 KW are not working when I get there I am doomed. Plugshare tells me I am good when I take off.

Wonder if there is enough room to run a heat sink sat on top of the contacts (maybe just the positives?). Hoses are right there to tie into so should not be a liquid problem? A plate with thermal paste and all just like a liquid cooled cpu/gpu ;). Wonder if it would work and keep them from getting too hot. Either that or make contacts that can take the heat.
 


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A permanent solution would be a complete re-design of the HVJB with better cooling and temperature monitoring.
... but rather a structural issue in the design of the HVJB.
I think you nailed it. And great schematics by the way.

Ford has already committed to replacing original HVBJB with 'beefier' versions, but only on 'as needed' basis... which I find frustrating because failures could occur unexpectedly, and possible strand Owners in locations that are inconvenient or possibly dangerous (in bad weather or remote locations).

What I would love to see is an alternate/additional resolution for those of us having the original HVBJB .... perhaps active cooling of that space, and temp sensors at each of the main contactors. even a few watts of energy will really heat an enclosed space up!

Adding a chill plate below, similar to what is under the batteries, would require dropping the battery tray and a significant amount of 'plumbing' to add a loop under the HVBJB.... which leaves me wondering if the easier fix might be to pull the front seats out, and install vents to circulate cabin air thru the HVBJB rather than leave it a sealed space with no good way to dissipate heat. Even a little 12v muffin fan would probably work.....
 
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RobbertPatrison

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I share your basic thinking path.
I see a max of 655A at WOT and a little over 300A while heavy regen. All that current is passing through just the two main HVB contactors so I presume they can get pretty hot. Then imagine stopping for a heavy DCFC session immediately afterwards. Maybe that could push things over the edge?
[...]
Interesting thought. 300A Regen is ~115kW so less than 150kW DCFC but it does heat up the HVJB.
If the scenario is a long sustained way down on a mountain highway pass that could heat up the contactors. But on the way up the power flow would be even higher over longer sustained climbs.
 

Blue highway

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DC charging is not likely the real culprit here. The rear motor is 210kw, AWD front motor is 50kw, the GT front motor is even higher. 150kw charging is below the steady state rating of the contactors and 150 kw is only for a few minutes. This is why WOT is more likely the cause of the degradation, not DCFC.
If a relay is dissipating 80W, during DCFC (article in the thread above), it is going to get rather hot during DCFC. A WOT event right after a long charge, adds more heat heat (i.e. more than 80W) to an already really hot device.

I can see where a series of WOT events right after a DCFC could push the relay over the edge.
As I recall from the data sheet, 500A "continuous" is only for 7.5 Minutes.
 

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All the failures I’m seeing are welded positive dc charge contactors after charging at an electrify America station…..
This is just so inaccurate. I'm not sure why there's so much focus on DCFC. I would say at least 10-20% of failures I've seen are on cars that have never once used DCFC. I have seen 0 failures, zero, when unplugging from a DCFC. Could there be some, sure, but out of all the failures I've seen it's never been the case.

I would say at least 50% of failures are realized in the owners driveway/garage.
 
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Blue highway

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Heat soak is a real thing apparently.
During the summer, I always plug in when parked. I do the thing where I lower my charge setting and open up the schedule so the vehicle won't charge the HVB but it WILL cool the battery if it gets hot.

When I park, I usually see the "It is hot out. Please plug me in" message. The vehicle usually does NOT start cooling right away. I figure that is because the battery is comfortable since it was being cooled while driving around town. But then I park it and it starts to warm up. Warmer and warmer until the A/C compressor comes on and it starts cooling the HVB. Usually takes about 15-30 minutes before it will start cooling.

I have noticed that the car will usually want to cool itself when parked after being driven. If the car just sits all day without being used, it normally doesn't want to cool itself, even in 113F. I assume the reason is because it doesn't generate heat while sitting parked. Although, it could simply be due to the car falling asleep and not realizing it is getting hot. Sometimes I walk by my car after it's been parked in the sun all day and it will start cooling but normally it doesn't do anything except sit there. Unfortunately there isn't an easy way or me to read the actual HVB temp while it's parked so all I can really do is make general observations and then speculate as to what is really happening. (hate having to do that...) 🤔
113 degrees... brutal. I can sense the engineer at Ford cringing.
 

