"It's A Brick" - Tesla Motors' Devastating Design Problem • Hacker News Board

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#251

Post by tlb » Wed, Feb 22, 2012, 9:10 PM UTC

noonespecial wrote: post #26

bradleyland wrote: post #15

Earlier quoted context omitted.

The account of the Tesla discharging while plugged in to a 100-foot extension cord strikes me as suspect. It's anecdotal at best. Have a look at the Tesla Roadster "Charging" page: http://www.teslamotors.com/goelectric/charging Using 120V @ 15A, you get a charge rate of +5 miles (of range) per hour. Obviously not the optimal solution, but not a net negative either. Adding a 100 foot extension cord isn't going to dimi…

120v @ 15A is 1800 watts. As I said, I was able to measure the wattage being delivered at the end of my 100 foot 16 gauge "home depot" orange extension cord connected to a space heater and found less than 900 watts being delivered to a load that normally pulls 1750. The voltage had also dropped below 100 volts. Its possible that the Tesla simply won't charge at all if the current or voltage on the line becomes too lo…

The charge circuitry probably turns on at a high charge rate, senses the line voltage drop below 100v, and shuts down for a few seconds. Stuck in this loop, it might never deliver much charge.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#252

Post by aidenn0 » Wed, Feb 22, 2012, 9:28 PM UTC

nknight wrote: post #243

pbreit wrote: post #189

Earlier quoted context omitted.

No it's not. There are a variety of ways to engineer around this property of the batteries.

Then perhaps you'd care to share one? Or maybe just start cranking out magic batteries and become uber-wealthy? Since you haven't done that, I find it more likely you have no clue what you're talking about.

Here's one:

Rather than brick the battery, if it is parked and below a certain level, release a normally open relay that completely disconnects the BMS from the cells. Recovering from this state would require special charging and recalibrating of the BMS (possibly done at a shop) but it would be better than bricking the pack.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#253

Post by aidenn0 » Wed, Feb 22, 2012, 9:28 PM UTC

aidenn0 wrote: post #252

nknight wrote: post #243

Earlier quoted context omitted.

Then perhaps you'd care to share one? Or maybe just start cranking out magic batteries and become uber-wealthy? Since you haven't done that, I find it more likely you have no clue what you're talking about.

Here's one: Rather than brick the battery, if it is parked and below a certain level, release a normally open relay that completely disconnects the BMS from the cells. Recovering from this state would require special charging and recalibrating of the BMS (possibly done at a shop) but it would be better than bricking the pack.

Here's one:

Rather than brick the battery, if it is parked and below a certain level, release a normally open relay that completely disconnects the BMS from the cells. Recovering from this state would require special charging and recalibrating of the BMS (possibly done at a shop) but it would be better than bricking the pack.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#254

Post by Steko » Wed, Feb 22, 2012, 9:32 PM UTC

ChuckMcM wrote: post #104

Steko wrote: post #50

Earlier quoted context omitted.

"The article indicates that a 100 foot cord connected to a standard outlet does not provide enough power to prevent a Tesla car from discharging..." Pretty sure they say that to make sure people don't just use any old cord. A 24 AWG cord with 66% voltage drop as the low end would change your cost analysis radically.

You probably meant 4 AWG, a 100' of 24 AWG cord has about 2.5 ohms of resistance in it. Since power dissipation is exponential with current pulling even 2 amps through it would have the wire trying to dissipate 10 watts and that would represent 100mW/foot, easily enough to raise the temperature of the copper to the point where it would be too soft and break. [1] http://www.cirris.com/testing/resistance/wire.html

I was just following an online calculator, will plead ignorance on the physics but I think the basic point holds for some gauge wire.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#255

Post by Steko » Wed, Feb 22, 2012, 9:32 PM UTC

ChuckMcM wrote: post #104

Steko wrote: post #50

Earlier quoted context omitted.

"The article indicates that a 100 foot cord connected to a standard outlet does not provide enough power to prevent a Tesla car from discharging..." Pretty sure they say that to make sure people don't just use any old cord. A 24 AWG cord with 66% voltage drop as the low end would change your cost analysis radically.

You probably meant 4 AWG, a 100' of 24 AWG cord has about 2.5 ohms of resistance in it. Since power dissipation is exponential with current pulling even 2 amps through it would have the wire trying to dissipate 10 watts and that would represent 100mW/foot, easily enough to raise the temperature of the copper to the point where it would be too soft and break. [1] http://www.cirris.com/testing/resistance/wire.html

I was just following an online calculator, will plead ignorance on the physics but I think the basic point holds for some gauge wire.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#256

Post by Arelius » Wed, Feb 22, 2012, 9:38 PM UTC

jambalaya wrote: post #118

moe wrote: post #54

Earlier quoted context omitted.

