trying to find a good discussion of high voltage vs low voltage in a hi-way capable ev.
decided to start my own as i need information to decide which way to go
for my own project.
i am considering converting a VW beetle with a body kit to electric but am unwilling to sacrifice performance. the body is quite aerodynamic and looks like a bradley gt left in the sun too long.
so performance minimums would be:
min range 250 miles to 90%DoD
top speed 100 mph.
0-60 in less than 5 secs.
price should be less than 50kUS.
sounds like prismatic cells or something similar is required.
there are a lot of little discussions in here i need to solve too, like ac vs dc, direct drive vs porche gearbox etc.
for now lets consider comparing hi-voltage ac unit with direct drive to a dc unit with a gearbox at lower voltage.
for the ac unit, would a ac150 get me this kind of performance? what kind of capacity(mah) would it take for the range? are we talking 500 volt range?
for the DC unit, maybe a warp 11 with a 800 amp controller at 144 volts? what would it take for this kind of range/current requirements?
some numbers:
ac-150 is 330-360vnominal, max 450 volts hot off the charge and 580A max
anyone know the gross weight of a vw chassis?
experiences with this stuff? conjecture?
OK in general terms Low Voltage = Poor efficiency and performance. So the takeaway is the higher the voltage the better. The problem with low voltage is it takes very high amounts or current to achieve high power levels. High curent means very large heavy expensive conductors that loose a lot of power with resistance.
As for the decision to use AC or DC, well efficiency and power is your goal, AC is the way to go using 3-phase induction with variable frequency drive. A 3-phase induction electric motor has constant flat current from 0 RPM up to Red line meaning excellent performance. AC motor efficiency is upper 90% where DC is down to as low as 70%
To get the performance you want which is a very tall order is pure physics and the laws that govern it. There is already one such vehicle for sale today that matches the range you ask for and exceeds the speed made by Telsa motors. The Telsa Roadstersounds to be about the same size and weight you are looking at and you can go look at the specs to see what they had to achieve that performance
For example the Telsa uses a 185 KW (250 peak HP) 3-phase induction motor, variable frequency drive, 390 volt DC battery bank rated at 100 AH (40 Kwh). The Telsa efficiency is 170 wh/mile giving it a range of about 220 miles with a top speed of 130 MPH.
i have seen the tesla… very cool looking machine.
problem with that car is it is $130k+ by the time
it is on the road.
i have been wondering if it might be better to wait for
some of the new EV’s coming on the market in the next year or so…
nah… gotta build my own… lol
the manufactured cars all seem to be either on the conservative side
or on the exotic side of the fence… nothing in between.
where is the 250 mile range, medium power level car for less than 50k?
[QUOTE=caspar21;6576] where is the 250 mile range, medium power level car for less than 50k?[/QUOTE]Good question because the CHEVY VOLT wins the Under Achievement award of the century. My gut tells me our government would block any such affordable EV that the masses could afford just like they do diesel vehicles. I mean who in their right mind would want a vehicle that cost 2-cents per mile to fuel?
One thing about AC wiring is with the high voltage three phase system is the wires can be smaller. I also seen the Telsa it has 7000 lithium laptop batteries in series and paralell. A small feat in itself!!!
thats a lot of batteries!
a roll of solder right there, lol.
anyone have experience with the efficiency of using over powered motors in light vehicles?
i am theorizing that i will not need near the amperage with a light car
that is over powered, compared to the same motor system in a heavy vehicle due to less power used to make it move. i think i need the math to make some models for comparison here.
am i going to use more power using an over powered motor in a light vehicle running at 10% of max avg, or is the small motor running at 80% of max going to use more power?
Here is some food for thought. It doesn’t matter if an electric motor is oversized or not. They are just as efficient at low power levels as they are at high levels. You just have that reserve when needed for acceleration and high speed.
However you need the high instantaneous levels of current to develop torque when accelerating.
For example my golf cart has a GE Raptor D398 motor rated at 9HP continuous powered by 48 volts. Will electrically all it needs is 150 amps. However it needs a 300 amp + controller to deliver the peak HP of 36 HP.
so power usage is determined(within limits) by the load/power supply rather than the size of the motor?
eg: small motor at 80% of max tolerance uses the same amount of juice as the hi power motor running at 20% of max tolerance as long as the output is the same?
(this is a generalization, not allowing for differences in efficiency of the different equipment etc)
am i on the right track?
[QUOTE=caspar21;6592]
eg: small motor at 80% of max tolerance uses the same amount of juice as the hi power motor running at 20% of max tolerance as long as the output is the same?
am i on the right track?[/QUOTE]You got it, if we are talking constant torque induction motors. That is the beauty of electric motors, their power curves are pretty much straight lines.
so, other than cost of the controller… is there any reason not to over power your EV?
would have more power on demand… and still have the range when you drive conservatively.
Weight and size come to mind.