2003 Prius Aux Battery - Any way to adapt?

That's an easy way to explain it to someone who's not owned one of these, and I've said similar - but it's actually the electric motor that starts the ICE. Yeah, the Hybrid battery starts the electric motor, after the Aux battery boots it.

 

If somebody was talking about a conventional car, and said the 12-volt battery started the engine, would it be necessary to correct them and say no, it's the starter motor that starts the engine, and the battery starts the starter motor?

 

Not for most people. The simple explanation works fine, as I said, and I've used it myself. In this case, KV seems like a passionate newbie who's trying to learn about these cars. Certainly no intent from me to "correct" Trombone. That seems pretty clear as I re-read my post. Maybe having a bad day, Chap?

And, it isn't the same, not a good analogy. The way Trombone describes - not because he doesn't know, just to simplify - KV could assume there actually is a starter. In a regular car, the battery is directly connected to the starter and sends 12v directly. These cars don't even have a starter, and the HV battery doesn't send juice directly to anything to trigger the ICE. It literally is the electric motor turning over the ICE.

 

You seem to be piling up technical distinctions as if they make or break the analogy, which seems a lot to ask of them.

«It literally is the electric motor turning over the ICE» in both cases. A starter is an electric motor. It turns over the engine.

«battery doesn't send juice directly to anything» in either case. If the regular car's battery were «directly connected to the starter», it would be hard to shut the car off. There are power-switching components between battery and electric motor, just as there are in the Prius. Power reaches the motor only when switched on.

In the regular car, the switching component might be electromechanical and called a 'solenoid', where the Prius uses big semiconductor switches that people call IGBTs. Still doesn't seem like the kind of difference that ruins an analogy.

The Prius IGBTs are turned on and off by an ECU, but that's likely true of the solenoid in a late model regular car too. In an older car, the solenoid may be turned on directly by the springy 'START' position of the ignition key, but how important a difference even is that?

The Prius MG1 has six IGBTs (total) connected to its three windings, directly. The regular car starter has just one solenoid switching one circuit feeding the motor. But that works because inside the regular car's electric starter motor are brushes and a commutator to make the current switch between the windings as it spins. The Prius has done away with the commutator and brushes and just uses six IGBTs to do the whole job. Either way, the motor power needs to be switched, and it needs to go through the right windings in sync with the rotation, and that happens in both cars. Does the difference in how it's done make the situations somehow totally disanalogous?

 

Of course, in the end all we really care about is that we see the “Ready” light and hear the ICE come alive when we turn the key to the “Start” position. And no warning lights on the display!