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Tesla to Buy Energy Storage Firm Maxwell Tech at $4.75 a Share (bloomberg.com)
253 points by joshe 15 days ago | hide | past | web | favorite | 148 comments

I miss the full power regenerative braking when using my Tesla in the cold. Like, I really miss it and don’t like driving the car as much when it just coasts when I lift the accelerator.

I actively dislike pressing the brake pedal anymore, and feel cheated whenever I have to touch it except to activate Hold at a stop.

If supercaps could give me full regenerative braking at 0°F then I’d pay an extra $1-2k for the feature absolutely.

In warm climates I can absolutely see brake pads never being replaced. The only time I use the brake pads to slow down is in sub-freezing temps and once in an emergency.

For those who haven’t driven an EV with strong regen braking, you drive with a single pedal. “Neutral” is the accelerator slightly depressed. Lift your foot to slow down, fully lifting your foot is a strong braking down to about 10 mph. I should look up how fast you get 60-10 with a warm Tesla on regen alone. You drive with a single pedal, and you can dart in and out of traffic very nimbly because over-accelerating for a lane change and then regen’ing back to cruising speed is very efficient and fun and you don’t have to move your foot to another pedal. But regen degrades as the battery cools.

A frozen battery will barely regenerate at all, at 0°F it’s actually disconcerting when you lift your foot and the car just... coasts. The display does have a gauge showing how much regen is available, so it’s not a surprise but it literally feels weird.

To each their own. I like my TM3 and enjoy regenerative braking but there really is not reason to use a blended braking system which keeps with the current petrol car model of, use the brake pedal to slow down. It also may be safer since your foot will be over the brake when needed.

Chevrolet used this on the Volt for normal driving, you press the brake pedal and it decides how much hydraulic brakes you need over what regeneration can provide. Audi is going this route too. What makes it even better is they can totally mask the loss of regeneration in cold weather which can be disconcerting.

If anything I think Tesla should make it an option, the loss of regen braking even when the pack is only saturated to 40F is bad enough and just useless below freezing. They can do wonders with OTA so there is no reason to not offer all options, low to regeneration, high regeneration, maximum, and blended.

Again, blended doesn't mean it uses the disc brakes, only that it can when it has too and this is safer than relying on one pedal driving.

The Volt also has a hand operated brake paddle behind the steering wheel to activate regenerative braking without engaging hydraulic braking. It's a very nice feature.

Does that make the brake lights turn on? I would imagine it should because you're slowing down nonetheless.

Yes, in all EVs now they must activate the brake lights if they are decelerating at a certain level of G-force. I can't remember the exact level, but it's mandatory that they do this, because, just like with a manual transmission, you can decelerate with the engine alone, and it's not fair to the drivers behind you to surprise "brake" with no indicator or brake lights.

Downshifting a manual transmission to slow down does not activate the brake lights, so not sure this would need to.

Depends on your goal. If you want to rules-lawyer, then sure, no need to turn on the brake lights. If your goal is to avoid rear-end collisions, then having brake lights illuminate no matter why the car is decelerating is a good thing.

My understanding is that in Gen 1 Volt, no. In Gen 2, yes, and also when you let off the accelerator quickly in 'L' (higher regen) mode, if your deceleration is beyond a certain point the brake lights engage.

To clarify, in a Gen 1 Volt there is no hand brake paddle.

I believe that on at least some electric cars there's a particular deceleration threshold above which it'll turn on the brake lights.

Teslas definitely turn on the brake lights in some circumstances for regenerative braking.

It would be great as an option! I would still keep it as separate functions on separate pedals.

Because I don’t want to use the pads, I have to drive a bit differently when less regen is available.

I really like single pedal driving in the first place (see note above about lane changes and such) and I would never want to the pads actuating just from lifting the accelerator.

The only enhancement I would be happy with is full regen under all operating conditions :-)

The Volt (and probably Bolt) offer a number of options.

In 'D', releasing the accelerator coasts; in 'L', it decelerates, presumably subject to the same limitations as the Tesla.

There is also a paddle on the steering wheel which activates regenerative deceleration independent of the brakes. This does not completely stop the car, and has a longer braking distance.

So with the car in 'D' the controls become: press accelerator, go, release accelerator, coast, press paddle, slow down, press brake, stop.

Don’t Tesla’s have the same option? You can set regen to low I believe.


Your point about safety raises an idea: Why not do the inverse? Your driver assist tells the car how fast it can drive (GPS, signage), break pedal as well as a configurable level of assistance tells it how much to stop. Steering is still mine, and I won't give it up until full autonomous cars with zero driver responsibility are mass produceable.

There's a lot more to how fast you can drive than GPS and signage. There's also weather, road conditions, if there's parked cars hurting visibility along the road, whether there's pedestrians near the edge of the road (especially children who might dart out quickly), etc.

You have to slow down to turn, too. I can't imagine a situation in which you could let speed be outside the driver's control entirely.

Yes, therefore you either

a) break yourself on turns, pedestrians waiting, even red light etc.


b) choose to let driver assist take over some of these tasks from you

the whole idea is that instead of doing one-pedal driving on the accelerator it's safer to do one-pedal on the break.

Because I want to drive over the speed limit.

I'm not saying take away the gas pedal - it could still be there as a 'boost' pedal, intended for overtaking for example.

