Posted by Mr. G on February 27, 2008, 11:18 pm
(Chas.Gill@gollum.btinternet.com) says...
>
> If I recall correctly from a couple of years ago, one of the biggest power
> drains is the dashboard display. In fact I recall hearing (or reading)
> somewhere that it's best to avoid using it in the accessories mode for more
> than 30 minutes as it had a tendency to discharge the battery. As a matter
> of course, therefore, if I happen to be using the radio in accessory mode I
> always turn off the display via the menu, as a precaution. However, the
> dealer didn't say WHICH battery and I'm fairly sure I've read somewhere else
> since that the 12v unit is really only there to power low wattage critical
> systems (such as engine management and other systems at start-up) and that
> everything else is energised by the HV unit, so I'm not really sure whether
> what he said was true or not. Perhaps there is an expert reading this that
> can clear this up?
When the Prius is off, the HV battery is physically disconnected from
the electrical system via a solenoid. (you can hear it "click" from the
back of the car when you are starting it.)
The solenoid will engage when the car is in the 'On' or 'Ready' mode; in
the 'Acc' mode (1 push of power without brake), it is still
disconnected, so the electrical power is only coming from the 12V
battery.
Posted by TKM on February 28, 2008, 1:38 am
>> In article
>>
>>> Thanks for the useful comments. A recheck of everything (lights, radio,
>>> etc.) indicated that nothing was left on; so it was likely the Smart Key
>>> System plus a 12 volt battery that was not at full charge because of
>>> short
>>> trips or heavy accessory use just before the week-long shutdown. Very
>>> cold
>>> weather during that time may have contributed too.
>>>
>>> What I plan to do (when the weather warms up!) is to check the current
>>> draw
>>> of the Smart Key System against the capacity of the battery to get some
>>> idea
>>> of what Toyota means when they say to turn off the Smart Key System when
>>> "the vehicle is left for a long time". I also think an indication of
>>> the
>>> state of the 12 volt battery would be a good addition to the display
>>> roster.
>>
>> Ah, now it comes out: "heavy accessory use" is the culprit here. The
>> ACC position should not be used for more than a very few minutes at a
>> time because it tends to kill the undersized 12V battery. Unless the
>> car is in an enclosed space, when accessories are in use it should be
>> left ON and in Park so that it can manage its own energy as it was
>> designed to do.
> If I recall correctly from a couple of years ago, one of the biggest power
> drains is the dashboard display. In fact I recall hearing (or reading)
> somewhere that it's best to avoid using it in the accessories mode for
> more than 30 minutes as it had a tendency to discharge the battery. As a
> matter of course, therefore, if I happen to be using the radio in
> accessory mode I always turn off the display via the menu, as a
> precaution. However, the dealer didn't say WHICH battery and I'm fairly
> sure I've read somewhere else since that the 12v unit is really only there
> to power low wattage critical systems (such as engine management and other
> systems at start-up) and that everything else is energised by the HV unit,
> so I'm not really sure whether what he said was true or not. Perhaps
> there is an expert reading this that can clear this up?
It would indeed be useful to know which battery powers what. Certainly the
Prius 12 volt battery is physically smaller than the battery in many other
cars.
What I recall doing before leaving the car off for a week was driving
several short trips at night in rain and snow with the wipers, electric
defroster, lights and heater motor all on. To me that's heavy accessory use
since the battery probably doesn't get fully charged. Cold weather also
reduces battery capacity. I very seldom use accessory mode and haven't for
some months. But, lesson learned. The Smart Key System gets switched off if
the car is to be left off more than a couple of days especially in the
winter.
TKM
Posted by Elmo P. Shagnasty on February 28, 2008, 2:00 am
> It would indeed be useful to know which battery powers what.
So turn the Prius on in accessory mode and find out.
Posted by Mr. G on February 28, 2008, 11:57 pm
Shagnasty (elmop@nastydesigns.com) says...
>
> > It would indeed be useful to know which battery powers what.
>
> So turn the Prius on in accessory mode and find out.
>
>
When the HV battery is engaged, there is an inverter which, among other
things, supplies power from the HV battery to the 12V bus. The only
need for the 12V battery is to supply power to the electronics when
first starting the car, and also for power in the ACC mode, which as
previously pointed out, is not a good thing to do for any extended
period of time.
Posted by TKM on February 29, 2008, 6:09 pm
> Shagnasty (elmop@nastydesigns.com) says...
>>
>> > It would indeed be useful to know which battery powers what.
>>
>> So turn the Prius on in accessory mode and find out.
>>
>>
> When the HV battery is engaged, there is an inverter which, among other
> things, supplies power from the HV battery to the 12V bus. The only
> need for the 12V battery is to supply power to the electronics when
> first starting the car, and also for power in the ACC mode, which as
> previously pointed out, is not a good thing to do for any extended
> period of time.
Thanks. That's very good information. Rather than jump start the Prius
next time the battery is down, maybe one of those battery packs that plugs
into the dashboard power outlet would do the job. It certainly doesn't
sound like much power would be required.
I"m also looking for a Prius wiring diagram. That ought to be good for a
few days of reading.
TKM
XML site map
> If I recall correctly from a couple of years ago, one of the biggest power
> drains is the dashboard display. In fact I recall hearing (or reading)
> somewhere that it's best to avoid using it in the accessories mode for more
> than 30 minutes as it had a tendency to discharge the battery. As a matter
> of course, therefore, if I happen to be using the radio in accessory mode I
> always turn off the display via the menu, as a precaution. However, the
> dealer didn't say WHICH battery and I'm fairly sure I've read somewhere else
> since that the 12v unit is really only there to power low wattage critical
> systems (such as engine management and other systems at start-up) and that
> everything else is energised by the HV unit, so I'm not really sure whether
> what he said was true or not. Perhaps there is an expert reading this that
> can clear this up?