Pics/Info: Inside the battery pack

[tom66]

Well if you looked at the eBay listing it is connected and powers on fine.

A Model S will not charge or drive with "PULL OVER SAFELY" message. The pack pyro fuse is blown, due to airbag detonation, or critical damage has occurred to the drive inverter, HV battery or power sub-systems.

The seller doesn't mention that the car powers up under its own power - you can get the dash etc to light up if you just connect a 12V source or if the 12V battery is charged.

The capacity meter just shows the capacity at the moment of the accident. Sort of like old cars where the purely mechanical rev-counter or speedo would jam in an accident. Ah, you can see who was being a fast driver.

 

[lolachampcar]

magnet,
Keep the comments coming......

Yeah that was JB's idea. The whole case of a cell is connected to negative which is why you wrap the whole cell for safety but it kills heat tranfer. With proper mounting you only need a ring



The present invention eliminates the adverse effects of the dielectric material covering the cylindrical case of a conventional 18650 cell by eliminating this covering and replacing it with a ring-shaped dielectric material, the ring-shaped dielectric material not extending down or otherwise covering the cylindrical outer surface of the cell's casing. Accordingly, the ring-shaped dielectric material provides access to the battery terminal while preventing shorting between the terminal and the edge of the cell casing. This design significantly improves cell heat transfer efficiency while providing a better surface, i.e., the bare cell casing, to which to bond, clamp, or otherwise attach to during cell integration within a battery pack or other package.

 

[yobigd20]

A Model S will not charge or drive with "PULL OVER SAFELY" message. The pack pyro fuse is blown, due to airbag detonation, or critical damage has occurred to the drive inverter, HV battery or power sub-systems.

The seller doesn't mention that the car powers up under its own power - you can get the dash etc to light up if you just connect a 12V source or if the 12V battery is charged.

The capacity meter just shows the capacity at the moment of the accident. Sort of like old cars where the purely mechanical rev-counter or speedo would jam in an accident. Ah, you can see who was being a fast driver.

Interesting to know. Wouldn't it be possible for someone to buy a new fuse then?

 

[tom66]

Interesting to know. Wouldn't it be possible for someone to buy a new fuse then?

Yes. I believe Otmar fixed the same issue with his Model S salvage, the Vanagon conversion project. His car had mostly frontal damage with some minor rear damage. He got lucky, his pack was OK. But with all that chassis damage to that car, I think there's a good chance of at least some damage to the battery pack.

 

[lolachampcar]

WRT using the battery in place of PV, I looked into this when I was considering the same project. Most inverters want to do maximum power point conversion where they continually change current draw from the PV array to determine which combination of voltage and current provides the maximum power harvest from the panels. Batteries do not require this attention so what happens when the battery is put in place of the PV array.

Firstly, the battery can source 85kw at 1C discharge. You will likely be sizing your inverter to your house needs thus 8kw AC was the number I used. The question for me became how gracefully does the inverter deliver yield power and how does it fold back when driven close to rated power? The other question is how does the MPP tracking react to the low impedance source that is the MS battery?

One option for me were some of the SMA inverters that provide up to 2KW of PV generated power to the home when the grid is down. You still have the MPPT problem to consider but at least the inverter will fire up and produce AC in the absence of a grid to sync to.

 

[NigelM]

If the car says "pull over safely" it's a fair bet in the very least that the main pack fuse is out.

In the case of the totaled car on eBay you may well be right, but as a blanket statement it's not true. The "pull over safely" message can be prompted by a variety of things (I had it recently as a result of sudden tire deflation).

 

[tom66]

In the case of the totaled car on eBay you may well be right, but as a blanket statement it's not true. The "pull over safely" message can be prompted by a variety of things (I had it recently as a result of sudden tire deflation).

Interesting - not heard of that before. Was it a "Contact Tesla Service" or "CAR IS SHUTTING DOWN" error (the latter usually a result of severe driveline/battery failure.) Or something else?

 

[NigelM]

Interesting - not heard of that before. Was it a "Contact Tesla Service" or "CAR IS SHUTTING DOWN" error (the latter usually a result of severe driveline/battery failure.) Or something else?

I got the ding with "Pull over safely" message and "Tire pressure VERY low", turned out I had picked up a large screw on the road, pulled into a parking lot about 100' up the road and as I opened the door I could hear the air still escaping from the tire.

Tesla were great btw, sent a flatbed, fixed the tire and returned the car to my house later the same day. (Had to buy a new tire though which was depressing as I had put on a complete new set only the week before).

[/off topic]

 

[tom66]

Interesting. In this case, I guess there are various types of shut-down errors. A high-voltage system fault is "Car needs service. PULL OVER SAFELY." or "CAR IS SHUTTING DOWN. PULL OVER SAFELY." I am not sure if these trigger for non-HV faults, since Tesla have not released any service documents yet.

 

[qwk]

theres an 85kW salvage up on ebay for $24.5k with a working battery pack. Tesla Model s 85 | eBay this might be good for someone else trying to do the same thing as you.

This car most likely has an "A" pack. Just something to consider.

 

[apacheguy]

This car most likely has an "A" pack. Just something to consider.

Was my immediate thought as well upon seeing the VIN.

 

[tom66]

Would be interesting to see the difference between the packs, my guess is maybe some cooling, if any difference at all. Might just be that the cells are not rated for the full 120kW/135kW.

 

[NuclearPowered]

Can you get a picture of the negative terminal of an individual cell?

The Rav4EV uses the 2900 mAh NCR18650PD with a C shaped vent designed to break the bond wire on the terminal when it opens. The C shaped vent is pictured in the Tesla patent but more recent patents also describe a circle shaped vent.

