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Author Topic: What is holding back electric car technology?  (Read 144275 times)

Offline peppercorn

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Re: What is holding back electric car technology?
« Reply #300 on: 05/02/2012 11:56:53 »
Yippee! Electric car range problem finally solved!

http://autos.yahoo.com/blogs/motoramic/one-inventor-wants-boost-evs-towable-turbine-210057167.html

I thought of that too... 'course thinking and doing are two very different things ::)   Kudos to him.

I also like the idea of a powered trailer (aka a pusher) - with driven wheels (from a traditional IC engine), which could potentially offer better fuel economy than the above trailer as it saves a conversion to electric and back again; though BSFC has to be factored in.
This is a particularly good supplementary power solution for BEVs with regen braking as the driver (or even better an Engine-s Management unit) can choose to overdrive the ICE slightly (pushing it nearer to ideal the BSFC region) at times when the battery pack needs topping up. The regen then partly switches on to trickle the batteries.
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #301 on: 02/03/2012 15:58:26 »
It is the oddest thing driving a 5-speed transmission and an electric motor.  One gets used to downshifting to get more power.  But, I seem to get higher amp draw (and thus higher acceleration) with upshifting.
That's quite funny, I would never have thought of that. You're obviously getting less back EMF off the motor at lower revs and so with fixed volts off the battery pack it gives you more torque/power (in some cases, if you really overdo the upshifting, it will probably go the other way).
« Last Edit: 02/03/2012 16:00:44 by wolfekeeper »
 

Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #302 on: 02/03/2012 19:03:48 »
True.

I wrote that a while ago.

I think my Ranger actually has a bit higher gearing than I had thought.

So, it is probably best to start in 2nd gear.
If I start in 4th gear, the acceleration is slow.

My old gasoline Ranger could barely handle the top 5th gear.  This electric one does fine with 5th, even though it has a lower top speed.

Amps seem to be closely related to power.  My target for maximum acceleration is 200 to 250 amps, which I get from the right gear.  Too high or too low of a gear and I don't get the maximum acceleration.

If I have it in too low of a gear, then the faster I go, the less amp draw (with pedal to floor)
If I have it in too high of a gear, then the faster I go, the more amp draw (with pedal to floor).

So, I suppose that it isn't so different from the normal gasoline vehicle, except that I am often driving in slightly too low of a gear, so more power is frequently gained from up-shifting.
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #303 on: 02/03/2012 20:22:11 »
If I have it in too high of a gear, then the faster I go, the more amp draw (with pedal to floor).
Is that the electric motor controller doing that?

An electric motor wouldn't normally do that I think.
 

Offline Geezer

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Re: What is holding back electric car technology?
« Reply #304 on: 02/03/2012 20:35:19 »
If I have it in too high of a gear, then the faster I go, the more amp draw (with pedal to floor).
Is that the electric motor controller doing that?

An electric motor wouldn't normally do that I think.


It depends. If the load is increasing because of increasing wind resistance, the power output has to increase, so the battery drain must increase.
 
Clifford, are the motor and battery currents the same thing? I imagine they are, but they could conceivably be different.
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #305 on: 02/03/2012 20:42:52 »
Presumably power/torque is voltage limited by the battery at the top end of the motor revs, but there's likely to be an artificial torque reduction on the low rev end, otherwise it's too easy to spin the wheels at low speed because that's where an electric motor naturally has the most torque.
 

Offline Geezer

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Re: What is holding back electric car technology?
« Reply #306 on: 02/03/2012 20:54:25 »
There has to be some sort of current limit, but I would imagine the "long" gear (small ratio) makes torque limiting unnecessary.

Mind you, diesel-electric and electric locomotives do have traction control systems to prevent wheel slip, but that's a somewhat different situation.
 

Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #307 on: 02/03/2012 23:53:28 »
Clifford, are the motor and battery currents the same thing? I imagine they are, but they could conceivably be different.
:-\
I need to go through the controller stuff a bit more. 

I think it is a DC setup.
With motor and battery voltages being the same, 144V.

One common way to "fake" variable voltage is to essentially create variable time slices at full voltage, I think, although one could potentially use capacitors to de-ripple it somewhat.

I would assume that "pedal to the metal" would give full voltage.  However, I believe the power is limited to somewhere around the 250A, and there is also some kind of RPM speed limiter.
 

Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #308 on: 03/03/2012 00:00:34 »
Oh...  and what is holding back the technology.
My winter range doesn't seem to be nearly as good as the summer range, with my range being about 40 miles last summer, it has dropped down to about 25 miles this winter.  I'm hoping some of it will come back as the temperatures warm up again.

If I choose to replace my batteries with a similar sealed lead battery array, I could easily spend $5000.

If I choose to upgrade to Lithium technology, I could easily spend $20,000.

It is a big chunk to bite off for a used vehicle.  But, with the right array, I should be able to more than double my range, and perhaps even improve my cargo capacity.
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #309 on: 03/03/2012 01:16:02 »
One common way to "fake" variable voltage is to essentially create variable time slices at full voltage, I think, although one could potentially use capacitors to de-ripple it somewhat.
You're talking about PWM. I don't see off-hand how that would be considered fake, the de-rippling can be done very well, particularly if the switching is at high speed. If they're very slow pulses, then yes, that would be bad!
Quote
I would assume that "pedal to the metal" would give full voltage.
It doesn't sound like it, I think there's a thing in there to give a more engine-like torque curve by effectively backing off the throttle at low revs.
 

Offline Geezer

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Re: What is holding back electric car technology?
« Reply #310 on: 03/03/2012 02:26:49 »
Yes, the voltage control to the motor is almost certainly some sort of switching regulator. Doing it with any sort of resistive control would be horrible in terms of the energy wasted - mind you, it would be a good source of heat in the Winter!

There was an article on the web today where someone pointed out a major problem with electric vehicles. 50% of the capital cost is in the battery. But the battery degrades, so after a few years, half the capital value has evaporated. Consequently, the resale value is going to be even worse than it is for a traditional vehicle.

I must say I'm a bit underwhelmed by modern battery technology. I have a 12 year old lead-acid battery in my boat that's still going strong. Based on what I've seen with PCs and the like, I'll be pretty surprised if anything can touch that sort of life. You might be wise to stick with lead-acids Clifford. They may be heavy, but they are pretty dependable if well treated, and they don't spontaneously combust either!
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #311 on: 03/03/2012 03:56:24 »
Yeah, Li-ions have a short shelf-life, and it's a shelf-life, they go bad without you doing anything, they lose capacity.

NiMh and lead acids are much, much better though.

And it's not actually that bad, even a battery with reduced life is still pretty useful and valuable. The batteries only lose about half their capacity after ten years or so.
 

Offline Geezer

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Re: What is holding back electric car technology?
« Reply #312 on: 03/03/2012 06:19:06 »
They always seem to quote Li-ions as having far greater energy density than lead-acids, which is true when they are new, but I wonder how they really compare if you factor in the degraded capacity over time. Lead-acids might not look all that bad!

They are also quite easy to re-cycle. Not sure about Li-ions.

Personally, I think we might do a lot better to forget rechargeable batteries and use recyclable primary cells like the Al-air battery instead. They have a whopping great capacity.

The apparent "downside" is that you would not be able to recharge it at home, but that actually might be a serious advantage. Once an infrastructure was established, you would just pop into the "gas" station and swap some of your batteries for new ones. No charge time, no nuthin. It should be no more difficult than buying gasoline.
« Last Edit: 03/03/2012 06:21:10 by Geezer »
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #313 on: 03/03/2012 16:55:10 »
I also like the idea of a powered trailer (aka a pusher) - with driven wheels (from a traditional IC engine), which could potentially offer better fuel economy than the above trailer as it saves a conversion to electric and back again; though BSFC has to be factored in.
I dunno. The problems are that the transmission adds extra weight, and running the engine under different loads and revs makes it far less efficient. You're much better off just running it at one speed and load. I mean that's basically how the prius works. Also having a trailer pushing you like that would induce potential issues with jack knifing.

It's just a bit too clever for its own good, whereas towing a trailer behind you with a generator on board is simple and straightforward. Also you don't need as much engine power because you can cruise and charge and the engine doesn't need to give you the peaks.
 

Offline Geezer

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Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #315 on: 04/03/2012 08:19:38 »
Do not brick your Tesla.
http://www.nytimes.com/2012/03/04/automobiles/Tesla-Battery-Failures-Make-Bricking-a-Buzzword.html?pagewanted=2&_r=1&emc=eta1
It sounds to me like a design flaw in the Tesla.  I can understand why nobody wants to fork out the dough for a $40K replacement battery.  However, the car needs an automatic power cutoff.  And, perhaps a manual cutoff too.  I'd hate to leave the Tesla in long term parking at the airport while going on vacation, only to come back to find the $100K+ car needs towed home.

