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Re: Questions on Electric Vehicle high power electronics
by plpeter
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> 2) Going to start with a battery bank consisting of Eveready GC2 Golf Cart
> batteries from Sams. 6V, 225 Ah, $75 each. A 144V system of 24 batteries
> will run $1650 + tax, no shipping and weigh about 1650 lbs.
The goal of the electric car is to be light, in view of the low power density of
the batteries. The law of diminishing returns kicks in fast if you end up with a
ton of batteries lugged around for no good reason. The best way is to use a
battery as small as possible and change it often (with another freshly charged
one). In the 70s and 80s there were trials with such changeable packs for public
transportation (electric bus). At the time they did not catch on.
Imho, try to work the problem backwards: how much do you travel between pit
stops, what class of EV can do that now (wikipedia helps), how much it
weighs/costs, then see how you could build a vehicle of that class or refurbish
a used one.
Available data suggests 20-100 km range for curb weight << 1 ton.
Electronics for electric traction are not so trivial. There is inrush limiting,
kickback handling, dynamic braking (motor tries to generate - you can't just cut
the drive, the voltage will raise high enough to blow the insulation on the
motor if you do that) etc etc. 'Simple' PWM requires a bridge circuit from >500W
or so and so on.
Plus the torque/rpm characteristics of usual electric motors are not suitable
for road traction use without some suitable controllers. The easiest hack is to
rely on the gearbox and implement a step relay that will shunt in more or fewer
cells (tapped series stack). This provides both drive and regenerative braking
in a brutal way, and is the 'old' (and tried) way of doing it. Fork lift trucks
and the like built according to these principles tended to last 30-40 years.
Imho obtain a book on electric traction control (road and rail) and read it. It
will likely open your eyes. I never did anything larger than 50-100A traction
(12-24V) and I think that just keeping cpu-deadly spikes and kickback under
control will keep you busy for weeks.
Most older (pre thyristor) battery chargers are of the variac type, manual or
automatic, newer ones are thyristor based. Charge equalization in a series
battery is a problem. Nothing is as simple as it seems. The price tags on the
items you quoted probably reflect the low production numbers and the man-hours
put into fixing the problems that had to be fixed.
good luck,
Peter
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> batteries from Sams. 6V, 225 Ah, $75 each. A 144V system of 24 batteries
> will run $1650 + tax, no shipping and weigh about 1650 lbs.
The goal of the electric car is to be light, in view of the low power density of
the batteries. The law of diminishing returns kicks in fast if you end up with a
ton of batteries lugged around for no good reason. The best way is to use a
battery as small as possible and change it often (with another freshly charged
one). In the 70s and 80s there were trials with such changeable packs for public
transportation (electric bus). At the time they did not catch on.
Imho, try to work the problem backwards: how much do you travel between pit
stops, what class of EV can do that now (wikipedia helps), how much it
weighs/costs, then see how you could build a vehicle of that class or refurbish
a used one.
Available data suggests 20-100 km range for curb weight << 1 ton.
Electronics for electric traction are not so trivial. There is inrush limiting,
kickback handling, dynamic braking (motor tries to generate - you can't just cut
the drive, the voltage will raise high enough to blow the insulation on the
motor if you do that) etc etc. 'Simple' PWM requires a bridge circuit from >500W
or so and so on.
Plus the torque/rpm characteristics of usual electric motors are not suitable
for road traction use without some suitable controllers. The easiest hack is to
rely on the gearbox and implement a step relay that will shunt in more or fewer
cells (tapped series stack). This provides both drive and regenerative braking
in a brutal way, and is the 'old' (and tried) way of doing it. Fork lift trucks
and the like built according to these principles tended to last 30-40 years.
Imho obtain a book on electric traction control (road and rail) and read it. It
will likely open your eyes. I never did anything larger than 50-100A traction
(12-24V) and I think that just keeping cpu-deadly spikes and kickback under
control will keep you busy for weeks.
Most older (pre thyristor) battery chargers are of the variac type, manual or
automatic, newer ones are thyristor based. Charge equalization in a series
battery is a problem. Nothing is as simple as it seems. The price tags on the
items you quoted probably reflect the low production numbers and the man-hours
put into fixing the problems that had to be fixed.
good luck,
Peter
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
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