This ignores, of course, the insanely higher rolling resistance as your tires push an unending wall of water out of the way Your front defogger *WILL* use a massive amount of power, though, as it engages the air conditioning compressor when in use. You can override it by forcing A/C off, but then it's not nearly as efficient at clearing your window.

 

You're absolutely right about the issue of friction/water resistance, of course, Chris, but I stand by the assertion that using power for all the accessories drains the battery enough to be noticeable in the mpg readings you see. And think about it in terms of energy usage. The car has to produce, by whatever means, the energy you use to do all the things you car does, from rolling the car forward to rolling up the windows. If the car produces a particular amount of energy, and some of it is diverted to other things, there is less remaining for rolling the car forwards. The other energy, for headlights and radio etc., doesn't come from nowhere. So it makes sense that you sometimes see an effect. If you don't see it, then presumably it's mostly because you aren't looking for it (or tracking what your mpg is in the absence of any other energy use- if you always drive at night or leave your headlights on during the day, it's not going to be possible to measure the energy lost to headlights, for instance).

 

But do you know which battery powers such devices?

My though would be it is the standard one under the hood and not the hybrid one behind the seat.

My theory is if it is the standard car battery that is powering them all, it shouldn't affect the mpg. I could of course be 100% wrong being so new in this world

 

It is the standard 12 V battery that powers those various accessories... but that's not really a relevant point. At the end of the day the power for everything your car does (and that's just as true for a gas-only car) comes from the energy in the gas. So if something is using more power, anywhere in the car, it has at least the theoretical capability to impact mileage (whether you'd actually ever see an effect over the noise is another issue)...

 

OK, let's look at this in greater detail then.

The IMA system is comprised of several modules, one of which the "DC-DC module", plays a very important role in powering up ALL the systems in the car. Why?
Because on the HCH-I, power flows and follows the following path:
1-Electrical generation (HV) at the IMA Motor
2-Electrical storage (HV) at & though the BCM module (Battery control module)
3-High Voltage (148V) is then provided to the MCM (motor control module) for assist operations.
4-High Voltage (148V) is provided to the DC-DC which then "powers-up" the 12V circuits.

Now, what I am saying is that your car has two power circuits (or power sub-systems, the High voltage, and the low voltage 12V system).
The 12V battery is at the very end of the 12V power system and provides only very temporary and limited usable power to operate all the devices tapping the 12 Volt circuit. Additionally, the 12V battery derives its charge from the 12V subsystem which is provided upstream by the DC-DC module.

All sorts of devices, primarily legacy devices (fan blower, lights, wiper motors, sound system, power steering, etc) are driven by the 12V subsystem. And to be correct, these all run not from the 12V battery, but by the "power" provided by the DC-DC module.

One other hybrid specific system is also powered up by this 12V subsystem: The IMA power unit modules. Yes, that is why the car wont even start if the 12V battery is dead. This is because the IMA system has no way of powering up since the IMA battery is totally off-line and not powering anything when the vehicle systems are off.

Of course, if the DC-DC (or the BCM, IMA battery, etc) were to fail or go off-line, the power would then be drained from the 12V battery. Makes sense?


Cheers;

MSantos

 

That all does make sense....

These cars are just different LOL


One of the first things I want to change is all the outside lights to LED. It should help a little and/or even it out because we have a GPS plugged in often

 

Indeed, lowering the power drain on the 12V subsystem is a significant key in attaining higher FE figures (at least for those of care). So if you succeed in removing the incandescent factor of your current lighting by replacing it with LED bulbs you'll be gaining a small but measurable improvement in FE.

The same goes for other higher drain devices such as Audio equipment (amps and bass) and power inverters and so on. When these devices are operating, they literally rob you of the precious electrical energy that would otherwise be directed to propulsion purposes. The increased power demands also cause the DC-DC to work a little harder and as a result stressing the thermal management of the IMA power unit. Amazing... how all is connected, isn't it?

Cheers;

MSantos

 

Thank you, msantos, for providing a detailed and thoughtful explanation for this. It's easy to say 'the energy has to come from somewhere!' like me, but it's much more convincing and comprehensible when you can trace the progression step-by-step.

 

This begs the question... since I haven't been able to really follow the serpentine belt around everywhere, do we even have an alternator, or do the spark plugs fire via HV-derived power?

 

No, we do not have an alternator... which means that if the IMA system has failed or is off-line then you'll have to keep charging the 12V battery with an external charger.

On the other hand, the HCH-I and HCH-II do have a small (legacy) starter that gets triggered on when a fault condition exists with the MCM... or it is too cold for the MCM/BCM to operate. In these situations it is quite surprising for the HCH to noisily "crank" like most other cars do.

The ignition coils that drive the 8 spark plugs provide the step up from the 12V subsystem and not the High voltage system. While it may appear a little lossy due to the 2 downstream conversions, it is still the best redundant/fail-safe path especially when the IMA is operating in restricted mode.

Cheers;

MSantos