Prius 12v battery charging while driving

[Tedl]

I have a 2019 Prius, and I have noticed that while driving the 12v system fluctuates between 14.1v and 12.5v. I bought a small voltmeter from Farnell that plugs into the cigarette lighter that shows voltage. On a motor way drive I noticed that for quite a while (½ hour) the voltage showed 12.5 volts. I understand that the prius doesn’t have an alternator so the Battery is charged from the hybrid system (I assume there is a dc/dc converter to get the 12v). Has anyone else noticed this? Due to Covid I had to keep connecting a Ctek Battery conditioner to top up the 12v Battery as well a running the car to keep the hybrid battery charged. I have emailed the technical dept at Toyota but they said they thought this dropping to 12.5 volts was normal, but I’m not so sure. As the car is out of warranty the end of 2022 and I intend keeping it for another year (as you can’t buy another Prius) I’d prefer to catch this 12.5v rather than having to cough up for a repair out of warranty. 

[TonyHSD]

Hi,

that's normal indeed. The converter [ alternators in standard cars} has voltage regulators to maintain required voltage when charging the Battery and to prevent overcharge and damage or risk of fire. When you see charging voltage drop means your Battery is fully charged and your 12v system is unloaded. If you start using a lots pf consumables like info screen, lights, heating fan higher speeds etc the 12v system will get loaded and the Battery will receive perhaps higher voltage charge. Nothing to worry here. If you stop charging your car with external charger perhaps your 12v battery will get constant 14.1v supply from the inverter, and again once reaches its threshold the supplying voltage will drop. 

Regards 👍

[Mooly]

23 hours ago, Tedl said:

I have a 2019 Prius, and I have noticed that while driving the 12v system fluctuates between 14.1v and 12.5v.

Exactly the same on the petrol 1.33L Auris. The alternator (in this case) has its output reduced to 12.5v under certain conditions so that the Battery is neither being charged nor discharged. Ease off the accelerator and the voltage jumps back to 14.4 to gain a little 'free' energy as the alternator then becomes harder to turn and so contributes a little to the deceleration (braking).

 

[Tedl]

Thanks for the replies, I have to say these replies were more informative than the one received from Toyota technical.

👍