Actually, it is a fault with many "modern" cars.  If one has a second vehicle that is only occasionally driven, then one needs to buy a battery disconnect to keep it from toasting the battery while it is sitting in the garage.

Like the Lithium batteries, Lead Acid batteries also don't like 100% Depth of Discharge.
 

Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #316 on: 31/05/2012 07:46:01 »
On NPR a few days ago, they mentioned a new Lithium-Tin battery design that is supposed to hold 3x the charge of the current Lithium based batteries.

http://www.npr.org/local/stories/KBSX/153886195
http://www.forbes.com/sites/uciliawang/2012/05/23/tin-the-secret-to-improving-lithium-ion-battery-life/

It appears if the Italians have been working on a similar process for a couple of years...  I have to wonder what the University of Washington added to it to justify the patent.
http://www.electrochemsci.org/papers/1030110.pdf
http://phys.org/news187526269.html

I'm also seeing notes of Manganese a few years ago giving possibly double the capacity of other materials.
http://www.rsc.org/chemistryworld/News/2007/May/10050701.asp

Anyway, I've been looking at possible upgrades for my EV battery array.  The current lead batteries that I have are HEAVY.  And, unfortunately there is a weight/range trade-off.

A direct conversion to Lithium should double (or more) my range from about 40 miles up to perhaps 100 miles which would be adequate for most local driving, but still be pushing it for "road trips".

I was thinking it might be good to set up a local battery pack which would be light and efficient.  A second battery pack could be added for longer trips.

But, if the capacity of the Lithium batteries could be doubled in the next couple of years, then that would make a HUGE step forward. 
The Tesla Model S is supposed to have a range of up to 300 miles or so.  Doubling that would be up to about 600 miles or so which would be a full day driving.  It would essentially mean unrestricted daytime driving, even for commercial applications, and recharging at night. 

100 to 200 miles would be fine for commuting.  What would be nice would be the ability to just add a range extension to one's vehicle.  Trailer?  Then maintain the lighter commuter.

And, as the battery size drops, efficiency will go up.

How long  can I put off dropping $20 Grand into a new battery pack?  There seem to be different estimates of the time until the implementation of the new technology.  NPR suggested a year or so.  I'd say perhaps half a decade would be more reasonable.
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #317 on: 31/05/2012 13:43:30 »
I think a trailer-generator is probably a better idea.

Build the battery big enough for your daily commute.

Then for the occasional times you need the extra distance, just attach the trailer, and turn it on when you need more range.
 

Offline peppercorn

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Re: What is holding back electric car technology?
« Reply #318 on: 31/05/2012 14:07:39 »
I dunno. The problems are that the transmission adds extra weight, and running the engine under different loads and revs makes it far less efficient. You're much better off just running it at one speed and load. I mean that's basically how the prius works. Also having a trailer pushing you like that would induce potential issues with jack knifing.

It's just a bit too clever for its own good, whereas towing a trailer behind you with a generator on board is simple and straightforward. Also you don't need as much engine power because you can cruise and charge and the engine doesn't need to give you the peaks.

I'm not so sure I would agree with it being too clever for it's own good.
Yes, a 'generator-trailer' has only to run at within a couple of percent of it's peak efficiency and no gearbox is needed but it may be heavy lump, needing to deliver over 8kw continuous output (Eg. driving at 70mph in a headwind); which the BEV motor(s) need to be able to accelerate and potentially overcome the negative aero effect at speed. A heavily upgraded onboard battery charger is also needed.  Obviously the initial investment would almost certainly be quite a lot higher for the self-builder, as old donor cars for a 'pusher' are cheap, whereas used gensets around ~10kW are not usually so.

The pusher trailer on the other hand is a cheap and cheerful solution.
Plus if you want to be more technical with it's design, it can probably get away with a low gear and a high gear, as the car would only ever pull away on electric and the Pusher would only engage above say 15mph.
The Pusher potentially doesn't even need an alternator or a charging hook-up if the BEV has regenerative braking capability, as to charge-as-you-drive the system would be able to slightly apply the 'brakes'.

The efficiency of the IC engine in the Pusher wouldn't suffer nearly as much as a normal car engine during the driving cycle as, if well matched, it should never be running at much less than 70% load or outside the (say) 2000-2500rpm ideal.
 

