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Can a Gen III Prius jump-start another car?

Discussion in 'Gen III 2010+ Prius Technical Discussion' started by Launch Vehicle, Apr 13, 2011.

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  1. Launch Vehicle

    Launch Vehicle Junior Member

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    ....SAFELY? :noidea:
  2. cproaudio

    cproaudio Speedlock Overrider

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    Not when it's in "READY" mode. You can do it when it's not in ready mode. People have done it in ready mode and fried the DC converter. Not sure how much it costs to repair but I've read somewhere around $4000.
  3. qbee42

    qbee42 My other car is a boat

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    And when it's not in Ready, all you have is a tiny 12V battery. I wouldn't do it. If you want to jump other cars (or your own Prius), carry a jump box. That's what I do.

    Tom
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  4. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Listen to this ^^^^^^


    The Prius 12v is tiny. It's not any bigger because it doesn't have to be powerful enough to crank over an engine - just powerful enough to boot up a computer or two.

    If you try and jump start another car off it you're likely to do serious damage to the Prius 12v, let alone any connected (and probably expensive) components.

    I'd not try it, your neighbour will think you're ignorant but you wouldn't want to be helpful and end up with an expensive repair bill!
  5. JThayer

    JThayer Cubic Zirconium Member

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    Hmmm...it sounds like I have been lucky then. In my ignorance, I have jump started my wife's car on a couple of occasions (battery was going bad -- it has subsequently been replaced...) Prius was in ready mode -- ICE rev'd so as not to deplete the 12v battery.

    But now that I look at the Owners Manual, I do see the following:


    In a way, that last sentence is a lie (a.k.a. CYA text). As I have successfully done so, clearly it _is_ possible to use it to jump start another vehicle. But whether it was wise of me to do so...it sounds as if the answer is "probably not".

    Now that I know better, I won't be doing it again.
  6. fuzzy1

    fuzzy1 Senior Member

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    After $uffering engine ECU failure in a past car $u$piciou$ly $oon after providing a jump to another vehicle (thank goodness the limp-home mode worked), I don't provide jumps anymore even with a regular nonhybrid.

    Prius boo-boos are 10x more expensive, and have been reported here numerous times.
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  7. DavidA

    DavidA Prius owner since July 2009

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    What is scary is even the Toyota people don't seem know that the Prius 12v battery is too small to jump a regular car. When I was at the Chicago showing of the PHEV and the v, the Toyota guy I was talking to thought the 12v battery was the same size as in regular cars. When I told him that it was about the size of a motorcycle battery he told me I was wrong.

    I said this... "The smaller 12v battery is used only to boot the computers of the car, and since there is no starter to speak of, there is no need for a conventional larger battery." I offered to show him so on one of the 2011's they had for test drives. He quickly went into another spin about the PHEV's other assets. So then we sat in the PHEV. I asked if I could see the display on the dash. "Sure!" Tried to turn the car on, and oooopsie! The 12v battery was dead! I am not making this up.
  8. David Beale

    David Beale Senior Member

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    Yuuuuup.

    Reving the engine WILL NOT give you more 12V power. The Prius does not have a belt driven 12V alternator (or any 12V alternator for that matter). 12V power is derived from the 201V traction battery through the invertor (there is a charge circuit in there). It works the same whether the engine is running or not, and is not affected by the engine RPM. Well, it may be affected a bit if the system is charging the traction battery, but you probably wouldn't notice it.
  9. CivicSky

    CivicSky Member

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    Maybe a little bit off topic. I connected my HID lights with relay harness directly from the terminal inside the underhood fuse box. Am I getting the power solely from the 12V or the 12V & traction batteries combined? I turn on headlights only when the car is "Ready".
  10. GBC_Texas_Prius

    GBC_Texas_Prius Member

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    Interesting that someone actually tried and were successful jumping another car off the Prius. I would never do that. When buying the car, I told the salesman that I considered it a feature that I can say, Hybrid, sorry, can't give you a jump.

    It seems like when I gave a jump off my former non-hybrid cars, the other car had a battery with a shorted cell giving smoke off the jumper cables.

