Ah, most helpful -- so I was thinking right about power flow (where the current is coming from) during a jump but wasn't factoring in tolerances for current handling of the involved parties like the DC-DC module.

This also helps me think more about an old hobby, custom car stereo -- I've often wondered about how much reserve capacity, in terms of amperage, the HCH system "has." I know a subwoofer is a dealer-installable option, so obviously there's some headroom there, but I've wondered how much beyond a small sub you can go before getting into debt on current. Or, for instance, how would the HCH handle (or not) a second (12V) battery. The world away from alternators and simple DC sure is different.

cheers --
doug

 

Doug, this is a wonderful point you brought up.

More than any other car I know of, the HCH-II is a textbook exercise in "balance" engineering. Everything was literally designed to operate within rather small tolerances and even though there is some headroom, it rarely allows for lossless deviations (small changes have big consequences). That is why a well setup HCH is so critical to optimal performance.

This is why I absolutely avoid larger loads on the 12V subsystem. In fact, I even go as far as supplementing even the smallest loads through other active means because not doing so will have a measurable impact on the fuel economy and environmental performance of the car. My average target is 100g of CO2 /km.
So no power hungry audio equipment for me. In my view, installing a sub-woofer and other power audio systems in an HCH (or Prius) upsets the energy/power balance... and in the end, simply erodes the efficiency potential the vehicle was designed to offer.

Cheers;

MSantos