My car already does this with radar-informed cruise control, except it doesn't force a certain speed on the driver. You just set it like normal cruise control.

But doesn't cruise-control ususally disengage when you hit the breaks? This is only half the idea of single-pedal driving on the break pedal.

it is an option. you can turn if off, or at least way way down in the settings

> A frozen battery will barely regenerate at all, at 0°F it’s actually disconcerting when you lift your foot and the car just... coasts. The display does have a gauge showing how much regen is available, so it’s not a surprise but it literally feels weird.

Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle.

> Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle

I wouldn't call it nondeterministic, there's a notification window alerting you to the limited reg and there's a "gauge" below the "speedometer" that shows power input/output. That being said, it's bad UX/UI and they could do a better job representing it. The power gauge is a hair thin line with no labels or scale that you must intuit the purpose of by observation.

The Gen1 Leaf isn't really better, it's just different. Theere's again a power gauge that shows power input/output. You can clearly see the scale of the gauge which is better but again you must observe it to understand it's purpose. The Leaf also has rings around each tic in the gauge that denotes if that level is accessible. When the batter approaches 100% charge or it's terribly cold you lose rings on the input side of the gauge and when the battery is exceptionally low you lose them from the output side. Again it's nice if you know what it means but the only way to know is through observation of the gauge.

I'm guessing other EVs aren't any better. We're probably going through a phase much like early automobiles where each manufacturer comes up with novel UIs to complete the feedback loop between car and driver. Eventually they'll all standardize on something universally understood.

From a human factors perspective, whether you can know what it will do isn’t sufficient. What matters is whether you will know when it matters, even if you’re tired or distracted and panicking because you’re rapidly approaching a kid that stepped onto the road.

I would expect the likes of Volvo to make the traditional brakes pull in when regenerative braking lacks power. They tend to have a huge human factors department.

Regenerative Braking comes in two forms, passive and active. The notifications regarding limited Regenerative Braking Capacity are specific to passive braking (e.g. backing off the accelerator, lifting your foot off all pedals). Active braking will working using either Regenerative Braking or traditional brakes so what it's doing is irrelevant as the behavior is identical to the user.

So in your scenario where an individual might need to actively brake, they would be able to without issue. Where it might be an issue is when you're driving in bumper to bumper traffic and you're expecting regenerative braking and it's not there and you roll into the car in front of you. Then again, you don't make it very far down the road without noticing a difference in the accelerator pedal characteristics in limited regen mode.

The way I understand this is that, most of the time, users will be braking by removing pressure from pedal A, and only in exceptional cases they would have to do it by applying pressure to pedal B.

If so, I think you cannot expect humans (most of them even amateur drivers) to make that switch under stress, no matter how well you signal that the car requires you to use mode B.

The Gen2 Nissan Leaf has an "e-pedal" that works differently so I can't speak for that, but for the Gen1 Leaf and a 2018 Model 3 you absolutely use the brake pedal. The difference is that Regenerative Braking just changes your timing when switching from Accelerator to Brake, it doesn't eliminate it entirely.

Have you driven a standard transmission ICE? Downshifting into a lower gear is a very similar experience to regenerative braking. It's an aggressive deceleration that will slow the car from high speeds but it's no replacement for actual brakes.

For someone inexperienced with an EV, the lack of Regenerative Braking would feel like driving a normal car. For someone familiar with it, you're immediately aware of it's absence. In an ICE you coast by taking your foot of the accelerator, in an EV you coast by applying 10% pressure to the pedal (I made that % up). The reason you need 10% pressure to coast is that anything under that amount is where regenerative braking functions. So there's a weight to the pedal that isn't there when regenerative braking is gone.

It's hard to explain without driving an EV but it would be like using a computer mouse without the scroll wheel. You're keenly aware of it and if it's not there.

> Again it's nice if you know what it means but the only way to know is through observation of the gauge.

Or you could read the LEAF's fine owner's manual. Search for "Power Meter" and it's described perfectly clearly.

> Or you could read the LEAF's fine owner's manual. Search for "Power Meter" and it's described perfectly clearly.

That doesn't dismiss the fact that the Power Meter is poor UI/UX.

In most other cars the instrument cluster has clear labels and/or iconography that's identifiable. Even in the Leaf there are signs of thoughtful design, Nissan adapted the standard Fuel Gauge Icon with a Power Plug pigtail to indicate the Battery Level Gauge, though bizarrely it also includes an incorrect port indicator, and they put a battery capacity gauge right alongside the battery level gauge to clearly differentiate the two AND show that they're related.

The Power Meter is fusion of two gauges (i.e. power input/output and available input/output) and there should have been a clearer delineation instead. It's easy enough to infer that the Power Meter is analogous to a Tachometer after observing it for a few minutes but it takes longer to understand the regenerative braking aspect. The disappearing rings based on Temp/Capacity of the Battery are a much harder thing to understand.

Pretty much the entire Tesla experience is a bunch of weird idiosyncracies. Not necessarily all of it is bad, even in some academic UX sense or whatever.

But there's definitely a strong correspondence between idiosyncratic experiences, personalities that find such experiences appealing, and personalities that actually buy expensive luxury goods. Most armchair QBs miss that last part.

Someone like you, who would scoff at this weird behaviour, will never buy a Tesla. So why do they care what you think? Some people, the people who actually buy Teslas, talk enthusiastically about the weird behaviours on the Internet, i.e. the most priceless form of viral marketing.