    At some point, I plan on buying one of those portable battery jumper boxes in case the Prius' laptop sized battery gives out. If the other car won't jump off that, it won't jump off the Prius.
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  11. macman408

    macman408 Devil's Advocate General

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    Any time it's in Ready, all 12V power is effectively supplied by the traction battery only via the DC-DC converter (which drops the traction battery's 201.6 V down to something around 13.8 V, which will trickle-charge the 12V battery. The 12V battery might supply some power in the event of a sudden drain (eg turning the lights on), but in the long run (by which I mean after less than a second) the 12V battery will be doing nothing. Once the car is in Ready, it's actually possible to disconnect the 12V battery, and the car can keep running because all 12V power is being supplied from the traction battery.
  12. cyclopathic

    cyclopathic Senior Member

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    UK variant? had to remove one on mine (US Gen III) and it is a full size battery.. nothing like M/C.
  13. PaJa

    PaJa Senior member

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    Sorry, but Prius 2010 doesn't have a full size 12V aux battery. The OEM battery has about 30Ah. The standard crank battery is about 55Ah for petrol engines and 70-80Ah for diesel ones. So our bootup battery is half sized.
  14. nickfromny

    nickfromny Member since 2007

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    Read your manual. Have jumped several other cars off my Gen 2's. have to remind myself how to do it by reading the instrcutions in my owners manual.
  15. twittel

    twittel Senior Member

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    Wow some very lucky jump starters here. Y'all better buy some lottery tickets while your at it.:)
  16. jayvee

    jayvee Member

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    I've jump started other cars twice, from the 12V Aux battery (not from the jump terminal under the hood.) No problems to report.

    While not having a lot of capacity, that battery does have enough power to jump another car if its only problem is a dead battery (you won't get much cranking time if the car has other issues and won't start.) But I'd ALWAYS do jumps with the vehicle powered down. Never in Ready mode. And even then, as mentioned above, you do run a risk of damaging the charging circuits - not so much from the extra current that the dead battery might draw, because I imagine the trickle charger is current limited, but from the voltage feedback that will occur once the other car starts and its alternator kicks in to charge the dead battery, trying to push 14+ volts into the Prius' charger circuits. Not sure of the circuit details, but there's likely some risk, as mentioned above.

    However, to be safe to the charger and other electronics, you should really disconnect the battery (+) terminal from the post before connecting the jumper cable to the post. Of course, that means you're going to need to do some re-programming of your radio presets, etc. that will lose power.

    However, there is a safe way to do this: If you're one of those folks who can't help but offer assistance to everyone with car problems (and thank goodness there are some people like that), you could buy a battery disconnect post switch, connect a smaller 12V sealed lead acid battery (such as used in alarm system backup applications, etc.) directly to the Aux battery cables, and then use the switch to disconnect the 12V Aux battery while leaving the small 12V SLA battery connected, to keep the vehicle electronics memories powered. This would allow you to not have to reset all of your electronics, and still provide safety to the Prius circuits when someone needs a jump.

    I may do this one of these weekends when I have some time....
  17. twittel

    twittel Senior Member

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    I'm taking Gbee42's advice and get myself a portable jump start battery. They're small enough to fit nicely in the back cargo area. I do like to help if someone is in need.
  18. qbee42

    qbee42 My other car is a boat

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    All Prius have a small 12V battery. You will discover this yourself once you have to replace it. No standard battery will fit without modifications.

    We can argue about whether it is bigger than a motorcycle battery, but that probably depends on the motorcycle. Many motorcycles have larger engines than your Prius. Regardless, the Prius battery is small.

    Tom
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  19. cyclopathic

    cyclopathic Senior Member

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    do we have a different understanding of what is "full size"?

    The 12v battery on US Prius is ~x3-x4 times bigger then typical motorcycle battery, and about the same size or bigger as used in compact cars Mazda, Honda Civic, etc. Not sure what the OEM rating for capacity or crank amps are, but it has enough to jump-start, been there/done it.
  20. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Lets put a stop to this!

    The Prius battery is smaller in size AND power output than MOST car batteries.

    I wouldn't want to jump start a diesel car on a cold morning using the small (small physically and in power output) Prius battery.

    There again it's your car, you do with it what you want - you're the one risking big repair bills.
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