Questions on Electric Vehicle high power electronics

[Byron Jeff]

Hi folks,

I'm kind of surprised that with the surge in fuel costs that a thread on
electric vehicles (EV) had not got jump started here.

I have questions at the bottom if you are not interested in the background.

I have the goal of quickly putting together a lead sled, a pickup full of
lead acid golf cart batteries, for daily driving in order to bring some
cost control to my transportation costs.

I'm well aware that there are a ton of other options, including lithium
based batteries. I'm also aware of the limitations. However, I'm determined
to get off gas for the regular commute in a cost effective manner.

If you're interested in seeing a video blog of an EV being put together go
to youtube and search for n2confusion. He has about 37 videos of the actual
destruction/reconstruction process of a lightweight EV.

Also there's a very active forum community at diyelectriccar.com. I'm
posting over there as ga2500ev.

An EV really isn't too terribly complicated, with only 4 major components:

1) Donor vehicle with manual transmission
2) Battery bank.
3) Electric Motor
4) Control, charging, and monitoring electronics

The first three are fairly stock entities with (so far) static costs. Find
a vechicle with a busted Internal Combustion Engine (ICE), pull the engine,
mate the electric motor to the transmission and hook up the battery bank to
the motor. My plan is to start this project with cheap available
components:

1) Still looking for a donor truck. Probably will end up with on off
craigslist. With a blown engine, it won't be more than $500.

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.

3) Still searching for good availably and price. WarP 9's have 6 week or
more lead times and run in the $1700 to $1800 ballpark.

That leaves the electronics. From both a cost and integration standpoint
there's a lot to be left desired with control electronics. The major
subsystems:

1) PWM motor controller. Not a fundamentally complicated piece of
equipment. Accepts a limited number of control inputs (5k throttle pot,
brake switch) and controls via PWM a high powered switch between the
battery bank and the motor. An example is the Curtis 1231C controller:

http://www.electricvehiclesusa.com/product_p/co-1231c-8601.htm

I'm almost ready to choke on the $1400 price tag.

2) Battery charger. Again not too complicated for lead acid battery packs.
A lot of DIYers use individual chargers to each battery. But a decent charger
runs upwards of $800.

3) DC-DC converter. Takes the battery pack and replaces the alternator with
a converter.

4) Voltage and current monitoring. A lot of systems have separate current
monitoring for display and for the controller to prevent overstressing the
motor. The battery charger also requires voltage monitoring.

The prices for these components seem outrageous when you consider that the
core of most of these modules are high powered switches. IGBT modules such
as:

http://tinyurl.com/3t86km

Are available surplus for less than $50. These modules are more than stout
enough to handle both the controller and charging loads.

It seems to me that a DIY electronics builder could put together an
integrated controller/charger for a fraction of the cost of the commercial
equipment. I think my problem is the difference in understanding the theory
and the actual engineering.

Questions:

For the controller does the power electronics consists of more than the
IGBT, freewheeling diode, and smoothing cap bank?

Any suggestions for a freewheeling diode for a 144V x 600A controller?

Battery charging is a voltage/current limited charge dump. Presuming that
you have a 240VAC source, would the best control be to rectify to DC then
use a buck converter to get the correct voltage/current? If that's the case
then any suggestions on how to get an appropriate inductor? Same for the
DC/DC converter.

It seems to me that a significant cost in EV development could be greatly
reduced with the judicious application of DIY electronics. With PICs,
IGBTs, and a bit of knowledge, a complete electronics system for an EV
could be realized for a couple of hundred bucks instead of a couple of
thousand.

Thanks for reading. Look forward to any suggestions you may offer.

