Fast charging

[doug]

Shark2k,

Yes, yes, and yes.

 

[TEG]

Very slow trickle charge may have downsides too. There is probably some sort of charge efficiency curve that starts out poor, quickly goes to optimal, then drops off as you try to charge quicker and quicker.

Then there is the whole issue of long term battery damage. Even if you could quick charge it, it might wear out the batteries sooner.

In practice, I think the best chargers probably have a lot of intelligence behind them monitoring how the batteries respond, being very careful not to ever overcharge, and maybe employ tricks like variable voltage, and pulse charging in ways optimized for particular types of batteries.

 

[Kevin Harney]

http://www.sciam.com/article.cfm?id=better-battery-lithium-ion-cell-gets-supercharged

well this is kind of key ....

The study notes that residences cannot draw enough energy from the electrical grid to quickly charge a hybrid car's battery containing the new material, though smaller batteries for gadgets and perhaps power tools should not have that catch. But future roadside plug-in stations (service stations selling electricity instead of gasoline) with greater power pull could do the trick for vehicles, Kang says.

and this ...

In theory, a large battery that would be used to power a plug-in hybrid electric car could be recharged in just five minutes, compared to up to six or eight hours at present. But this would only be possible if a beefed-up electricity supply were available.

 

[SteveF]

Yes, the things Kevin Harney points out ARE key, but it still doesn't diminish the importance of this quick-charge development for Li-Ion batteries, if it does indeed come to pass. I don't NEED the quick charge at home, since I can fill up overnight even if my battery is fully discharged (a rare event in itself). Where I need a quick charge is when I'm on a long road trip, and don't want to spend 4 hours (at best) over a very long lunch charging up. So with a few locations that have the higher power capabilities situated along the various routes I might drive, I'm a happy camper. I hope this is true, because if it is it really does seem to address the range issue that is currently one of the biggest sticking points for some people regarding EVs.

 

[mpt]

Here's some rough numbers:

Assuming a 55KWhr battery similar to the Tesla Roadster; You've got a pack that takes 4hrs to charge at 80A (220V); that's 4hrs of power at 17½KW or, 70KWhrs of power. (Note that the extra 15KWhr disapears as heat).

If you wanted to charge in 5 mins at the same 220V, you'd need to get a supply at a smidge under 4,000A... Most US houses have a 200A feed... and the wiring would be like railway tracks!

If you wanted flexible wiring at say 80A then the voltage would need to be 10,500V. That would be risky; at that voltage the insulator has to be impecable; just the slightest crack in the insulation and the sparks would fly.

Some middle ground like 200A at 4,000V that was connected to the car by an automated robot arm or underbody connector might be fairly cheap to design and install; and by cheap I'm thinking a few thousand USD. Flip over a ScaletriX slot car for a design prototype example.

In the US, the next step up from Home and Office supply is called Primary Customer, and that offers 13,000V and 4,000V feeds; the 4,000V feed can be ordered online!

I'm sorry, hydrogen to power a car??? What next Custard to power space rockets?

 

[Kevin Harney]

If a nice big business feed is 480 V and you had a 70 or 80 A cable then would this new tecnology effect your charge times ? Or would the capacity of the battery exceed the typical capacity of most businesses ?

 

[mpt]

At 480v, 80A a roadster would take 2hrs to charge; that's a long lunch.

 

[Kevin Harney]

so the answer is no it would not effect your charge time because the battery would exceed the typical business capability. right ?

 

[stopcrazypp]

At 480v, 80A a roadster would take 2hrs to charge; that's a long lunch.

The fastest demonstrated charger right now is 250kW. It'll take around 13-15 minutes to charge the Roadster using that charger (if the Roadster's batteries can handle it).

The ones that are actually being used to charge airport baggage loaders and also being used to demonstrate EV rapid charging are 60-80kW chargers, which will take 60-40 minutes to charge the Roadster.

Keep in mind that the Roadster has a lot more range than the typical more affordable EVs that are slated to come out. So the charge times will be halved for EVs with only 100-150 miles of range.

 

[Kevin Harney]

OK what I dont get is when you change the specs and say 250kw charger - what does that mean for us non-engineer types

 

[stopcrazypp]

OK what I dont get is when you change the specs and say 250kw charger - what does that mean for us non-engineer types

250kW is just the power output. Power = Current * Voltage.

