High voltage to power electric cars.
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Posted by sinebar@bellsouth.net on May 10, 2008, 3:04 pm
Please log in for more thread options knowlege is somewhat limited. Now my question. I presume that storing high voltage at low current is more efficient than storing low voltage at high current? I also presume that capacitors can be charged much faster than a lead acid battery? So I was thinking why not charge up a bank of high voltage capacitors with high voltage low current and then step it down to low voltage high current using a transformer which then could maintain a charge on a conventional lead acid battery that is operating the cars electric motor. My thinking is that the caps could be charged fast and the high voltage which is useless to run an electric motor, could be converted to high current which is usefull for running a motor or maintaining a battery charge. Now, could such a system have the advantage of extending the milage of an electric car significantly with out having to wait hours to charge? | ||||||||||||||||||||||
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Posted by John Larkin on May 10, 2008, 4:07 pm
Please log in for more thread options Not really. There's a very wide voltage range over which electronic chargers and motor controllers can work well. >I also presume that
>capacitors can be charged much faster than a lead acid battery? Only because capacitors store such a tiny amount of energy compared to batteries. What matters is joules (or horespower-hours) per pound and per cubic foot. Changing the voltage rating of a capacitor or of a battery doesn't materially alter that ratio [1], and batteries are hugely better than caps, by a factor ballpark 1000:1. John [1] any bunch of batteries, or of capacitors, can be connected in series (high voltage, low current) or in parallel (opposites) but the energy storage capacity doesn't change. There's no free lunch. | ||||||||||||||||||||||
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Posted by Michael Black on May 10, 2008, 5:36 pm
Please log in for more thread options On Sat, 10 May 2008, sinebar@bellsouth.net wrote:
> Please bear in mind that I am not an electrical engineer so my
JUst because there is good reason to have high voltage/low current
> knowlege is somewhat limited. Now my question. > I presume that storing high voltage at low current is more efficient > than storing low voltage at high current? I also presume that > capacitors can be charged much faster than a lead acid battery? So I > was thinking why not charge up a bank of high voltage capacitors with > high voltage low current and then step it down to low voltage high > current using a transformer which then could maintain a charge on a > conventional lead acid battery that is operating the cars electric > motor. My thinking is that the caps could be charged fast and the > high voltage which is useless to run an electric motor, could be > converted to high current which is usefull for running a motor or > maintaining a battery charge. Now, could such a system have the > advantage of extending the milage of an electric car significantly > with out having to wait hours to charge? > long distance transmission lines does not mean that batteries should be the same thing. As recently discussed, transmission lines use low current to avoid losses, and thus in order to transmit enough power they use high voltage. What's "efficiency"? You can take one single point, and it can be very efficient, but looking at the overall system, it can be inefficient. This isn't just about power storage, but about the actual motor used for propulsion, and the charging system may also come into effect. Now, maybe there are good high voltage motors, and good reason to use them. I don't know. But unless they exist and for good reason, then you have to deal with converting a higher voltage to the needed voltage, and that's bound to introduce ineffeciency. Likewise, one has to charge them, and unless one can deal with the charging at the higher voltage, one has to do conversion, again introducing inefficiencies. Of course, those other points become far more relevant because there is no suggestion that higher voltage/lower current batteries are more efficient. Note that one traditional thing that runs off batteries are the pre-atomic submarines. They'd run on the surface at night off diesel motors, which were better than electric, and then during the day when it was risky, run under the surface off electric motors. The batteries were charged during the evening when the diesel motors were running. You couldn't use diesel motors underwater because there was no way to vent them. But, one thing they did for "efficiency" was in how they combined the batteries. Put them in series to get higher voltage, put them in parallel for greater current. Read up on that sort of thing, and it might help you build the better electric car. For that matter, there was a time when electric cars were "common", right in the early days of cars. Look into what was used then. As for capacitors, they take less time to charge compared to batteries because they barely have any storage capacity. Charge it up in a hurry, and you basically used up the charge in a hurry too. It takes longer to charge a battery because that battery when charged will supply the needed voltage and current for quite some time. Michael | ||||||||||||||||||||||
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Posted by Tom Biasi on May 10, 2008, 7:02 pm
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> Please bear in mind that I am not an electrical engineer so my
> knowlege is somewhat limited. Now my question. > I presume that storing high voltage at low current is more efficient > than storing low voltage at high current? I also presume that > capacitors can be charged much faster than a lead acid battery? So I > was thinking why not charge up a bank of high voltage capacitors with > high voltage low current and then step it down to low voltage high > current using a transformer which then could maintain a charge on a > conventional lead acid battery that is operating the cars electric > motor. My thinking is that the caps could be charged fast and the > high voltage which is useless to run an electric motor, could be > converted to high current which is usefull for running a motor or > maintaining a battery charge. Now, could such a system have the > advantage of extending the milage of an electric car significantly > with out having to wait hours to charge? And, where are you going to get that DC transformer. | ||||||||||||||||||||||
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Posted by sinebar@bellsouth.net on May 10, 2008, 10:12 pm
Please log in for more thread options >
> > > Please bear in mind that I am not an electrical engineer so my
> > knowlege is somewhat limited. =A0Now my question. > > I presume that storing high voltage at low current is more efficient > > than storing low voltage at high current? I also presume that > > capacitors can be charged much faster than a lead acid battery? So I > > was thinking why not charge up a bank of high voltage capacitors with > > high voltage low current and then step it down to low voltage high > > current using a transformer which then could maintain a charge on a > > conventional lead acid battery that is operating the =A0cars electric > > motor. =A0My thinking is that the caps could be charged fast and the > > high voltage which is useless to run an electric motor, could be > > converted to high current which is usefull for running a motor or > > maintaining =A0a battery charge. =A0Now, could such a system have the > > advantage of extending the milage of an electric car significantly > > with out having to wait hours to charge? >
> And, where are you going to get that DC transformer. I believe DC can be converted to AC for driving a transformer. I think it can be done with an inverter. | ||||||||||||||||||||||
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>knowlege is somewhat limited. Now my question.
>I presume that storing high voltage at low current is more efficient
>than storing low voltage at high current?