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2021 Rav4 Prime XSE Pro Audio/Dynamic Nav/Weather Packages Build date: June 2021
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As previously mentioned, the Prime does in fact charge the 12v Aux battery when the Prime is plugged in AND charging.
Is it possible w/ your gizmo to leave the EVSE attached for as many hours as you can live with after the charge is complete to monitor for voltage loss during that time? There is a contention that keeping the EVSE attached after charging the car that parasitic draw will commence, but we have no idea how much and for what period of time. Thanks in advance if you can do this!
 

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Is it possible w/ your gizmo to leave the EVSE attached for as many hours as you can live with after the charge is complete to monitor for voltage loss during that time? There is a contention that keeping the EVSE attached after charging the car that parasitic draw will commence, but we have no idea how much and for what period of time. Thanks in advance if you can do this!
I don't have data for parasite loss over several days following a full charge as I typically charge on a departure schedule.
Here is a screenshot of a 24h period of a typical driving day from a few weeks back.

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Jan 5th, From midnight to 7 am, stable voltage until I leave for work where it spikes to 14.15v when I'm driving. Then another spike at 15:30 when I leave work, and then a lull, (I was at Costco) then another spike on my return home. I did not plug in that night. The voltage was 12.75 at 1700 (5pm). Ignoring the spikes and dips, it slowly crept down to 12.4 just before I took off again the next morning.
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I'll try to get some data of the Prime plugged in for a long period of time with no charging going on and see what that says.

dp
 

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As previously mentioned, the Prime does in fact charge the 12v Aux battery when the Prime is plugged in AND charging. As seen in the graphic in this screen shot I just took. The voltage was only 12.2v and goes up to 13.42 when I initiated the charge cycle.
View attachment 176646

But, even after 20 minutes, the charging voltage is still only at 13.42v
View attachment 176647

For those charging on L2 @ 6.6KWh, this will not be long enough to fully charge the 12v Aux battery. It barely maintains it. This problem is worsened in winter, because if you use mostly HV mode because of the cold, the battery does not discharge as much and requires less charging time and compounds the energy deficit for the 12v Aux battery that the cold already imposes.

I personally think a small smart charger/maintainer is an easy fix to alleviate possible issues. Every few week during the coldest months should be enough.

I also carry a small booster pack (Noco GB40) in my trunk just in case.

dp
Doesn't the 12V battery get a charge when running the ICE? I know there is no alternator, but doesn't one of the MG's help maintain the 12V? Otherwise, on a long trip in HV only mode you would lose the 12V battery all the time.
 

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2021 RAV4 Prime XSE in Magnetic Gray
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Doesn't the 12V battery get a charge when running the ICE? I know there is no alternator, but doesn't one of the MG's help maintain the 12V? Otherwise, on a long trip in HV only mode you would lose the 12V battery all the time.
No. There is a DC-DC inverter that steps down the high voltage traction battery to low voltage 13-14V DC in order to maintain the battery. This is active when the vehicle is in a READY state, a charging state, and maybe another state I'm forgetting at the moment.
 

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I'll try to get some data of the Prime plugged in for a long period of time with no charging going on and see what that says.

dp
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Thanks so much for that it will add to the useful dbase for sure! BTW, what gizmo is that? Monitoring electrical information seems like it could be worth if for me!
 

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No. There is a DC-DC inverter that steps down the high voltage traction battery to low voltage 13-14V DC in order to maintain the battery. This is active when the vehicle is in a READY state, a charging state, and maybe another state I'm forgetting at the moment.
Then it should be maintained when running in HV mode. Correct? In other words, I should be able to run entirely in HV mode without ever plugging in and still maintain the 12V battery.
 

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As soon as any Toyota hybrid or plug-in starts in READY mode, it will start charging/topping-off the 12v. You can see OBD 12v voltage jump up into charging ranges (13.7v - 14.4v) when the R4Prime starts (READY), or when you plug in the EVSE and start a charging session (as see in video below). We need to check what else triggers energizing the Rav4 Prime DC-DC converter that powers all 12v components and charges the small/puny 12v battery.

Hi Chazz8: What parameter in the ScanGauge-2 provides the traction battery current draw? I'd like to get that on my ScanGauge "home screen". Thanks!
 

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Then it should be maintained when running in HV mode. Correct? In other words, I should be able to run entirely in HV mode without ever plugging in and still maintain the 12V battery.
While the vehicle is on, yes. Regardless of the mode the drivetrain is in, the 12V battery is being charged/maintained with a voltage exceeding 13V.

The crux of the issue is something draining these batteries while the vehicle is off.
 

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Do you leave this attached to the aux. battery all the time, or do you attach and detach it as needed? Thanx.
I leave it attached to the battery.

Before someone asks about the power draw of the monitor itself, I can't remember exactly how much, but I remember when I tested it a few years back, I considered it to be negligible and well worth it considering the information I get from it.

dp
 

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On a side note, I think many of the 12v ACC battery issues stem from the charging voltage being too low. A smart charger will charge a 12v SLA at 14.5v (Some will do over 15v for a deep cycle). But the Prime only charges at around a measly 13.5v. Not enough in my opinion. Resulting in the 12v battery almost always sitting in and under charged stated. I predict that many prime owners will have premature failure of the 12v ACC battery. Lasting only 1 to 3 years instead of 5 or 6.

dp
With many cars of recent vintage, they use different charging voltages based on the state of charge of the 12v battery. If the battery is not fully charged, the charging voltage is 14.4 volts plus or minus. When the battery becomes fully charged, the charging voltage drops to 12.8 to 13.5 volts or so. This is done to save fuel and to help extend the life of the battery. The Toyota hybrid system also does this.
 

