Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.

Old Roadster pack is recovering after going below CAC 76?

A very odd thing has happened.
Since the last 2 months the CAC has climbed from 76 to 88.78. Range has also increased from standard 122 to 154 now as well as maximum range 100% is 220 km.

Outside temperature is a normal 6 degrees Celsius winter in Holland. All temperature readings of the pack, motor and PEM through OVMS are normal. Pack is 20 degrees Celsius.

The obvious reason of course will be that the pack was out of balance. But this is not true. My pack has always been in balance. 2 months ago voltage difference individual cells was max 0.03V. Now difference is 0.04V. In the VDS menu I always find 99 times zero at menu option balancing.
So if pack is balanced, what could be the reason than?
Maybe algoritme is confused meaning that reporting 154 km is in reality less and CAC is also wrong calculated. So I checked energy content: today I charged on AC 121 km range using 25 kWh. Efficiency of AC loading at 24A is approximately 70%, so energy into battery is 17.5 kWh, meaning full capacity is around 32 kWh (max range 100% is 220 km).
I also did a DC charging with the JdeMo unit and charged 33% with 12.5 kWh. So 100% is 37kWh with a heat loss of 10% is 33 kWh.
Pack energy content is therefore around 32 kWh which points to a CAC of more then 90 (32/53 * 160).

It looks nice that range increases but I can not find a solid technical explanation, meaning I do not feel comfortable which can result in a big bang in the near future as end of life of the pack

I have seen sometimes in the past jumps up from CAC of max 2 points but never 12 points. Does anyone have had the same experience and can explain what is happening?
  • Helpful
Reactions: Mark77a
Pack is from april 2012 with 403000 km on the ODO with this pack


That's 250413 mi for us in Imperial system holdout countries.
Just a wild guess would be algorithm issue finally getting updated data and self-correcting. If the charge amount is correct, even approximate, then the CAC appears to be close to the current state of the battery...perhaps/probably it was wrong when it fell to the 76.

That mileage looks like you've REALLY enjoyed the car... :)
  • Helpful
  • Like
Reactions: eHorses and markwj
CAC stays on 90. However I have now encountered error 261 which means humidity in the pack. To solve this, pack has to be taken out. I do not trust Tesla being capable to solve this so for now it is in Germany with repair shop Marsorbiter.
You made a good choice. I remember that you were waiting for an R80 upgrade. What is the status of your replacement battery pack?
Quick question...

Is the CAC that is listed under the Vehicle Info on my OVMS accurate? Right now I'm at 112.67 on my 2008 with about 63k miles... I'm assuming original pack. Standard charge nets me 135 miles. I've never pulled the logs.

OVMS just shows the same as on the 1050 diagnostics screens. It should be accurate, but typically only significantly updated after a charge.
My CAC has dropped quite a bit, it was around 154 end of September but once the cold weather hit its now 136, standard charge gets me around 161 miles ideal range. I don’t think there’s a weak brick, balance is good at 97,000 miles. Hopefully it looks like it’s leveling off