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This is just so inaccurate. I'm not sure why there's so much focus on DCFC. I would say at least 10% of failures I've seen are on cars that have never once used DCFC. I have seen 0 failures, zero, when unplugging from a DCFC. Could there be some, sure, but out of all the failures I've seen it's never been the case.

I would say at least 50% of failures are in the owners driveway/garage.
Not me that said that and totally miss quoted. Tell us are the parked failure stuck open and not welding shut. There are two separate conditions a stuck open contact and a stuck closed one. There is an obvious difference in these two. Have no idea how they over heat turned off in park.
 

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even DCFC peak current is lower than WOT, it typically runs long time (tens of minutes) comparing to seconds of WOT. the contactors and box is in an enclosed environment, heat could accumulate over time.
The 150 kw is only for about 3 minutes, then it ramps down to 120kw. Current is always below the contactor rating for either of these values.
 

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Not me that said that and totally miss quoted. Tell us are the parked failure stuck open and not welding shut. There are two separate conditions a stuck open contact and a stuck closed one. There is an obvious difference in these two. Have no idea how they over heat turned off in park.
From my understanding that happens because the contractors become molten while being driven, then when cooling after power off they weld in an open state.

Open contractors amounts to maybe 10% of the cases I've seen. Closed is much more prominent.
 

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TLDR: Probably not

Longer version:
Thanks to John Kelly's excellent video we can lift the mystery of the operation of the High Voltage Junction Box (HVJB) in the MME. We can also figure out the likely problem that triggered the recall for the contactor. How? Buckle up and let's get technical!

What is in the HVJB?
Here is the full schematic that I reverse-engineered from this and several other sources:

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983


Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983


The main task of the HVJB is to distribute the high voltage battery energy and maximize safety. It contains the following major parts:
  • Main Contactor+ which connects the positive battery terminal. All current flows through this contactor.
  • A Pre-charge contactor + resistor to prevent sparks during startup. Since Main Contactor+ is the last one to close there will be 380Volt across the 2 pins. The pre-charge contactor closes first, charging the terminal slowly through a 24 Ohm resistor. After the voltage is equalized Main Contactor+ can be closed spark-free. Without the precharge circuit, a huge inrush current would flow. The high current and sparks could potentially weld the contacts, or damage the contacts. All EVs apply this trick.
  • Main Contactor- connecting the negative battery terminal. This switches both motors and the HVAC parts.
  • A 630A Rear motor + DCFC fuse. This supplies either the powerful rear motor or the negative terminal of the DCFC port.
  • A smaller Front Motor Fuse.
  • A Cabin HVAC Fuse that protects both the air conditioner compressor and the electric PTC heater. Both these parts heat or cool the cabin as well as the battery. See my earlier post here for details on how that is plumbed.
  • A charger contactor with a charger fuse that connects to both the onboard 240VAC->380VDCcharger and the 380DC->12DC charger. This is switched separately, allowing for L2 charging without powering up both motor inverters. More on that later.
  • Two beefy DCFC contactors isolate the high voltage pins of the charge ports. They are the same type as the Main Contactors.
What is the problem?
The subject of the recall is a malfunction of one of the 4 large contractors. According to Ford: "Direct Current (“DC”) fast charging and repeated wide open pedal events can cause the high voltage battery main contactors to overheat. This overheating may lead to arcing and deformation of the electrical contact surfaces, which can result in an electric relay switch remaining open or a relay switch that welds close from heat. An overheated relay switch that opens while driving can result in a loss of motive power, which can increase the risk of an accident."

What does the contactor look like?
A contactor (AKA a relay) is just an electrically controlled switch. When a 12V low voltage is applied to the primary input, the main contacts close which can conduct a very large current. Cars contain dozens of smaller contactors. The ones that switch the high voltage battery need to be particularly strong. The 4 large jampot-shaped contactors in the HVJB are made in Mexico by TE. This is the datasheet:
Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983


Notice that the maximum rated continuous current is 500Amps . We'll come back to that later.

