AutoblogGreen

"Unfortunately as the temperature of a circuit climbs, the resistance tends to go up creating a cascading effect of rising resistance and temperature making the problem even worse"

Actually, I believe the resistance goes down, not up, therefore causing the same voltage across that resistance to draw more current and cause more heat and lessen the resistance and so on... Thermal runaway is a term that is used for this situation.

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A slight mistake in the ABG writeup: "the high voltage cables that connect the motor to the PEM have been switched from a copper/aluminum composite to pure aluminum"

The wires were actually changed from copper clad aluminum to pure copper.

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Typo in the article:
"switched from a copper/aluminum composite to pure aluminum"

That should read "to pure copper."

Stephan, in metals electrical resistance increases with temperature, for the most part.

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I too was wondering about the aluminum used for conduction, is it the better choice?

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"The terminal connectors have been redesigned and the high voltage cables that connect the motor to the PEM have been switched from a copper/aluminum composite to pure aluminum."

Uh... huh? Aluminum has *higher* electrical resistance than copper, and melts at a significantly *lower* temperature. How is this helping? It is also more troublesome to work with, thanks to its potential to fatigue and corrode when thermal cycling; a home wired with aluminum wire is 55 times more likely to have an electrical fire, and most jurisdictions no longer allow it. Where it is used, aluminium is generally used instead of copper to save money at the expense of it having inferior electrical properties.

Either way, good to hear that the range is getting boosted by this.

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Sam, that's ok, we're all human and make mistakes from time to time.

I was really impressed with this blog from Tesla, very good info presented well, with lots of details and photos. Nice work from JB Straubel.

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Follow-up to comment #3:

Just to be clear, there are common examples where electrical resistance goes down with increasing temperature. In some semiconductors, for example, higher temperature promotes more carriers from the valence band into the conduction band, thus increasing conductivity.

Also I should mention that superconductivity occurs not just from lower temperature, but involves a phase transition. Spin +1/2 (up)and spin -1/2 (down) electrons (fermions) group together to form Cooper pairs (bosons) thus allowing these many pairs of electrons to form a Bose-Einstein condensate. If, for example, you were to place a superconductor in a high magnetic field, the spin up and spin down electrons would be forced into different energy levels, thus breaking the Cooper pairing and causing the superconductor to go normal without adjusting temperature.

Anyhow, the relationship between temperature and electrical resistance is in general complicated and not always monotonic.

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Aluminum? That doesn't sound right. Copper is a better conductor than Aluminum. The electric power industry uses aluminum on the overhead power lines only because it's lighter. The drawback is aluminum conducts less therefor more energy is lost as heat.

Voltage loss in conductors due to resistance is lossed as heat. Thinner wires have more resistance per foot and that's why when you use a thin extension cord with a heater the cord starts to heat up (bad). Wires made with aluminum have a higher resistance per foot than copper therefor more heat will be generated for the same current.

Not unless aluminum is unique and has a negative temperature coefficient. while just about every other metal has a positive coefficient.

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I can't keep the Tesla drivetrain versions straight. Anyone have a program?

As best as I can remember it, first it was a two-speed transmission from vendor 1. Failed. Then a two-speed from vendor 2. Failed. Two-speed from vendors 3 and 4. Failed. Single-speed design, let's call that 5. Failed. Now we have yet another design.

Why is it, exactly, that you believe a single word that comes out of Tesla? The only thing that Tesla has proved that they can actually deliver is a press release.

Do us all a favor and stop working for the Tesla marketing department. Or change the name of this blog from autobloggreen to we-suck-up-to-tesla.

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I think the first design was poor. For one, using aluminum and copper for a conductor was not very smart. Also, the two speed box was also a very poor choice. Today, motor controls can control speeds from 0 rpm to full rpm by varying the frequency as opposed to the old method of varying the voltage. With the old method the motor would lose much torque but with the frequency method it doesn't, thus not needing a two speed transmission.
If they started that badly and kind of wonder how the finish product will be. Maybe what it's a case of bad reporting and not with the engineering.

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Jared -- nothing ever works on the first try. The trick is to not sell it until it does work. The major manufacturers go through iterative development too. They just don't tell the public about it like Tesla does.

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"For one, using aluminum and copper for a conductor was not very smart."
Don't see how you can make that statement. I don't think it's a bad first choice. It wasn't the limiting factor in powertrain 1.0 at any rate.
Depending on the application, copper clad aluminum wire can be a good compromise balancing conductivity versus weight and cost. If the AC frequency is high enough, most of the current flows at the surface anyhow (skin depth is frequency dependent).

"Today, motor controls can control speeds from 0 rpm to full rpm by varying the frequency as opposed to the old method of varying the voltage."
They were and are already using a variable frequency controller.

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It's interesting how people can criticize a company for not getting a transmission right the first time on a car that is developed from scratch based on nothing similar before it. How many times do every other automaker try something that doesn't work? How many times do they redesign different things over and over again? Keep in mind that cars are for the most part the same basic designs done over and over again and that everything in them has for the most part been improved from something before it. Even 5 different transmissions isn't bad when it comes to designing from the ground up. If they found ways to improve it, that's a pretty good reason to do it again.

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Jared: There were only two versions of the two speed transmission that proved to be inadequate, there are not many makers of two speed transmissions! The first "single speed" design worked and was reliable, but the Tesla Engineers figured they could do better - and they did, just before the Signature 100 series went into production.

Jim: The original plan to use copper coated aluminum cables was to reduce weight, but since the cables are short, switching to pure copper improves conductivity with little increase in weight or cost.

Tesla Motors has always used variable frequency controls - it is required for the variable speed induction motor used. Ver. 1.5 adds a current boosting voltage reducing circuit for low speed operations to improve low speed torque.

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@Peter
That's certainly true, but I guess all the openness means people just scrutinize them even more.

@Jared
Just to make the record clear it goes like this:
1. Two speed from vendor 1: failed
2. Two speed from vendor 2: failed
3. Planned to try a two speed from vendor 3 & 4.
4. Found better plan during development in Whitestar: go with a single speed while increasing power, so plans for two-speed dropped.
5. Production cars 2-40 gets/will get 1 speed (AKA the "temporary transmission") which works in every way on target (durability and etc), except 0-60 is 5.7 seconds instead of 4 seconds. (Production car #1, AKA Elon Musk's car, has a 2 speed)
6. Production cars starting with #41 is getting the single speed "drivetrain 1.5" described in this article, which does get 0-60 in 4 seconds.

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Peter: So I was pretty close. The reality is that they are on their 6th design. They still have not delivered a final version. They claim that this time, really, believe us know, this design will work.

And you guys believe them? Why, exactly?

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