Shayne

Well-Known Member
Joined
Aug 9, 2020
Threads
18
Messages
3,235
Reaction score
2,429
Location
Northern Ontario Canada
Vehicles
2021 MME4x Prem
Occupation
Retired
Country flag
As an engineer with related experience, I can tell you that heat removal should not be required in a properly designed contactor. The welding is indeed due to arcing which is caused by either improper intermittent contact or too little surface area of contact for some reason. Also, while the bus bars do conduct heat, the thickness and other dimensions are primarily designed to keep electrical resistance down to minimize production of heat. It does seem to me that this problem is a design flaw. It is apparently a subtle one that took thousands of vehicles in real world conditions before it was even identified. Just one of the drawbacks for early adopters like all of us!
You and @smoke20 sound like two sides of an old discussion. Once it is part of the design it is inherent in them all. My first failed hvjb they had no idea what was going on. It took some time finally pointing to stuck open contacts followed by an extended wait for the part. The second all the bells and whistle went off with TSB's and everything.

Sounds like thicker bus bars are a no brainer to throw in even if not the complete fix. Don't really care what fixes it but could use the saga over. Engineers should know it is best to fix the problem professionally and point fingers afterwards. This one has gone on way too long with a poorly engineered software bandage fix which was of course no fix at all for under designed hardware.

Similar type of software bandage has again been dropped on us early adopters. We should have our L2 charging speed fixed also without Ford being forced to fix it. I don't want a defective overheating charging port beside my home; if it is throttled or not. The sagas of software trying to fix design defects in their hardware continues.
Sponsored

 

RandyMache

Well-Known Member
First Name
Randy
Joined
Sep 30, 2023
Threads
3
Messages
142
Reaction score
58
Location
San Marcos, California
Vehicles
2023 Mustang Mach e Premium
Occupation
Private Investigator
Country flag
This is super interesting. Thank you for adding this insight. So in the end, it remains heat that is the root problem. I would love to see an actual broken contactor cracked open: what caused the problem>? did the plastic deform, and were there any manufacturing defects?

The higher the current, the more heat, so the higher the chance that teb HVBJB problem occurs. GT models and 4WD models with a long-range battery have the potential to draw more current during driving. During DCFC charging a peak 150kW is running constantly, which also generates heat, but apparently, that is less of an issue because that current is the same across all models.

The cause remains the insufficient cooling of the HVBJB. The design of that part has not changed, so I am curious what the recall solution will be. Just putting in new contactors does not solve the heat generation problem.
Your kind of implying that the design was sound and Ford just miscalculated the power going through the connector. I would suggest the more likely aspect of this issue, is that the vender cut corners and provided Ford with a sub-standard connector not to spec. Just my thoughts…..
 

ChasingCoral

Well-Known Member
First Name
Mark
Joined
Feb 3, 2020
Threads
372
Messages
12,259
Reaction score
24,162
Location
Maryland
Vehicles
GB E4X FE, Leaf, Tacoma, F-150 Lightning ordered
Occupation
Retired oceanographer
Country flag
Your kind of implying that the design was sound and Ford just miscalculated the power going through the connector. I would suggest the more likely aspect of this issue, is that the vender cut corners and provided Ford with a sub-standard connector not to spec. Just my thoughts…..
Or more likely a bit of both. The design wasn't robust enough when production resulted in more variability in the construction than the engineers intended. A really robust design can overcome variance around specifications. However, when the production has to tightly follow specifications it is much easier to have a failure.
 

