Should it be 13.7 or 14.7 volts.

I am not sure where did you get that information...

Prius Gen3 charges the battery depending on various factors ... some people referred to it as a two-stage charger...

I was monitoring this with Scangauge before.... and checked it again reading this thread.

Here my general observation, immediately at startup it starts charging battery with 14.8-14.5 V and as a matter of fact will charge with this voltage anytime the car is in the Park status even AFTER dropped to lower charging voltage (see later).

Then in normal driving the voltage stays at that level depending on the status of the battery (and temperature) and then it drops around 13.8-13.6 while you drive... (this maybe what you refer to "floating")

This charging time varies quite a bit for example yesterday driving home this took about 10 minutes to drop .... but this morning (parked overnight and much colder temp) it took almost an hour to drop ...

Also, note that running the headlights (or heating fan) will increase the voltage reading back to 14.5-14.6V range (not sure if the car senses the dropped voltage resulted by the increased current through the battery (most likely) .

In my experience when the lights/fan is on it never dropped back to the lower level either the battery did not came up to full charge or this is the intended way (i.e. higher floating voltage over a certain load).

And then when you turn off the car you can actually see the battery voltage for a little while (as ODB bus is powered for a little longer like a minute) if you had headlights on then it is not the "open" circuit voltage but if not it is pretty close now ... mine is slowly goes from 12.8 to somewhere 12.3 guessing battery is in trouble if that lower number drops under 12V.

If anyone has different observations let us know.


Cheers

 

While there is a slight temp variation as described above, the 14.6V is a normal voltage for BULK charging. Since startup will eat some substantial juice from the tiny battery, bulk charging is necessary. As SOC increases, charging will switch to FLOAT charging, just to keep battery full. It would take forever to replenish a substantial charge by float charging at 13.8V. Smart battery chargers do it, why Prius should be different?

 

I've had my Gen. III for a year now. I drive almost exclusively short (1-5 miles) trips. I've noticed that during the winter, voltage seemed to ALWAYS stay at 14.5-14.7 v.. Now that it has REALLY (too early for these temps) warmed up, I've noted that upon start-up, I'm at ~14.6 v. for a minute or two. It then drops (and stays) at 13.5-13.7 v.. As has been otherwise observed-even when at that lower voltage, when you put it in Park, it goes back up to 14.6 v.. I don't understand why it goes back up to 14.6 just because it is now in the Park mode. I've read all the other posts, but (unless I overlooked it) I don't see an answer to this. Any responses? Thanks.

 

Try playing with your headlights and or AC/heater. I noticed my voltage would drop down to 13.6v or so and at other times with was 14.7v. I think it was based on the use of my headlights or other electric feature. I'll try and remember to test it tomorrow.

 

I have a small solid state, DC data logger. This thread encourages me to connect it to my 12V battery for a couple of weeks and provide the readout here. If I sample infrequently (like every minute), I can cover a really long time interval.

 

personally i think the 12 volt battery is charged when it drops below a certain voltage which may account for the fact that the voltage is always varying. as for me, i dont really recall seeing it above 14.5 (i drive the Leaf, 95% of the time)

 

Totally normal ... this is how it should be ...

The car is charging your battery !!! but it is charging it depending on many things but one of the thing is temperature ... in colder temp it will try to charge it longer with the HIGHER voltage. Temperature is actually measured at the battery .... so the car doesn't really know if the battery is warm (by the charge) or by the external weather ...

During cooler days car will keep charging the battery seemingly longer with the higher voltage then warmer weather (also if the battery "hot" that indicates that lower voltage would be better) ...

However Prius may not be able to fully charge your battery during 1-5 miles trip ... IF it is depleted over a certain point ... good healthy battery will tolerate this but not forever .... this could result an "under charged" battery .... and could result shorter than expected battery life .... I am using could because very difficult to give hard number on this ....

But either way without any other adverse events related to the battery, of course, this should be OK (if you drive the car over 5 miles maybe every two weeks or so...)

I am not toyota so they may advise otherwise....

If you really concern leave the car P mode for a little bit longer (that forces the higher voltage charge ....) in normal operation you do not really need that much time to top off the battery (here the smaller size in on our side)

 

Let me add that the higher voltage will kick in if higher load on the system detected ..... like headlights turned on or the cabin fan is on .. (I found that cabin fan varies ...) ....

On the question of P increases the voltage ... I think it is by design ... so the car will definitely push some charge to the battery right after start up ... (could be some other reason .... as well but make sense) and could be used as sure way to charge your battery ... turn on the car leave it in Park for some time and 12V battery will be charged (normal car in idle doesn't really charge the batter by the way ....) in other word you do not really need to drive it ... just turn it ON if you have traction battery power you do not even need ICE to charge the 12V battery to health ....

 

I messed around with the headlights today and driving around with the DRL on the voltage was 13.5-13.7v. Switching the headlights on caused the voltage to climb to 14.5-14.7v but not instantly. I would then switch the headlights off and back to the DRL and withing about 3-5min the voltage would drop back to 13.5-13.7v. Switching the headlights back on would cause the voltage gain again. I took a small video of it and may post it to tomorrow but it's a pretty simple description.

 

Although I do not "know" exactly how toyota designed this but makes sense .... that voltage would be raised over a certain load (headlight on a good example) ... and by some manner similarly "charge" the battery with the higher voltage when it is somewhat depleted .... (when I do not use the car for several day .... that time is noticable even up to an hour driving (and if the headlight is off) it goes back 13.5 v the same afternoon this time 10 minutes even less (after car sitting in am indoor the parking garage 8-9 hour )

So I can confirm the same behaivor ...

and if you put it in Park it will jump to the higher voltage I can not really figure what that is ...

 

may be this is a secret way to speed up charging the 12V battery. like when the car sits in a dealer's lot for months, you put it in ready while in park rather than drive around.

 

For sure this will do that .... but I do not see that as a practical reason or the only one ???

Firstly, without some external monitoring THE CAR doesn't tell you if the battery is OK, charging or full etc. and ready so the dealer wouldn't know either way ....

 

In the eleven weeks since that post, I never saw Ready mode bus voltage drop to the lower operating level in my 2010. But after putting the ScanGauge in a three day old 2012 today -- also our warmest day of year so far, starting in the morning at 59F -- the Ready mode voltage was 13.5-13.7 all day.

I'll check the morning Off voltage tomorrow, then start monitoring both with age and weather.

 

That could mean 2 things (or more).

1. you have load on the 12V circuit that could be just the fan ... or runing the headlight

2. your 12V battery can not keep the charge

3. or you are not running long enough for the battery fully charge or go back 2.

My 2010 was actually bought in July 2009 !! and my battery still OK and I can see the drop (depending on circumstances 10 minutes or 40 minutes in the mornings). By spec the battery charging current is 4.3A so it could take a while to actually charge up even a modestly discharge battery