I'm not saying you're right or wrong. That's beside the point. I'm saying you could be right, but you don't really have a solution for, "Idiosyncratic stuff is what payers talk about."

> But there's definitely a strong correspondence between idiosyncratic experiences, personalities that find such experiences appealing, and personalities that actually buy expensive luxury good. Most armchair QBs miss that last part.

Tesla has always sold itself as having a rapid plan to move from niche expensive luxury good to broad mass market everyman vehicle.

Some Tesla cheerleaders seem to miss that point.

The key to the mass market is to get the ownership cost down below what it is for gasoline cars. Make something which is cost competitive on total cost of ownership but still gives people social status for fighting climate change while going 0-60 in under five seconds and many people will forgive a certain number of idiosyncrasies.

Which may produce enough customers and revenue to make the next refresh less exotic.

Since when did 0-60 numbers matter so much? I bet most Tesla owners don't even know then acceleration numbers for their previous cars. Tesla puts it front and centre (being an advantage over some ICE), and now we hear it in every conversation. Tesla advertised it for their transport truck for crying out loud.

Hate to break it to people, but 0-60 times aren't really relevant day to day, and a sub 5 second time in a $50k+ luxury car is not exceptional (the ~3 second times of the bigger models are another story).

> Since when did 0-60 numbers matter so much?

I want to say since pony cars came out in the 1960s. Maybe earlier than that.

> Tesla advertised it for their transport truck for crying out loud.

It's actually more of a problem for large vehicles. If your car goes 0-60 in nine seconds instead of four, fine. If your fully loaded truck can't get there in thirty, that's more of a concern.

> Hate to break it to people, but 0-60 times aren't really relevant day to day

There is an onramp to a highway where people drive 75MPH around here. The onramp is a 270 degree spiral that ends in a stop sign two feet ahead of the highway. The highway there goes up a steep hill. People have died. It can be relevant.

You can say the government should fix the ramp, but that doesn't mean they have or will any time soon.

> and a sub 5 second time in a $50k+ luxury car is not exceptional

The whole idea is to get the car with the sub-5 second time below $30K.

>Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle.

When you're buying a high end vehicle "quirky" is the preferred adjective.

20yo $1500 German cars are "unreliable". Chinese EVs are "buggy". When you buy a Tesla, a new high end Mercedes or some other status symbol it's all just part of how it goes. Unreliability or odd behavior is not a negative at that price point. It's all part of the ownership experience. You don't get to complain about it. It's implied by the price point that you knew what you were getting into and can handle it.

In my experience, what you are talking about applies to exotics, not a run of the mill sedan. I absolutely want my Merc or Bmw (they are the same class really) to run without a hitch. They should be exciting to drive, but not quirky. I appreciate the engineering behind a Tesla or a Mercedes, but I have no passion for it, so quirkiness will get on my nerves.

A Ferrari might be quirky, a Pagani Huayra might have an endearing decel pop that's unique to it. I have passion and admiration for these exotic cars, so quirks become distinguishing features. A sedan has to get me comfortably from A to B.

Or maybe there is a room on the market for a new, non-quirky upper class vehicle.

I think warranty support and dealer network plays a role in that.

Warranty coverage is not that great and dealers are few and far between once you get into exotic stuff. The German stuff available at the Model S price points is not much better (in terms of warranty). The line between exotic and not gets kind of blurry because a lot of the lower end exotic stuff shares a platform with something else so most service can be done at that dealer network.

In any case, price determines whether technology is given the benefit of the doubt when it fails. Someone breaks a Harbor Freight tool and everyone blames the tool. Someone breaks a Mac or a Snap On and everyone blames whoever broke it. When Walmart has to recall food it's Walmart's fault for not choosing better suppliers. When Whole Foods has to trash a bunch of lettuce people blame the lettuce makers.

When cheap things break, act weird or somehow go wrong they get blamed. When expensive things break or act funny that's how they were meant to be and if you don't like it you were using it wrong or your expectations were wrong. People will do all sorts of mental gymnastics to avoid making expensive things look bad.

Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate.

This seems safer to me and also easier to control: you press the brake and it brakes. If it can regen, it regens, if not, it uses the disks. If you hit the brakes hard and the regen won't be enough to slow you down, it will use disk to the extent it needs to (or just switch to disk entirely).

Coasting is also good: no reason to regen if what you really want to do is coast, and no reason to have to keep your foot on the accelerator in that case either.

Prius do regen slightly in coasting mode, but it's not very noticeable.

> Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate.

Well, they actually do regen in Drive with the foot off the pedal; the brake pedal engages traditional brakes (with the regen also). Coasting requires slightly engaging the accelerator.

Prius also has an “engine braking” mode (which actually uses either regen or engine braking, depending on hybrid battery charge state) on the shift lever.

> Prius do regen slightly in coasting mode, but it's not very noticeable

The difference between pedal disengaged regen and pedal engages to coast is quite noticeable.

> Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate.

It also makes way more sense: your drivetrain can't be perfectly efficient so being unable to coast (and regen-braking every time you would be) is a double energy loss, first waste energy converting kinetic to electric, then you waste energy again converting back from electric to kinetic.

Regen-braking instead of coasting only makes sense in an "engine braking" analogue: have the car regen-brake to try and keep below some set speed on downhills.

