[hinalea]

My 6 month new 3,000 mile Prius 2004 just surprised me. After whisking us from Palo Alto to San Clemente (LA) 412 miles at 75MPH, even up and down the Grapevine (4400 ft. Tejon Pass) and getting 47MPG anyway, it got a well-deserved rest.

I went out and used the NAV to look up a couple of addresses, and forgot to turn the car off, I guess. Bad move. About 4 hours later, I went to take my wife for an appointment, and was perplexed to find the engine check light on, the 'Park' light on (dimly), and it would not turn on. Trying various functions, it would run the window down, but very slowly, and the reading lights worked, but very dimly.

I surmised that I'd run the 12V battery down, and had to call a tow truck to get a jump start. The Toyota dealer said 'tow it in', and denied that it could be jumped. Growing up doctoring my cars has led me to think for myself in these matters, so I searched the owners manual and found the 'jumpstarting' section. I had to use the front, engine compartment terminal (nice of Toyota to think of this!).

Not nice of Toyota to not build in a way to 'self-jump' from the well-charged main battery! Stupid, stupid, stupid to make the car so it cannot start up if its tiny 12V battery is low, when gobs of electrical energy is stored nearby.

The jumpstart immediately allowed the car to start up, and it seemed to recharge the battery quickly enough that after a couple of minutes, though the engine turned itself off, it kept operational.

I immediately went out and bought a very compact battery-containing jumpstart device from Kragen Auto for $45. You charge its battery up, and it will jumpstart anywhere. It now rides in the trunk. I cannot afford to have this happen at a trailhead, or in an airport parking lot after a long trip, or just before a critical appointment or meeting. So for just $45 I added a self-fixing backup feature Toyota neglected to provide. I recommend it if you own a fly-by-wire car that freezes without auxilary power. If you can run the 12V battery down this easily and quickly, I imagine that a light left on would do it overnight, too.

If I had hammered in the habit of ALWAYS locking the car on leaving, even in my own garage, it would have complained and refused to let me leave it on. It is good about that.

One odd thing is, although the Prius is so dependent on its little 12V battery, there is no way to monitor the condition of the 12V battery charge!

 

[SkipHuffman]

I immediately went out and bought a very compact battery-containing jumpstart device from Kragen Auto for $45.

I have heard that you can jump a Prius from a couple of 6V lantern batteries in series. Anyone tried this?

 

[johnson487682]

I immediately went out and bought a very compact battery-containing jumpstart device from Kragen Auto for $45.

I have heard that you can jump a Prius from a couple of 6V lantern batteries in series. Anyone tried this?

You don't need very much juice, so it is not necessary to get a portable jump-starter. I bought a portable air compressor for only about $40 at Walmart (Campbell Hausfeld CC2300). It has a "cigarette lighter" outlet for plugging small equipment (e.g. cellphone) into its internal 12V battery. I made a jumpstart cable that has a "cigarette lighter" plug on one end and two clips on the other. Not only can it jumpstart my 12V battery if it goes dead, but I periodically use it to maintain my tire pressure at 42 psi, so it's not just dead weight in the trunk.

I heard a theory that a 9V battery has enough juice to boot up the Prius computers and keep them running long enough to turn the key and bring the main battery online, but I haven't heard of anyone who had tested that theory. It should be pretty easy to do by simply disconnecting the 12V accessory battery and connecting a 9V with clip leads, but you'd want to disconnect the 9V battery immediately upon turning the key, because the DC-to-DC converter would want to charge it up to 13.8V as soon as it comes online.

Douglas (2002 Silver, Wisconsin)

 

[hinalea]

Jumpstart the computer

The air compressor is a good idea, thanks. It happens I have live air in my home garage, so I don't need that. This jumpstart rig is similar, very small, so it works for me. It is a brick, though.

It would be interesting to hear just how little/light a battery would do the job without disconnecting the 12V. I suspect a little 9V battery would get run right down trying to charge the 12V, but who knows--even discharged, it may be above 9V.

It probably doesn't take many VA to start the control computer; the question is how much drain a discharged aux battery would be.