How does the HVJB operate during normal driving?
Before entering the car all HVJB contactors are open (that is, not conducting). The MME is powered by the 12V battery only. When you press the start button in the MME the following sequence of events will likely commanded by the computer:
  1. The Main Contactor- (right side) closes. No current can flow yet because Main Contactor+ on the left is still open. The computer commands the inverters, compressor, and heater to be off.
  2. The computer verifies the voltages to check whether Main Contactor- is indeed closed (0 V across) and Main Contactor+ is open (~380V across). It also verifies that DCFC contactors are indeed open (and not weld shut).
  3. The pre-charge contactor closes to charge the left bus up to 380V.
  4. The computer verifies that the voltage on the left bus is high (~380V).
  5. After that Main Contactor+ closes.
  6. The pre-charge contactor opens, as its job is done.
  7. The computer verifies that the voltage on the left bus remains high (~380V) to verify that the contactor is closed. Likely it briefly commands a little load on the bus to check whether voltages remain stable. If not, this could be a contactor issue and it will throw an error.
  8. The front and rear motor inverters probably run a self-check.
  9. If all is OK, we are ready to drive!
After this, the HVJB will be switched like this, with both main contactors conducting:

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983


How much current flows while driving?
Normal steady driving commands about 25kW. This means that a current of (25,000/380=) 66Amps through the two contactors. Maximum regenerative braking is about 70kW, resulting in a reverse current flow of about 185Amps. During pedal-to-the-metal acceleration the peak current through the contactors will be ~900Amps in the GT. In the dual-motor MME it will be about 690A peak.

How does the HVJB operate during DC Fast Charging?
The likely chain of events is as follows after the car is plugged into DCFC:
  1. The Main Contactor - (right side) closes. No current flows yet because Main Contactor+ on the left is still open. The computer commands the inverters, compressor, and heater to be off.
  2. The computer verifies the voltages to check whether Main Contactor- is indeed closed (0 V across) and Main Contactor+ is open (~380V across). It also verifies that DCFC contactors are indeed open (and not weld shut). It will error out if that is not the case. and the car needs to be towed.
  3. Both DCFC contactors close.
  4. The computer verifies the proper voltages, verifying that the contactors are indeed closed and that the DCFC charger does not deliver power.
  5. The pre-charge contactor closes to charge the left bus up to 380V.
  6. The computer verifies that the voltage on the left bus is high (~380V). If not, the car needs to be towed.
  7. Main Contactor+ closes.
  8. The pre-charge contactor opens
  9. The computer verifies that the voltage on the left bus remains high (~380V).
  10. The computer commands the right amount of charge voltage and current from the DCFC charger. It constantly verifies that the voltages are as expected.
After that, the HVJB will be switched like this:

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983

The DCFC charge current flows through all 4 contactors. If needed, the AC compressor is run to cool the battery, or the PTC heater is run to (pre-) heat the battery.
The battery cooling is needed because of the internal losses in the battery. The parasitic resistance of the battery can be calculated from the voltage drop under load. When flooring the pedal I see a from 380V to 350V with a current of 250A. So the internal resistance is (30/350=0.09Ohm). That is approx. 2kW of heat in the battery during charging that needs to be sucked out.

Do the contactors get hot?
It seems so! The contactor is rated for 500A continuous and 1000A for 1 minute at a hot 85C. Hence the limitations in the GT. According to the datasheet, the internal resistance of the contact is (0.1V/200A =) 0.0005 Ohm maximum. That seems tiny, but at the rated 500A continuous current that would generate (500*500*0.0005=) 125Watt of heat. During DCFC charging at 150kW the current will be about 400A, so the 4 contactors will generate up to 80Watts of heat each. That is pushing it, as all that heat will need to go somewhere. On top is that the primary coil in the contactor also gets quite warm: 650mA minimum hold current at 12V is another 8 Watts of heat.

The 80 Watt heat is not insignificant: it will get as hot as an incandescent light bulb. It does not look like there is any dedicated cooling in the plastic HVJB assembly. The only way it is cooled is indirectly from the battery pack behind it. Hopefully, the actual contact resistance is lower than that.

So it is possible that during DCFC and/or frequent heavy accelerations the contactors get so hot that they break down or age prematurely. At 85C (hot coffee) the rating is 1000W for 1 minute. But given the likely poor heat conductivity, 80W continuous heat could make the contactor much hotter than 85C. So it could get out-of-spec. Most contactors will survive some abuse, but some unlucky ones will melt plastic and break open or weld themselves shut.

What could a software fix do to prevent the contactors from blowing open or welding shut?
There is a tiny possibility that a bug in the software causes the pre-charging contactor to open too late (or not at all). That would degrade Main Contactor+ quickly. The fix for that would be simple. This scenario is quite unlikely given the information we have from the recall.

