What is the 12 volt battery for?

toad · 01-28-2007, 12:18 AM

This may be a stupid question but why does the prius have a 12 volt battery rather then power everything from the traction battery? I understand the 12 volt battery powers the normal things (radio, headlights, etc.) but why can't you power this from the hybrid battery?

Thanks.

Frank Hudon · 01-28-2007, 12:32 AM

<div class='quotetop'>QUOTE(toad @ Jan 27 2007, 09:18 PM) [snapback]381852[/snapback]</div>

Quote:

This may be a stupid question but why does the prius have a 12 volt battery rather then power everything from the traction battery? I understand the 12 volt battery powers the normal things (radio, headlights, etc.) but why can't you power this from the hybrid battery?

Thanks.
[/b]

short answer is, it's used to boot the computer which closes the HV relay which then powers the car. Also the 12 volt is charged from the inverter so in reality it's charged from the HV battery.

Orf · 01-28-2007, 01:12 AM

Written on my battery are words to the effect that it powers the brake system.

qbee42 · 01-28-2007, 11:04 AM

In addition, having a separate 12V battery allows the traction battery to be completely disconnected when the car is shut down, preventing a costly total discharge in the event a door was left open or something like that. Furthermore, the inverter would have to run to power any 12V items, such as lights and the radio, unless you want to have purpose designed lighting and electronics, plus high voltage wiring running around the car.

Tom

Frank Hudon · 01-28-2007, 11:49 AM

<div class='quotetop'>QUOTE(Orf @ Jan 27 2007, 10:12 PM) [snapback]381868[/snapback]</div>

Quote:

Written on my battery are words to the effect that it powers the brake system.
[/b]

and the power steering

Allannde · 01-28-2007, 01:39 PM

<div class='quotetop'>QUOTE(qbee42 @ Jan 28 2007, 08:04 AM) [snapback]381932[/snapback]</div>

Quote:

In addition, having a separate 12V battery allows the traction battery to be completely disconnected when the car is shut down, preventing a costly total discharge in the event a door was left open or something like that.
<snip>

Tom
[/b]

This is the real reason.

If you ever have to replace the 12v battery, thank your lucky stars it wasn't the traction battery. Toyota engineers went to amazing lengths to protect the traction battery. We need to be grateful that they did.

duanelaugh · 01-28-2007, 04:30 PM

<div class='quotetop'>QUOTE(Allannde @ Jan 28 2007, 01:39 PM) [snapback]381983[/snapback]</div>

Quote:

This is the real reason.

If you ever have to replace the 12v battery, thank your lucky stars it wasn't the traction battery. Toyota engineers went to amazing lengths to protect the traction battery. We need to be grateful that they did.
[/b]

Excellent answer!!!!!!!!!!!!!!!!!!

toad · 01-29-2007, 10:02 PM

Thanks everyone.

All are very good points. I guess it would be very bad to have the traction battery completely drained.

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01-28-2007, 12:18 AM	#1
toad Join Date: Jan 2007 Posts: 41 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	This may be a stupid question but why does the prius have a 12 volt battery rather then power everything from the traction battery? I understand the 12 volt battery powers the normal things (radio, headlights, etc.) but why can't you power this from the hybrid battery? Thanks.

01-28-2007, 01:12 AM	#3
Orf Senior Member Join Date: Mar 2006 Location: Devonport, Tasmania Posts: 335 My Car: 2006 Prius Package: I-Tech Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Written on my battery are words to the effect that it powers the brake system.

01-28-2007, 11:04 AM	#4
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 5,691 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 6	In addition, having a separate 12V battery allows the traction battery to be completely disconnected when the car is shut down, preventing a costly total discharge in the event a door was left open or something like that. Furthermore, the inverter would have to run to power any 12V items, such as lights and the radio, unless you want to have purpose designed lighting and electronics, plus high voltage wiring running around the car. Tom

01-29-2007, 10:02 PM	#8
toad Join Date: Jan 2007 Posts: 41 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Thanks everyone. All are very good points. I guess it would be very bad to have the traction battery completely drained.