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Discussion in 'Model S: Battery & Charging' started by rtz, Jan 25, 2015.
How to get Tesla to get one of these batteries and test it out?
Batteries - Shorai Lithium Batteries
Why would this be better?
No. While it might work in the south, it would not work in colder climates.
Problem being Lithium needs to be at or above 33*F (1*C) or higher to charge. At or below freezing, the internals of the cells will Electroplate, causing permenent capacity loss. This would then require a 12v battery heater, and also a chiller. It can, believe it or not, get rather hot in there, especially when supercharging, and Lithium also likes 113*f or lower.
It can be done, but question is should it. Lead acid is actually fairly robust. As long as you get a DECENT quality battery to begin with. That, and follow proper charging and maintaining of the batteries.
And I have lots of experience with the Shorai's, and... my experience shows... very low quality product.... They were so bad, Batteries Plus pulled them from EVERY store. My local rep said they were coming in with a 95% failure rate within 30 days of purchase.
Ok. Dumb question. Why not just get rid of the 12 V completely and supply all electronics with the main pack and just have a transformer in the middle? Would also solve the contactor issues - no need for them. Is it safety related?
Well if Tesla insists on staying with lead for the 12v; this may be the best battery made? Rolls Battery - Home
This may be second? Concorde Battery - Aircraft Batteries
It would be interesting to know the reasons Tesla has for using the battery they do use: C&D Deep Cycle Battery
I was just thinking maybe for the cars that get the cold weather package; they could use whatever battery; and the rest of the cars could use something that lasts longer/more reliable.
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What if someone took out their 12v battery and wired one of these DC/DC converters in it's place? http://store.evtv.me/products.php?cat=19
Wont work. The power from the 12v battery initiates the contactor to enable the High Voltage pack. No 12v power, no contactor, meaning no power flow from the High Volt pack to the car. Or in other words, no DC to DC converter (thats already installed in the car).
When the 12v requires a top off while parked, the contactor, powered by the 12v battery, closes, allowing the 12v battery to charge. It is a safety feature.
Yep. Exactly what I was alluding to in the post above yours. So the only reason for the 12 V is safety? Just because there has to be some way to isolate a HV pack? Seems like there could be better solutions.
Besides isolating the traction battery there needs to be a way to power the power brakes and steering if the traction battery fails for some reason. Kind of hard to do if you don't use a battery.
Fair point. Although most failures have resulting from the contactors failing, which you wouldn't have if you could bypass the 12 V system. For the rare instance where a module failed and caused catastrophic loss of power then I can absolutely see that as being a valid reason.
It would be very dangerous and very expensive to get rid of the 12 Volt system and wire and power everything with 400 Volt DC from the main pack. Direct Current at 400 Volt is extremely dangerous and it would be all over the car. It would also require that everything in the car needs to be special made for 400 Volt. Every light bulb, switch, wipers, fan, audio system, windows, seats, ABS, steering, every electrical component would have to be special design instead of standard 12 Volt parts. It would be impractical.
The problem isn't that a 12 Volt system is bad. It works just fine for every car, thus the solution isn't to eliminate the 12 Volt system. The root of the problem is that Tesla isn't 'taking care' of the 12 Volt battery well. We don't know why so many of these batteries fail. It could be that they are not charged properly, it could be that they are too small for the load, it could be that they got bad units, it could be just an oversensitive monitoring system that shuts reports the 12 Volt battery going bad when it isn't. It could be a combination of several things. We don't know. Speculating and concluding solutions doesn't help. Tesla needs to find the source of the problem and fix it. Everything else is just digging in the dark and hoping something will stick.
The topic of vampire drain and its effect on the 12V battery is discussed in this thread in great detail. The root of the problem is the vampire drain. Fix that and the 12V problem could likely go away.
Near annual replacement of 12V battery is typical according to Tesla Service Tech - Page 10
Well, no. You could easily have a DC DC converter in the middle to step down the voltage. Not so dangerous then until a module fails and brings down the whole pack and you're left without power steering on the freeway. That's where the safety implications come into play.
Every car that has a "big battery" has a small 12V battery, and for the cars I'm familiar with all the owners complain about it failing. The problem is that you don't get a warning when it's about to fail. With an ICE car, you can hear the starter motor cranking more slowly so you know you had better do something soon. An EV or hybrid just needs to power some electronics and throw a couple of relays, so it can be very weak and still get the job done. I was able to start the Prius with two dead cells.
The only explanation I have for the Model S' short 12V life is that the battery gets cooked. AGM batteries don't like to be overcharged. The back of the napkin solution is two 12V batteries used on an alternating daily schedule. That would keep them from being cooked and still have the right amount of power available.
I agree with the Cooking/Overcharging of the batteries. While Monitoring the 12v batteries voltage, While the car was "off" I always saw 13.2-13.5v (SLIGHTLY high side, especially for a aged battery), and while car was in operation, saw 14+ volts. This is high for a AGM.
First responders / extraction equipment operators really appreciate the HV being isolated to the battery pack when it comes time to cut the car open with hydraulic extraction equipment. You don't want those big orange cables alive after an accident when we need to roll the dash off someone.
That's the primary reason that contactors exist in the battery pack - for safety.
The Model S does have a DC to DC converter to charge and power the 12 Volt system/battery. There is a good reason you need a 12 Volt battery and not rely on the DC-DC converter alone. Every production EV has a 12 Volt battery.
If the 12 volt battery is being overcharged(on purpose); then maybe Tesla would rather work with a 16 volt battery instead?
TurboStart a division of Axion Power
Is there anything in the car that couldn't handle the slightly higher voltage?
Yep, I'm aware of all that. Just think there could be more elegant solutions down the line that achieve the same purpose and degree of safety.
It looks to me like the issue is constant moderate cycling from vampire load. If we're proposing hardware changes to fix the problem, a float charger powered from the J1772 inlet (a la "Battery Tender") would prevent cycling while the car is plugged in.
This would imply that those who don't use power saving mode are probably going to go through more 12v batteries than those that do.