Extending Battery Range

[Lou B]

Is it Possible to over ride the battery Management System?
Can Battery Management be controlled external to the car?

The weakest brick will Charge the fastest and The weakest brick will discharge the fastest as it loses
Capacity with age.
Brick Vmax Voltage controls when charging will stop and Brick Vmin Voltage controls when driving will stop.

Can The bleed resistor Be controlled so that when a Vmax voltage is reached
On a weak brick, the roadster can disregard this or be overridden so
That charging of the remaining bricks can continue To a higher potential.

Brick temps could be monitored to monitor any dangerous thermal situations
Or cell shorts.

this could be Dynamic control as weak bricks might vary or may be consistent
In the ESS.

Wondering if this is possible,
Please let me know if you have thought about this also ?

 

[markwj]

The weakest brick will Charge the fastest and The weakest brick will discharge the fastest as it loses
Capacity with age. Brick Vmax Voltage controls when charging will stop and Brick Vmin Voltage controls when driving will stop.

In my experience, the weakest brick limits the distance you can drive, and the strongest brick limits the level you can charge to. The weakest brick may (as you say) charge the fastest (I have no input to that theory), but it will certainly only be able to charge to a voltage comparably lower than the other bricks.

The controls for this are all in the vehicle firmware, and cannot be customised.

The bleed resistors are controllable via a diagnostic interface, but that information has not been generally published.

 

[Mark77a]

I learned a lot about Tesla BMS system and how its used on Model 3 from this popular thread > How I Recovered Half of my Battery's Lost Capacity
Ok not a roadster, but it gives a good account of the logic behind cell balancing, range calculations etc.

What we really need in the roadster world is some more canBUS hacking, of the 4 Roadster canBUS systems .. tough job but possible. It has largely been done for Model S modules (I use a sweet little system called simpBMS which works directly with model S modules, based on EVTV and friends hacking code).. there are more and more tools such as savvyBMS for the Pi, which makes hacking a BIT more realistic for people who are not GODS of code gods such as: @markwj, Damian Maguire, Jason Hughes etc.

 

[Tiger]

See also Tesla veteran tuner (Gruber Motors) showcases how to revive an aging Model S battery pack

 

[markwj]

What we really need in the roadster world is some more canBUS hacking, of the 4 Roadster canBUS systems .. tough job but possible. It has largely been done for Model S modules (I use a sweet little system called simpBMS which works directly with model S modules, based on EVTV and friends hacking code).. there are more and more tools such as savvyBMS for the Pi, which makes hacking a BIT more realistic for people who are not GODS of code gods such as: @markwj, Damian Maguire, Jason Hughes etc.

CAN1 has been pretty thoroughly understood and documented. I would say 90% or so of the messages, and 100% of the very useful ones.

OVMS also connects to CAN2 and CAN3. I have started to look at CAN2, to try to get individual brick voltages and temperatures. It seems possible, but the process is ongoing. If anyone wants to help (particularly with remote access to their car via wifi to OVMS), that would be appreciated.

I think the issue is volume. There are hundreds of thousands of S3XY cars, but only a couple thousand original R. Just not a lot of people looking into it.

 

[Lou B]

Hi Mark,
When the car stops charging and you hit
Top Off, the car will re start charging for
A while. Is the car balancing as it
Tries to charge?
Could you control Top Off remotely ?
And Top Off and disregard The lowest Brick Vmax voltage until all the remaining bricks
Get closer To their theoretical max voltage.

 

[markwj]

Is the car balancing as it Tries to charge?

No. It will only balance after a charge completes normally with vehicle left plugged into EVSE.

Could you control Top Off remotely ?

Yes. For example, OVMS can start such a charge.

And Top Off and disregard The lowest Brick Vmax voltage until all the remaining bricks
Get closer To their theoretical max voltage.

I think you mean disregard the highest brick Vmax voltage until the lower bricks come up? Anyway, the answer is no. All bricks are charged at the same time and there is no way to individually control which bricks do / don't get a charge.

IMHO, such a system that could selectively charge individual bricks would be a much better balancing system, but that is not how Tesla does it. Tesla charges all bricks together, and has a balancing system that has the capability of selectively discharging on an individual brick basis.

 

[Mark77a]

CAN1 has been pretty thoroughly understood and documented. I would say 90% or so of the messages, and 100% of the very useful ones.

OVMS also connects to CAN2 and CAN3. I have started to look at CAN2, to try to get individual brick voltages and temperatures. It seems possible, but the process is ongoing. If anyone wants to help (particularly with remote access to their car via wifi to OVMS), that would be appreciated.

I think the issue is volume. There are hundreds of thousands of S3XY cars, but only a couple thousand original R. Just not a lot of people looking into it.

Interesting, Mark. canBUS always seemed scary without an electronics background, but fascinating nevertheless. With hacking tools (like savvyCAN and M2 Macchina and others the pro's use) .. maybe, the Roadster may be fully decoded after all ? That might open the possibility of using alternative batteries and yet still keeping all the other systems.

There is a lot of chat about canBUS amongst the EV conversion crowd and people putting Tesla Motors into Porsches etc. using info Damien Maguire has extracted, even before savvyCAN. The problem there is getting canbus driven instruments to play with the tesla outputs rather than original ECU's, without having the ECU signals to copy. At least we have both ends of the canBUS.