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Discussion Starter · #1 ·
Ford Halts Mustang Mach-E Sales: Safety Recall With No Current Fix (msn.com)
in this day and age why are they using relays
why is anyone, even gm using relays , ramp resistors, when they have all the safety control where,
mounted on the trans axle, makes no sense
they should have all the power control, next to the battery and any power leads coming out are protected by the fused inverters, vfds. they can take care of voltage , no voltage over current, undercurrent, ramp the current up and down, full control and no relays
maybe they know something i dont know :)
 

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maybe they know something i dont know :)
$ ?

The forum points to a lack of parts for the fix. Ford doesn't expect to have a fix for the problem until Q3 2022. Once the fix is determined and the parts become available for order, Mustang Mach-E owners will be alerted by Ford via first-class mail.
Again demonstrating long wait times for replacement parts are not just a GM problem. My guess is some Ford Mach-E owners are now saying, "I'll never buy another Ford because they have stopped supporting my car" or some such.
 

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I finally saw one of these "in the wild" the other day.

Ugly as sin, to my eyes. I'd never buy one. If you gave me one, I'd sell it.

Besides, I hear Ford's have supply-chain problems. ;]
 

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Like a potato on wheels? Where are you folks buying your potatoes?
The one I saw was a dropped, broken, nasty green potato on wheels.
 
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Discussion Starter · #11 ·
Ford Halts Mustang Mach-E Sales: Safety Recall With No Current Fix (msn.com)
in this day and age why are they using relays
why is anyone, even gm using relays , ramp resistors, when they have all the safety control where,
mounted on the trans axle, makes no sense
they should have all the power control, next to the battery and any power leads coming out are protected by the fused inverters, vfds. they can take care of voltage , no voltage over current, undercurrent, ramp the current up and down, full control and no relays
maybe they know something i dont know :)
liked the potato

so i post this, and on face book comes up this, clicked on the link, had my full name already on the application filled out
things that make you go hummmm,
altium caught my eye
Mary i have a job:)
Product Automotive lighting Motor vehicle Font Vehicle
 

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so i post this, and on face book comes up this, clicked on the link, had my full name already on the application filled out
things that make you go hummmm,
When the machines first started to get smart enough to track stuff, I began getting popup ads for Rogaine and Viagra. When I commented to my sweetheart, I as told, "that's what's called 'target markinting.'"
 

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Discussion Starter · #13 ·
When the machines first started to get smart enough to track stuff, I began getting popup ads for Rogaine and Viagra. When I commented to my sweetheart, I as told, "that's what's called 'target markinting.'"
yep, been noticing this lately
for me, up until this time, its been lets try and sell you something
this is different, hey come to school, something to you
besides, i have no time, still into sex, drugs and rock and roll :)
 

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Found-On-Road-Dead. Fix-Or-Repair-Daily. F-It-Again-Ton.... wait now its Run Away Man! We import turn-of-the-century-Y2K era F-150s in Austria. The 5.7L Triton V8s are then pulled and the rest is discarded ha!
 

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They have to use relays. I'm not sure you understand how relays are used in high voltage/high current circuits, though you seem to be familiar with VFDs.
The relays cut all current--a completely open circuit with regards to the traction battery. That's why the 12 VDC battery is part of every EV.
 

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Discussion Starter · #16 ·
They have to use relays. I'm not sure you understand how relays are used in high voltage/high current circuits, though you seem to be familiar with VFDs.
The relays cut all current--a completely open circuit with regards to the traction battery. That's why the 12 VDC battery is part of every EV.
complete opposite with regards to relays
i have seen just about every failure with regards to relays, seen the contacts welded together, the contacts fall off, oxidize
seen the arm that holds the contact, bend, break, seen the pivot for the arm fail, the core of the coil become magnitized and the coil itself fail.
the local news paper heard about me and dragged me in becouse the 20 or so electrician before me could not find the intermittent problem with the press line, the control cabinet must have had 50 control relays in it, all in a row. i gave them no guarantee that i could fix it, before i started, see what you can do they said, got them to get the line up to speed, took my control screw driver with the handle covered with rubber, and one by one tapped the relays down the line, got through 3/4 of them and then hit the bad one, the line shuddered and did not shut down, but i saw 20 heads all look up at the same time , that looked funny. main guy then comes over, thats what it does, what did you do, change this relay i said, really he said not believing me. he shut the line down, we changed the relay and fired it back up again, went through the relays again and no shuddering. was there all of 1/2 hour, have a nice day i said and left
when ever i work on a machine its the first thing i do
you said The relays cut all current--a completely open circuit with regards to the traction battery.
well when the contacts weld together that doesnt happen and becomes dangerous
if you move the vfd or inverter to the battery location and protect them with fuses and a disconnect thats there anyways, the vfds and inverters are more than capable of protecting everything down stream
the relay is a failure point that you are relying on, as a safety point, that doesnt cut it
 

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Contacts welding is usually either a sizing problem or some unexpected surge. Using force control relays lets the system know that there is a failure.

I don't have any knowledge of the dangers of a failing VFD because we only use them in conjunction with safety relays and a safety circuit. I assume they occasionally fail, as any device would.

I would need much more information to be convinced that relays are not appropriate for EV applications. I suspect that Ford made some sizing mistake or implemented some shortcut for cost savings. That doesn't mean that using relays is problematic.

Also, I thought the high-voltage relays were at the traction battery assembly.
 

