How does the Prius charge its 12V battery?

There is a 201 v DC to 12 v DC inverter in the Inverter, (silver box in engine compartment) which mostly converts the 201 v HV Battery voltage to the 550 v M/G voltage.

 

No.

No.

Unfortunately, no. Fortunately you found Priuschat where you'll learn lots of interesting things about your new vehicle!

As Jimbo has already stated, there is a DC to DC voltage converter that draws from the 201V battery and supplies the 12V system. The 12V battery charges from this while the vehicle is in "ready" mode.

When the vehicle is in ACC mode or is turned off, the 201V battery is disconnected, and the 12V system runs entirely from the 12V battery. If you accidentally leave an interior light on and drain the 12V far enough, it won't be able to provide enough power to boot up the computers and close the relays to re-connect the 201V battery.

The Prius can be "jumped" from another vehicle, but be extra careful not to get the connections wrong. There have been reports of expensive electronic components needing to be replaced from connecting jumper cables incorrectly.

The DC to DC converter isn't really designed to provide the amperage needed to turn the starter motor on a non-prius vehicle. It is best not to try to jump another vehicle from the Prius.

 

It is often interesting how different the Prius is underneath, not better or worse, but different, yet you just get in a drive it like normal.

 

Interesting indeed, but I would say better different. In regards to the alternator vs. smps, clean output power is favoured.

 

Speaking as a EE who's seen his own fair share of busted parts, "nothing in it to wear out over time" isn't quite true. Yes, brushes and such will wear, but, unless somebody tells me differently, most modern alternators don't have brushes, anyway. They have a small permanent magnet in there somewhere; when the alternator spins, this small magnet creates an AC voltage/current which is fed into a regulator. The regulator then feeds a regulated version of this current into the main windings of the alternator; the more current into the windings, the bigger the main current out of the alternator. That AC waveform is then rectified and fed over to the battery and such.

So, from a mechanical point of view, it's not like the old DC generators of yore that required regular brush replacements. It is a piece of rotating machinery, however, so there's another set of bearings and such that can fail. If I had to guess, I'd guess that the bearings probably have a higher failure rate than the rest of the electronics in the system. However, this then leads us to electronic failures.

In no particular order:

1. Silicon/germanium parts are made on large silicon wafers, with many, many parts being made on said wafer. A diamond saw is used to slice and dice the parts before packaging. However, before that happens, the components, built on the underlying crystalline silicon (or germanium) wafer are built with photoetching and diffusion of various chemicals and metals onto the wafer. There are all sorts of things that can go wrong with this process:
   1. The silicon crystals aren't perfect. Despite best efforts, there are yea many defects per square inch, where "yea" varies from single digits to the 100's or so. These spots can leak current and are entirely random.
   2. Errors in the masking and photoetching. It happens. More leakage points.
   3. Interesting issues with the laying-down of the (usually) aluminum conductors on the top of the wafer. Wafers aren't precisely flat on top, no matter what the eye says. At the scale that wafers are made, aluminum traces that are, say, 10 microns thick might go over steps down or up in the silicon that are 20 or 30 microns deep, leading to thinning in the aluminum.
   4. Dust particles. Despite all those bunny suits those guys wear, dust lives. Not good for silicon.
2. After the wafer is built, manufacturers usually 100% test the individual components on the wafer with a stepper probe test. The (obviously) bad ones get marked with a red dot and saved in a handy computer database.
3. Slice and dice the wafer and toss the bad ones.
4. Attach the die to packages. This leads to more fun: Little bitty bonding wires go from the lead frame of the package to square aluminum spots on the die. Mostly those bond wires are reliable; sometimes they're not. Yes, there are G-force limits on silicon components, and its those bond wires, how well they're attached, and any strange things like vibrations that are an issue. You haven't lived until you've calculated out the acceleration stresses on an IC at 10,000 Hz and a millimeter of movement.
5. Electrostatic discharge. You people may have thought it funny, scuffing your feet across the carpet, then zapping the nearest sibling with a spark. It sure doesn't do silicon any good, blowing holes in ICs wholesale, despite Human Body Model ESD-resistant pins. But ESD can also be near invisible. All it takes is one ungrounded handling tray in the wrong spot and a whole bunch of parts can have more V and I than they can handle. The bad part about this is, once one has partially melted the inside of the chip a bit, failures may come anywhere from immediately to 5 years down the line as a result. Nasty. Detectable, usually, but only if one is doing 100% testing of the components, NASA-expensive style.
6. Attach the chip to a board. This can lead to more fun: Bad solder joints, corrosion, pins-bent-slightly-out-of-spec-and-therefore-not-making-contact, and lots of other fun.

So: A fair number of the above defects are affected by temperature. Suppose one has a thin spot in the aluminum: Push significant amounts of current density through a thin piece of aluminum and the passing electrons have enough mass to push the atoms away, leading to Aluminum Migration. (real term, no kidding.) Less aluminum means more resistance, the spot gets hotter, the migration picks up, and three years down the road, blooey. (another technical term. )


Defects in the silicon, registration of the solder masks, and other fun stuff often leads to leakage. Leakage usually gets worse with temperature, which is one reason a great many industrial grade electronic systems get stuck in a heat tank for 24 hours to get rid of the weak sisters. And even with that, Murphy rules: Anything that can go wrong, or can go wrong later, will. Remember: Those defects (dust, silicon) are truly random, pernicious, and don't always cause defects right off.


So, high power, hot components tend to die early on. They do have the advantage of having significant size, so, if, for example, one gets a defect in the collector of a transistor, perhaps the leakage current isn't significant enough to cause problems.
ICs with zillions of transistors have transistors tiny enough that, usually, a single defect takes out at least one transistor. Speaking as a guy who's had to design the test vectors for ICs, we aim (but usually miss) making a part 100% testable. We can usually achieve 95%-99%. However, what that means is that with, say, a 1% "can't test this" limit, that, of every 100 faulty parts, one of those will escape into the wild. Functional test can catch more of these parts, perhaps only 1% will escape that: But that means 1 in 10,000 faulty parts will escape. And you wonder why IC manufacturing engineers get ulcers?


Even so, it's possible to do something about these kinds of problems. IC layout, process improvements, and so on can get you components that have failure rates of 1e-8 or 1e-10 out-of-the-box, which is probably on the same order as, say, bad pistons in the engine. Good (expensive) testing helps, too. Buying parts with Really Good, Proven qualification data helps, too, and keeping a Real Close Eye on Bad Lots is another thing companies do.


Now that I think of it, the last time I had a bad generator was on my old '71 Beetle, and that did use brushes. Every car I've owned since then has never had a bad alternator. That's just me, but my suspicion is that alternators are pretty reliable. Other than the bearings, of course.


KBeck