I hope Toyota has done their homework in designing components to handle the high capacity high voltage DC. I have a piece of laboratory research equipment where 20 lead acid 12 volt batteries are feeding a 10 amp load. Shutting down this equipment takes nothing less than a rather hefty design DP porceline knife switch. Openning that switch puts the fear of God into any operator. Hissing, blinding copper green arcs requiring about a 1/2" gap on each pole to break the circuit; pitted contacts; hungry evil thing! The voltage is in the same range as the Prius NiMH pack; not sure about the capacity which is only 7 AH in the lead acid source. Make no mistake, DC is a whole new ballgame compared to AC. Point being, what kind of horror stories can we expect from freak accidents, salt water & dirt contaminations, component failures, or if you're unlucky enough to find yourself submerged in a very deep puddle?! Actually, I have every faith in Toyota's usual superb engineering, and can't wait to get my hand on my new Prius, expected in August. Still, food for thought ...

One of the key components of the Hybrid system is an inverter that converts DC to AC current. Look at your maintenance manual, and you'll find that a inverter coolant change is a regular service item, leading one to believe Toyota had a pretty good idea on how to design a robust system. I would imagine that high current switching to the motor is done on the AC side for the exact reasons you mentioned.<br>Let the sparks fly! (too bad they can't come out the tailpipe to strike fear into the hearts of mere combustion powered vehicle operators!)<br>Harald

"porcelain" "opening" .. ugh, where's the spell checker ...

Switching of the DC voltage is done by BIG power transistors called IGBT or Insulated Gate Bipolar Transistors (no, I don't really know what that means). These are truely amazing wonders of modern science, able to switch huge voltages and amps on and off 10's of thousands of times per second under the control of a tiny (5V?) signal!!! Not only that, they're extremely efficient, going from "close" to infinite resistance while off to "close" to zero resistance while on. No arcing occurs inside these transistors (if it did, they would be destroyed very quickly).<br><br>Under all but the most dire of emergency situations, the THS computers make sure all the IGBTs are turned off before connecting or disconnecting the HV DC battery via the relay. So the relay never has to be concerned with arcing either since there is never a circuit when it is halfway between off and on.<br><br>Finally, as an additional safety measure, both sides of the HV battery are isolated from vehicle ground. The computers constantly monitor this condition and will disconnect the relay if either side ever makes a connection to ground. So even if you throw your Prius into the ocean, bathing its HV connectors in salt water (kids, don't try this at home), the relay will disconnect the battery.<br><br>Of course after that, the battery terminals themselves would probably start doing a lot of underwater electrolosis, filling the trunk with a convenient bubble of hydrogen and oxygen which would float the Prius back up to the surface, allowing the occupants to be rescued. That's a, ah say that's a joke, son!<br><br>Robert Snyder<br>NJ-PIKACHU

Notice that someone in the other group measured the battery current with a Hall-effect probe and discovered that it peaked around 100 Amps. At 280 volts, that is *28 Kilowatts*, truly an awesome amount of power. This is on the same order of magnitude as an entire single-family house peak power use.<br><br>On the other hand, I'm not sure DC is all that much worse than AC. Edison suggested calling the electric chair the "Westinghouse" after the proponent of AC power (Edison favored DC).<br><br>But regardless, this much power is nothing to fool around with. As Robert Snyder pointed out, there should be no big grungy arcs since the only mechanical disconnect happens when there is little if any current flow anyway.<br><br>Burns

In Message 5409 : casagiannoni mentioned:<br>&gt; I hope Toyota has done their homework in <br>&gt; designing components to handle the high <br>&gt; capacity high voltage DC.<br>&lt;snip&gt;<br>&gt; Actually, I have every faith in Toyota's usual <br>&gt; superb engineering, and can't wait to get my <br>&gt; hand on my new Prius,<br>In the meantime, get thee a "New Car Features" and "Electrical System" books.<br>The HV pack is COMPLETELY isolated from the chassis and there is a VERY sensitive GFI on the lookout.<br>There is a step-start relay system to control start "surges" and also isolate BOTH sides (+ and -) of the pack when they drop out.<br>In addition, the HV fuse is in the middle of the string, along with the manual disconnect.<br>They appear to have ALL the bases covered.<br><br>Still in love at 12,000+ miles,<br>Bill Powell - NJ HALFGAS<br>(Prius: Just Drive It!)