For example your 80A, 480V would mean 80A*480V = 38400W = 38.400kW charger.

It's just make it easier to compare, since what the charge time depends on in the end is the power (as well as battery capacity) and not the specific voltages or currents.

 

[Kevin Harney]

but a typical LARGE business would not have the capacity to go over about 35-40Kw right ? so what is the point of a battery capable of more than that if no one can really use it ?

 

[mpt]

When you look at charging a battery, you're looking to push power into the battery; the unit of power is the watt, a thousand watts is a kilowatt.

When you look at storing electricty or measuring how much can I fit into this battery you look at amount of watts it can send out for how long; you bring in time to get Killo-watts per hour or KWhr; a 1KWhr battery can produce 1 killowatt of electricity for one hour; or enough to warm up a small electric heater for an hour. Gives you some idea of just how much power is in the Tesla Roadster battery; enough power to warm a small room for two days!

Electrical power is offered at different voltages, 1.5v AA batteries to 240V wall sockets. Think of voltage like water presure; the higher the voltage the more the pressure.

The flow of electricity is the amount of electricity going past or current in the water example, it's measured in amps A.

Watts relates to volts and amps:

Watts = Volts * Amps

1 w = 1v * 1a

so: 1000w can = 240v x 4.1a or 1000 can = 480v x 2.05A

See as the voltage rises the current comes down?

Good and bad; high voltage is like more pressure and more difficult to contain; needs better insulation otherwise it leaks! High current means more flow; thicker wires.

However you get your battery charged it's a balance between voltage, current and time. a 55Khr battery needs 55KW for 1 hour or 55hours at 1Kw to charge... roughly; there's a catch.

Usually, with todays battery chemestry there's a tradeoff in the chemestry that determines how quickly they can charge; the faster you try to charge a battery the hotter it gets (wasting energy) until ultimately it can be damaged.

This new MIT idea lowers that so that you can force more power into the battery faster without it getting hot... if you have lots of power that is.

Todays Roadster battery chemestry limits maximum charge rate to a 40 minute charge... any faster and it'll melt!

Tommorows battery can do better but you'll need to bring in a bigger supply which is available today just not commonplace.

 

[Kevin Harney]

Are you saying that a business may choose to have NO transformer and put the primary through to the plug ? Therefore approx. 17,000 volts ???? if so what Amp would that be like 4.7A am I doing that right. so with a 15A circuit it would be reduced to like 5 minutes or so ? Am I learning or just getting confused ?!?!?!!?

 

[mpt]

Pretty much, that's it.

In the US, 13,000V and 4,000V supplies are available to factories.

For a five minute charge, at 13,000V you'd need 70Aish

13,000 * 70 / 12 = 75KWhr or one Tesla Roadsters worth of charge

 

[Kevin Harney]

Thanks MPT that was VERY helpful and a good explanation :smile:

 

[stopcrazypp]

but a typical LARGE business would not have the capacity to go over about 35-40Kw right ? so what is the point of a battery capable of more than that if no one can really use it ?

If I remember correctly, someone here said a decent sized supermarket can get a 1MW service. That kind of power source can handle twenty 30-40kW chargers. But typically, I think most businesses will offer much slower chargers as a convienience.

I think only the dedicated charging stations will have fast chargers, so the a battery capable of fast charging will still be useful for dedicated charging stations. For example, the 1MW source can power four 250kW chargers which takes 13-15 minutes to charge up battery of the same size as the Roadster's.

I believe the 250kW charger feeds 600A max (this is the max for other existing chargers) at 440-480V. It won't be a crazy high voltage like 13000V or 4000V. A rapid charger typically uses a 480V 3 phase source.

 

[Kevin Harney]

but why is my math coming up with like 4-6 A I am dividing 80Kw or 80,000w by the voltage of 13,000 and getting the wrong number where am I mistaken in my rusty math skills?

 

[Kevin Harney]

By most Large businesses I am taking like hotels and gas stations etc that you might be able to go to as quick stop. In the US I believe that most of those are 480V service so that would be a little short of a 0.5Mw right ? I am sure that some are larger but they would be few and far between. BUT Grocery stores would be a good route to go I had not thought of those they are a dime a dozen. :biggrin:

 

[Kevin Harney]

AND I am relatively certain that in this are the Primary voltage is 17,500 but not definately sure so I will go with the 13,000 you mention.