How do you find the 1 bad cell, of 74 in a brick Tesla S?

M

Matt Gruber

1 MW
Joined
Feb 8, 2007
Messages
2,594
Location
New Smyrna Beach FL
https://www.youtube.com/watch?v=LVpCCJwsFpQ&ab_channel=GruberMotorCompany
:?:
This is a quiz :twisted: if you know the answer, give others a day or 2 to figure it out 8)
 
Check which cell generates more heat (infra red camera device) when the whole pack is being charged. The one that heats the most is the one with highest DC IR, thus the bad one. This would also work when the pack is being discharged. Ohms law says heat (power lost in watts or delta P) is related to voltage sag (delta V) times current (I in amps). And voltage sag itself (delta V) is related to battery internal resistance times current (I in amps). Thus dP = R x I², where R is the DC internal resistance (DCIR) of the cell. Bad cells have high DCIR, and thus lose more power in heat loss because the sag more voltage... Spot the heater in the pack.

Do I win a Gruber assist (Vivax) if I get this right ?
 
flir
https://youtu.be/xtY3RRJVs4I?t=55
 
i was more curious whether that was Matt in the video
probably his brother
 
i like to think that, in an alternate universe, that could be me 8) :lol:
since anyone that can fix a pack can make $20,000 on an S, keep those ideas coming. I like the infrared camera idea, but how to do it without one? :?:
Also don't miss this FIRE at 9:00 https://www.youtube.com/watch?v=0-z423zPswc&ab_channel=GruberMotorCompany
How do you plan to handle occasional fires? :?:
.
EXTRA CREDIT: how do you find cells with low capacity, say have only 2ah and were 4ah?
 
to find weak cells, i'd use the voltage drop during heavy load from the cell spot weld to a given distance, like 2 or 3", like a shunt works. Maybe you see a .003 v. drop on say, 70 cells and 2 are .001. these 2 cells are weak.
or during charging you see one higher than the others, say .006v drop
on one cell- this one is shorted. yes it will heat up, could use an IR gun and compare cell temps.
 
adamsavage79 said:
What a horrible design. So much wasted space in there, and near impossible to find the bad cell.
Click to expand...

i challange you to make a more compact design that is automotive grade.

answer: charge the pack, cool it down in a fridge overnight and put a high current draw on it. the busted cells will be visible on a IR camera in a few minutes.

dont forget to cut the equal amount of cells from the other blocks to keep the battery in balance.

lower capacity modules i would not even bother with. let the active balacing of the bms figure that one out. if the bms cant keep up you will see the voltage imbalance and you just yeet the module at that point into the trash. there is hardly any value that warrants dicking around for hours/days trying to save 200 bucks worth of used cells that might still be good.


fun fact: anyone notice that the "safety fuse" did nothing? :roll: its like its not even a fuse at all....
 
I'd look into designing a pack that installs from inside - before the seats go in. Then to service, remove seats and if it is designed with service in mind, it will be easy to fix. :bigthumb: Could just put the drivers seat in, and could check cell temps after a drive or while charging. Then pop out the seat and do the last group.
Under the car makes no sense to me.
.
in the case of 1 bad cell, i'd look to replace it, but the cooling system may be a problem.
 
Matt Gruber said:
I'd look into designing a pack that installs from inside - before the seats go in. Then to service, remove seats and if it is designed with service in mind, it will be easy to fix. :bigthumb: Could just put the drivers seat in, and could check cell temps after a drive or while charging. Then pop out the seat and do the last group.
Under the car makes no sense to me.
.
in the case of 1 bad cell, i'd look to replace it, but the cooling system may be a problem.
Click to expand...

the entire battery of a model S/X/3/Y can be pulled out form under the car in less then 5 minutes if you know what you are doing.
why would you even bother with a battery under the interior? you would need to pull out everything from window to window to get into the battery. there is a reason why nobody builds a car this way.

tesla packs are still the most reliable by FAR considering the competion. and tesla packs are being fixed. its just that its often simply just not worth it.
 