Unlike a laptop, the Tesla was never designed to be run while plugged in. Which is actually an amusing thought. Perhaps they could ship them with really long extension chords, just enough for a city-commute...

How about a driving around a generator :p It would be cool though to have wireless power from beneath the road or something.

Isn't that basically what a hybrid does?

Also, it'd be neat if you could attach to the wires for buses that are in many major cities.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#257

Post by danbmil99 » Wed, Feb 22, 2012, 9:59 PM UTC

It's hard to imagine that, after all the hundreds of millions of dollars poured into this company, they would choose to charge the customer > $30K for a new battery in the few cases where this occurred. Is it really worth a few hundred thousand dollars to get the PR this article implies?

And, why isn't there a failsafe mechanism that simply stops draining the battery completely before this happens? Then at least you can tow it home and recharge it -- inconvenient, but not $30K inconvenient.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#258

Post by nknight » Wed, Feb 22, 2012, 10:03 PM UTC

aidenn0 wrote: post #252

nknight wrote: post #243

Earlier quoted context omitted.

Then perhaps you'd care to share one? Or maybe just start cranking out magic batteries and become uber-wealthy? Since you haven't done that, I find it more likely you have no clue what you're talking about.

Here's one: Rather than brick the battery, if it is parked and below a certain level, release a normally open relay that completely disconnects the BMS from the cells. Recovering from this state would require special charging and recalibrating of the BMS (possibly done at a shop) but it would be better than bricking the pack.

Disconnecting the BMS does not eliminate self-discharge, only the parasitic load. Draining your batteries to the point of being functionally dead, and then leaving them in that state for an extended period, will still "brick" them just as badly.

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#259

Post by fryguy » Wed, Feb 22, 2012, 10:04 PM UTC

jdietrich wrote: post #75

Tesla are a sideshow and we desperately need to stop talking about them, because they're harming efforts to improve energy efficiency. Nissan are now in full production of the Leaf, a practical electric car that's half the price of the Model S. Renault have the Fluence ZE on sale in Israel and ready to go internationally this year. Mitsubishi are selling the i-MiEV in quantity in Hong Kong and Japan. All of these big…

I think you're looking at this the wrong way. Let me make an analogy to a different market - hobby r/c aircraft. 10 Years ago, the only practical way to get certain sizes of aircraft was to use gas powered engines. Nowadays most people use brushless motors for everything, not because they think "hey these are better for the environment" or "these are more efficient", but because they are much more convenient and much more powerful. That is what Tesla is going after - more powerful. Their target market is people that have tiny sports cars and saying "electric motors have an insane amount of torque at low rpms", and then as this other thing, way over there - by the way, they don't use as much fuel too.

There is a whole another ideology that the "green" movement is, which is saying we need to get people to drive less, and when they drive, they should use the most fuel efficient car they should, because you know, the environment and stuff. Generating power at a central power plant (which can happen to be solar/wind/other renewable method rather than coal) and using that energy to power cars is much more efficient than having thousands of miniature power plants burning gasoline/diesel carrying people around town. However, most people don't care about the environment the way that people that want to push everyone to drive electric vehicles. I certainly don't.

A year or two ago, I wanted to get a new car, from my 1998 ford mustang. I had two desires, one was to get a more powerful car. The other was to spend less money on gas. My friend had bought a Prius recently and I liked the features of it, so I went to the Toyota dealership and took one for a test drive. When I finally got to do it (I would not recommend the Rosevilla Toyota to anyone, for the record), the power was completely unacceptable to me and there was no way I was buying that car. I ended up buying a Mini Cooper S, which was more powerful, and had better gas mileage. I think that is the goal of Tesla, to get cars which are more powerful than the gasoline cars, and cheaper to operate.

Do you really think that the customer needs to adapt to the car, rather than the car adapting to the person? Isn't that like the opposite of everything Hacker News stands for?

Re: "It's A Brick" - Tesla Motors' Devastating Design Problem

#260

Post by Tossrock » Wed, Feb 22, 2012, 10:32 PM UTC

Domenic_S wrote: post #248

Tossrock wrote: post #231

Earlier quoted context omitted.

Carpool lanes are two people in the Bay Area. Did you mean you had zero rather than one companions, or were you unaware of the law?

Huge swaths of 80 and 880 are three-person HOV lanes. Take a look at the interactive map here: http://rideshare.511.org/

Well, I'd quibble about 'huge swaths', but I was in the wrong, so my mistake. I guess this is what I get for going to Oakland once per year.