BAJ
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[Byron Jeff]

On Sun, May 25, 2008 at 02:15:40PM -0400, Djula Djarmati wrote:

> > 3) Still searching for good availably and price. WarP 9's have 6 week or
> > more lead times and run in the $1700 to $1800 ballpark.
> >
> > That leaves the electronics. From both a cost and integration standpoint
> > there's a lot to be left desired with control electronics. The major
> > subsystems:
> >
> > 1) PWM motor controller. Not a fundamentally complicated piece of
> > equipment. Accepts a limited number of control inputs (5k throttle pot,
> > brake switch) and controls via PWM a high powered switch between the
> > battery bank and the motor. An example is the Curtis 1231C controller:
> >
> > http://www.electricvehiclesusa.com/product_p/co-1231c-8601.htm
> >
> > I'm almost ready to choke on the $1400 price tag.
>
> Before doing the electronics all by yourself, I would try FANUC CNC
> spindle motors and controllers like these:
>
> http://cgi.ebay.com/Fanuc-spindle-motor-a06b-0759-b970_W0QQitemZ180243520740
> (30kW at 40%ED, 22kW continuous)
> http://cgi.ebay.com/FANUC-DC-SPINDLE-SERVO-DRIVE-MODEL-SP12_W0QQitemZ220237949247
> (I don't know if this one fits the motor, it's just an example)
>
> These motors and controllers are very rugged, protected from overload,
> short circuit, etc. and you also get regenerative braking since they
> brake by dumping energy to DC rail. The controller keeps the set rpm
> automatically and goes in reverse.
>
> The only drawback is they expect 200V 3-phase which is around 300V on DC
> rail. The price for these starts at $1000 for each item.

Which makes it a non starter. Used EV controllers can be had for about 1/2
that price.

My point is that the component costs are only about 15 percent of the
retail price of these controllers. Paying $1400, or even $1000, doesn't
make a lot of sense when the parts can be assembled for $150.

> If you make it work, you can experiment in making your own by looking
> the way FANUC did it. If you go this way, let me know and I can find
> some datasheets.

As I stated in my original post, nothing about any of the technology is too
particularly complex. The controller is little more than a PIC driving a
IGBT driver which drives the IGBT with a PWM signal. The input comes from a
standard 5k throttle pot going right into the ADC input of the PIC.

The battery charger, for lead acid, again is little more than taking full
wave rectified DC and buck regulating to thre required voltage. Same for
the DC to DC converter.

I'm really just wanting to make sure I don't miss a crucial design
component. And looking for suggestions on some of these high power
components, such as inductors and ultra fast recovery diodes.

BAJ
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[Byron Jeff]

On Sun, May 25, 2008 at 02:32:33PM -0400, Peter wrote:
> > 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.

My goal is to build something that I can afford. I battle with the guys on
the DIYEV list all day long about investing tens of thousands of dollars
into lithium batteries. But it's an investment that doesn't make sense to me.

When lithium batteries are reliable, easily available, and about double the
price of lead acid, then I'll consider switching. Until then, it's lead
acid because from a cost standpoint, there's simply no comparison at this
point.

> 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.

Can't store a battery bank at work, which is the only logical place to
swap. The bottom line is that I'm stuck carrying the bank around.

> 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.

All that analysis is already done. That really wasn't the purpose of this
thread, though I'm happy to talk about it if you like.

The bottom line is that if you carry enough lead around, you can get
reasonable ranges for a daily drive. That's my goal.

> Available data suggests 20-100 km range for curb weight << 1 ton.

I'm well aware. The challenge is that to carry enough lead to get a useful
range, you exceed the GVWR of the vehicle.

Trucks are designed to carry that kind of weight.

A better tack is to improve the aerodynamics of the vehicle. Trucks are
pretty much a rolling brick with awful coefficients of drag. If you improve
the CD with sloped bed caps, mirror deletion, wheel covers, and the like,
you can greatly improve the range of the vehicle without changing the
weight. See a sample here:

http://ecomodder.com/forum/583-commercially-produced-aerodynamic-pickup-bed-cap.html

> 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.

OK. That's a start. Why kind of hardware is necessary to handle these
issues? I thought the dynamic braking and back EMF was handled by the
freewheeling diode?

> 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).

No. Bad idea. The one thing that I've learned in my research is that you'll
destroy the pack using that technique.

The whole point of PWM is that the full pack voltage is applied all the
time. That means that you'll get maximum torque as limited by the
controller and the switch and max RPM generated by the PWM ratio.

All of this is known engineering. No modern PWM controller ever does
anything but apply the full pack voltage to the motor. Soft start and rmp
are controlled by the PWM ratio, and nothing else, from my research.

> This provides both drive and regenerative braking
> in a brutal way, and is the 'old' (and tried) way of doing it.

Series wound motors. Not going to do regen braking. That energy is just
going to be lost.