good Q :thumb: why have floor TOP access?
1. on the fly diagnosis- as you drive the car the pack can be checked :thumb:
2. no need for lift- so it can be worked on without using a shop bay :thumb: huge savings for the repair shop.
3. can be repaired outside the shop so a rare fire only burns the car :thumb:
the fact that tesla packs work great covers up the weak service points of the design.
Let's see how many 20+ year old EV's are still on the road. I've done engine swaps on most of my cars, a good engine can last decades- i built my 61 350 in 1992 and love it :bigthumb: EV battery is high priced, even more than a gas engine. EV's make great fleet cars, put a million miles on them and junk them.
i bet guys like me do keep them going, at least i hope so :bigthumb: teslas are nice looking cars
 
Matt Gruber said:
good Q :thumb: why have floor TOP access?
1. on the fly diagnosis- as you drive the car the pack can be checked :thumb:
2. no need for lift- so it can be worked on without using a shop bay :thumb: huge savings for the repair shop.
3. can be repaired outside the shop so a rare fire only burns the car :thumb:
the fact that tesla packs work great covers up the weak service points of the design.
Let's see how many 20+ year old EV's are still on the road. I've done engine swaps on most of my cars, a good engine can last decades- i built my 61 350 in 1992 and love it :bigthumb: EV battery is high priced, even more than a gas engine. EV's make great fleet cars, put a million miles on them and junk them.
i bet guys like me do keep them going, at least i hope so :bigthumb: teslas are nice looking cars
Click to expand...

1: you dont need to be inside the battery, that is what the bms is for.
2: even the most basic garage has a lift. a car without a lift cant even do a exaust fix or oil change.
3: they are not meant to be serviced. so complaining about poor serviablitty is a non-argument. no battery from any company is servicable. legally not even a trained mechanic is allowed to remove a battery pack, let alone open it and start mucking around in it. if you work for a company your employee need to have a licence (and specialized tools to work on high voltage systems otherwise you are going to have a massive insurance issue if he gets killed or injured, not to mention the OSHA flavour in your country is going to shut your ass down and drown you in fines.
 
Got a better idea. i just saw where the location of the faulty cell is available from the software(plug in a laptop) :thumb: so diagnosis is not needed :thumb:
So if they made the 1200# pack out of 4-x 300# modules in separate sections from under the car(all you need is a floor jack/dolly), it would be easy to replace a faulty module- in this example the $5k would buy an entire NEW 300# module instead of just fixing the 1 cell :bigthumb:
So when another section has a problem, owner is looking at another $5k and at that point 50% of the cells are NEW. So the owner gradually replaces the pack, if it is worth it. Of course replacement 300# modules should come down in price over the years. Say 10 years from now, aftermarket suppliers might sell plug in ready to go packs at a very reasonable price :bigthumb:
 
you already have like 8 years of warranty on the thing.

your ideas are getting even more impossible by the minute.

replacing modules does NOTHING for adding capacity. its still dependant on the lower module capaicty.

think a few seconds longer before you commit these ideas in your head.
 
you are too short sighted. after the 4th module is replaced, it will be close to the range when new.
Think ahead before you post :bigthumb:
8 years is nothing. my 61 is 60 years old 8)
You flunked the no lift pack removal test. Rich Rebuilds does it now with floor jacks 8)
Funny that you attacked your own idea, which was to stay with under the car pack install. I accepted your idea and you don't like it :roll:
 
just because you can do a battery swap with floor jacks does not mean you should.

if i recall correctly the guy has a bona fide garage now. using jacks for that job is litteraly an osha violation.

just because you see 1 idiot do it on the internet does not make it a good idea. just like the "fuse wire" bullshit from tesla. some moron thinks its a "fuse" and suddeny everyone wants to copy that even tho it was never supposed to work like that.

i doubt that anyone will be driving a 2005 model S in 2060.
 
