A look at the new Tesla cells

11913 Views 124 Replies 14 Participants Last post by Kevin Sharpe, Dec 1, 2017

PhantomPholly

Discussion Starter · May 28, 2017

2170 cells replaces 18650 standard at the Gigafactory.

Doubtful they will be available to DIY community, though. The big boys will probably contract full production.

Save

1 - 8 of 125 Posts

major

· #22 · Jul 30, 2017

Solarsail said:
... Also the lack of a 2nd gear in the Tesla causes the motor to operate in an inefficient region, draining more current.
...

Hi Sol,

You think you could show us a quantitative analysis or reference supporting your statement?

Thanks in advance,

major

Save

major

· #24 · Jul 30, 2017

riba2233 said:
Internal resistance is closer to 40-42 mohm, but yeah, still a lot heat at max power levels. That's why it can only be used as burst power, they efficiency drops to around 65%.

Hi riba,

A battery's maximum power output is at half its open circuit voltage so discharge efficiency is 50%. For a resistive load that would occur when load resistance equals the internal resistance of the battery. At maximum power the power converted to heat in the battery is equal to power delivered to the load.

major

Save

major

· #27 · Jul 31, 2017

Solarsail said:
This must be a trick question? The torque curve is pretty flat until it reaches a threshold speed whereby it declines by speed. Namely the motor efficiency drops rather steeply with higher speeds. The decline in torque is faster than the increase in RPM and thus power drops and efficiency decreases and motor thermal energy increases.

So in order to have a faster car, the RPM must be dropped below the threshold, which means the gear should be increased. Thus we need at least two gears.

If you provide me the spec sheet for Tesla's motor, I will try to work it out.

Hi Sol,

Mr. Karter2 has been kind enough to supply the data, so please provide the analysis to substantiate your statement concerning inefficient operation and draining current due to direct drive. I just don't see it.

major

Save

major

· #35 · Jul 31, 2017

If we're talking motor efficiency then why not look at efficiency plots. I couldn't find one for the Tesla. Odd, I thought I had one stashed in my files. But it would be similar to this except scaled and likely optimized.

You can see like about a 1% efficiency point difference between maximum output at 8000 and 4000 RPM. This is what I am basing my skepticism on. The above chart is for a PM motor I think. The second attachment is for and induction motor. Typically such plots will include inverter losses along with the motor. Cooling and auxiliary system power is unknown.

When you design with sufficient motor, the shifting gearbox becomes a liability. We have numerous threads discussing this topic.

Regards,

major

See less See more

Save

major

· #38 · Jul 31, 2017

His dyno # was 588hp, not kW. And wheel power is measured the same regardless of the power plant; engine (ICE) or electric motor or steam engine. hp or kW are just units. Power is the same .

major

Save

major

· #44 · Jul 31, 2017 (Edited)

Solarsail said:
So power is not the same if marketing says so.

I don't care much about marketing. Never have believed a car salesman.

Save

major

· #57 · Jul 31, 2017 (Edited)

Solarsail said:
Does the inefficiency also reduce the torque, or just the output power?

What is causing this sudden drop in efficiency?

It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.

Hi Sol,

Doesn't seem the place to answer those two questions and you really need a study in motor design and a look at the particular one in question. The only "sudden" drops in efficiency which I see are near zero torque or zero speed, areas where the motor spends little duration and/or are of such low power that poor efficiency accounts for little loss. Obviously if you push any motor beyond its intended application you can encounter consequences.

You seem to imply that multiple ratios can buy performance at the top end, high speed & high power. I fail to follow that logic. When you have sufficient motor properly geared to handle the top end, you'll have plenty for the entire operational region in most applications. Even the drag race is better handled with one ratio.

I realize there are those who disagree. One in particular is John Metric. He occasionally visits this board. You might look at his efforts in the electric 1/4 mile. Lonestar Racing IIRC. NEDRA.com

Regards,

major

Edit:

Solarsail said:
It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.

I reread the above statement and can't make any sense out of it. But I think it is academic anyway because nobody would operate a motor at such a condition.

See less See more

Save

major

· #58 · Jul 31, 2017 (Edited)

dcb said:
yep, flat top means you are at the limit of the controller.
...

Well sure, but that limit is set to prevent exceeding or closely approaching breakdown torque in the case of the induction motor. Beyond BDT, more motor current doesn't produce more torque, less in fact.

Edit: attachment from: http://what-when-how.com/induction-...-control-constant-voltshertz-induction-motor/

See less See more

Save

1 - 8 of 125 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

A look at the new Tesla cells

PhantomPholly

major

major

major

major

Attachments

major

major

major

major

Attachments

Top Contributors this Month