The 2nd gen Prius (probably 1st gen too) has a distinct pre-travel during which it only regenerates, and only past a certain point does it apply mechanical brakes.

When the battery is full (after descending a long hill) the pre-travel does nothing at all. Of course there's no engine braking during coasting when the battery is full, so you'll know ahead of time.

On newer models, the pedal behaves in the manner you describe.

You can turn on full engine-braking in a Prius and it works fairly well (but also uses the ICE). It's enough that I use it entirely in most cases to get down to coasting speeds.

I drove a Toyota CR-V and was really amazed how it manages to burn fuel while decelerating. It is a disgrace of a hybrid vehicle.

Does it actually burn fuel? I've coasted an ICE car down a mountain in the winter and the temperature gauge didn't budge (and thus the heater never warmed up), implying no fuel was used. Surely a hybrid could do the same?

Naive question: Couldn't they "just" simulate the regenerative braking effect by automatically engaging the brakes when you lift the foot from the accelerator, so that the behavior would be identical over all temperature ranges?

Or by using some sort of capacitor/resistor. Elon has made claims about the longevity of brakes in Teslas due to rarely touching the brake pedal. And I agree, I don't want my brakes wearing out just to simulate the effect.

Why not use resistive braking to warm up the battery pack?

This is how locomotives implement braking; the drive motor operates in regen and the current goes to massive grid resistors. There are no brake pads.

There are brake pads in a train, each car has them. I'm assume the engine does too but I'm not an expert. You are correct that the resistive braking is preferred - the energy to stop a train would eat brake pads if that is all they used. (I suspect air brakes don't allow as much control - but again here I'm outside my expertise)

The Model S and X have a dedicated battery warmer, the Model 3 does not as a cost cutting measure (it uses the motor windings to heat the coolant loop, but it appears this solution, while clever, is inadequate).

Why not resistively heat that cooling loop? Or release it to the cabin? Turn on the de-frost?

I kinda wish my ICE car would crank everything up while engine-braking down a hill to reduce brake and fuel use.

It shouldn’t be that expensive...

that's what the model 3 does. it induces resistance in the motor at 0 rpm to generate heat which is then transferred to the coolant loop to heat the battery.

but in order to warm up the very large battery pack, on a cold morning you need to turn the car on (well) before you start driving to have it warm enough for full regen.

You can, of course, do this from the Tesla app. It’s not like an ICE car where (usually) you have to physically be in it to start it.

With my ice car in the summer I often only turn on the AC only while going downhill or exiting the freeway.

I just wish it was more automatic. Hard to say if I'm saving pennies or dollars, but a $1 chip to do it should pay for itself quickly.

An modern (Last 20 years) ICE engine shouldn't use any fuel while engine braking. The ECU should just cut the fuel to the engine and allow it to run under vacuum.

My 15 year old Golf does and engine braking is why I've still got the original brake pads after 180K miles.

Just about every modern car cuts fuel when you're engine braking.

I’m not so sure this is how locomotives brake. After living beside a train track for 4 years I can tell you the cars are not using regenerative breaking to slow down. They use air brakes that are audible due to the brake pads and air.


This specifically addresses the air brakes you're hearing:

>Dynamic braking alone is insufficient to stop a locomotive, as its braking effect rapidly diminishes below about 10 to 12 miles per hour (16 to 19 km/h). Therefore, it is always used in conjunction with the regular air brake. This combined system is called blended braking.

That's improved with AC locomotives. Regenerative braking now works down to zero speed, if desired.[1] Locomotive motors today are three-phase variable frequency synchronous motors, run as servomotors. Like other servomotors, they can be controlled all the way down to a stop. At some point the friction brakes are applied, but that's usually done only at slower speeds.

Large modern locomotives often have "wings" with ventilation slots and fans. That's where the heat from the braking resistors gets dumped. This is a big win when moving heavy freight down long mountain grades. Friction brakes tend to overheat, but fan-cooled resistor banks can dump heat all day.

It's amazing that semiconductors for that kind of power not only exist, but are not that big.

[1] http://www.republiclocomotive.com/ac-traction-vs-dc-traction...

Other commenters have similar thoughts but here it is said more directly: the car should not drive differently at all depending on temperature. There is no reason it has to be that way. The motor can regen fine at any temperature. The battery cannot, but dumping power resistively into air heat is one of the easiest things to do electrically, and they could definitely do it.

With one counterpoint being that maybe this is a feature, not a bug, and may save drivers from excessive non-productive braking.

I checked around, and a 2 kW dump resistor is about 3" diameter by 20" length. You'd need, say, 16 of those at a packing fraction about 0.5 for sufficent air flow, so you're looking at a cuboid which is 20" long and 4*3"/sqrt(0.5/0.9) = 16" to a side, or 2560 cu.in. Then you add the fans and the intake and outlet ducting etc. you can probably figure 3500 cu.in. total volume.

For comparison, the Model 3 "frunk" seems to be 28" x 15" x 9" = 3780 cu.in. So you'd have to sacrifice the entire frunk for your resistor pack.

I think there are still some reasonable solutions:

* smaller resistive heaters with higher airflow

* dump the heat into resistively heating the battery. Then use the battery again!

* Just use disk brakes to achieve the same feel. Which is also, basically, dumping heat.

