In most cars the main purpose of the 12 volt battery is to crank the engine in order to start it. Powering the lights, radio, 12 volt outlet, etc. are ancillary functions. In the TCH the 12 volt battery does not start the engine, that's performed by MG1. So I have several questions which I'll post here, but may be better asked on the Prius board.

1. Since the major portion of a car's 12 volt battery function is not required (starting the engine) does the 12 volt battery last longer than in non-hybrid cars?

2. Normally the battery is charged by the alternator. What charges it in the TCH. I assume it's either MG1 or MG2.

3. When a battery dies it's too weak to generate the power necessary to turn the starter fast enough to start the car requiring the jump-start. What causes the 12 volt battery to be considered dead in a TCH? Is it when it cannot power the computer adequately? It seems that it can be "deader" and still work since it doesn't have to provide the power necessary to turn a starter motor.

4. On a related note when a battery dies you have to jump-start the car, allowing the other vehicle's battery to do the work for your dead battery. What are you doing when you jump-start a TCH? Are you providing power to adequately power the electronics?

5. It's pretty obvious by the sound of the starter trying to turn that the 12 volt battery is having problems in a non-hybrid car. Since the car "starts" without the ICE running how does it manifest itself in the TCH?

Hi,

1. Life - assuming ordinary use, it does last longer. However there are latent battery loads associated with the key-less access system that put a small but steady load on the battery. The recommendation is to disconnect the battery if the car won't be started for more than three weeks. Worst case I've read about was a car that self-discharged over a month or so in the winter and froze the battery.

2. Charging - the power inverter provides 12 VDC. In the case of my NHW11 Prius, up to 1 kW, ~70 A. The power comes from the traction battery which is charged by MG1 when stationary and MG2 during regenerative braking.

3. Definition of dead - when the control electronics won't work. I don't know of any tests to identify the minimum battery voltage but I've had my Prius down to 11.48 VDC and it kept working.

4. Jump start - there is so much FUD so I'm loath to answer. IMHO, the safest way is to use the jumpers to put a charge on the dead hybrid battery. Then remove the jumper cables before attempting to start the hybrid. The reason is we don't know the quality of power from the source vehicle and there is a risk of voltage transients when disconnecting jumper cables. Caution first.

5. How to tell if weak - it looks to be a binary situation, either the control computers work or they don't. I'd use a VOM and measure the voltages.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
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Thanks for the answers Bob. We answered the post about jump-starting a hybrid car yesterday. That just got me wondering about it. Thanks again.

Not really, It is easily degraded by a small number of full cycles (as in leaving your dome lights on for a few days by accident)

It is charged from the main traction battery via an inverter whenever the TCH is in use.

Yes, but a weak auxilliary battery can cause miscellaneous problems that occur randomly.

Yes

As above, a low Aux battery voltage (ie. below 12v) will cause random problems. If it is really weak, the system will not power up. You can jump your TCH with a small 12v external battery very easily.


JeffD
(I am extrapolating experience from my 2004 Prius - a sibling of your TCH)

Excellent questions, things I've been wondering myself! As a matter of fact, the questions I had were even more generic than that. For example: what is powered solely by the 12volt battery vs. the NiMH battery, and/or when do they share power distribution to the various components (besides the obvious propulsion functions discussed ad nauseam in this forum, duh!)? Items that come to mind are the smart-key, the dash, lights, etc.

Might be a good guess that the 12V battery would last longer. You would think the battery has less charge / discharge cycles. The 12V battery is charged by the DC-DC converter from the traction battery. If the 12V battery dies, I believe what will happen is the traction battery will disconnect itself to prevent it from going dead endlessly charging the 12V battery. I believe it's kind of a safe mode. Boosting the 12V battery will power the electronics, but also if the traction battery has disconnected it will allow it to assume it's safe to reconnect. I believe that is why sometimes you can't just attach booster cables and start up right away. YOu might need to let the booster battery stay connected for a while to allow the traction battery to come out of it's safe mode (I guess once it sees the 12V system will no longer drag it down below safe charge level).

Two climate control systems, one inside and the other at the tailpipe.

Distance: 29169km (75% city - 20 min trips)
FE: 6.77L/100km or 34.7 mpg
Operating Cost: $0.066/km / $0.107/mile

The 12V converter charges the 12V battery from the 245V battery pack. I have no idea if the TCH 12V battery has a longer life than a traditional 12V starting battery. Like any 12V lead acid battery, it will fail early if run flat (map/trunk lights left on.)

If the 12V battery dies, only a few amps of power is required to "jump" the TCH. The battery only needs to start up the TCH computer. Once the computer is running, the HV battery powers the TCH and starts the ICE.

If the there is not enough power to "boot up" the TCH computer, I imagine you would know it right away. Only a few amps are needed, and if not present, I doubt the power door locks, radio or dash lights would work either.

Edit: relays disconnect the HV traction battery when the TCH is off, for safety and to prevent parasitic loads from draining the HV battery. I just came back from a 23 day vacation, and the TCH started right up. No problem with the 12V or traction battery.

Orcrone,
Please do *not* double post threads. The topics have been merged.

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A friend of mine ran down his Lexus and talking with him reminded me of a story I read somewhere else. Apparently someone came back to a dead 12V battery so they took a pair of 6 V. lantern batteries, wired them in series, disconnected the 12V battery, and started the car. While it was running, they reconnected the 12V battery and once it had a charge, they disconnected the two lantern batteries.

For the life of me, I can't remember went or where I read the story and it may have been speculation. Still, 'any port in a storm.'

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

I tried two lantern batteries w/2001 Prius and it was not enough for booting up. There is supposed to be a deeper trick where you pull the brake pump fuse so that it does not present a large load during boot-up but I've never tried that. Expect a warning light if the brake pump is asked to run, but does not.

DAS