> 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.

They are called Isolated Gates for a reason. What makes you think those
kickbacks are going to cross back into the gate?

> 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.

Thanks for the encouragement! ;-)

But I'm going to press on. Because at the end of the day my time is
currently worth less than my dollars. So if I can spend time solving these
problems instead of spending money, then I'll come out ahead in the end.

BAJ
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[Byron Jeff]

On Sun, May 25, 2008 at 03:35:44PM -0400, Harold Hallikainen wrote:
> When I attempt to do high power electronics, I tend to generate a lot of
> smoke and dead parts. Good luck on the controller!

Thanks. What do you find is the typical cause of the release of the "magic
smoke"?

> On the charger, I did a very simple one for an EV. The high voltage
> battery circuitry is isolated from the chassis.

That's my game plan. Did you have a DC/DC converter and 12V backup battery?
If so then I presume that negative is connected to the chassis?

> The neutral of the AC line
> is connected to the negative side of the battery string. Each phase (two
> sides of a 240VAC line or thee phases of a 3 phase wye) goes through an
> SCR, then are commoned, then go through an incandescent lamp to the
> positive end of the battery string. The SCRs allow you to turn the charger
> on and off. The incandescent lamp provides a current limit. By choosing
> battery voltage and lamp, you can charge the battery string pretty simply.
> The brightness of the lamp starts bright, then dims as the batteries
> charge.

Sounds like a plan.

> To power 12V equipment, I used a universal input switching supply (one
> that takes 90VAC to 250VAC with no line voltage switch). It can be driven
> directly by the battery string.

Again did you ground it to the chassis?

> To monitor battery condition, I did a simple PIC based monitor on each
> battery. It measures battery voltage, temperature, and current. Current is
> measured by measuring the voltage drop on the cable going to the battery
> "below" this one in the string.

Interesting. Did you do empirical measurements to figure out the current
draw on the cable?

Also how exactly did the individual PIC monitors affect the overall state
of charging? You only dumped charge current at the top of the string,
right? So if some batteries were above the set point and others were below,
then what did the overal charging system do?

How much difference would it be if there were only an overall voltage and
current of the string?

> The monitor also has a big resistor and an
> FET driven by the PIC. When the battery voltage gets too high, charge
> current is shunted around the battery (power dumped into the resistor) by
> PWMing the FET. If the battery voltage is higher than the set point, the
> duty cycle is stepped up. If the battery voltage is below the set point,
> the duty cycle is stepped down. Finally, the battery condition is reported
> over an opto isolated "Aloha" network. Each unit randomly sends a packet
> of data out its uart. The uart drives an opto where the LED is off in the
> mark condition and on in the space conditions. The phototransistor on the
> opto drives an open collector bus that is isolated from the PIC. The bus
> drives another PIC that drives a display and control system that shows
> battery condition and controls the charger (drives those SCRs).

Cool.

> This was done for a friend's EV. I ride the bus to work...

Wish I could. It would literally take 3 hours each was for me to ride the bus
between work and home. And I haven't even dealt with the pickup and
delivery of kids to school yet. Just isn't an option.

>
> Harold
>
>
>
>
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[Djula Djarmati-2]

> 3) Still searching for good availably and price. WarP 9's have 6 week or
> more lead times and run in the $1700 to $1800 ballpark.
>
> That leaves the electronics. From both a cost and integration standpoint
> there's a lot to be left desired with control electronics. The major
> subsystems:
>
> 1) PWM motor controller. Not a fundamentally complicated piece of
> equipment. Accepts a limited number of control inputs (5k throttle pot,
> brake switch) and controls via PWM a high powered switch between the
> battery bank and the motor. An example is the Curtis 1231C controller:
>
> http://www.electricvehiclesusa.com/product_p/co-1231c-8601.htm
>
> I'm almost ready to choke on the $1400 price tag.

Before doing the electronics all by yourself, I would try FANUC CNC
spindle motors and controllers like these:

http://cgi.ebay.com/Fanuc-spindle-motor-a06b-0759-b970_W0QQitemZ180243520740
(30kW at 40%ED, 22kW continuous)
http://cgi.ebay.com/FANUC-DC-SPINDLE-SERVO-DRIVE-MODEL-SP12_W0QQitemZ220237949247
(I don't know if this one fits the motor, it's just an example)

These motors and controllers are very rugged, protected from overload,
short circuit, etc. and you also get regenerative braking since they
brake by dumping energy to DC rail. The controller keeps the set rpm
automatically and goes in reverse.

