2017 - 2022 Prius Prime - 8.79 kWh Battery and charging system info

Yes, I keep it plugged until the temperature averages above freezing. Then I unplug once charging has finished. Although we drive it at least a few times a week and it never drained the 12V.

 

The 12 volt does not charge during g4 traction battery charging. I wish it did.

A lot of speculation, get a battery monitor and behold, much more information.

 

@Mr.Vanvandenburg has had battery problems in his G4 Prime, and I think has needed to replace his 12V at least once - the car hasn't managed to keep it charged with his amount of driving.

The truth in his statement is that the HV battery charging is not a solution to charging your 12V battery overall. You can't rely on it to refill a low battery, or to be the sole source of maintenance charge, or to compensate for very little driving. (And that's effectively what the manual warning about leaving it plugged in is about - to try to dissuade people from thinking that plugging it in is a battery-top-up solution).

It doesn't provide that high a voltage, and only during actual HV charging (and maybe a bit more during heating for up to 3 days, if temperature is between -15 and +5°C or so.) A short period of trickle charge is not going to achieve that much. So the net 12V battery gain of plugging in is low, or it may even be a loss, depending on the ratio of charging/heating time to idle time.

Don't read his "12 volt does not charge" as "it just runs from the 12V battery drawing it down" or "it's not supplying anything to the 12V battery".

 

Just bought this

https://a.co/d/4HBUcVf

I'll get a definitive answer in a few days. It's forecasting cold nights next week (below-10°C), so I'll see if the heater tops off the battery.

 

Great ! keep us informed ! BTW heater should kick in when the traction battery temp in close to 0C . So after charging it could take a while for the battery to drop in temp and permitting the heater to do it's thing.
Also the heater is divided into 2 heating circuits ,it is not clear when it calls for one or two circuits

 

If I recall the circuit diagram correctly, they're not independently controlled, so I assume the split is just for some sort of redundancy and system checking. Two circuits, two relays, two fuses, two temperature sensors, but switched on and off together.

 

Thanks ! good to know

 

Here's a 12 volt battery diagnostic thread started by @Rob43 in April 2020 that has 21 pages of posts.
It helped me learn more about the 12 volt charging system for the Gen 4 Prime.
12v Battery Is Discharging, Re-Charge Now ! | PriusChat
So far there are no quick answers to exactly what is going on, either while plugged-in or un-pluged, running in EV or HV mode or how many amps are being provided at any particular time, mode and if there are differences in behavior at very high or very low temps, except what is included on the subject in the owners manual.

My impression to date after some observations is that the 12 volt battery is not charged at all like would be typical of a gas car with an alternator. Although I've never measure amps in to the 12 volt battery, I suspect the amps is lower than would normally be seen in a car with an alternator. And I've seen floating voltages in the low 12.x range many times, and never gotten a floating / static ( no or as little draw from the Prime as possible ) 12 volt reading from the Prime 12 volt battery of more than 12.6 volts at the batteries terminals.

 

The battery monitor tells most everything except an amp number. It isn’t that necessary to know, can’t be changed, but by the rate the charge climbs in % gives some indications. There are shunt battery monitors that would show the amp number.
Right now the simple battery monitor shows charging yes or no, soc in %, and a running graph of the voltage. So a lot could be known.
Like I saw the charging stops when the voltage goes below 13, and back on again above 13.
I readily adopted the battery monitor idea from salamander. Best thing I learned so far here. I wonder what the road block is for others who keep wondering what the 12 v is doing.

 

You might have already seen it but just in case, this video shows how the Inverter/converter supply its 12V power to the car.

 

post # 62 of the thread by Rob43 linked above:
12v Battery Is Discharging, Re-Charge Now ! | Page 4 | PriusChat

The prime does have hall effect sensors, it's just getting the correct PID and knowing what that PIDs sensor is measuring. Shouldn't be too difficult to add to an app. Car Scanner has both the, 12 volt battery temp and amp sensors, displayed in the apps All Sensors feature, except the PID for the temp doesn't match and the Primes PID so the reading is way off, and the 12 volt batteries amp measurement shows no reading.

