Tesla module charging to full/degradation

Batteries, Chargers, and Battery Management Systems.
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jimbo69ny   1 W

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Tesla module charging to full/degradation

Post by jimbo69ny » Apr 25 2018 9:44pm

I have been thinking about this for a while now and I haven't read anything about it. This might be a stupid question but I need to know.

It is no secret that 18650 cells/Tesla modules degrade with time. I assume that something inside the cars software knows how much degradation is there and how high of voltage to charge the batteries to. But is that true?

For all of those people using Tesla complete packs or individual modules, what is stopping them from using an external charger and charging degraded cells to the full 4.2 volts per cell?

Id really love an answer on this. Thanks!!!

Punx0r   10 GW

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Re: Tesla module charging to full/degradation

Post by Punx0r » Apr 26 2018 2:45am

AFAIK the cells are charged to the same voltage (I believe it is a little lower than 4.2V) whether the pack is new or old. The pack will just take on less charge and give less on discharge as it ages (and make more heat doing so).

dustNbone   10 kW

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Re: Tesla module charging to full/degradation

Post by dustNbone » Apr 26 2018 12:40pm

Yeah pretty much what punxor said. As cells' capacity degrades, their full charge voltage doesn't change, they just reach that voltage quicker during charge (at the same charge current).

jimbo69ny   1 W

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Re: Tesla module charging to full/degradation

Post by jimbo69ny » Apr 26 2018 12:49pm

oh ok. I was wrong. Thank you!

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flippy   10 kW

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Re: Tesla module charging to full/degradation

Post by flippy » Apr 26 2018 3:53pm

Fyi: tesla charges to 4.05V normally and 4.1v in range mode. And that mode resets to normal every time you charge. 4.05V seems the target for maximum cycle life.
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jimbo69ny   1 W

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Re: Tesla module charging to full/degradation

Post by jimbo69ny » Apr 26 2018 5:20pm

Oh good to know. I have a 2014 Rav4 EV. The car is made by Tesla and has a Tesla 41 kwh battery pack. I have noticed degradation after only 3.5 years. The peak voltage I have seen is 376 volts. The pack is a 92s40p. 4.1 volts x 92 cells = 377.2 volts so that makes sense. I was wondering why my pack didnt go up to 386 volts. I guess I wrongfully assumed that was a voltage representation of degradation.

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flippy   10 kW

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Re: Tesla module charging to full/degradation

Post by flippy » Apr 26 2018 10:32pm

That pack is half the size of a regular "proper" pack used in model s/x. So the cells have to do double the load for normal driving. Xombined with going to 4.1v means the pack wears a lot faster then a model s pack.
Lithium beats liquid dinosaurs.

jimbo69ny   1 W

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Re: Tesla module charging to full/degradation

Post by jimbo69ny » Apr 26 2018 10:41pm

With all due respect, I dont think that is it at all. I dont have the specs in front of me but the Rav4 Tesla motor isnt nearly as demanding as the Model S and X motors.

The big important difference is that the Rav TMS only operates when the car is on and in "ready" mode or when charging. All of the Teslas have TMS that are always running. That is the reason mine has degraded quicker than Tesla packs.

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flippy   10 kW

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Re: Tesla module charging to full/degradation

Post by flippy » Apr 27 2018 1:14am

Peak power in a tesla is huge. But average power to drive at speed is the same. You still need the same amount of power to get highway speeds. But the cell count is half. The average load on the rav packs are much greater during normal cruising. Tesla packs have to deal with more peak loads when hammering it but those are very short in comparison to normal driving loads and speeds.
Lithium beats liquid dinosaurs.

Punx0r   10 GW

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Re: Tesla module charging to full/degradation

Post by Punx0r » Apr 27 2018 4:16am

The interplay of cycle- and calendar-related degradation can be complex and I'd think you're both correct in your observed differences between the RAV4 and Model S/X systems.

Completely irrelevant to this thread, but I'd be kinda cool if you could unlock a "ultimate mode" on the Tesla by tweaking the software to permit a charge to 4.2 VPC :D

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flippy   10 kW

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Re: Tesla module charging to full/degradation

Post by flippy » Apr 27 2018 4:34am

There would be very little gain. Top speed is already limited to 250 and accelerwtion is on the limit simply due to lack of weight and traction. Ludicrous mode already needed a 3600usd digital fancy fuse upgrade for the battery. You wont get much more amps with the higher charge. Not ones you can put on the road at least. If you pull the right fuses you can already do 4x4 burnouts and doughnuts.

I am waiting for the roadster with dual battery pack and upgraded cooling (the biggest problem) so it can be used for track runs. The S and X overheating and power reduction is its biggest performace hit after ~5min of flooring it.
Lithium beats liquid dinosaurs.

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