Perhaps someone will notice this and post their experience--"I jumped my Prius with my transistor radio...". It would be light and easy to carry a pack of 8 AA batteries if you knew it would do the job! I have some electric shades that use a tube of 8 in a row to get 12V.

This does avoid the question of why Toyota put us in this situation! Fortunately, our bodies evolved with a little more fault tolerance than this, or we'd be in trouble.

 

[DanMan32]

Toyota disconnects the hybrid battery completely for safety reasons. Both poles of the battery are controlled by relays, which are energized by the battery ECU. The hybrid ECU instructs the battery ECU for hybrid power.
This was done over many concerns about crash safety. This keeps the high voltage well maintained unless it is absolutely safe, as communicated by the ECUs, that it is safe.
It is the aux battery that provides power when the hybrid is not running. When the hybrid is running, the DC-DC converter takes over the 12V power, so the aux battery is no longer needed, other than to filter out power transients. There isn't much of a load to start the electronics, which is why they put a smaller 12V battery.

Toyota did consider situations where we may accidentally drain the battery. The dome lights automatically shut off after 15 minutes, in case we left the door open. However, if their switches are left at ON instead of DOOR, the body ECU can't turn it off.
Also the headlights will turn off automatically if the car is shut off and then the driver door opened.

 

[hinalea]

Thanks for the info

Thanks to DanMan32 for the interesting details.

It would be nice if Toyota monitored the condition of the 12V battery, and if the car is turned on via the two non-driving modes, powered down automatically with still enough power left to power up again. It's not so good if it just quietly dies, since there is no way up again without a jump.

It would also be nice to be able to display the condition of the 12V battery, as well as other things the car computer knows about. I think the NAV system is way underused now. It could easily, for example, keep a log of your travels and mileage results via the GPS (unless you don't want your spouse to know...), keep long-term mileage/performance statistics and let you look at them, let you know when you're using your actual brake linings rather than just regenerating, etc..

It's a shame to have all this computing power onboard and not take advantage of it (or alternatively, allow you to add a recreational computer that can use the NAV screen only, to protect the mission-critical computer).

 

[efusco]

I'm not going to be able to provide exact details, but nearly a year ago someone on one of the Yahoo groups permanantly installed an auxilary 12v 'jumper' battery. This baby fit into the same area that the current 12v is (it was a small marine or motorcycle battery I think). He permanantly attached cables but with a decent heavy duty switch such that in the case of failure of the main 12v he could just go to the back, pull off the one panel where the battery is, flip the switch and start the car. Once started you can open the switch again and move on.

Once in a while he would close the switch just to allow the small battery to charge up.

This seems a pretty elegant solution. One could also probably rig something similar under the hood.

 

[AgentElrond]

So for just $45 I added a self-fixing backup feature Toyota neglected to provide. I recommend it if you own a fly-by-wire car that freezes without auxilary power.

...and anyone with a different car should do... what instead?

Sorry, but maybe I'm missing something here (it's been one of those days/weeks/etc. anyway). I don't know of any vehicle that handles a low (or dead) 12V battery any better/differently; i.e. if you run it down, you're stuck until you address the issue. It would seem that, if one expects this to happen often, one should have an alternative available - regardless of what type of vehicle it is. I've only ever run a battery down once (and not in a Prius) - once was enough of a lesson "not to do that again".

It does seem unusual for the 12V to drain while the HV battery had a decent charge, unless the HV battery was "low" also and this is just another example of an (undocumented?) "self-preservation feature".

 

[ehurtley]

Well, the reason it's 'annoying' in the Prius is simply because the Prius has such a huge battery already. I understand the annoyance, but I also understand why to leave it disconnected. It would have been nice for them (since they have already designed in all these electric wonders,) to add an 'automatic' backup 12v battery. My idea is that the ECU would actually be powered by this second 12v battery, so that even if you left every other 12v device on for two weeks straight, the ECU could always start up to turn on the hybrid system. And if it detects the secondary 12v getting low for whatever reason, it trips a breaker, whereupon you have to manually cycle it under the hood or something. Basically, so that you never EVER have to jump the car under any circumstances, and most of the time, even if you left things on, you wouldn't even have to get out of the car to 'jump' it. And even under the worst circumstances, you'd just have to flip a switch under the hood. (Or maybe even a small switch inside next to the SE/SS on/off switch.)

