Battery charging system

The 12v in a Prius is a very small battery, used mainly to turn on the cars computers (start the car) and is very sensitive to being discharged quickly and when discharged a vew times it needs replacement and that isn't cheap. So you have the correct advice, just do it and let the computers sort out the charging. The HV battery will not charge the 12v in acc mode but it does in Ready mode.

 

Steve ready mode is the only mode where the 12v battery is being charged by the HV battery, "as long as the car is not in neutral" the engine can start and stop to keep the HV battery in a healthy state, and is then able to keep the 12v charged.

The 12v battery is relatively of small capacity, and as it ages this capacity is reduced. Hence the reason for the recommendation to keep the car in ready mode.

John (Britprius)

 

It is not true that the traction battery charges the 12V battery. The situation is more complex than that.

When the Prius is READY, the traction battery will power the inverter. A DC to DC converter within the inverter will provide power to the 12V bus which powers most of the electrical accessories, and the voltage typically will be ~13.8VDC. The 12V battery is attached to that bus, and consequently is charged only when the Prius is READY.

When the Prius is ACC-ON or IG-ON, the inverter is not operating. Hence the 12V battery provides power to the 12V bus under those operating modes. The current draw is especially high in IG-ON mode and that mode should not be utilized for any prolonged period. IG-ON is the mode where all instrument panel warning lights are on.

The ACC-ON mode can be used to listen to the stereo, assuming your 12V battery is in decent condition. If you should find that the battery dies after listening to the stereo for an hour or so, then obviously the 12V battery is in sad condition and needs to be replaced or at a minimum, fully charged.

 

Patrick the 12 volt battery is charge from the HV battery "the power source when the ICE is not running" I agree that there is a voltage conversion, but to say the HV battery does not charge the 12v is akin to say your electricity supply does not charge a battery when using a battery charger.

John.

 

I'm trying to explain to the OP that the DC to DC converter within the inverter is the means by which the 12V battery is charged, and not via some hypothetical direct connection to the traction battery. That is why the 12V battery is charged only when the Prius is READY.

 

Unless the car is READY, those relays are open and no electricity goes into or out of the HV Battery, so the 12 volt battery is on it's own. (So you can never drain the HV battery dead listening to the radio)

 

While I agree completely with the way you describe the system unless the ICE is running the electricity that charges the battery comes from the HV battery however it is controlled or supplied. Your first line says " It is not true that the traction battery charges the the 12 volt battery".

 

Yes, very good conversation . H

 

The ultimate source of Prius power is the gasoline that you pump into the fuel tank. The gasoline engine, converting the chemical energy in the fuel to rotational energy, will power the car when at speed.

The traction battery provides power to start the gasoline engine by spinning MG1 and also powers the Prius under low speed acceleration conditions, by spinning MG2. That battery is charged via the motor generators when regen braking and will also be charged when the hybrid vehicle ECU determines from the traction battery ECU that the traction battery needs to be charged.

The inverter serves three different major functions:

1) convert high voltage DC (~200+VDC) from the traction battery to ~500V three-phase AC and vice-versa, to power MG1 and MG2 and also convert regen braking power from the MGs back to the traction battery.

2) convert high voltage DC from the traction battery to high voltage AC to power the air conditioning compressor.

3) convert high voltage DC from the traction battery to 13.8VDC to power the 12V bus (which most electrical accessories are powered by, other than the air conditioner compressor) and also charge the 12V battery. The 12V battery provides power to boot up the various ECUs and energize the system main relays which allow the traction battery to be connected to the inverter. It also serves as an emergency power source when the DC/DC converter in the inverter fails.

Therefore, in my opinion, the inverter is more than a conduit of power (I think of a wire cable as a conduit), but it's up to you to decide how you wish to characterize it.

 

My Gen 2 also used 13.8 volts, but my v is consistently 14.4 volts. In my dreams, this means it would charge a low battery quicker.

 

Yes, that would be a reasonable conclusion. Is the 12V battery in the Prius v similar to 2G, with regards to physical size and being AGM?

 

I will be in my sister's v before my own. I have been assuming they are identical, but I can't document that.

 

Just one point to add to the above the car must not!!! be in neutral with this procedure, as in neutral the engine cannot start to recharge the HV battery.

So that it is possible to discharge both the HV battery and the 12volt battery. Obviously the best and safest mode to be in is park.

Things will still be ok in reverse or drive, but as the engine starts and stops to maintain the condition of the HV battery the car will try to move.

John (Britprius).