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Bricked Roadster - How to manually charge it to try to preserve cells?

lmore

Member
Nov 6, 2011
126
14
Trondheim, Norway
I am looking for a tecnichal description on how to manually charge a bricked Roadster without removing the battery from the car. Tesla service is not an alternative, I know that Gruber offers such a service but they are not near and I would like to know how it is done.

I tried to open the small lid on top of the PEM to acccess the cables coming from the battery, but the battery poles did not show any voltage.

I opened the battery near the top of the PEM and found 11 holes (I assume one for each sheet) with one 8-pin connector and one 12-pin connector with only 4 connected. I assume these are used for balancing/bleeding (bleed test) and getting data from the pack. Any documentation is highly appreciated.

I was hoping I could find somewhere to connect my voltage source and apply a very low current, this could sit for several days to charge the pack. Hopefully charge the whole pack in one operation, but each sheet/brick could also be charged separately.
 

ggr

Expert in Dunning-Kruger Effect!
Mar 24, 2011
6,976
27,511
San Diego, CA
I can't directly help you, but I will say two things that might help:
1. BE VERY CAREFUL NOT TO OVERCHARGE. If you are bypassing the PEM the responsibility is all yours... You don't want a Gruber-esque fire situation.
2. @TonyWilliams might be able to help but I don't think he regularly reads/posts.
 
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lmore

Member
Nov 6, 2011
126
14
Trondheim, Norway
Thanks, yes overcharge is dangerous. I posted some pictures in this post.

I hope someone on the forum can explain if there is a way to monitor the voltage of each brick using the connectors that are available (see picture)?
 

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nick

Member
May 22, 2012
155
134
I am looking into this myself.

The big wires to the PEM are isolated by relays inside the battery - you won't see any voltage until the battery decides to turn on the relays.

Playing with alternative ideas today... will post if I figure anything out.
 
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ML Auto

Member
Mar 8, 2014
716
717
SW Florida
You can charge the bricks individually, but only after you remove the BMB boards. They slide out the top after you disconnect the connectors pictured. You have to make a dummy BMB board with a connector on the bottom to extend the terminals from the sheet. Each brick and the temp sensors are connected there. Small wires to the bricks and riveted connections (unless updated) limit charging current (I wouldn't use more than 1 amp). Charging all 99 bricks takes forever. Using 11 chargers (one per sheet) still takes weeks.

Charging the entire pack at once requires you to somehow activate both internal solenoids that are controlled by the CAN network.

The biggest problem with charging a bricked pack is that if you have any bad cells, they will absorb the charge current and get hot. Then you have a fire just like what happened at Gruber. Every one of the three bricked packs I have seen had bad cells that got hot when charged. The only way to do it safely is to remove the sheets from the ESS and closely monitor the temps of each cell while charging.
 

nick

Member
May 22, 2012
155
134
I pulled one of the Battery Monitoring Boards...

Bottom end has direct access to each 69P brick of cells which is what is needed to monitor for safe charging.

Top end has opto-isolated communication. Microchip microcontroller on the boards.

Working on the low-end pinout
 

nick

Member
May 22, 2012
155
134
After soldering some wires to the BMB I now have access to the cells.

Pretty sure this battery is toast but running some tests anyway.
 

lmore

Member
Nov 6, 2011
126
14
Trondheim, Norway
Very helpful.What is the purpose of the 8-pin and 12-pin connectors on the BMB boards?

Could any of you that has made a BMB-card please post a picture and/or provide some description?

"Every one of the three bricked packs I have seen had bad cells that got hot when charged."
I wonder why the fuses that are on each cell don't disconnect these bad cells, is it because the bricking of the cells cause a chemistry change that the fuse-system is not able to handle?
 

ion_1

Member
Aug 11, 2016
205
184
NJ
is it because the bricking of the cells cause a chemistry change

exactly.. beyond a certain point (low voltage) there is a very significant and irreversible change in the chemistry of the cells themselves.
At the minumum the impedance of the cell will rise, true lithium capacity will be loss, cells will be unbalanced, in the worst case it could lead to an internal soft short and be very dangerous. If you do revive a bricked battery, keep it to yourself, do not sell the roadster with the battery without full disclosure. Or better yet, just don't sell it as it is simply very, very wrong. People try to do things with no clue what is going on within the cell chemistry, a really dangerous situation...this isn't a semiconductor device, it is much more complicated and dynamic situation.
 
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ML Auto

Member
Mar 8, 2014
716
717
SW Florida
Very helpful.What is the purpose of the 8-pin and 12-pin connectors on the BMB boards?

Could any of you that has made a BMB-card please post a picture and/or provide some description?

"Every one of the three bricked packs I have seen had bad cells that got hot when charged."
I wonder why the fuses that are on each cell don't disconnect these bad cells, is it because the bricking of the cells cause a chemistry change that the fuse-system is not able to handle?

The fuse attached to the cell will blow at 15 amps, but the cell will get hot and explode at less than one amp if you let it charge long enough.
I remember when the roadster was first being discussed in the media, people asked what happens if just one of the 6831 cells goes bad. Tesla's response was always that the cell would disconnect and the pack would keep operating. Just another load of B.S. from them.
 
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nick

Member
May 22, 2012
155
134
Test... I put 20mA through a sheet (in car) while monitoring the cell voltages via the BMB interface...

3 bricks are charging.
1 brick is a maybe.
5 bricks are shorted.

Shows how important it is monitor the individual cell voltages... short = full current through a single cell, and short = risk of over voltaging the other bricks in the chain.

Figure all the cells in this car are bad due to undervoltage.

(this is a damaged Roadster that has been sitting for a long time... not my daily driver which is going strong)
 

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