Pansonic recently released the NCR18650BE cell which is also an NCA cell rated at 2C max just like the PD cell, but rated at 3300 mAh! This cell has the same triangular postive terminal as the PD cell but has a circular vent. No other Panasonic cells besides the PD and BE have negative terminal vents! The nominal voltage of a NCA cell is 3.65V so a 3.3 Ah cell would result in a 85.5 kWh pack

The 3400 mAh NCR18650B is a high energy cell not suitable for EV use. The latest high energy cell is the NCR18650G rated at 3600 mAh. Neither of these cells has the Tesla vent on the neg terminal.

Tesla does not use the BMS to balance the pack. They use active impedance control to shuttle charge between bricks. It is always working and it much safer than a typical BMS (battery murder system)

Can you expand on the variable impedance balancing? And why you consider BMS a murder system?

 

[JRP3]

Probably because faulty BMS's have a tendency to kill the cells they are supposed to protect.

 

[magnet]

Can you expand on the variable impedance balancing? And why you consider BMS a murder system?

The BMS is connected to each brick of cells in parallel to monitor voltage, temp, etc using ONE PCB.

A normal BMS would use the connections to each brick on THE SAME ONE PCB to ALSO do the balancing (either by shuttling or bleed resistors). If that board fails/malfunctions it is a big problem since the potential is up to 400+V on the board (since that board is connected to every brick in the pack all at a different potential from ground to max pack voltage). Some will say just use optoisolators, but even then the BMS is more likely to start a fire or totally drain your pack (murdering it in either case).

The Tesla pack as I understand it has a BMS to do centralized monitoring, but the actually balancing is done brick only brick to brick by using a rail capacitor to shuttle charge. The max potential the circuit between bricks "sees" is only one brick to the next brick in series. By shuttling you can move charge to any brick in the pack eventually. This variable impedance balancer can act totally independent from the BMS and is a very simple circuit. It doesn't need a sleep or off mode because if it is not shuttling it is using almost no power

 

[NuclearPowered]

Not by design, I hope.

 

[wk057]

Alright, so, tinkered with the pack a little. I've been able to trickle charge it as a whole a bit, but, decided that I should just wait until my HV charger comes in before I mess with it more.

Figured out a few things, but not too much.

First, with the pack disconnected from the car, the BMS boards do NOT appear to be functioning in any capacity. There is no usable voltage anywhere on the boards from what I can tell, which means they probably need a 12V feed from the car to power them, just like the contactors.

There does appear to be a buck converter configuration on the main BMS board where the HV entire pack is connected to it. I wasn't able to find any voltage on anything I thought should have voltage from it, however.

There is a small board connected to part of one of the main bus bars, presumably for current sensing. None of the leads from it to the main BMS board appeared to have any voltage.

Took a few close ups with the FLIR E5 and no components that should have a heat signature were showing as active.

So, looks like using the stock BMS is probably out of the question since it is doubtful I'll be able to even safely determine how to power it, let alone communicate with it in any useful fashion. At least if it were running off of the pack itself I'd have a chance to chat with it, but, I'm not about to start feeding in 12VDC randomly looking for results.

Other notes, appears I was mistaken about there being any large resistors on the individual BMS boards. There do appear to be some large surface mount resistors on the boards which could likely sink a watt or so each. Looks like one for each sub-section of the modules. So, thats probably the balancing right there.

All that said... I'm probably going to end up dismantling the pack and use it as a ~48V configuration (44V nominal with 8 sets modules in series hooked in parallel). This will probably make the pack more manageable anyway as a lot of off the shelf hardware will do useful things at this voltage. I really would rather not have to, but, it seems like doing so would just make every other aspect of my project simpler.

 

[scaesare]

The BMS is connected to each brick of cells in parallel to monitor voltage, temp, etc using ONE PCB.

A normal BMS would use the connections to each brick on THE SAME ONE PCB to ALSO do the balancing (either by shuttling or bleed resistors). If that board fails/malfunctions it is a big problem since the potential is up to 400+V on the board (since that board is connected to every brick in the pack all at a different potential from ground to max pack voltage). Some will say just use optoisolators, but even then the BMS is more likely to start a fire or totally drain your pack (murdering it in either case).

The Tesla pack as I understand it has a BMS to do centralized monitoring, but the actually balancing is done brick only brick to brick by using a rail capacitor to shuttle charge. The max potential the circuit between bricks "sees" is only one brick to the next brick in series. By shuttling you can move charge to any brick in the pack eventually. This variable impedance balancer can act totally independent from the BMS and is a very simple circuit. It doesn't need a sleep or off mode because if it is not shuttling it is using almost no power

Very interesting.

Is this speculation or do you have some authoritative source for this?

 

[tom66]

A lot of battery management systems I've seen work on modules-at-a-time. A short between modules is therefore extremely unlikely, as each module is isolated from the next.

Very interesting.

Is this speculation or do you have some authoritative source for this?

He has the pack in pieces.......

 

[scaesare]

A lot of battery management systems I've seen work on modules-at-a-time. A short between modules is therefore extremely unlikely, as each module is isolated from the next.



He has the pack in pieces.......

wk057 is the OP and he certainly does... but I did not know that about magnet as well?

Is this documented anywhere we can see? I ask because magnet is suggesting active impedance and/or a capacitor to shuttle charges between bricks, yet wk057 is reporting resistors on the BMC PCB's that imply a charge-bleed system.

I'm trying to reconcile the differences, but don't have any background context that magnet is supplying, whereas we have pics of what wk057 is doing...

(don't get me wrong, I'm not imputing bad motive to magnet... I just want to understand how accurate this info might be)