The "Dreaded Clunk" and a great service experience

[SteveS0353]

It's just an idea, with little proof so far - it could be quite incorrect.

Keep in mind, the high voltage contactors are fairly similar in design to a relay - 12V power is going to an electromagnet that holds the contactor closed while a spring tries to push it open.

Thus, what I was suggesting is that if the car's 12V voltage becomes low or has a lot of ripple in the voltage from an overloaded DC-DC converter, it could cause the contactor to not stay fully closed, possibly leading to bits of sparking and then the overheating and failure suggested above.

I'm pretty sure what I just described can happen with the types of pieces the Model S has in its system. I have no idea if that is what is actually happening to the cars experiencing the failures.
Walter

The contactor may be a latched permanent magnet type, magnetically held closed with a spring to open the contacts on detection of a failure. That won't take power from 12V to keep it closed. The failure mode is thermal -- too much heat in the contacts, heats a bimetallic strip which applies force to oppose the magnet, and the spring flips the contacts open.

The reported clunk is not so much the movement of the contact arm as it is the arc -- think of lightening and a thunderclap. Breaking a circuit which has hundreds of amps flowing is not simple. Mechanical contacts is the only reliable way to ensure an open circuit. A solid state relay can fail short circuit.

 

[apacheguy]

The contactor may be a latched permanent magnet type, magnetically held closed with a spring to open the contacts on detection of a failure. That won't take power from 12V to keep it closed. The failure mode is thermal -- too much heat in the contacts, heats a bimetallic strip which applies force to oppose the magnet, and the spring flips the contacts open.

From what I've read most of the failures occur at > 50% SOC. If the failure mechanism were as you described, I would expect many more failures at lower SOC where resistive heating is far greater in the pack.

 

[CRinATL]

I tend to drive with a "light foot" and have had no issues, other than significant range degradation with my A-pack. Is there a correlation between high acceleration and the "clunk"?

How much range loss have you seen?

 

[bluetinc]

Mine let go with 159 Rated mile remaining: so not a particularly low SOC, really.

Mine was 158...

 

[napabill]

Mine was 158...

I was at 220, having just come off my nightly charging.

 

[wycolo]

Contactors in photo draw 4.0 Amps @12.6 volts so most likely of traditional config, not self-latching. Being round they might have circular contacts always randomly positioned on MAKE thus using newish conduction areas for longer life.

Driving 'Tesla Style' with a light foot to save battery, contactors, tires, wildlife, windshield, etc until I just can't stand it any more . . . :crying:
--

 

[Cottonwood]

Contactors in photo draw 4.0 Amps @12.6 volts so most likely of traditional config, not self-latching. Being round they might have circular contacts always randomly positioned on MAKE thus using newish conduction areas for longer life.

For safety reasons, it is very important that the relay (contactor) is not a latching style. Tesla has made it very clear to first responders that all they have to do is disconnect 12V power, just like in an ICE, to shut the car down and get rid of any high Voltage sources. If 12V power goes away (the firemen cut the 12V wires), then the relay in the battery pack opens, and any high Voltage danger is contained inside the armor plated battery.

 

[DrGuest]

I had my brief time on the side of the road today on my morning drive to work this morning. I got a tow truck and my model s is home, safe in my garage. A Tesla Ranger was dispatched from Spokane, WA and will be here in Bozeman this evening. I suspect he will pick it up in the morning and trailer it to Seattle. Thank you Stevezzzz for this thread. Reading about this in advance of it happening helped me think to put it in Tow Mode before I lost all power making it real easy for the tow truck driver to glide it up on his truck without having to remove the nosecone. I am also glad I keep a Tesla sheepskin blanket folded up on my Parcel Shelf and put it on my legs since we lost all heat and it was chilly by the time the tow truck got there. Tesla then called a local Enterprise Car Rental that then called me to ask if I could use their assistance. That was really great to be called by the car rental with most of the paperwork already filled out by info that Tesla had on me. My wife was less than 5 minutes away so she stayed with me till the tow truck arrived and got my car home. I was told my the Tesla Technician that my car sent out a "little SOS" just before it shut down and they felt that my car was in Tow Mode so they cautioned me to stay with the car and to make it sure it would not roll away on me. The Freemont, CA Technician sent me an email to my iphone with his direct phone number, towing instruction pdf, nose cone pdf file and a nose cone removal video, All this info helped to keep me relaxed and know what I needed to know when the tow truck arrived. My odometer had just crossed 15,000 miles in 11 months so I have been driving this car more than any other. More to the story as it unfolds. I am very happy and grateful that it happened when it did and am very happy that Tesla is doing all that they can to get my car serviced and back to me. Tow truck cost covered by Tesla, Car Rental cost covered by Tesla, All repairs covered by Tesla. A little patience and gratitude on my part and all this will soon fade away as a distant memory. Soon I will be back in the drivers seat of the most amazing vehicle I have ever owned and driven!