AKgrampy

Well-Known Member
First Name
Mike
Joined
Jan 29, 2022
Threads
5
Messages
2,717
Reaction score
2,657
Location
Fairbanks, Alaska
Vehicles
Ford Expedition, Ford F-150, Mach E GT
Occupation
Retired
Country flag
Or more likely a bit of both. The design wasn't robust enough when production resulted in more variability in the construction than the engineers intended. A really robust design can overcome variance around specifications. However, when the production has to tightly follow specifications it is much easier to have a failure.
Obviously just speculation but the contactor has a continuous rating and then over that rating the current limit is based on a curve. My thought is that heat causes the time/current curve to begin to weaken by degrading the metal and eventually become exceeded at which point it would become damaged. It would also increase in resistance which is how Ford’s software detects potential failure. What I believe Ford did was to install contactors with a better time/current curve so the chances of failure are greatly reduced. My thought is also that even the new contactors can develop the same issues but at a much lower rate and I think that may be all Ford can do without redesigning the unit.
 

dtbaker61

Well-Known Member
First Name
Dan
Joined
May 11, 2020
Threads
102
Messages
3,902
Reaction score
3,597
Location
santa fe,nm
Website
www.envirokarma.org
Vehicles
MME (delivered 2/26/21), DIY eMiata BEV
Occupation
Solar Sales/install
Country flag
Last year I posted a detailed technical analysis of the HVBJB problem that has affected many. I suspected that software cannot fix a hardware design problem.

Let's look at the schematic of the HVB Junction Box in our MME:
Screenshot 2023-10-17 at 09.42.56.jpg



The current flows from the positive battery connection (+380V) though Main Contactor+ and then through both motors and then through Main Contactor-
back to the battery (0V).

The recent recall notice for 30K Mach-e EVs gives more information about the possible cause and fix for the HVBJB proglem. This is the text:
Screenshot 2023-10-17 at 09.46.49.jpg


Ford's software remedy 22S41 did not fix the root problem of Main Contactor+ or Main Contactor- overheating. Rather, it attempts to detect the deterioration of the contactors by measuring increased resistance as a sign of trouble. When higher resistance is detected, the MME will go into a 50% low-power mode and the MIL light will switch on. The car remains drivable as long as the contactors still work normally. If a contactor is welded shut or is stuck open, the MME will be bricked and needs to be towed. That is the dangerous case as the car suddenly loses propulsion.

The resistance is measured by tracking the voltage drop between A and B and between C and D while the vehicle is pulling heavy power. The normal contactor resistance is 0.0005 Ohm according to the datasheet. At 500 Amps that would only be a small 0.25 Volt drop, while any sign of decay should give more drop and a lot more heat. They hoped to detect this and then dial down the maximum power by 2X to reduce heat. Notice that at 150kW charging power the heat in each contactor is a hot 80 Watt per contactor. If the heat cannot be hauled away this will cause problems.

From the new text, it is clear that Ford admits that this strategy does not work well. Too many vehicles still fry their contactors without the software detecting increased resistance beforehand. This is not surprising IMHO. Ford does think that the regular battery with its lower current rating reduces the probability of a fried HVBJB.

This is the jampot-shaped contactor, of which there are 4 identical ones in the HVBJB:

screen-shot-2022-08-05-at-7-36-59-jpg.jpg


and this is what it looks like when it welds itself shut:
screen-shot-2022-08-08-at-12-54-33-jpg.jpg



I am a little puzzled about what the recall fix for this is,. The replacement HVBJB looks the same as the old one and does not have temperature sensors either. It might use some upgraded contactor. Within the same form factor, the same problem is likely to happen again. What it needs is a design change with better thermal properties.
exactly.

a sealed contactor with inert gas inside only stays sealed if temps are controlled. sitting in a sealed HVBJB with no thermal management, and adding heat to a sealed container with high current dumping heat is ....obviously... recipe for death of sealed contactors.

There ARE several ways to fix the issue, but all will require different hardware, additional sensors, and plumbing changes to add a coolant loop where needed.

There are also 'open' contactors less sensitive to temp designed with bigger magnetic 'blowouts' to suppress arcing when contactors open and close. Switching to open contactors might be an option since the whole shebang is in a sealed enclosure already. Open contactors would avoid the issue of losing their internal seal of inert gas and *maybe* reduce failures due to pitting or welding.
 
 




Top