If no flir camera.available, on could us a temperature probe. But tedious.
 
just saw a video- 10-15 powerwall turned into a brick- BMS never shuts off :roll: drained pack to ZERO v
https://www.youtube.com/watch?v=M1_qY5ta54g&ab_channel=HBPowerwall
.
Hill
that is what gave me the idea for 4 smaller packs.
for me i'd make 1/4 pack- save 800# and i'd have 75 mile range, plenty for me. maybe do 90 mi due to less weight.
 
Matt Gruber said:
just saw a video- 10-15 powerwall turned into a brick- BMS never shuts off :roll: drained pack to ZERO v
https://www.youtube.com/watch?v=M1_qY5ta54g&ab_channel=HBPowerwall
.
Hill
that is what gave me the idea for 4 smaller packs.
for me i'd make 1/4 pack- save 800# and i'd have 75 mile range, plenty for me. maybe do 90 mi due to less weight.
Click to expand...
its highly uncommon to see a bms drain a pack down to 0. considering tesla uses active balacing it seems highly unlikely to happen from the bms as tesla bms only moves power, it does not burn it off. it more probable the inverter or the 48>500V DC/DC board failed wich drained the modules.

still. separating into 4 sets is dumb. that means you have 4 things to fail instead of 1. the only reason the pack in the video died is because it has been stored for years.
 
the S pack is not 1 thing. it has 7,104 cells. there are 12 - 15 modules. the 1 pack is easy for factory assembly but as you put it dumb for service and eliminates low cost repairs.
Dewalt knows how to make packs that don't self discharge- mine went 2 - 5 years no problem. I'm no expert, but i know a good design when i see one. Kudos Dewalt :bigthumb:
I could picture the Powerwall with something like a 2.9v cut off breaker. once v goes too low, the breaker trips, stopping all drains. Push to reset :thumb:
I'm amazed you look at my idle conversation as if i was about to go into mass production :lol: calling me dumb for talking to you :lol:
 
what a dumb comparison. a dewalt battery on a shelf does nothing. its just the cells and bms. a tesla powerwall has coolant pumps, a 48>500>48V DC-DC converter and a 3kW inverter powerd on when it leaves the factory.

you let your modern 60V dewalt battery on a tool for a few weeks and it will be as dead as a politicans soul. ask me how i know that....
 
Matt Gruber said:
Dewalt knows how to make packs that don't self discharge- mine went 2 - 5 years no problem. I'm no expert, but i know a good design when i see one. Kudos Dewalt :bigthumb:
Click to expand...
Please explain "good design" that negates self discharge with high energy dense cells used in power tools. Are you basically implying that your Dewalt cut-off voltage is higher than the norm ... more like 3.3V (if the cells were 18650) ?

Anyway, you'd have to believe that as intelligent as Elon Musk is that he'd design the Tesla bricks so as to prevent just one cell from shutting down one of Tesla's bricks. My take on that video is that the guy is blowing it out of proportion for his own business interests ... REALLY ... just one cell will shut down an entire brick ? Here's one of the youtube's comments ...

azspotfree 2 days ago
"That's interesting that one cell out of 7000 can take down the entire battery pack."

Will one cell shut down an entire Tesla battery ?
 
eMark said:
Will one cell shut down an entire Tesla battery ?
Click to expand...

No. Unless it had extreme self discharge. Very unlikely.
 
You must log in or register to reply here.

Similar threads

E
90's Model Suzuki GSX1100 Shaft Drive
Replies
4
Views
393
E-GSX
E
B
Cell Logger question
Replies
1
Views
218
john61ct
J
R
    • Like
Really good article comparing Bafang vs. Tongsheng vs. CYC
Replies
12
Views
10,404
999zip999
999zip999
R
    • Like
A critique of mid-drive riding recommendations (and hub drive criticisms)
Replies
15
Views
5,087
Bullfrog
B
kmxtornado
How to charge (3) 12v SLA batteries in series
Replies
20
Views
5,928
john61ct
J
Back
Top