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Hi Chazz8: What parameter in the ScanGauge-2 provides the traction battery current draw? I'd like to get that on my ScanGauge "home screen". Thanks!
The Hybrid Battery Current (amps) shows amazing (high) power draws for the Synergy Drive, when accelerating fast. I feel like toyota finally gave their Plug-in a big enough battery to power everything (including Rear Motor for AWD) and achieve a peppy EV feel for a heavy-ish SUV. Now add the ICE to the peppy EV and you get POPPING power.
R4P section is 2nd from bottom of Toyota-etc. list, and ‘Hybrid Battery Current’ is 2nd item from top, from; » TOYOTA – LEXUS – SCION
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A few Gauges don’t work as expected for R4P but I don’t remember which ones.

Edit; Want to finish on thread topic.
The Auxiliary Battery Current (Amps) gauge looks like it could show how much power is coming from DC-DC converter to 12v when it raises voltage when EVSE is plugged in.
 
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With many cars of recent vintage, they use different charging voltages based on the state of charge of the 12v battery. If the battery is not fully charged, the charging voltage is 14.4 volts plus or minus. When the battery becomes fully charged, the charging voltage drops to 12.8 to 13.5 volts or so. This is done to save fuel and to help extend the life of the battery. The Toyota hybrid system also does this.
I agree with you completely. This is also similar to a charging profile smart chargers would do, but the trend i'm seeing is when the Prime is in Ready mode/driving, the charging rate is around 14.23v, but when it is plugged in AND charging, the charging voltage is only 13.42v, weather the 12v Aux in charged or not.

I have a small solar setup for our sugar shack, and when the battery or batteries are fully charged from a charger when they are sitting in my basement during the off season, they hover between 12.9 and 13.1v for weeks after the charger is removed.

Most of the time I check the voltage on the Prime's 12v Aux, it is usually around 12.2v and I consider that to be too low for long term SOC, that is why I believe the 12v will not last the 5, 6 or 7 years that we usually get from our other car batteries around here.

dp
 

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I agree with you completely. This is also similar to a charging profile smart chargers would do, but the trend i'm seeing is when the Prime is in Ready mode/driving, the charging rate is around 14.23v, but when it is plugged in AND charging, the charging voltage is only 13.42v, weather the 12v Aux in charged or not.

I have a small solar setup for our sugar shack, and when the battery or batteries are fully charged from a charger when they are sitting in my basement during the off season, they hover between 12.9 and 13.1v for weeks after the charger is removed.

Most of the time I check the voltage on the Prime's 12v Aux, it is usually around 12.2v and I consider that to be too low for long term SOC, that is why I believe the 12v will not last the 5, 6 or 7 years that we usually get from our other car batteries around here.

dp
I assume that with your solar batteries, there is no load at all when they are sitting. With the Prime or any modern vehicle, there is some load that consumes a bit of the battery storage power such as the headlights staying on for a couple minutes, interior lights when the doors are open, and powered doors. In addition, there are small loads from computers in the vehicles. All these loads tend to lower the battery voltage somewhat, but really should not affect longevity unless the battery is continually run down such that the Prime will not start.
 

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Discussion Starter · #78 ·
I assume that with your solar batteries, there is no load at all when they are sitting. With the Prime or any modern vehicle, there is some load that consumes a bit of the battery storage power such as the headlights staying on for a couple minutes, interior lights when the doors are open, and powered doors. In addition, there are small loads from computers in the vehicles. All these loads tend to lower the battery voltage somewhat, but really should not affect longevity unless the battery is continually run down such that the Prime will not start.
We have had the inconvenience and frustration of two overnight discharges of the 12 v battery in our Toyota RAV4 Prime. In order to better understand the system, we have been observing the voltage of the 12 v battery when the vehicle comes out of the garage and again at the end of the service day when the RAV4 Prime goes back in the garage. Recently, the vehicle was operated on 8 out of 12 days with an average days run of about 25 km. All operation was in electric mode. With power on, system voltage at the cigarette lighter was steady 14.2 During the 12 days, power off, the voltage of the 12 v battery hovered etween 12.3 and 12.5 volts - that is, about 1/2 capacity. Overnight discharge was less than could accurately be measured but less than 0.5 volts.

Our conclusion is that, however it operates, the on-board charging system of the Toyota RAV4 Prime is deficient because it maintains the 12 v battery at about 1/2 charge which will certainly reduce the reliability of starting the vehicle and shortens the life of the battery.
We hope that Toyota will come up with a fix, but in the meantime, whenever the vehicle is plugged in, a 1.5 Amp battery maintainer is directly connected to the 12 v battery.
This Toyota deficiency in failing to properly maintain the charge state of the 12v battery probably has nothing to do with the mysterious occasional overnight discharge of the 12 v battery. So, we carry in the vehicle, a 12 v Li-ion jump start battery.
We resent having to take these measures to overcome deficiencies in the Toyota RAV4 Prime.
 

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Make sure that nothing is plugged in on any power supply outlets ( 12 v ou usb etc ) I have seen a similar problem on another make ( nissan ) , The car system would stay in standby mode instead of sleep mode and would draw about .25 amp , not much but enough to drain a battery that is already low .
 

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Discussion Starter · #80 ·
Thanks for the advice. How can we check that the RAV4 P is in sleep mode ? The drivers display appears to be "off". The battery maintainer is connected after the power is switched off.
Incidentaly, I was informed by a Toyota technician that the vehicle likely has a residual load of 150 to 200 milleamps which would completly discharge a 100 amp-hr battery in 100/0,2 = 500 hours = 20 days.
 
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