Battery Recharge Voltage & Amperage..

Little PbA battery: nominal 13.8 volts, max 4 (or so) amps

Big NiMH battery (2004 onwards) Nominal 202 volts, max 80 amps. But if you are talking about extended charging, much less than 1 amp. Doing *anything* to the NiMH battery requires unusual knowledge and skills.

 

Actually it charges at 14.8 volts.

 

No, it charges at either 13.8 to 14 V depending on how much
charge it's drawing, or reduces down to 13.6 in certain temp
ranges when you shift to D or B per the VLO output from the
hybrid ECU. The system tries to be more compatible with the
known float voltage differences appropriate for PbA in different
ambient temperatures.
.
problemchild, please check the voltmeter you used against some
other reference.
.
_H*

 

So it never applies a fast charge to the 12V battery?

 

Hi Richard,

No. The battery is just connected to the 12VDC bus, and the main purpose of the bus is to power the various ECUs, the stereo system, the lighting, and other accessories requiring 12V power. Hence the voltage on the bus is tightly regulated.

With a conventional automobile, the voltage produced by the alternator will increase somewhat as engine RPM increases. Hence if the 12V battery needs charging, the usual advice is to drive the car around for a while to allow a quicker recharge.

With Prius, since the 12V bus voltage is held relatively constant, all that is necessary is to make the car READY and leave it alone if the battery needs to be recharged; there's no need to actually drive the car.

 

Well, actually the 12V battery is "fast charged" sort of. My simple mind is boggled by how it works, but I left my amateur radio on for 5 hours last weekend by accident (more than 1 Amp draw) and noticed the 12V system voltage rose to 14 V when I started the car. It usually sits at 13.8 V. So a circuit that puts out more voltage when it sees a draw of more current is rather unique.

I say "fast charged, sort of" because it raised the charge voltage when it noticed the current draw was higher. This results in higher current still, which results in faster charging. It's not a traditional "fast charge" (20-40 Amp type) which would be undesirable for the deep discharge small capacity battery we have in the Prius.

 

How 'bout 0.2? Prius HV battery assemblies have been damaged or destroyed by enthusiastic charging. When the car does it there is temperature monitoring and active ventilation. You sure you want to do this stuff?