The only drawback is they expect 200V 3-phase which is around 300V on DC
rail. The price for these starts at $1000 for each item.

If you make it work, you can experiment in making your own by looking
the way FANUC did it. If you go this way, let me know and I can find
some datasheets.

Djula
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[plpeter]

> 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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[Byron Jeff]

On Sun, May 25, 2008 at 05:33:15PM -0400, William Chops Westfield wrote:
>
> On May 25, 2008, at 3:33 AM, Byron Jeff wrote:
> > I'm kind of surprised that with the surge in fuel costs that a
> > thread on
> > electric vehicles (EV) had not got jump started here.
> >
> [This part of the discussion moved to [OT]]

Thanks.

> The EV idea seems fundamentally flawed to me.  At best, it doesn't
> scale to being used by large numbers of people just because the
> electric grid isn't set up to handle that additional load.

We certainly can talk about infrastructure. The two key points about
electrical infrastructure is that it's both local and distributed.
Electricity can be generated almost anywhere without an inordinate amount
of infrastructure setup. The only reason that it hasn't been done is
because the cost of alternatives (solar, wind) is much most costly than
simply buying from the grid.

But there's nothing other than cost that's keeping these supplemental
electrical generation methods from coming online. As demand goes up, cost
will go up, and as cost go up, alternatives will come into play.

>  Worse,
> you may be making less efficient use of energy (lugging all that
> extra weigh around) that is only cheaper (if it IS cheaper) due to
> artificial and perhaps temporary pricing structures for electricity
> (being able to plug in your electric at work and charge it for free
> is well within [doesn't scale, artificial, and temporary], for example.

Considering that gas is only 25% efficient with the rest being waste heat.

This article points out tank to wheel efficiency of different types of
drive trains:

http://www.memagazine.org/mepower03/gauging/gauging.html

Batteries are nearly twice as efficient as gas engines.

> IMO, EVs were originally aimed at the pollution problem, where you
> could get significant improvements by replacing IC engines in dense
> (car-wise) urban environments.  They weren't, and aren't, very good
> at addressing an energy crisis.  (This of course assumes that we have
> an energy crisis rather than just a gasoline pricing problem.)

My current stance is that the severe dependence on oil in the US is a
threat to national security. Any tital shift of the infrastructure to
something that weans the country from that dependance is a good thing.

One avenue that looks really promising is the production of biodiesel from
growing oil rich algae. This site: http://www.oilgae.com outlines the
possibility. Here is a University of New Hampshire article:

http://www.unh.edu/p2/biodiesel/article_alge.html

That suggests that we can meet all of the US transportation fuel needs with
a mere 15000 sq. miles of land growing algae.

It also outlines at the bottom of the article of the efficiency of using
electric cars for transportation.

Gas prices are never coming back. With the severe demand in India and
China, coupled with instabilities in oil producing nations, the price is
only going to get worse.

So we need a new infrastructure, be it electric, biodiesel, or ethanol.

Right now as a early adopter, I'm choosing electric.

BAJ
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[Harold Hallikainen-2]

When I attempt to do high power electronics, I tend to generate a lot of
smoke and dead parts. Good luck on the controller!

On the charger, I did a very simple one for an EV. The high voltage
battery circuitry is isolated from the chassis. The neutral of the AC line
is connected to the negative side of the battery string. Each phase (two
sides of a 240VAC line or thee phases of a 3 phase wye) goes through an
SCR, then are commoned, then go through an incandescent lamp to the
positive end of the battery string. The SCRs allow you to turn the charger
on and off. The incandescent lamp provides a current limit. By choosing
battery voltage and lamp, you can charge the battery string pretty simply.
The brightness of the lamp starts bright, then dims as the batteries
charge.

To power 12V equipment, I used a universal input switching supply (one
that takes 90VAC to 250VAC with no line voltage switch). It can be driven
directly by the battery string.