 

Well, right off the bat, I can confirm it's not charging the 12V battery when the HV battery is being charged. I'm currently charging at 240V/16A and this is what the device shows...

 

Here's an interesting one. First section is the car sitting in the driveway, unplugged. Second section is after I started the AC (well, heat pump as it was close to freezing). The dip is when I opened the door and the car shut off. The third section is while in Ready mode and then driving (no change in voltage between just being in Ready mode and driving). Odd that the voltage went up while AC was on but not as high as when in Ready mode...

 

Thanks,i think that the reading of 12.68v is indicating that the SOC is really close to 95% SOC and not needing to charge the 12v battery

 

This one is when I got home. When the voltage increased once parked, I heard the battery (or charger, not sure) fan spinned then stopped shortly after.



During the night (stayed above freezing), I don't see an indication that the battery heaters started. The peaks you see are when we drove the car yesterday and today. I don't know about that dip though. Maybe it's what some say about the car waking up when connected to a charger?



It's forecasting -8°C tonight. I'll see what happens when the battery heaters turn on.

 

So last night it got cold enough for the car to turn on its battery heater.

That's for the last three days.



The high (14.5V), narrow peaks are the time we drove the car. The last, not as high wide peak is last night. So while heating up the traction battery, it did charge the 12V battery with the help of a voltage increase to 13.55V.

When my wife got home yesterday, she plugged the car in (forgot to plug it in the day before) and it does look like it tries to keep the voltage higher (12.75V) while the car is charging (from 16h45 to 18h15) then the voltage starts to go down. It doesn't always do that though, so I guess it does it when it sees the 12V battery is low enough? It will need more data points to figure out a pattern for that one.

Edit: My wife started the car a few minutes ago, and although it's -9°C outside, the battery was already above freezing with the help of the heaters last night.

 

Car Scanner showed the running battery heater temps at 140 F and 138 F . With the Prime plugged in and after finished charging to 100% SOC, I pushed the ON button twice, foot off brake pedal, I was also seeing the ODB11 12 volt readings fluctuate between 12.3 and 13.6 It was noticeably different to me than what I typically see the Prime showing while unplugged in both ON and Ready mode.

 

These gadgets are accurate, the three I have. It’s just the way it is at that time. the 12 v isn’t isolated from the system voltage. The explanation for 12.68 v isn’t the device is defective, unless his is. Then he could exchange it within 30 days. I bet it isn’t. The explanation is having more data to ponder what the car is doing and take it from there.

 

It's very accurate. I checked against my multimeter which read 12.45V and the device read 12.44V. The device's specs mentions a 0.03V accuracy and I'm within that.

This is the last five days. For the last two days, it's been cold enough for the battery heater to turn on when plugged and those three flats at 13.5V I believe they are when the battery heaters turned on. The car has been plugged the since last evening, except when I moved it this morning to shovel the driveway (that last big spike to 14.5V). I see small dips there as well. I'm wondering if these are when the computer turns on to check if a cable is still connected, although it does it at times when there is no cable connected (ie, car parked at work). I see too the voltage being a bit higher after a drive back home when the car is plugged in. These close to 13V flats are there only when back at home, but don't last for as long as the car is charging.

 

Watching my battery monitor, I can’t make out reasons for why the voltage spikes up then down while driving, turning the 12 volt charging off and on at 13 volts threshold. Accelerating moderately up a steep hill turned charging off and the volts dropped below 13. Stays below 13 after that. Get at driveway, back up, volts go back above 13 and charging starts. Too late, car gets turned off. Sometimes I sit for a while and watch the charging proceed a few %. The other day it charged steadily, system stayed over 13 v, and my 12 volt was up to 98%. Felt like having a party.