Tesla phantom draw - surprising

[OVERKILL]

That's a bit overly dramatic, but not unexpected when a bias exists. Tesla having a particular problem does not mean all EVs have a problem. The last thing a typical EV driver needs to worry about is the traction battery discharging by itself.

I don't care much about the Model 3 but I understand they have placed the 12V DC-DC convertor inside the battery casing so that it can operate either all the time or at least more frequently without having HV present outside that housing. Perhaps that results in a higher drain, who knows? It certainly doesn't affect owners of the many other EV brands.

In others that I'm aware of the DC-DC unit is separate and is only active when the main contactor inside the battery housing is closed. While parked the EV will use the 12V battery to handle telematics and other chores. The 12V battery is charged either when the traction battery is on-charge, or on a schedule, often either daily or every 4 hours. On older models of Leaf it's only when the car is powered-on for driving, so there are occasional issues with that design.

While the 12V battery is charged it's provided with a constant voltage of about 14.6 V, exactly as in an ICE car. Once the battery is full, very little current will flow and the main battery only has to support the operating overhead for the remainder of the period, perhaps about 200 W.

While driving, in the case of Hyundai at least, the 12V system is maintained at around 13.1 V to ensure that the 12V battery is not discharged for the duration.

In the same thread the Chevy Bolt is brought up and apparently it doesn't suffer the same eye-opening consumption that the Tesla does, so this does indeed to be a Tesla "quirk". I'm interested to see how the Mach-E compares.

 

[Kiwi_ME]

There's no question that manufacturers other than Tesla are far more conservative in their systems-level engineering, more or less designing them with similar architecture as ICE cars. Breaking these boundaries with vertical integration are what Tesla are famous for but that will raise additional risks along with victories.

The Bolt and Kona are very similar in specification and underlying design, but one difference is that the Bolt is more proactive at taking care of the battery pack when parked in low-temperature climates. This I see as one of the bigger challenges in EV design as 25°C is optimal. Performance deteriorates below that and below -20°C it becomes very challenging.

 

[JHZR2]

On the Volt, the owners manual states it is best to leave the battery at the minimum, depleted, state when leaving the car unused for long periods of time. I forgot how long they were talking about, months I guess. This seems contrary to what is being said here. The depleted state still has the buffer, which is like 1.5 kwh.

Maybe it said store at 30% charge or less, I don't have the car now. I know I have bought some power tools and they were somewhat old stock, the batteries have like one bar left, it's supposed to be best for them to store that way. So it couldn't have been drawing anything to make it over a two year period.

The volt/GM is correct. No battery manufacturer has a secret sauce to reduce oxidation of the electrodes and electrolyte when sitting at high voltages. Going too low can be dangerous too (copper current dissolution), but that would take a long time in a 30% SOC battery in good condition.

A full battery will keep trying to resistively balance, and the closer all cells get, the more wasteful it will become (because you’re bleeding more energy off of more cells to get the lowest ones charged more). I’d suspect this has something to do with it...

 

[Kiwi_ME]

I doubt an EV's BMS would bother with continued balancing once an acceptable deviation is reached. The main purpose of balancing is to fully exploit the normal cell voltage range without being limited by any individual cells that are lower or higher than the others. Once you're down to about 0.02 V there's little to be gained.

 

[JHZR2]

I doubt an EV's BMS would bother with continued balancing once an acceptable deviation is reached. The main purpose of balancing is to fully exploit the normal cell voltage range without being limited by any individual cells that are lower or higher than the others. Once you're down to about 0.02 V there's little to be gained.

Id agree with thst, but we have no evidence how well/fast/completely the cells balance... and if there’s high parasitics and differences in impedance and self discharge, it could keep on going...

 

[Kiwi_ME]

But in practice this is not an issue that the vast majority EV owners have. If may be if you're building something in your garage out of recycled parts but the BMS in a modern production EV will be smart enough to figure out if something is wrong and trigger an error. Nothing is going to "keep on going," that's a ridiculous assumption.