To monitor battery condition, I did a simple PIC based monitor on each
battery. It measures battery voltage, temperature, and current. Current is
measured by measuring the voltage drop on the cable going to the battery
"below" this one in the string. The monitor also has a big resistor and an
FET driven by the PIC. When the battery voltage gets too high, charge
current is shunted around the battery (power dumped into the resistor) by
PWMing the FET. If the battery voltage is higher than the set point, the
duty cycle is stepped up. If the battery voltage is below the set point,
the duty cycle is stepped down. Finally, the battery condition is reported
over an opto isolated "Aloha" network. Each unit randomly sends a packet
of data out its uart. The uart drives an opto where the LED is off in the
mark condition and on in the space conditions. The phototransistor on the
opto drives an open collector bus that is isolated from the PIC. The bus
drives another PIC that drives a display and control system that shows
battery condition and controls the charger (drives those SCRs).

This was done for a friend's EV. I ride the bus to work...

Harold




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[Byron Jeff]

On Sun, May 25, 2008 at 06:17:40PM -0400, Olin Lathrop wrote:
> Byron Jeff wrote:
> > Paying $1400, or even $1000,
> > doesn't
> > make a lot of sense when the parts can be assembled for $150.
>
> Try the real world for a change.  You've clearly never designed a commercial
> product and dealt with it all the way into production.

Hobbyist. Not trying to sell it.

>
> Parts                                      150
> Knowing which parts to put where           100
> Assembly, test, fallout, and repair         50
> Paying back cost of setting up produciton  200
> To pay for support when you call after
>   having done something stupid             300
> To cover liability costs when you do
>   something stupid but blame us anyway     100
> Cost of capital to get into this business   50
> To pay back regulatory compliance and
>   testing costs                            100
> To make a living                           300
> ----------------------------------------------
> Total                                   $1,350

I understand each and every one of those costs. But as someone who has the
wherewithal to assemble and program it myself, everything after the first
three or possibly four items have no meaning to me.

I didn't say that charging $1400 wasn't reasonable. I said that my paying
that price wasn't. Two completely different things.

I have no problems paying for houses, cars, appliances, flooring, and the
like for exactly the reasons you outline above.

But when it's an item as a hobbyist I can actually put together myself?
That's a whole nother argument.

BAJ
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[William "Chops" Westfield]

On May 25, 2008, at 3:33 AM, Byron Jeff wrote:
> I'm kind of surprised that with the surge in fuel costs that a  
> thread on
> electric vehicles (EV) had not got jump started here.
>
[This part of the discussion moved to [OT]]

The EV idea seems fundamentally flawed to me.  At best, it doesn't  
scale to being used by large numbers of people just because the  
electric grid isn't set up to handle that additional load.  Worse,  
you may be making less efficient use of energy (lugging all that  
extra weigh around) that is only cheaper (if it IS cheaper) due to  
artificial and perhaps temporary pricing structures for electricity  
(being able to plug in your electric at work and charge it for free  
is well within [doesn't scale, artificial, and temporary], for example.

IMO, EVs were originally aimed at the pollution problem, where you  
could get significant improvements by replacing IC engines in dense  
(car-wise) urban environments.  They weren't, and aren't, very good  
at addressing an energy crisis.  (This of course assumes that we have  
an energy crisis rather than just a gasoline pricing problem.)

BillW

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[Gerhard Fiedler]

Byron Jeff wrote:

>> 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.
>
> They are called Isolated Gates for a reason. What makes you think those
> kickbacks are going to cross back into the gate?

At least through gate capacity, possibly also ground effects.

Gerhard

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[Olin Lathrop]

Byron Jeff wrote:
> Paying $1400, or even $1000,
> doesn't
> make a lot of sense when the parts can be assembled for $150.

Try the real world for a change.  You've clearly never designed a commercial
product and dealt with it all the way into production.

