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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