Help: technical question on Hybrid battery

[tode]

Evening all,

Back in September I picked up our new E300e which, on the whole, we both like . . .
However I've been trying to work out how the 400V and the 12V batteries work together. I've just found out that when the car is being charged up, the 12V battery is automatically put on charge as well (which seems logical).

I was told that the car has no starter - apparently it's the electric motor that acts as the starter for the petrol engine. Fine, but does anyone know what happens if you run the 400V battery down to zero - how do you start the petrol engine?

Been searching on the Interweb, but have found no documents explaining how the system works. Does anyone know of a source for info ?

 

[KennyN]

Is it possible that the run down battery would show a "virtual" zero reading , which would leave something in reserve to start the vehicle.

There is always one way to find out

K

 

[Ted]

I can only comment for Toyota/Lexus but I think that Mercedes will be similar.
There is no starter motor or alternator in the traditional sense. There is a motor/generator attached to the crankshaft.
No solenoid, no pinion, no engagement fork. no brushes.
To start the engine, a high voltage AC current is applied to the motor from an inverter - supplied by the DC high voltage battery. Because this is a direct connect and mounted effectively to the crankshaft this is a very smooth action and hardly noticeable.
When the engine is running, the motor/generator supplies a high voltage AC current to the inverter. This is rectified to DC and is used to charge both the high voltage battery and the 12 volt battery (via the inverter)
This means that the 12 volt battery is only really used to bring the hybrid system to a state of readiness, and to supply voltage/current to lights and other ancillaries when the hybrid system isn’t active.
The high voltage battery will never in theory run down to zero (or to 100%) there will usually be a minimum of 20% before the engine kicks in to charge it.
With the hybrid system ‘off’ the battery is fully isolated and there can be no parasitic drains other than self discharge.

 

[tode]

Thanks for the replies - that's more-or-less how I had understood things.

As Kenny says, there's one way to find out what happens when the 400V battery is empty . . . it's just that I'd prefer some-one else to try it out !

Anyone know of any technical documents concerning the PHEVs ?