Remember that the problem to solve is that a car shouldn't drive differently at different temperatures...

Now where could one get this said airflow in a vehicle moving through a medium that is commonly referred to as air? :)

Heating up the battery with this airflow for a certain amount of time should warm them up relatively quickly and evenly since done via convection too. Now I genuinely wonder if there is a reason why Tesla didn't go with that.

For something that generates a lot of heat when bringing the car (and air!) velocity towards zero, you really need to have forced air cooling available.

> dump the heat into resistively heating the battery. Then use the battery again!

Will make your car prone to fires.

How about just dumping that heat into the battery coolant loop.

Oh wait.

gasoline cars power output varies with temperature, tire grip varies a lot, braking performance varies too.

But that's not a good thing...

Me too. I live at the top of a steep hill, so if I charge fully I can't regen all the way down in the morning, and I have to press this large pedal that hydraulically clamps some friction pads around steel disks attached to the wheels. So I set it to charge a little less than full, and gain about 6 miles of range on the way down.

A resistive dump of 20-30 kW would improve the cold weather deceleration experience, but that's a big honking resistor that'd need forced air cooling.

Why not 2-4 kw to heat the cabin really fast when it’s cold? Pre-heating the cabin instead of the brakes would save cabin heating energy later.

The model S already has a 6 kW cabin heater, which is presumably fully on when starting out cold. Electric heat is great -- the cabin starts warming up immediately.

Braking normally goes up to 60 kW. Another 2-4 kW would barely make a difference.

I’m making up numbers, but I think braking is like insurance: most payouts/utilization is at the low end.

You need the 60kw available for hard braking, but what percentage of the area under the curve is below the 5kw mark?

60 kW isn't hard braking -- that's the normal level you get in a model S when you take your foot off the accelerator anywhere above 20 mph. So coming to an anticipated red light, you'd normally brake at the full 60 kW tapering down to zero at about 10 mph, then use the mechanical brake. That's makes for a comfortable stop and wastes the minimum power.

Hard braking, like slamming them on at 80 mph, can exceed 1000 kW.

2018 Nissan Leaf owner here driving with e-pedal, essentially a single pedal driving from movement to complete stop. I've driven from summer conditions down to -10dC (14dF) conditions.

For winter, the car is on squishier winter tires. This confuses the traction control unit enough to cut out regen on full pedal lift off and switch over to caliper brakes, still single pedal. The car still slows and comes to a complete stop, but deceleration is much stronger with regen. I've adapted to no longer fully lift off the pedal, expecting a more gentle deceleration, providing a more consistent stopping distance.

The brake pedal still responds normally and it gets used in surprise situations.

Even at -10dC (14dF), the regen operates similar compared to warmer temps with the Leaf. At -30dC (-22dF) the battery heater supposedly kicks in, but have not taken the car into those kinds of conditions. I would think it's a software update on the Tesla to kick on the battery warmers in colder climates for consistent regen. Or software update to engage the brakes when regen isn't available.

This advice is dangerous. You still need brakes for emergencies (and in modern day driving, there are tons of cases where you need to have the car come to a full stop, without the delay of regen braking)

Agree... intentionally getting in front of another driver with "over-acceleration" then slowing faster than normal torque converter coasting levels without activating your braking lights is asking for a rear-end collision.

Not to mention, it is delusional to consider this style of driving "efficient" because of regeneration. You're paying a premium for acceleration speed, and then being taxed by regneration efficiency...

Regenerative breaking does activate your brake lights though, at least in the Tesla. I would assume it is the same in all EVs, as it would be a massive safety issue and asking for rear-end collisions otherwise.

I may have overstated it. What I meant was simply when changing lanes you need to accelerate faster than cruising speed to make up for the distance of the lane shift if you want to stay evenly separated from the cars around you, versus drifting backward about a car length as you move between lanes.

In addition I like to have some forward movement while changing lanes on a highway, so that if there is someone (several car lengths) behind me in the adjacent lane they know they won’t have to slow down.

So you can add a bit of speed as you make the lane change and then bleed it off in regen to return back to that lane’s cruising speed. It should not be enough of a delta to involve any kind of brake light.

The energy loop is extremely efficient e.g. if you are going 60mph to bump up to 65mph and then back to 60mph, like 90% is reclaimed, from the energy chart display, you get a spike up and then down in consumption whichs appear to be symmetrical.

Actually, if you lane change in AutoPilot I believe it will do something similar. It does not change (semi-)autonomously lanes without applying some power.

I had Toyota Yaris hybrid and after 3 years I had to replace brake pads twice due to rust. Apparently with regenerative braking I had not used them much. This prevented them from heating that normally removed any water buildup. Granted that was in Bergen, Norway where it rained a lot, but I learned that even in dryer climates this was a problem.

After the first replacement I was asked to brake hard periodically to heat the pads. I started doing that, but it did not help much.

It seems like the cases where regenerative braking doesn't work coincide perfectly with the season where you want simple resistive loads for fast acting interior heating.

This is the same experience one has with an ICE engine and manual gear box at higher RPM. Much easier to drive aggressively in that mode for reasons you state.

Yes, it’s like the joy of a stick but without any gears or RPMs it means the feel of it is much smoother and very easy to attenuate.

