Re: what is the max bus voltage, 300V?

[Lee Hart <leeahart@earthlink.net>]

Victor Tikhonov wrote:
> It is understood that when I'm talking about >80% OEM EV, I'm
> talking about EVs of the similar performance as gas cars - at least
> capable of running on the same freeways, i.e. EVs people would
> consider as transparent alternative replacement for their normal ICE.
> 
> This leaves out fork lifts, HEVs Citicars and such. Obviously,
> people will not trade Toyota Camry for fork lift or Citicar, but
> will (consider) - trade for EV1.
>
> You know well what common people mean saying a word *vehicle*.

Sorry, Victor. I'm not trying to be difficult. I thought we were talking
about electric vehicles in general, not specifically about any
particular size. What I was trying to say is that you pick the system
voltage to suit the vehicle size and power requirements:

a. start with some vehicle
b. figure out how much horsepower you need for it
c. pick a battery voltage and current that can supply this power
   without getting into extremes (unreasonable size or number of
   batteries, dangerous voltages, excessive currents, etc.)

So smaller vehicles will be lower voltages; larger vehicles will be
higher voltages. There is a fair amount of lattitude (at least 2:1), but
you're not going to pick 330v for an NEV or 36v for a bus.

I think Victor is considering EVs about the size of a Toyota Camry or GM
EV1 (roughly 3000 lbs). A typical driver would probably want it to have
about 50 HP ~ 50 KW to feel like a "normal" car. The EV1 has 100 KW to
feel like a sports car.

50kw at 300v is 167 amps. The voltage is rather scary, but the current
is reasonable. It takes a lot of batteries and a lot of interconnects,
but you can borrow 240vac industrial control technology.

Or, 50kw at 150v is 333 amps. Now the voltage is modest, and so is the
current. Motors, controllers, and batteries are fairly easy to get.

Or, 50kw at 75v is 666 amps. The voltage is easy, but the current is are
getting very difficult to deal with. You need huge bus bars and
parallelled batteries, but can borrow industrial fork lift technology.

I contend that all three voltages would produce equally competent
vehicles. Assuming a level playing field, the middle voltage (150v) is
probably the best compromise. Higher voltage (300v) tends toward higher
cost, complexity, and safety issues. Lower voltages tend toward more
weight, lower performance, and also higher costs.
-- 
Lee A. Hart                Ring the bells that still can ring
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