Parts                                      150
Knowing which parts to put where           100
Assembly, test, fallout, and repair         50
Paying back cost of setting up produciton  200
To pay for support when you call after
  having done something stupid             300
To cover liability costs when you do
  something stupid but blame us anyway     100
Cost of capital to get into this business   50
To pay back regulatory compliance and
  testing costs                            100
To make a living                           300
----------------------------------------------
Total                                   $1,350


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[Sean Breheny]

I have to agree that there is a LOT more involved in this than you
seem to be taking into account, Byron. High power motor drive
electronics is NOT easy to design. Consider this for a moment: if you
want to keep your heatsinking requirements to a minimum, you will need
to turn the IGBTs on and off very fast. This means that the current in
some parts of the circuit will have rise/fall times of something like
100 ns. Now look at the di/dt which you have in 600 amps switching in
100 ns. That's 6 gigamps per second. If you have a 1 nanohenry stray
inductance (which is nothing), you will see a 6V drop across it during
this turn on/turn off transient. 6V is easily enough to cause any one
of a number of bad things to happen: destruction of digital I/O,
spurious triggering of IGBT gates, IC latchup, etc.

What tends to happen in this arena is that you pile a whole bunch of
FETs or IGBTs together and expect it to work and a whole string of
tough problems spring up due to stray inductance, gate capacitance,
etc. Since a sudden glitch can cause a short circuit (if both high and
low side IGBTs are turned on at the same time), you can destroy your
IGBTs in a fraction of a second.

I once had a motor driver prototype running on a bench when suddenly
there was a tiny "tink" noise. Before I knew what was happening, the
fuse inline with the battery pack burst into two 4-inch long blue jets
of flame. After I disconnected the battery, I found that a whole bunch
of the FETs were toast. Something had turned on high and low side FETs
together, they instantly failed shorted, which caused something like
1000 amps to flow, which exceeded the interrupting rating of my fuse,
caused it to arc over, carbonizing and then igniting.

If you want a learning experience, then build it yourself. If you want
to save money, buy the stuff new or used. You will go through several
sets of parts in your development and it will end up being 2x the cost
of the whole thing new.

Sean


On Sun, May 25, 2008 at 6:17 PM, Olin Lathrop <olin_piclist@...> wrote:

> Byron Jeff wrote:
>> Paying $1400, or even $1000,
>> doesn't
>> make a lot of sense when the parts can be assembled for $150.
>
> Try the real world for a change.  You've clearly never designed a commercial
> product and dealt with it all the way into production.
>
> Parts                                      150
> Knowing which parts to put where           100
> Assembly, test, fallout, and repair         50
> Paying back cost of setting up produciton  200
> To pay for support when you call after
>  having done something stupid             300
> To cover liability costs when you do
>  something stupid but blame us anyway     100
> Cost of capital to get into this business   50
> To pay back regulatory compliance and
>  testing costs                            100
> To make a living                           300
> ----------------------------------------------
> Total                                   $1,350
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> [phone].  Gold level PIC consultants since 2000.
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> http://www.piclist.com PIC/SX FAQ & list archive
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[Russell McMahon]

> ... which caused something like
> 1000 amps to flow, which exceeded the interrupting rating
> of my fuse,
> caused it to arc over, carbonizing and then igniting.

A good but expensive lesson to learn. This is where the
reason that "HRC"* fuses exist and are specified, or
required under certain standards.

One discussion. Much more available on HRC.

        http://www.panickker.net/article5.htm

        Russell


* High Rupture Capacity.


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[Spehro Pefhany]

At 12:04 PM 5/25/2008, you wrote:


>They are called Isolated Gates for a reason. What makes you think those
>kickbacks are going to cross back into the gate?

*Insulated* gates, not isolated gates.

> > 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.
>
>Thanks for the encouragement! ;-)
>
>But I'm going to press on. Because at the end of the day my time is
>currently worth less than my dollars. So if I can spend time solving these
>problems instead of spending money, then I'll come out ahead in the end.
>
>BAJ

In knowledge, anyhow. Assuming you have the time, background knowledge,
test equipment and dollars to get all the way to a reliable system.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@...             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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[Byron Jeff]

On Mon, May 26, 2008 at 11:35:03AM -0400, Peter wrote:
> Byron Jeff <byronjeff <at> clayton.edu> writes:
> > My goal is to build something that I can afford. I battle with the guys on
> > the DIYEV list all day long about investing tens of thousands of dollars
> > into lithium batteries. But it's an investment that doesn't make sense to me.
>

> So don't buy lithium. But why buy an immense golf cart battery stack? It
> will work for sure,...

I presume you mean why not buy the golf cart battery stack?

That's exactly my game plan.

