How do you put the Prius in neutral to push or tow it?

Except that those of us who have driven with the 12 volt battery disconnected find it to be quite possible indeed.

Your experience may pertain more to having a 12 volt battery that is connected, but is in such bad condition (shorted cells, perhaps) that it creates a heavy load on the electrical system.

Disconnected, it would not do that.

 

nope, 12v is disconnected out of the vehicle for charging. Replaced it with a HF booster pack because the 12v is just needed for starting (that's the belief) Booster pack has an auto shut off feature, when it turned off Prius is dead on the road.. I have to turn on the pack again and it's back on the road.

 

We apparently live in completely different realities then, or the HF pack's auto shutoff works in some interesting way, or something else is also wrong with your Prius.

There do seem to be only two realities, not three, seeing as hobbit lives in the same one I do.

 

When my Combo meter was in its death throes the only way i could shut the car off was to unplug the main 12 volt battery lead lead from the positive battery post fuse assy.

This is the 100 amp wire from the 12 volt battery to the front jump point/fuse box. Car shuts off instantly.

No 12 volts to the front fuse assy that power's all the relays and ecu's in the car. Same thing as disconnecting the 12 volt battery post leads only easier and quicker.

I suppose if you remove the battery without unplugging the 2 power leads in that positive battery post assy maybe it is powered off the 5 AMP wire from the DC to DC Inverter as there in parallel. But I highly doubt it.

That battery positive post fuse assy has to 2 leads plugged into it both protected by 2 fuses in that assy the 100 amp fuse for the main battery cable that runs under the car to the front jump point and other is the 5 amp fuse wire form the INVERTER that's the charging voltage/sensing wire. Maybe the car will run off that 5 amp wire. Its going to have a much bigger load on it 5 amps though.
Other than that I don't see where your getting 12 volts with alot of power to the front jump point with the battery disconnected.

Here's a pic of the battery post fuse assy:

 

The "5 amp wire" is a red herring for the purpose of this discussion. You're talking about this one:



That wire carries effectively no current in either direction, ever. It is only there so the converter can sense what the voltage at the battery is. It connects to the converter's S terminal, which doesn't draw any more current than a digital voltmeter does.

That's done with a separate wire because of course the big black frame wire carries real current, and real current means real voltage drop, and if the converter were trying to regulate the voltage by looking downstream on that wire, it would see a different voltage than what's at the battery.

You definitely need the 12 volt battery before you make the car READY. The converter is turned off then, and the current flow looks like this:



Once you make the car READY, the converter turns on, and supplies 13.5 to 14.8 volts out its AMD terminal. At that point, the current flow looks like this, and the 12 volt battery is being charged:



If you then disconnect the 12 volt battery, the picture only changes to this:



and that's why both hobbit and I can tell you in documented direct experience that the car stays happily READY without a blip when the 12 volt battery is disconnected if it was READY to start with.

So what's interesting here is we also have two people reporting that they got shutdowns when they disconnected theirs. At least, that could be interesting if people were saying "ok, so what was different about those cars or those cases?"

Just going "is not!" "is too!" doesn't have the same learning potential.

 

Ok

How does the output of that AMD leg carry all the various 12 volt current loads when the car is running? All the relays all the ecus's that are hanging off that 12 volt buss? At 12 volts that's alot of current right there. What happens when you turn on the headlights in bright that's probably 20-30 amps right there. Then maybe turn on the heater and the radio all current serviced by that little IC output. You have 30-40 amps at least maybe more @12 volts.

All out of a IC output designed not to exceed probably 10 amp at max.

Its a magical car.

But I can assure you I have killed my car many times by pulling that 100 amp cable. Just unclicked it. Dead jim.

 

All the magic is in your last assumption right there. How in blue tunket did you come up with "probably 10 amp at max"? The Gen 3 converter rating is published, 120 amps:



It wasn't as clearly published for Gen 2 or Gen 1, but has been measured and reported by various folks (including Bob Wilson, pretty carefully) as 100 amps, an order of magnitude higher than your guess.

That's fairly consistent with the DC/DC fuse on its output being 125 amps in Gen 3, and 100 amps in Gen 2 and Gen 1.

100 amps at 13.5 to 14.7 volts is 1350 to 1470 watts. Your guess of 10 amps would be no more than 147 watts. Have you stopped to wonder why this thing is out under the hood with pumped coolant piped through it? At 147 watts it would look like a free-air-cooled laptop power brick.

Is that enough for the remaining parts of your question to start to fall into place?

And I can assure you I and others have done the same thing without a blip, and written about it, years before this thread came up. This is just back to the "is not!" "is too!" that nobody learns from. Something is different.