Offline peppercorn

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Re: What is holding back electric car technology?
« Reply #319 on: 31/05/2012 14:24:43 »
Anyway, I've been looking at possible upgrades for my EV battery array.  The current lead batteries that I have are HEAVY.  And, unfortunately there is a weight/range trade-off.

A direct conversion to Lithium should double (or more) my range from about 40 miles up to perhaps 100 miles which would be adequate for most local driving, but still be pushing it for "road trips".

The trouble is your truck is by it's nature pretty heavy before even adding batteries; plus has pretty diabolical aero I would imagine.  It's not the best vehicle for long distances or most commutes I'd guess.

The win on going to a Lithium or NiMH battery tech would be be more visible (in outlay for batteries, as well as kWh needed daily) if the vehicle's unmodified kerb weight was much lower.   Unless you are constantly running a truck for carrying or hauling a short distance most days I'm not sure BEV is much cop in such a package; whatever the battery tech allows.

Thanks for the new battery technology links BTW!
 

Offline wolfekeeper

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Re: What is holding back electric car technology?
« Reply #320 on: 31/05/2012 14:29:27 »
Obviously the initial investment would almost certainly be quite a lot higher for the self-builder, as old donor cars for a 'pusher' are cheap, whereas used gensets around ~10kW are not usually so.
About a grand from what I just looked up. They're standard bits of kit.
Quote
The pusher trailer on the other hand is a cheap and cheerful solution.
No, it's a complicated and difficult solution, you have to handle the gearing and control issues from the car in front. Both trailers and generators are standard items, that are easily available.
« Last Edit: 31/05/2012 14:31:44 by wolfekeeper »
 

Offline CliffordK

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Re: What is holding back electric car technology?
« Reply #321 on: 31/05/2012 17:40:48 »
As far as a generator, the charging system in my pickup is about 6KW.
The drain is, say around 144V x 100A, or about 14KW.
A 6KW generator is relatively cheap, and would give me about a 30% duty cycle.  So, one couldn't just drive on the freeway all day, but one could drive longer distances with brief stops and layovers.
A larger generator would also have to have a redesigned charging system.

A "pusher" would be awkward to drive.  One would certainly have to carefully tie the engine and brake systems together.

I think the small pickups were frequently converted to electric as they already have good enough suspension to handle the extra weight of batteries. 

I have a classic VW Caddy that I've been considering converting.  About half the weight of the Ranger unloaded.
 

Offline peppercorn

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Re: What is holding back electric car technology?
« Reply #322 on: 31/05/2012 22:45:05 »
No, it's a complicated and difficult solution, you have to handle the gearing and control issues from the car in front. Both trailers and generators are standard items, that are easily available.

It's still cheaper for most cases, and remote throttle-control is not rocket science; though a four-on-the-floor gearbox may be more of a challenge admittedly!  Automatics have 'lock-up' speed I believe (never worked on one) so that might be a way around.
 

Offline crimsonknight3

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Re: What is holding back electric car technology?
« Reply #323 on: 14/07/2012 13:56:03 »
I'm not sure if someone has mentioned this yet but there is currently being developed a carbon 'slurry' that can store and discharge electricity at massive rates depending on the size of the slurry tank/converter, if this could be utilized for electric vehicles, they could run on a tank of said slurry, then when they need more power, go to a petrol station, attach the car and have the negatively charged slurry extracted and replaced with positively charged slurry?

http://www.sciencedaily.com/releases/2012/07/120711104809.htm [nofollow]
 

Offline Geezer

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Re: What is holding back electric car technology?
« Reply #324 on: 14/07/2012 19:38:53 »
I'm not sure if someone has mentioned this yet but there is currently being developed a carbon 'slurry' that can store and discharge electricity at massive rates depending on the size of the slurry tank/converter, if this could be utilized for electric vehicles, they could run on a tank of said slurry, then when they need more power, go to a petrol station, attach the car and have the negatively charged slurry extracted and replaced with positively charged slurry?

http://www.sciencedaily.com/releases/2012/07/120711104809.htm

Interesting article. Thanks for posting it!

If I understand this it's a sort of supercapacitor. I'd be a bit worried that the energy density will be insufficient. Currently, supercaps have only a fraction of the energy density of chemical batteries, and even they are barely adequate.
 

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Re: What is holding back electric car technology?
« Reply #324 on: 14/07/2012 19:38:53 »

 

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