 

[DrGuest]

Having the main pack contractors open is no more dangerous than throwing a timing belt on an ICE car, and probably a lot less dangerous than having a tire suddenly depressurize. There's no need to blow it out of proportion: an instantaneous and total loss of power from the traction pack doesn't mean you can't control the car. In this case I coasted half a mile to a safe pullout without endangering myself, my passengers or anyone else: the friction brakes, power steering, signals and displays all worked fine. If I'm not mistaken, the car turned on its emergency flashers automatically (at any rate they were on when we stopped and I don't remember turning them on myself).

I agree with you Stevezzzz, These cars really coast well and I had plenty of time to pull over, had full power steering, my blinkers and all my monitors were working. It was only after I was pulled over for 5-10 minutes that I lost all the interior power and there was even a warning that let me know when power was beginning to be shut down. The emergency flashers remained functional the whole while as well as while towing all the way home. It happened just as I had entered the freeway and was accelerating up to the 75 MPH, so I obviously was making sure my lane was safe as I entered the freeway and so pulling over was not dangerous for me at all. Like you said, less of a big deal or less dangerous than throwing a timing belt, or having a flat tire. Nothing is perfect but the service so far has been stellar!

 

[apacheguy]

@DrGuest - Which hardware revision is your battery? Guessing B or D, but would be very surprised if you said D.

 

[DrGuest]

@DrGuest - Which hardware revision is your battery? Guessing B or D, but would be very surprised if you said D.

My car was just loaded up and is heading to Bellevue, WA. It will be a day or so before I know much more. My Ranger drove 8 hours to get to Bozeman from Spokane. Was here at my home at 6 am, less than 24 hours from when the incident of occurred. I'm tracking his progress west via my iPhone App. He used to work for BMW and said joining Tesla has been a great decision. More later.

 

[DrGuest]

@DrGuest - Which hardware revision is your battery? Guessing B or D, but would be very surprised if you said D.

I do have a D pack.

 

[apacheguy]

Wow, I thought they had this thing sorted out with the D packs. Also interesting that your 12 V only had 5 min to live once you pulled over. It does seem to support the theory that the 12 V has a difficult time keeping the contactors shut at low voltage. Anyone know what causes the 12 V to discharge to such a low voltage?

 

[stevezzzz]

Sorry to hear you've joined the club, DrGuest, but kudos to Tesla for their response. And it's nice to know that reading about my experience helped prepare you for yours.

 

[tezco]

Wow, I thought they had this thing sorted out with the D packs. Also interesting that your 12 V only had 5 min to live once you pulled over. It does seem to support the theory that the 12 V has a difficult time keeping the contactors shut at low voltage. Anyone know what causes the 12 V to discharge to such a low voltage?

The 12V is a very small battery, so it doesn't take long to discharge with the loads from power steering, climate control and all the computers running at full power. Normally, the DC to DC converter is on whenever the car is powered up, and the 12V functions more like a smoothing capacitor than an energy source. I don't expect that low 12V voltage causes the contactor failure as the DC to DC converter can supply a lot of power. I think the contactors just have a higher than anticipated failure rate. The Sig contactors probably have a lot more cycles on them because in the early days with our high vampire losses, the DC to DC converter had to switch on countless times every day to keep the 12V from completely discharging. From the photos in the battery teardown thread, the contactors don't look very large considering the power loads that they carry. Just a tiny increase in internal resistance can cause a huge increase in generated heat.