I’ve never driven a high performance stick shift, only a cheap beater stick as my first car, but I found high RPM stop and go in 1st or 2nd gear was always somewhat hard work and jerky. The TM3 is absolutely not hard work or jerky, the single pedal driving is actually quite a joy IMO.

This is kind of odd. You mean that the battery can't take the power when cold?

The obvious fix is to use that power first for heating the battery. You'd still slow the car via power generation, giving the exact same braking feel.

Trains often do something similar, except that they dump the power as heat to the air. That would work too.

Tesla could totally fix your concerns with software only changes.

By changing the motor drivers to have a much higher current in all coils of the motor, the I^2 R losses are much higher, and the car will slow down while heating the motors up.

Then run the cooling pumps and the heat will go into heating the battery.

Coasting is better then regen'ing, pretty sure.

If you regen, you have to slow down, only to have to speed back up again, but at a worse efficiency loss than just coasting.

What do you think happens if the car in front of you is coasting, and you're trying to match its speed?


It's possible to get in an 'envelope' behind another car and get pulled along with it.

I wasn't talking about drafting. I was just saying that you can "coast" in a one-pedal car by pressing on the pedal by an appropriate amount... and most drivers will do that every time they drive, because they'll be behind other cars that are coasting.

I'm saying that harvesting energy while coasting is probably not efficient.

Having your car's braking behaviour change so markedly seems poor. Couldn't they just use the regenned power to run the battery heaters?

>For those who haven’t driven an EV with strong regen braking, you drive with a single pedal. “Neutral” is the accelerator slightly depressed. Lift your foot to slow down, fully lifting your foot is a strong braking down to about 10 mph.

So basically like an old pickup from back when 4.xx was a typical rear end ratio and transmissions didn't have overdrive so you were doing 3000+rpm at 60.

This is a smart move by Tesla, Maxwell's supercap technology is a really good way to moderate power needs and to extend range.

It also seems like the first step in the "Okay, we have the basic system that works, lets start knocking off the biggest problems with it." mode that internal combustion cars have been doing for the last 100 years.

I dunno, I could be using them wrong but I have not been impressed with their (or any) supercapacitors. At the 1000s of Farads, they seem to bleed charge like crazy, and it gets a lot worse when they need to deal with mechanical shocks and vibrations, even the "durablue" ones.

Their low voltage also makes them hard to use; you need to balance them, and their capacitances vary considerably. Most range from -20/+80% to -10/+20%, but I guess big customers have options to deal with that. Still, if your battery pack is 300+V, and your supercapacitors can only charge to 3V...that seems difficult.

I used to be really bullish on them for regenerative braking - I think some kinds of buses do use them for that - but having tried to use them, I can't see them being robust enough for consumer, and especially consumer automotive, requirements in the immediate future.

Also, it's on the order of 10x the cost for similar capacity to lithium chemistries, and that comes in a package that weighs on the order of 10x as much as a similar battery.

But hey, I'm just a layman. It sounds like you probably know more.

Was Maxwell a sinking ship?

I wonder what life is like for the new employees of elon.

I heard it will not be good.

Here's my first thought: Put both supercapacitors and batteries in an electric car. The supercapacitors can help greatly in a couple of ways. When doing a fast charge, the supercapacitor bank can absorb the energy super fast, much faster than a bank of batteries could. Then a microcontroller could control the transfer of that power more gradually over to the battery. (Unfortunately, super capacitors, when I last read something about it, could only hold their charge for 4 days or so, so they couldn't replace batteries themselves.) Perhaps this could be the key to the 5 minute recharge for cars?

Second, supercapacitors could also save some wear and tear on the batteries during rapid acceleration and regenerative charging.

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries do so this would require reducing the car's range by something like a factor of 5.

A capacitor much smaller than the batteries acting as a buffer for rapid acceleration and braking might make sense, though.

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries

I was under the misapprehension that they had a much larger energy density. However, my next thought is that not all charging is the same. Only the 1st 60% of a charge is in the constant current part of the charge curve. After that, the charge rate falls off. Charging the last 10% of a battery's capacity takes much longer. What if the supercapacitor bank had about 10% of the capacity of the battery? That would still be a large increase in the size and weight taken up by energy storage, though. It looks like just putting more batteries in the car is the economical thing to do.

In general capacitors have much higher power density but much lower energy densities than batteries and supercapacitors are somewhere in between.


Using a capacitor for the last 10% might make sense, or it might not. It's all about the specific numbers. It might be that a larger battery charged up to 90% might be better than a slightly smaller battery charged to 100% with the assistance of a capacitor. If you're adding a capacitor for power reasons anyways this might be a way to get more use out of it.

You could go other ways and downsize the battery a little bit, or tweak the definition of 100% and 0% (they play with those to keep the batteries from damaging themselves.)

I could see it used for the superChargers, so they could have more chargers feeding off a smaller power connection. (especially for the ones needed for the semi).

I doubt they will be used for either side of charging. Super/Ultra capacitors cost a lot more than batteries per watt hour.

In the context of a Supercharger the critical metric would probably be cost per charge/discharge cycle for a given capacity bank. While a car probable averages a fraction of a charge cycle per day, a busy supercharger might be on the order 10 cycles per day. Super capacitors degrade more slowly than batteries with cycles.

The use which might make sense is to use the capacitors to supplement the grid supplied power during the initial fast charge phase, then in the slower final charging phases or idle time recharge the capacitors from the grid for the next customer. This levels out the demands on the grid and can result in a lower electricity rate from the power company.

