12V Battery questions from a prospective buyer

[Boji]

Hi everyone,

I've been learning a lot from everyone here, and I'm in the market for a 2010 Prius, and had a few questions about the 12V battery, specifically:

1) What is its purpose?
2) What does it power exactly in the current gen Prius?
3) Also, since there's no conventional alternator in the Prius, how is it recharged?

Pretty basic questions I guess, and I'm sorry if they're somewhere else but I tried finding them before posting this and wasn't successful.

Thanks!

[sandsw]

Hi Boji,
I am picking up my Gen III in a couple of weeks, so the answers below are what I have gleaned while lurking.

1) What is its purpose?
I believe the 12v batteru powers the low voltage electronics - radio, lights along with all the computers that reside in the Prius.

2) What does it power exactly in the current gen Prius?
I don't know.

3) Also, since there's no conventional alternator in the Prius, how is it recharged?
The 12v battery is recharged from the main high-voltage battery. I tend to think of the 12v battery as a mammoth capacitor that helps reduce ripple from the main supply.

Cheers
Warwick

[maxjlone]

One common situation is when you get up in the morning or are leaving work after many hours of freezing rain or snow/ice. There are times when your car looks like it's been in an ice cube tray in the freezer. In these cases, there's not much you can do but start the car and let it idle while you scrape the snow and ice off the windows. It sucks, but it's a fact of life. I left my '90 Toyota pickup at the Manchester, NH airport for a week and when I got back the entire truck was encased in about an inch and a half of solid ice.

[pinzvidz]

1. Its purpose is to power conventional automotive electricals/electronics. Plus, when the vehicle is switched off it is maintaining power to ECUs (for learnt adaption), SKS (smart key system), trip computer/audio system/clock to retain memory.

2. 12V battery powers everything except MG1/2 and A/C compressor.

3. DC-DC converter in the inverter unit. Converts 201V (from hybrid battery) to around 14V to keep the 12V battery charged.

[qbee42]

One important point not listed: When the Prius is powered off, the high voltage battery is completely disconnected. Some sort of power source is needed to power up the computers and reconnect the HV battery. The 12V battery serves this purpose. Think of it as booting up the Prius.

Tom

[Boji]

Originally Posted by pinzvidz

1. Its purpose is to power conventional automotive electricals/electronics. Plus, when the vehicle is switched off it is maintaining power to ECUs (for learnt adaption), SKS (smart key system), trip computer/audio system/clock to retain memory.

2. 12V battery powers everything except MG1/2 and A/C compressor.

So, basically, everything that's lit up in the car? Also, does it include the headlights and LED rear lights?

3. DC-DC converter in the inverter unit. Converts 201V (from hybrid battery) to around 14V to keep the 12V battery charged.

That's amazing... thanks!

[adrianblack]

Originally Posted by Boji

That's amazing... thanks!

If the 12v battery is drained, you will not be able to turn on the Prius. You need a "jump" -- but really only enough to boot up the Prius as once it's "READY" the HV battery and DC-DC inverter is supplying 14v to the electrical system. (And charging the 12v battery.)

Because there is not high draw starter like on a normal call, the 12v battery is much smaller than on a normal car ... and those little jump start kits would very easily supply enough power to the car to become "READY."

Also, if the HV (high voltage) battery is completely drained (After sitting for years, I suppose) you are SOL and the car would need to be towed to a dealer. There is no way to jump start a prius in that condition. I assume the MFD (multi-function diaplay) would show a "MAIN BATTERY FAILURE" message and the car would not be able to become "READY."

The manual says you need to drive the car at least every six months (if I recall the right time interval) to make sure the HV battery stays charged. Luckily NiMH batteries loose their charge pretty slowly, especially compared to LiION batteries.

[hotbrass]

Anyone know how many amps are required to jump start?

Would a 7amp sealed lead acid battery have enough amps to boot the Prius to "Ready?"

Also would a low amp trickle charge from a solar cell keep the battery up enough without hurting anything?

[Boji]

Originally Posted by adrianblack

If the 12v battery is drained, you will not be able to turn on the Prius. You need a "jump" -- but really only enough to boot up the Prius as once it's "READY" the HV battery and DC-DC inverter is supplying 14v to the electrical system. (And charging the 12v battery.)

Because there is not high draw starter like on a normal call, the 12v battery is much smaller than on a normal car ... and those little jump start kits would very easily supply enough power to the car to become "READY."

Also, if the HV (high voltage) battery is completely drained (After sitting for years, I suppose) you are SOL and the car would need to be towed to a dealer. There is no way to jump start a prius in that condition. I assume the MFD (multi-function diaplay) would show a "MAIN BATTERY FAILURE" message and the car would not be able to become "READY."

The manual says you need to drive the car at least every six months (if I recall the right time interval) to make sure the HV battery stays charged. Luckily NiMH batteries loose their charge pretty slowly, especially compared to LiION batteries.

I'm learning a lot, and now understand why Toyota didn't put Lithium Ion batteries in the current gen Prius--they'd probably get tons of complaints about the batteries discharging too rapidly. I'm sure it also has something to do with their contract with Panasonic (the supplier of the batteries last time I read)

On the same topic, I'm familiar with how to boost the car should it ever need it, but it begs the question, can anyone with a Prius boost someone else? Would anyone here do it? I wouldn't really be comfortable, and don't even know if that'd be feasible.

[David Beale]

There's a measurement on this forum (graph of amps vs time) that shows what is used to get to "ready". My measurements (DVM, not graphical) showed about a 50 A 1/2 sec. pulse, one for the brake booster and one for the electronics.

A 7 a-hr gel cell battery -might- be able to do it, but they aren't designed for that high a current. I recommend a portable "booster", sold in auto parts stores. I think the best type are the ones that plug into the cig. lighter socket. That would ensure you -don't- have to remember to charge it from time to time. Note that when the car is off the cig. lighter socket and the accessory socket are both shut off. You will still have to connect the device to the boost terminal under the hood. It's covered by a flit-open red plastic cover. Use a bolt above the fuse box for the -ve lead.