Confirmed - Home charging HV battery charges Aux 12V battery too!

DETAILS MATTERS....
I don't have a gen5 to experiment with, but on a gen4 the DC-DC converter is ONLY actively charging the low voltage system ONLY WHEN the traction battery is actively being charged. Just plugging-in the car DOES NOT automatically charge the low voltage system. That's why the Toyota manual states "unplug the car, when if finishes charging". Leaving it plugged-in will force the ECU to perform more frequent readiness testing powered by the 12VDC battery alone, that isn't receiving a charge - because the traction battery is already FULL (see first sentence).
FWIW; The only reason the low voltage system is active during charging is to ensure cooling fan operations, so the traction battery doesn't overheat during the process. Up there in Canada, the DC-DC converter may also activate to keep the traction pack warm and ready for vehicle operations. If that has changed for the gen5 - GREAT, but I doubt it - since there's been many reports of dead low voltage batteries.

YMMV....

 

But he's actually correct in this case. Yes, the gen5 will charge the 12V while plugged in, but ONLY when the HV battery is also being charged.

So imagine you come home with your HV battery almost completely full. You automatically plug it in because you've gotten in that habit. But then you don't end up using the car again for several days. Because it's plugged in, some of the computers stay active(the ones that monitor HV battery temp and state of charge). Those computers draw power from the 12V battery. Let's also say it's reasonably warm, so the car never needs to use the HV battery heater. The HV battery started full, and there's been no draw on it, so it hasn't needed to be charged over those several days. But the 12V has been slowly depleted by the extra draw from the awake computers. It's this issue the manual is trying to prevent.

Now if you're in a cold enough climate, the HV battery heater will kick on from time to time. That's powered by the HV battery, so eventually it will deplete enough to kick on the HV charger. When that happens, it also checks the 12V battery and tops it up if necessary. Also, if you come home with your HV battery significantly depleted, the HV charger will stay on long enough to charge up the 12V at the same time it charges the HV. The main problem areas are if you plug in a car with a full HV battery in a warm climate, or if you leave the car plugged in for several days in a warm climate.



As to the video, what he's saying is that the gen4 Prime had two DC-DC converters, while the gen5 only has one. In the gen4, there was the big converter in the engine compartment, but there was a second converter as part of the HV charger and that one handled charging the 12V battery. But in the gen5, Toyota eliminated that second converter and integrated its function into the main converter. But that doesn't change the behavior of the system. It still only charges the 12V when the HV is also charging.

 

You're only contradicting known information and instructions if you were seeing 14V when the green LED on the charging cable was off and it wasn't charging the main battery or running the heater.

The belief is that it won't take any action to maintain the 12V battery except as a side-effect of being on for charging or heating.

And Hammersmith just said that.

 

Thanks guys; I didn't think Toyota's army of technical writers and/or lawyers would make a glaring mistake like that in the operations manual.

@WaikikiPrius This wasn't a personnel attack, I'm just trying to tamp down on incorrect or inaccurate information - especially when your telling everyone to contradict the OEM manual. That's fine, if your information is correct, but there's already been a lot of discussion about this since the first gen5's came out. Sorry.... Who knows; maybe your one of the first to get a new firmware upgrade to address that 12V battery depletion issue, but we don't know until a TSB or something else comes out. If this was a fix, it wouldn't fix the non-plugins 12V battery issue.

YMMV

 

The safety protocols of the charging standard call for the high power cables to be energized after the EVSE establishes communication with the car, and only when the car calls for the power. There isn't another cable in the charge cord that c an supply power to charge the 12V when the high power cables are de-energized.

 

Would it be possible for a manufacturer to add a circuit from the hybrid battery to the 12v when the car is off?

 

A step down DC-DC converter right at the battery that then feeds the battery would be possible.

Simpler way would be to just monitor the 12V, and when it hits some low point, the car just re-engages the traction battery to top off its charge. Some EVs do this. Another solution is to build a 12V section in the traction pack, and ditch the lead-acid battery(Hyundai). Have a button to charge from the main battery if the 12V portion ever 'dies'.

 

The 12 v doesn’t charge when traction battery is being charged on my 20 Prime. I charge it every day using free to me wall socket or level 2. Weber State video has the 12 v charging with a gen 5. Have to look at it again to remember the specific conditions it charged.
So after hundreds of charging sessions and looking at my 12 volt battery monitor every time,I can say it does not charge the 12 volt. Many times when I get home after traction charging, I have to get the 12 v maintainer out and charge the 12 v.
I rarely finish charging the traction battery, it’s always still charging when I stop it. No idle time with cord plugged in.