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Discussion Starter · #18 · (Edited)
Contacts welding is usually either a sizing problem or some unexpected surge. Using force control relays lets the system know that there is a failure.

I don't have any knowledge of the dangers of a failing VFD because we only use them in conjunction with safety relays and a safety circuit. I assume they occasionally fail, as any device would.

I would need much more information to be convinced that relays are not appropriate for EV applications. I suspect that Ford made some sizing mistake or implemented some shortcut for cost savings. That doesn't mean that using relays is problematic.

Also, I thought the high-voltage relays were at the traction battery assembly.
the relays are at the battery
heres my experience with the hv relay in my volt
my car shut down because the high voltage relay stayed "on" not because the contact were welded but becouse of temperature. when it hit -25 the car would shut down, when it warmed up it started to work again. two winters of having my command start working when it felt like it, was enough for me . i had to force gm under warranty to replace the relay.
been good since. that relay is giving you a false sense of security. the other problem with that of a relay, they dont like vibration, something that goes hand in hand with vehicles. and the final nail in the coffin for me is, as you said, maybe the relay is to small, as you increase the current through the contacts the mass of the relay gets bigger compounding the vibration thing
as far as a safety thing for the vfd, they dont monitor the relay they monitor for voltage after the relay. the same can be said for the vfd, monitor for voltage after the vfd. i see no difference
sound like you have some smarts - i say "cool"
 

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I've been retired from academia for 22 years now. Several decades ago I worked in software verification, better understood as bug finding rather than achieving freedom from bugs.

This discussion of contactor welding has got me interested in identifying failure modes that can lead to welding, with the goal of reducing vulnerability to such failure modes. The following is just some initial thinking on my part; I'm sure those who design power distribution units have thought far more than me about all this.

That said, I'm interested in where additional attention to failure modes might be of use. This is relevant to me personally as my newly electrified Delorean has battery and inverters and just needs a reliable power distribution unit. (I have two contactors already, one for each of the two battery leads, plus a precharge resistor for each as well as 200A fuses as basic fire protection.)

The power at a contactor responsible for welding is P = E*I. When open, I should be zero and when closed E should be zero. So in theory at least, welding can only happen in one of four ways: (i) during the transition from open to closed; (ii) during the transition from closed to open; (iii) I is large when the contactor is considered open; or (iv) E is large when the contactor is considered closed. If there's a fifth way I'd love to know what it is.

So to prevent welding it should be sufficient to deal robustly with each of these four cases.

(i) Open-to-closed: E and I should both be zero throughout this transition. At the start E is large and I is zero. So E needs to be reduced to (approximately) zero before starting the transition and then held there during the transition. This is normally done by precharging a capacitor through a big enough resistor. The capacitor needs to retain its charge until the transition is complete and the contactor is closed; if it doesn't (for example by a short somewhere or leakage in the capacitor) then an arc could be created resulting in welding. Are there other failure modes in this case that are not covered in (iv) below?

(ii) Closed-to-open: Again E and I need to be zero throughout this transition. At the start I is large and E is zero. So I needs to be reduced to zero first. This depends on the inverter being able to reduce its demand or regen to zero and keeping it there until the transition is complete and the contactor is open. An arc will almost certainly be created during the opening, but won't be a problem as long as I is kept low enough. If the inverter malfunctions at that point it could increase I and heat the arc to the point of welding. Any other failure modes?

(iii) I large with an open contactor. The most obvious failure mode here is the system believes the contactor is fully open when it isn't. Another would be an open contactor but with some sort of conductive material between the contacts. In either case this could be detected as resistance R dangerously low, measurable by monitoring current I independently. In either case the inverter should cut I to zero, though surely it would be doing that anyway if the system believes the contactor is fully open, so this seems an unlikely failure mode. What else?

(iv) E large with a closed contactor. In this case R is supposed to be zero. It is straightforward to measure R at the end of (i) (open-to-closed transition) before the inverter starts demanding current, so if it's nonzero then the inverter should not start. But what happens if R increases while the contactor is closed? In this case the system would see E rising, so the inverter should immediately cut I to zero, regardless of whether it was powering the motor or recharging the battery. Could it do this in time to prevent welding?

The logic for handling all these situations should be in triplicate so that a vote can be taken in the event that the failure is in the logic itself. The three voters need to be powered independently, e.g. from three separate supercapacitors, and located separately, to reduce the probability of two of them failing at the same time.

Are today's power distribution units more or less robust than a design taking all of the above into consideration? If more then how is it that welding is happening? What have I overlooked?
 

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Ford Halts Mustang Mach-E Sales: Safety Recall With No Current Fix (msn.com)
in this day and age why are they using relays
why is anyone, even gm using relays , ramp resistors, when they have all the safety control where,
mounted on the trans axle, makes no sense
they should have all the power control, next to the battery and any power leads coming out are protected by the fused inverters, vfds. they can take care of voltage , no voltage over current, undercurrent, ramp the current up and down, full control and no relays
maybe they know something i dont know :)
The answer to your questions has to do with how electric wires can interfere with each other. I had a 2002 Pontiac Montana AWD that kept burning out one ABS hub. Pontiac's engineers finally got involved and the underlying problem was that the power line to that hub was receiving inductive interference from the cable harness as a whole. The power, both voltage and amperage, leaving the source was correct but the power being received by the ABS hub was double the voltage, leading to the ABS hub failing. The solution was to reroute the power cable. The bottom line is that modern cars have so many electrical cables in them that you have to monitor at the destination.
 
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