It all depends on the constants if it makes sense. Or maybe it doesn't make sense and Tesla needed something out of Maxwell's patent portfolio.

Why not in the charge control circuitry in the supercharger? Don’t those use some pretty big caps?

This is far more plausible, where space is abundant outside the vehicle to keep a cache of supercaps to charge from. Especially if the usage pattern tends to be very bursty. But if the superchargers are (or will be) continuously near 100% utilization it's pointless, they'll need the current at the mains.

The trouble spot with Superchargers is usually the end of the charge, not the beginning. The batteries can usually absorb energy rather quickly when at a low rate of charge. What is really painful is the last 10% where the charge rate drops line a stone.

What would be an interesting use of this idea would be to have 10% capacity onboard in capacitors. Once you get within 10% of the desired charge level in the batteries, you quickly charge the capacitors, which then trickles into the battery over time.

This might allow you to increase the overall charge rate for the car which would help reduce wait times at Superchargers.

Far better would be to add 10% battery capacity, which would have the same net effect for cheaper.

If you're not going to be using the high power of a supercapacitor, there's zero reason to pay a premium.

The trouble with that is to a certain extent we're just kicking the can down the road. Modern Tesla vehicles have more range than older ones, yet people still charge modern ones to 100% for various reasons.

The idea here is to leverage their incredibly fast rate of charge and short term nature to reduce time spent Supercharging. Very roughly speaking, you can charge from 0-90% in an hour, but to go from 90-100% can take almost another hour.

If you could get the car to 90% and then very rapidly charge the capacitors with the remaining 10% that trickles in, you get the car off the charger faster. In theory you could almost double the number of cars you could serve at that station.

That's just lying to yourself about what "100%" is, by excluding the caps. It's again easier to add more battery and pretend it doesn't exist for reaching 'full charge'. That will also give you better battery longevity.

Tesla is rolling out a firmware update that will prevent you from charging above 90% at high contention Superchargers. Simple solution.

Tesla just filed a patent for a new battery chemistry out of their Nova Scotia R&D facility that supports faster charging and superior longevity. I expect batteries to become supercapacitors faster than supercapacitors become batteries.

If supercapacitors have any role, it’s at EV charge stations to reduce demand charges from utilities. VW just agreed to buy a whole lot of Tesla batteries for this purpose at their Electrify America charge stations. Space is not an issue, as you can bury your storage under the charger stalls.

> If supercapacitors have any role, it’s at EV charge stations to reduce demand charges from utilities

Especially here I'd expect batteries to win out as transfer capacity is roughly proportional to storage capacity with batteries.

For this to work you'd need as much capacity in supercaps as in batteries. In that case you'd want to use that capacity, except it self-drains. The UX would be strange and difficult to manage.

EDIT: The above comment was meant about supercharging, not regenerative braking.

You wouldn't need an equivalent capacity in supercaps as batteries, only as much as the vehicle can use or create in a short amount of time.

The UX would be invisible: If demand is greater than the supply available from the battery pack, drain some energy from the supercapacitors. If it's less, gradually shift some energy into them. If the driver is not in the vehicle, drain it all out, when they come back, recharge the supercaps.

The problem is that these capacitors and transfers add cost money, space, weight, energy, and complexity.

Looking at some numbers, batteries are ~20x more energy dense in both volume and weight. Batteries have 1/10th the power density, but efficiency drops significantly with discharge rate and they have fewer lifetime charge cycles and poorer temperature response. Batteries also have much, much lower self-discharge, and cost a lot less per kilowatt-hour.

Right now, lithium-ion batteries are simply good enough and supercapacitors are not that much better, so it's the cost-benefit analysis says it's better to take the costs you would have spent on supercaps and just put in a few more batteries.

That balance could shift, though, with improvements in supercap technology, or - paradoxically - with improvements in battery chemistry. If a battery with much better energy density and/or lower cost was found, with a reduced discharge rate that was sufficient to cruise but insufficient to accelerate or do regenerative braking, you could add supercaps to make a vehicle based on that battery feasible. It's similar to the electric grid - the base load would be handled by the slow batteries, similar to coal or nuclear power plants, while peaking loads would be handled by the supercapacitors, like a gas turbine.

I agree this could work with regen, but not for "supercharging".

No it wouldn't!

You could preferentially store the regenerative braking energy into the ultracapacitors (and discharge from them from a stop, instead of the main battery). You're not talking a huge number of them (order of magnitude of ~100) for a cycle brake cycle at Model 3 mass, highway speed, and normal braking.

I think car brands are already designing hybrid power circuits. The benefits of low resistance caps as small bursts / buffer, and avoiding wearing the usual li-ion banks is too good to pass on.

How much space would sufficient supercapacitors require and would they be heavy? Would it add significantly to the cost of a car?

It seems they are quite light, at least according to this guy who built a home-made hybrid car battery using super capacitors: https://www.youtube.com/watch?v=VJhJ5TfQ6DU

Or could they even be structural and offset some other components’ weight.

This is an interesting idea. Is this really possible though? Is it just a cost challenge?

I admittedly haven't read up a ton on fast charging options but I also don't think I've seen super-capacitors mentioned as an intermediary source in any discussions. Given the article mentions Maxwell wanting to get into the automotive industry, a fast charging use is probably still a long ways out at this point.