The software could reduce the system current when the contactors are hot. This inevitably means some performance degradation or longer charge times. The problem is that there is no temperature sensor in the HVJB or anywhere near the contactors. Ford's software would have to guess the heat based on the average current and the battery temperature. I don't think that can be done accurately without being conservative, causing a noticeable performance degradation.

The software might attempt to detect whether a contactor is about to go bad. The problem with that the voltage drop of a loaded contactor is small (<0.1V) compared to the voltage drop of the battery under load (~30V). The voltages on the battery side of the Main Contactors likely cannot be measured accurately enough to detect contact degradation. With any increase of resistance due to a dirty contact, the contactor will get much hotter very quickly due to the high currents. It will blow or weld shut very rapidly. So, I don't think this is feasible.

I could be missing something, but I don't see a way that a software fix can avoid the hardware problem of overheating without some noticeable degradation of the specs.

What could the software fix do?
It does not seem likely that the OTA software fix prevents the problem from occurring. So it probably just mitigates the problem. Let's analyze what could be done:
  • Case 1: One of the Main Contactors is stuck open. No current can flow so the car will be bricked. No way around that.
  • Case 2: One of the Main Contactors welded itself shut. This is detected in the startup sequence. Rather than bricking, the MME could be put in a limp-home mode to significantly reduce contactor current. That is likely what Ford's fix does. Since the other Main Contactor can still open there should be no significant safety risk.
  • Case 3: One of the Main Contactors opened itself while driving due to overheating, or some discontinuity is detected while driving. This will result in a 'stop safely now' event. Rather than bricking the car in the middle of the road, the software could attempt to restart after a brief cool-down period l. The it can switch to the reduced power limp-home mode. This is likely what happens.
  • Case 4: One of DCFC contactors is open. In that case, DCFC is INOP, but the car should otherwise operate normally.
  • Case 5: One of the DCFC contactors is welded itself shut. This is a slight safety issue but should not have to result in the car going into limp-home mode.
What about a hardware fix?
Any hardware fix would be very expensive for Ford because removing and opening the battery is significant labor and requires skilled people. It would probably run at $3K-$5K per vehicle. I suspect that Ford is monitoring the statistics. They decided that the problem is still rare enough to fix a HVJB on a case-by-case basis. There is no significant safety risk, especially after the software fix.

A permanent solution would be a complete re-design of the HVJB with better cooling and temperature monitoring.
Ford could also replace just the contactors in the HVJB with a better version. This is what the repair seems to do. I suspect that significantly better contactors in the same form factor are not available. Therefore this does not guarantee the problem from re-occurring. It does not seem to be a real manufacturing defect, but rather a structural issue in the design of the HVJB.

How does the MME operate with AC L2 charging?
Both the DC-DC and AC-DC chargers are on a separate (lower-power) contactor. This allows the 12V battery to be re-charged without switching on the entire car. This saves energy because the motor inverters will be off. L2 AC charging is also possible without switching on the entire car:

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983

In that case, only the Main Connector+ and the charger connector need to close. The cooling of the DC-DC converter and the Charger runs entirely of the 12V battery so it does not need HV to be active.

As soon as the battery needs to be heated or cooled the rest of the circuit needs to wake up. In moderate temperatures that is not needed because L2 charging produces little heat.

Hope this helps!
Disclaimer: The above is my speculation based on my research. It might be inaccurate or contain errors.

Ford Mustang Mach-E HVJB Deep Dive: Is there any way that software fixes the problem of overheating contactors? 1659977231983
Very informative, but in the end, the Mach-e is UNDER ENGINEERED, like most domestic manufactures. The Electro-mechanical part is NOT robust enough! FORD's solution, NEUTOR the cars power just like they have they gutted maximum acceleration of the GT due to the battery thermal bottle-neck issue. Yeah FORD, just keep screwing us with your inadequate software sleight of hand (not fixes).
 

ZuleMME

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The 150 kw is only for about 3 minutes, then it ramps down to 120kw. Current is always below the contactor rating for either of these values.
From what I see the DCFC doesn't overheat the contactors. But, it DOES heatsoak them. Running about max continuous power continuously. So when you leave a DCFC you certainly have the highest chance of roasting the contactors in a non-GT. In GT's all bet's are off as they always can push excessive power without proper temperature sensing to control it.
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