> > Can't store a battery bank at work, which is the only logical place to
> > swap. The bottom line is that I'm stuck carrying the bank around.
>

> Why is it the only logical place to swap? And why swap if you only have
> one set? Swapping is an idea to keep in mind. Today you swap lead acid,
> tomorrow lithium or who knows what. You have to start somewhere, why not
> start small and see where it is going.

You probably needed to keep the context of the poster that asked the
question. Let me see if I can add it back in...

Here it is...

---------------------------------------
> 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.
---------------------------------------

As I stated, not an option.

>
> > > Available data suggests 20-100 km range for curb weight << 1 ton.
> >
> > I'm well aware. The challenge is that to carry enough lead to get a useful
> > range, you exceed the GVWR of the vehicle.
> >
> > Trucks are designed to carry that kind of weight.
>

> True, they are also designed not to drive very fast and fuel efficiency
> was not quite so high on the priority list for US pickups afaik. Most
> electric cars aren't speed cars either.

They can be if you make them light enough. But not my priority.


I'll tackle the rest of the post later.

BAJ
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[plpeter]

Byron Jeff <byronjeff <at> clayton.edu> writes:
> My goal is to build something that I can afford. I battle with the guys on
> the DIYEV list all day long about investing tens of thousands of dollars
> into lithium batteries. But it's an investment that doesn't make sense to me.

So don't buy lithium. But why buy an immense golf cart battery stack? It will
work for sure, in fact there is an ancient (circa 1900) electric truck (pickup)
in the local technical museum. The bed is paved with lead acid batteries and
there is a cover above it so it can take some cargo too. The entire body and
cabin was made of wood, as expected, and the batteries were not 100Ahish from
the size. It has been a long time since I saw it, I was a kid at the time.
 
> Can't store a battery bank at work, which is the only logical place to
> swap. The bottom line is that I'm stuck carrying the bank around.

Why is it the only logical place to swap? And why swap if you only have one
set? Swapping is an idea to keep in mind. Today you swap lead acid, tomorrow
lithium or who knows what. You have to start somewhere, why not start small and
see where it is going.
 
> > Available data suggests 20-100 km range for curb weight << 1 ton.
>
> I'm well aware. The challenge is that to carry enough lead to get a useful
> range, you exceed the GVWR of the vehicle.
>
> Trucks are designed to carry that kind of weight.

True, they are also designed not to drive very fast and fuel efficiency was not
quite so high on the priority list for US pickups afaik. Most electric cars
aren't speed cars either.
 
> OK. That's a start. Why kind of hardware is necessary to handle these issues?
> I thought the dynamic braking and back EMF was handled by the freewheeling
> diode?

What freewheeling diode? Surely you know that most design topologies will not
scale for a power level 1000 times greater than that of the original design?
Please locate the relevant course curriculum at your university (you are on an
edu domain) and see the reading list there for recommended articles and books.

Try Google with:

  electric traction power electronics site:.edu filetype:pdf

for >10k links.

> > 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).
>
> No. Bad idea. The one thing that I've learned in my research is that you'll
> destroy the pack using that technique.

Not if the voltage equalization devices work as deisgned (i.e. in *both*
directions).
 
> Series wound motors. Not going to do regen braking. That energy is just
> going to be lost.

Too bad. Literature seems to indicate compound or parallel motors with separate
excitation are best for traction if using simple pwm controllers as you intend
to use.
 
> They are called Isolated Gates for a reason. What makes you think those
> kickbacks are going to cross back into the gate?

There is no need for the kickbacks to cross into the gate. You will have
something like 200 Amps at 150 Volts switched (at pwm frequency if you do it
your way) into  a loop of wire at least a meter long with a coil of several
Henrys at the other end (the motor) inside a reflective metal box, with
harmonics into VHF and UHF. That will put enough volts into circuit board
tracks nearby to glitch almost anything even without pwm.
 
> Thanks for the encouragement!

I just said what I know. I doubt whether the 'expensive' controler makers break
even when the market is slow (like it seems to be all the time for some
reason).
 
> But I'm going to press on. Because at the end of the day my time is
> currently worth less than my dollars. So if I can spend time solving these
> problems instead of spending money, then I'll come out ahead in the end.