It's interesting. Maxwell has been around for decades. Publicly they were known for ultracapacitors (non-expert opinion is that this would be a sweet spot for regenerative breaking capture in Teslas). But seems like nothing worth acquiring the company over - there are other vendors and they could just set up a multi-year supplier contract.

There are some articles/rumors out there about dry electrode battery tech Maxwell was working on.

> There are some articles/rumors out there about dry electrode battery tech Maxwell was working on.

If this acquisition included any breakthrough-level battery technology, it'd be for far more than $218M as it probably would have involved a bidding war considering the stated electrification plans from all major auto manufacturers.

Why do you think Tesla acquired Maxwell, then? Why did Maxwell sell existing lines of business several months ago to focus on the dry battery tech and ultracapacitors?

I don't know enough about dry battery electrode tech to know how much progress there is, how much an of an improvement they are above existing commercial technology, or who else has IP in the space.

Your response seems a bit high on the cynicism/information ratio, but I would be genuinely grateful for more information about this.

I persume it's to bolster their battery tech and R&D dept. It just doesn't seem like anything obviously game-changing from where I'm sitting.

In my opinion this is also a talent acquisition. Maxwell's decades of experience would be helpful to Tesla's battery ambitions.

This seems to make more sense for optimizing 0-60mph acceleration metrics than just about anything else. Using SuperCaps, a base Model 3 could have the 0-60 times of a P100D for much less than the cost of the required batteries.

4WD off road vehicles could also have much higher torque for brief periods of time.

While true, I think cold temperatures might be the more applicable scenario. When the batteries are cold, the amount of power you can extract is limited, as is the amount of power you can inject by regen braking. This is one factor that leads to crappy range in cold climates.

Capacitors can smooth out the power curve - need 1000 amps of current for 4 seconds? No problem, that comes from the capacitors and the battery only sees a draw of 200 amps. Need to regen 600 amps for 15 seconds? No problem, dump that into the capacitors and recharge the batteries at 50 amps for the next minute.

Knowing Tesla, they will use capacitors to offer both; a super-plaid mode that can supply 1800 amps momentarily, as well as better cold weather performance.

Can you market the cold temp regen? Maybe? Can you market 0-60 numbers or 4wd capability? Absolutely. Which one is sexier? I think Elon would say the performance numbers.

There is literally no reason why they have to pick between the 2. It's one system that can do both depending on the situation. Some countries/areas will care more about the cold temp regen and some other markets will care more about 4wd or the 0-60 performance. The great thing about EVs is that you can just redirect power to whatever you need at any given time.

Ok we know that ultra-capacitors carry about 10x less energy/kg than current li-ion batteries.

This means they have limited use in small consumer cars, other than maybe helping the brakes or conditioning power. What they lack in weight, they make up in charge/discharge times.

Being that a truck weighs multiple times more than a sedan, it's batteries are unlikely to absorb regen braking. So a small capacitor bank makes sense. A large capacitor bank would be useful if the truck was using overhead charging cables for a small section of the road. Or if a public transport bus was quickly charging between every few stations, it could then function all day.

The large weight of the capacitor bank isn't a problem if it's used in a charging station, where 3-phase 400+ volt power may not be available. This means that any level 1,2 charger can be upgraded to a level 3 without needing to dig any trenches, further improving the user experience of the car owner and reducing range anxiety to a minimum.

The cars already have heat pumps in the form of air conditioners. They could be designed with minor modifications to also be used for heating, improving the energy efficiency of cold vehicles a lot.

Why do journalists always change units? Usually they report a sale by valuation but with price per share I first have to look up the company and find the number of outstanding shares.

It's journalists' job to highlight what's noteworthy, and in an acquisition it's not always the valuation of a company. In this case, the price per share is headlined to highlight the premium (55%) Tesla is paying for Maxwell Tech's shares.

Can these capacitors be used in any way for faster charging of the car? Like have a capacitor bank pre-charged and then unload it into a car for much faster charging.

I hope this doesn't affect the supply of Maxwell supercaps in the overall market. It really is star trek level technology.

Why is this newsworthy, other than Tesla is acquiring a micro cap company in an all stock offer? There's not even a blog post on Tesla.com or a tweet by Elon regarding Maxwell.

Because Maxwell is a fairly popular name in the field; and this is interesting for hackers...

Certainly more fuel for the fire with Tesla bears, given that Maxwell has been in trouble with the SEC on multiple occasions for financial shenanigans:



One broken link and one article from 8 years ago about a settled FICA case?

It's a $50B company acquiring a small, technically related company for $200M. I don't think even TSLA bears would care.

edit: perhaps you meant https://www.sec.gov/news/press-release/2018-48 (without the 'x')? It's never good news when there's an SEC investigation, but this seems relatively minor (channel stuffing under a Sales executive, and then a < $3M settlement by the company that it should have caught it).

Fixed the link. I just think with all the conspiracy theories out there (which I'm also skeptical about) it is kind of amusing.

Is Musk pulling this to try and distract attention from the sales estimates in Jan 19? It's looking like an enormous, enormous plunge.

I don't think so. The China Gigafactory news was enough to silent many of the shorters and Tesla critics.

What is a sales estimate? Are you talking about production targets from the shareholder letter?

Try harder

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