 

[Victor]

It does seem unusual for the 12V to drain while the HV battery had a decent charge, unless the HV battery was "low" also and this is just another example of an (undocumented?) "self-preservation feature".

I think you missed the point that the HV is disconnected from and seperate from the 12V system. When the car is off, and the 12V is dead, how could the HV help?

You need the 12V to cause the HV relay to activate to provided power. Only then is the HV able to supply 12v (via the inverters).

uting a tap into the HV battery at the 12V point is theoretically possible, but then you will (could have) a whole lot of problems with the system.

By far, the best solution is the one mentioned above about a 2nd 12v battery and a switch. I think I will investigate this and try to get my dealer to install a similar system.

 

[Jim Biggs]

Jump Start

A jump start point was the first thing my salesman showed us how to do! He showed us the Positive 12 volt point under the hood and told us to pickup the ground anywhere.
Jim
:wink:

 

[DanMan32]

Victor may have stumbled on something here.
It could be possible to provide a low current 12V source from the HV battery for emergency jump only. I think one of the problems though is ground isolation. They seemed to have designed the HV system to be floating from chassis ground.

I wouldn't go beyond an emergency jump though. You definitely do NOT want to drain the HV battery. Having it connected only when in READY mode completely prevents, or at least well minimizes that problem.

Repair manual's solution in fixing a drained HV battery is to replace it.

 

[zinzindorff9]

Toyota spent eight years developing the best system. I'm sure they examined all the previous mentioned POSSIBLE problems and obviously dis counted them. If they thought they would have had a problem, they would have thrown in a fullsize 12 volt drycell like one of the new Optimas. By use of the "jump start" port they feel they have solved this very slight future problem. Remember, you are not jump starting an engine starter, you are adding power to the "ECM"

 

[AgentElrond]

By far, the best solution is the one mentioned above about a 2nd 12v battery and a switch.

So then every car, hybrid or otherwise, should be equipped with a second 12V battery in case the driver runs the primary 12V battery down. Okay...

 

[BIF]

Hmm...I have a spare tire. And spare fuses. And extra aspirin in the glovebox.


...so maybe I should carry a spare 12v battery too!

 

[zinzindorff9]

When was the last time you used your spare tire?

 

[SkipHuffman]

When was the last time you used your spare tire?

I use mine to fend off the affections of young women.


Oh, you mean the one in the car? Almost never. I lost the jack handle on my truck eight years ago (stolen along with the radio). I haven't had a need for it. I don't remember if I ever used it before that (since 1993).

Modern tires are really, really good. I have considered just carrying a can of fix-a-flat instead of a spare.

 

[Victor]

By far, the best solution is the one mentioned above about a 2nd 12v battery and a switch.

So then every car, hybrid or otherwise, should be equipped with a second 12V battery in case the driver runs the primary 12V battery down. Okay...

Not quiet what I said. Of the solutions offered, I personally find the 2nd battery and switch a good one.

All cars can get a flat battery, but you dont get so many questions about how to solve the problem on non-prius models. Naturally, the best solution is not to let it go flat in the first place, but it does happen.

 

[zinzindorff9]

OR, My point about the "spare tire" when then was the last time you had your battery "jumped" The Prius should have taken care of all the previous reasons by completely shutting every thing down unless you have really "fowled up"

 

[Fredo]

About 15 years ago, several manufacturers were selling batteries with a second section so you could "jump-start" your own car. From what I remeber, they were larger than a standard battery, so they didn't fit all cars, and about 50% more expensive. I haven't seen them in a long time, and I think they were mostly discontinued.

Rather than a pack of AA cells, which will probably also be dead when you need them, how about a capacitor than can be manually charged. I'm thinking something like a shaker flashlight. Rather than shaking, though, I'd put a 2 foot long lever inside the rear hatch that you could pump a few times to charge the capacitor. This way, you could almost guarantee a start every time, and be much more convenient when the 12 V battery eventually dies.