That's a good excuse to buy, borrow most of the relevant books you can lay
hands on. There is no point in rediscovering hot water or repeating other
people's mistakes. You could make your own ^^ . Besides $100 in (used) books
should get you further than $1600 in batteries at this time imho.

$0.001
Peter
 

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[Harold Hallikainen-2]

> On Sun, May 25, 2008 at 03:35:44PM -0400, Harold Hallikainen wrote:
>> When I attempt to do high power electronics, I tend to generate a lot of
>> smoke and dead parts. Good luck on the controller!
>
> Thanks. What do you find is the typical cause of the release of the "magic
> smoke"?
>

I think the chief cause is inexperience in design of high power circuitry.
I used to work in broadcast and could keep 20kW stations running, bud did
not have to design the transmitters.


>> To power 12V equipment, I used a universal input switching supply (one
>> that takes 90VAC to 250VAC with no line voltage switch). It can be
>> driven
>> directly by the battery string.
>
> Again did you ground it to the chassis?

The high voltage string was isolated from the chassis. The negative side
of the 12V was connected to the chassis.

>
>> To monitor battery condition, I did a simple PIC based monitor on each
>> battery. It measures battery voltage, temperature, and current. Current
>> is
>> measured by measuring the voltage drop on the cable going to the battery
>> "below" this one in the string.
>
> Interesting. Did you do empirical measurements to figure out the current
> draw on the cable?

Yes... A clamp on DC ammeter was used to come up with a scaling factor.


>
> Also how exactly did the individual PIC monitors affect the overall state
> of charging? You only dumped charge current at the top of the string,
> right? So if some batteries were above the set point and others were
> below,
> then what did the overal charging system do?

There was one of these monitor and charge balancing boards on each
battery, so power was dumped on each battery that had excessive voltage.
Something I did not mention before is that the circuit boards are mounted
on the negative side of each battery. I used a TO-220 resistor for the
power dump. The thermal path heat sunk the resistor to the battery
negative terminal, since it has a lot of mass.

Harold

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[plpeter]

Jeff, please take a look at this document. It contains several interesting
items, including a drive scheme and DOT road testing schedules:

http://scholar.lib.vt.edu/theses/available/etd-102497-12366/unrestricted/final.pdf

good luck and keep us posted,
Peter

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[Byron Jeff]

On Mon, May 26, 2008 at 07:50:14PM -0400, Crist?v?o Dalla Costa wrote:

> On Sun, May 25, 2008 at 1:04 PM, Byron Jeff <byronjeff@...> wrote:
>
> > > This provides both drive and regenerative braking
> > > in a brutal way, and is the 'old' (and tried) way of doing it.
> >
> > Series wound motors. Not going to do regen braking. That energy is just
> > going to be lost.
> >
>
>
> Then why bother at all?

Because the design is a balance of cost, efficacy, complexity, and range.
It takes quite a bit of infrastructure, and therefore cost and complexity,
to implement regen braking. You have to have a certain type of motor (AC or
shunt wound), you have to have a controller than can handle it. You have to
have improved battery management systems.

> A significant part of the energy used to move cars
> and trucks ends up as waste heat in the brakes. IIRC something in the order
> of 60% -- specially with a heavy vehicle in city driving where speeds < 80
> km/h and aerodynamic drag is not the dominant factor.

All true.

> Now factor the increased weight of the lead batteries you want to carry over
> the empty truck/car and you just waste that much more energy. Consider how
> heavy the batteries will be and the waste accelerating and stopping that
> mass that will just end up as heat on the brakes.

I'm well aware.

> I'm sorry, but if you're going to all that effort to make an economical
> vehicle, either go all the way and do the regenerative braking, or don't.

Don't do regen braking, or don't do the vehicle?

> A
> half-assed solution is probably going to be a headache in the long run.

What headache? As you stated the wasted energy will be burnt on the brakes.
What you lose in efficiency, you gain in spades in simplicity and lower
costs.

> I have a pdf of a paper of the Catholic University of Chile where they
> converted a truck to electric power using batteries and a ultracapacitor
> bank for regenerative braking. I don't know if I can post it, but just
> google "regenerative braking university chile" and a downloadable pdf will
> be among the first links.

I'll certainly take a look for it.

BAJ
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