12 VDC Aux Battery (AB)

Well I was really hoping one of those technical hot shots would answer because I haven't measured the Voltage in my Prius yet. But I have measured other cars and when it's not charging the Voltage should most likely be 12 or 12.5 Volts. When it is being charged, i.e. when the car is turned on, it will be 13.5 to 15 Volts I think. For example my Chevy pickup runs at about 13.8 and both of my Hondas have run at 14.8 to 15 and there is no reason the Prius 12 Volt system should be much different.

To answer your first question I believe (notice I'm hedging a little) there is a low Voltage output off of the HV battery inverter which is rectified, filtered, and regulated to charge the 12 Volt battery. So the ICE does not need to be running to charge the 12 Volt battery but I think the car does need to be on.

It would almost certainly be a constant Voltage circuit with some current limiting for protection. That is the Voltage will remain constant unless the current demand goes to high at which time the Voltage will decrease to keep the current under some preset value.

Experts please comment.

 

My scan gauge used to show about 14 to 14.2 volts when the car was charging the 12 volt battery.

I assume this will vary some with temperature but now I use a Can View, with HV battery info but not the 12 volts.

 

The inverter changes the DC from the HV battery to simulated* AC for the synchronous motors MG1 and MG2. A small portion of this AC power is applied to a transformer which lowers it's Voltage so it can be rectified, filtered, and regulated to the proper Voltage (14 to 14.2 Volts measured by tomdemois) for the aux battery charger. The majority of the power from the inverter is available to be converted to 500 Volts for use by the motors.

The reason it is refered to as an inverter is because it creates AC (actually simulated AC) by inverting (changing the polarity) of 1/2 of the DC. This actually produces a square wave which is rounded off with some reactive componants. The frequency of the inverter, which is controled by the computer, determines the speed of the synchronous motor(s).

*Edit: Actually it is the sine wave that is simulated not the AC.

 

Very difficult to regulate as you said and if the the circuit opened, such as it would if you removed a battery terminal, you would have the whole 200 Volts right there at your finger tips, ouch. Also not very efficient due to the loss across the resistor.

 

There is a completely *separate* inverter to charge the aux battery
off the HV battery when the system is fully powered up. Remember,
there are like 5 inverters in that block-o-stuff under the hood --
one for each MG, the buck/boost converter, the A/C pump, and the 12V
charger. [The buck/boost sort of half-counts because it's a little
different.] From what I and others can determine, the 12V system
is actually brought up to right about 14V *at the battery*, using
that very thin extra white wire that goes to the battery connection
as a voltage sensor input back to the inverter [that otherwise
carries no load].
.
This voltage is actually a tiny bit higher than you really want to
"float" a lead-acid battery with, so it will eventually bubble the
battery dry. The ivory-tower conjecture is that Toyota decided to
compromise between a faster recharge and a lower, more "correct"
float voltage. But the point is that there's yet another inverter
dedicated to this, no dropping-resistor kludges clipped into some
other unrelated piece of the electronics. Physically, I believe it's
in the bottom part of the under-hood block.
.
_H*

 

Thanks Hobbit that helps quite a bit. Did you get that information from the maintenance manuals or did you have to reverse engineer someones car? I would like to learn more about this machine. But I've run out of resources short of buying the shop manuals, and I wasn't sure how much information was in them.

 

Mostly the repair manuals and "new car features" documents available
up at TIS. I highly recommend spending the $10 for a day's
subscription and then downloading the entire thing to your own
machine. For the '04, you can probably use the contents of
http://techno-fandom.org/~hobbit/cars/TIS/ as an index for grabbing
the actual files -- they may be somewhat different for '05 and up,
I haven't checked.
.
I've also found *numerous* good papers and other articles
that go into techie details, as well as the fine folks on the
prius_technical_stuff yahoogroup. I've got a bunch of
pointers to much of this stuff up at
http://techno-fandom.org/~hobbit/cars/prius-linkfarm.html which
I suppose I should periodically remind people of the presence of.
And it's by no means a complete list of prius/hybrid resources
out there; many lessons have come from various electric-vehicle
enthusiast site archives, the Honda Insight crowd, etc.
.
_H*

 

Also,
Can any of you technical hot shots tell me WHY THE PRIUS ICE CAN'T BE STARTED BY THE MAIN BATTERY WHEN YOU FIRST START UP IN THE MORNING. I HAVE HAD THIS HAPPEN WHEN THE CAR HASN'T BEEN DRIVEN FOR A FEW WEEKS. THE 12V (AB) IS DISCH AND CAN'T CRANK THE STARTER. MAYBE THE MAIN HV BATTERY COULD CHARGE UP THE 12V BATTERY IF THE IGNITION WAS LEFT ON FOR SOME TIME? THANKS

 

I "jump started" it and then drove it to the dealer. They informed me that most any new car that has a computer will not start after about 2 to 3 weeks. The battery has to keep these circuits alive. This is not just a Prius problem. Dealers are constantly starting or charging cars all over their lot.