GM Volt Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
7 Posts
This looks like a spammy topic, but I'll chip in because I'm an electrical engineering student and graphene is actually one of my main fields of interest.

Graphene is great because it has a high surface area. High surface area is very good for electrodes in power supply elements like batteries and capacitors. That means that graphene can be used to increase the capacity of existing Li-Ion technology, but it can be used to make "supercapacitors" as well.

Now, supercapacitors haven't yet reached the energy density level of batteries, but they are superior in the sense that they have extremely fast charging times, seconds to minutes.

Since I'm only an electric car enthusiast and don't own one myself, I'd love to hear how long it takes you to fully charge a Volt from zero, and how much of an impact it would make on your driving if you could charge it in one minute.

EDIT: No offense to the OP if it's just his english that sucks and this was not a spam topic.
 

·
Registered
Joined
·
236 Posts
Full charge on the volt w/a level 2 charger is about 4.5 hours...full charge on 110 is around 12 hours. I have always thought that there is too much focus on electric "range" as the main impediment to more universal acceptance of the electric car. Range is important, but, shorter range could be compensated for by much quicker charge times.

In my most humble (ha ha) opinion, they should design electric cars around my bladder. Range about 2 hours, and recharge time about 15 minutes....
 

·
Registered
Joined
·
7 Posts
Yeah, 12 hours, or 4.5 hours even sounds like a lot of time. All rechargeable batteries in general suffer from the same problem, which is a high equivalent series resistance. It means that each battery has an internal resistance which is the consequence of its chemical nature. When you charge a battery, this resistance is connected in series with the battery. So when you decide to charge it, the battery heats up. If you want to charge a battery quickly, you need to charge it with a high current, and high currents heat resistors more. So basically, there is no way around that - batteries will always charge slowly.

On the other hand, supercapacitors are basically capacitors, only supersized (and miniaturized using new technology). They have a low series resistance which allows for high charging currents. I don't know the exact numbers off the top of my head, but if the site above is correct (http://graphene-battery.net/graphene-supercapacitor.htm), the charging current can exceed 100 amperes which is tens of times more than the charging current of a typical Li-Ion. So yeah, charging times can be tens of times shorter for supercapacitors. The numbers look about right, it even compares a supercapacitor to an ordinary battery in terms of energy density and so on.

Graphene is a really fascinating material, here is one more source which says that an iphone running on supercapacitors could fully charge in 5 seconds and have a comparable battery capacity: http://www.dailymail.co.uk/sciencetech/article-2286714/The-battery-breakthrough-charge-iPhone-SECONDS.html[/U][/B]
Dailymail, but yeah.

And if electric cars were indeed engineered around a human bladder, we wouldn't be talking about battery problems. You need 15 minute pauses after driving for 2 hours straight anyway :)
 

·
Registered
Joined
·
362 Posts
I want to add to RedneckRoyalty's answer that when charging on Level 2, the charging rate is 3.3KW. 244V @ 13.5 amps. Charging level 1 is about 1.5 KW....120V @ 13 amps. The limiting factor in charging is not the battery's ability to charge, but the capacity of the Volt's on board charger, which is limited to 13.5a and 244V. If GM used a higher output charger, the Volt's battery could easily charge at 6.6 or 9.x KW. When the Volt is going downhill in full regen, I think the battery is being charged at over 50 KW.

-Eric
 

·
Registered
Joined
·
7 Posts
I doubt that the batteries could charge at 50kW for extended periods of time (they would need to work on some serious cooling for that), but yeah, I believe there is space for improvement.

A general rule of thumb says that you should charge Li-Ion at 50% to 80% maximum power output. If I'm not mistaken, the Volt has a ~16 kWh battery so in theory, yeah, it should be able to charge at more than 13 amps.
That's still weak when you compare it to a supercapacitor at >100 amps. Maybe they ramped down the power intentionally to increase battery life or reliability? Or maybe they have cooling issues when the car is stationary?
 

·
Registered
Joined
·
236 Posts
Not that I'm an expert or anything, but, the problem with fast charging (if it ever happens) is that it usually also carries with it the capability for fast discharging...If you put the Volt's current 16KwH charge into a capacitor, it would scare the bejeebers out of me....and I wouldn't want to go anywhere near it.
 

·
Registered
Joined
·
7 Posts
That's a valid point, the discharge could kill you on the spot. I guess that can be prevented by using many smaller capacitors (if there's an internal short in one of them, it won't blow up) - just as a battery is made from many individual cells. Also, a system of fuses could prevent (or try to prevent) damage and injury.

I haven't thought about it that way, it's an interesting train of thought (i'm more about what's useful and not about what's dangerous :D) but the fast discharge could be a good thing too. Imagine all the acceleration you could get with a much higher maximum power output! :)

Edit: here's a youtube link describing the fun you could have with an ultracapacitor in an unsafe way : http://www.youtube.com/watch?v=EoWMF3VkI6U
 

·
Registered
Joined
·
718 Posts
spam bot. posted that link.


but lets keep the topic going
 

·
Registered
Joined
·
1,797 Posts
There's another often overlooked issue with faster charging. Even if you had an ultracapacitor that could store 16kwh (or I believe in the Volt's case it really uses about 10 Kwh)... Imagine how much power it would require to be able to charge the thing up in 1 minute. For that one minute a car would be consuming the same amount of power as several office blocks.
 

·
Registered
Joined
·
7 Posts
It's simple to calculate:

16 kWh = 16 000 W * 3600 s = 56.7 megajoules of energy stored in the battery/capacitor

56.7 megajoules / 60 s = 945 kWh for the charger (this is the necessary power rating for the charger)
At this rate, if the battery/capacitor voltage is 12v, the current is 945 kWh / 12 V / 60 s = 1300 amps

That does sound a bit excessive, but if we have a charging time of 10 minutes instead of one, the current drops to 130 amps and the power supply rating drops to 94.5 kWh which are both achievable in a commercial charging station.

Definitely beats 4.5 hours :)
Please correct me if i'm wrong in my calculations, i'm a bit tired so there's room for error.

EDIT: This video shows what ultracapacitors are capable of doing in a car application: http://www.youtube.com/watch?v=z3x_kYq3mHM
Note that these are "conventional" supercapacitors. Graphene supercaps will beat conventional supercapacitors in size and weight (and they're even actually flexible - not particularly useful in a car, but they'll be able to power wearable computers or flexible cell phones - fun stuff :))
 

·
Registered
Joined
·
1,785 Posts
There's another often overlooked issue with faster charging. Even if you had an ultracapacitor that could store 16kwh (or I believe in the Volt's case it really uses about 10 Kwh)... Imagine how much power it would require to be able to charge the thing up in 1 minute. For that one minute a car would be consuming the same amount of power as several office blocks.
That's been discussed. The concept is that the EVSE would contain a capacitor that was gradually charged up. When the EV was plugged in - zap. I guess they'd need enough capacity for several vehicles during rush hour.
 

·
Registered
Joined
·
1,051 Posts
Do the 2013 Volts take 4.5 hours to charge with level two chargers? My 2012 takes only 3.5 hours.
My 2013 takes 3:45 at 240v. Typically 9:20 - 10:30 on 120v. Variance seems to be dependent on temperature and voltage drop at the outlet. I rarely need to charge from fully depleted though, so I don't have a great set of historical data points for this.
 

·
Registered
Joined
·
477 Posts
Spam-bots, or not, here is an interesting vid on graphene:

Clipboard01.jpg

 
1 - 15 of 15 Posts
Top