20 Aug '11 03:54

http://www.physorg.com/news/2011-08-energy-storage-device-recharge-electric.html

I did a quickie analysis and figured this: suppose the battery stores 25 Kwh of energy.

Suppose you want to charge that battery in one hour. That means pumping in 25,000 watts for a full hour. But suppose you want to charge it in 30 minutes. Then you need 50,000 watts running a half hour. But suppose you want to do it in 3 minutes. Now you need 500,000 watts running for 3 minutes to get that 25 kwh battery to peak.

So how do you do that? Run 500 volts, you need 1000 amps. 100 volts, 5000 amps.

So it looks like, in order to keep the cable under the size of a 2X4, you have to way up the voltage, say 5,000 volts at 100 amps. 50,000 volts at 10 amps. Something like that.

So what technological answer is there for such a charging station?

Also, am I correct in my assumptions here? Anyone want to think this one through and see if they come up with the same problems?

I know how we insulate at 50,000 volts, I work with 200,000 volt power supplies and it ain't easy, especially for public use. For geeks like me, we are used to that kind of energy, and we know how to handle it, buddy system kind of thing but most of the cables we use only insulate around 30,000 volts. And if that cable got a crack in it somehow and a little bit of moisture, say a rainstorm......

So high voltages in public hands? I don't think so.

So how high a voltage could we build a power cable, to be flexible and robust enough for public customers to handle safely? We could do 5000 volts at 100 amps.

Even that can be extremely dangerous if a crack in the insulation showed up.

So it sounds like the cable is going to have to be a pretty complex affair, say a double insulated or triple insulated cable with conducting coatings inside or like coax with several coaxial layers and the outer layers having sensors that detect the presence of current flow that would indicate leakage, like a ground fault indicator but for 5000 and up voltage systems.

Even then you have to explicitly trust the current leakage sensor to work almost 100 percent of the time the cable is in use.

Assuming such a battery comes online there is going to be serious issues trying to cram that much energy into a short space of time. Anyone want to verify my analysis?

I did a quickie analysis and figured this: suppose the battery stores 25 Kwh of energy.

Suppose you want to charge that battery in one hour. That means pumping in 25,000 watts for a full hour. But suppose you want to charge it in 30 minutes. Then you need 50,000 watts running a half hour. But suppose you want to do it in 3 minutes. Now you need 500,000 watts running for 3 minutes to get that 25 kwh battery to peak.

So how do you do that? Run 500 volts, you need 1000 amps. 100 volts, 5000 amps.

So it looks like, in order to keep the cable under the size of a 2X4, you have to way up the voltage, say 5,000 volts at 100 amps. 50,000 volts at 10 amps. Something like that.

So what technological answer is there for such a charging station?

Also, am I correct in my assumptions here? Anyone want to think this one through and see if they come up with the same problems?

I know how we insulate at 50,000 volts, I work with 200,000 volt power supplies and it ain't easy, especially for public use. For geeks like me, we are used to that kind of energy, and we know how to handle it, buddy system kind of thing but most of the cables we use only insulate around 30,000 volts. And if that cable got a crack in it somehow and a little bit of moisture, say a rainstorm......

So high voltages in public hands? I don't think so.

So how high a voltage could we build a power cable, to be flexible and robust enough for public customers to handle safely? We could do 5000 volts at 100 amps.

Even that can be extremely dangerous if a crack in the insulation showed up.

So it sounds like the cable is going to have to be a pretty complex affair, say a double insulated or triple insulated cable with conducting coatings inside or like coax with several coaxial layers and the outer layers having sensors that detect the presence of current flow that would indicate leakage, like a ground fault indicator but for 5000 and up voltage systems.

Even then you have to explicitly trust the current leakage sensor to work almost 100 percent of the time the cable is in use.

Assuming such a battery comes online there is going to be serious issues trying to cram that much energy into a short space of time. Anyone want to verify my analysis?