what charges, what powers what?

The 12volt only turns on the computers in the system, once on, the main battery takes care of everything and the engine charges both batteries. The 12 volt will be used when the car is in Acc mode, and you can run the lights, radio, etc., but not for very long, most on this board will tell you never to use acc mode.

 

The Wikipedia article is quite comprehensive:
Hybrid Synergy Drive - Wikipedia, the free encyclopedia

 

When the car is "off" the HV battery is isolated from the rest of the system by contactors (basically big relays). Its ground is also isolated from the 12V / chassis ground to reduce the chances of an inadvertent and potentially damaging / dangerous short between the 240V lines and the chassis ground. Most everything in the car is powered by the 12V power domain. In ACC, and ON mode the 12V is supplied by the Aux battery. When going to "ready mode" ("starting the car") the HV ECUs come up on the battery supplied 12V and run a series of diagnostic tests on the HV system looking for any potentially dangerous faults (shorts/leakage from HV + to -, or HV + or HV - to chassis ground, battery state of charge and balance, etc). If everything looks ok, the contactors are closed and the HV system is energized connecting the HV battery to the inverter. The inverter contains a dc:dc converter that feeds up to 100A of 12V power onto the 12V supply domain, charging the Aux battery and running all the 12V electronics (like an ICE driven alternator in a traditional vehicle). The inverter also contains the motor speed controller (and a voltage boost converter) for the drive motor MG2, a speed controller for the AC Compressor, and a bidirectional controller for MG1 used to start/spin the ICE as well as provide regenerative braking and/or generate electrical power from the ICE. The battery ECU tracks the amount of energy going into and out of the HV battery (by "coulomb counting") and reports its current state of charge (SOC) and max charge/discharge current for current conditions to the Hybrid ECU. The hybrid ECU instructs the inverter to take energy from or put energy back into the HV battery according to a complex function of speed, gas pedal postion, various temperatures, current battery SOC and charge/discharge limits, amongst other things. Its goal is to maximize the efficiency of the system by deciding how much ICE power and electric drive or generation to use to meet the drivers requests, and maintain the battery within safe operating parameters. It also continues to monitor a variety of safety related parameters from various sensors and controllers during operation and will shut the HV system down if a fault is detected.

So to answer your specific questions:
1) The dc:dc converter is the only direct connection between the 240V and 12V power domains. The battery ECU is powered by the 12V, and has specially isolated connections into the HV battery for monitoring purposes.
2) The 12V Aux battery is charged by the dc:dc converter, the HV battery is charged by MG1 (either from braking or spun by the ICE).
3) The Aux battery can be charged with most AGM compatible 12V chargers or maintainers. There are HV "grid chargers" on the market that can be used to charge/condition the HV battery.
4) The HV battery is connected only to the inverter via the contactors.

Rob

 

Same as what Rob said (!)

 

I would add to #4: I believe the air conditioning compressor is powered off the HV system as well. I can't think of anything else that is directly powered from the HV side; only indirectly through the DC-DC converter to the 12V side.

 

Now you have more information than you will ever need.....

 

If you want more.......or to find it worded differently........do a search or 3 on here.
It's been discussed before, a really LOT of times.

 

It is, but not directly from the battery. The inverter contains the speed controller for the compressor.

Rob

 

sorry, I tried to place a link it did not work out well.