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Jump starting another car using a Prius

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by EricS, Apr 5, 2004.

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  1. EricS

    EricS New Member

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    Does anyone know how to jump start another car from a Prius? The manual tells how to jump start a Prius from another car, but not how do do the reverse. Since the engine will be off when the car is stationary, the 12 volt battery won't be being charged. Doesn't this mean that the Prius' 12 volt battery will quickly be drained by the other car?
  2. N9IWP

    N9IWP New Member

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    The 12v battery on the Prius is probably not beefy enough to start a conventional car.

    But, If you set it up in the jump start configuration, with ready on, the ICE will come on to charge the 12v battetry (or will come on to chare the big battery which charges the small battery)

    If you levae it hooked up lang enough, you will charge the other cars battery. *Unhook the cables* and then start the other car.

    At least that is how I think it would work.

    Brian
  3. bookrats

    bookrats New Member

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    As I understand it, other cars can jump-start your Prius, but the opposite is not possible (or not practical, one of the two.).

    There's a section in the Owner's Manual -- pages 238-241 -- that talks about how to jump-start your Prius.
  4. randalla

    randalla Member

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    Has anyone attempted using those jumpers that work from the cigarette lighter?
  5. DaveG

    DaveG New Member

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    The only way to "jump" another car from the prius is to hook the other car's battery up to the prius (probably with the front jump-start lug in the fusebox), and let the other car's battery charge for a few minutes.

    Then disconnect the prius before trying to crank the other car over.

    If you try and crank with the prius still connected, you can blow the master fuse and then you're not going anywhere either until it's replaced.

    Dave.
  6. tmorrowus

    tmorrowus Member

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    I'd be careful trying that.

    The other car's battery could be low enough that it'll pull the voltage on the Prius 12V battery so low it won't be able to run the computers and electronics in the Prius, so the Prius would shut down.

    Maybe everything would be fine in the Prius if you disconnected the other car battery and started up, but you may have discharged the prius battery enough that it won't start the computers. That's unlikely unless you leave them connected a long time, but possible if the Prius battery is marginal to begin with. You might lose computer settings (e.g. front window auto-up) and it seems possible but unlikely that running the computers at too low a voltage could cause them to corrupt their EEPROM or other memories.

    If there were other cars around I'd try using them to jump rather than the Prius. And if there were no other cars around, I might be afraid enough of damaging the Prius (and then having all cars disabled) that I might forgo trying this.

    If I were in the middle of a desert and needed to start both cars, I might try the following MacGyver maneuver:

    1. Disconnect the dead car battery from its car by removing the negative clamp.
    2. Disconnect the Prius battery from the car by undoing one or both clamps.
    3. Connect the Prius battery + to the dead battery + with jumper.
    4. Connect the Prius battery - to the chassis on the dead car.
    5. Start the dead car off just the Prius battery (note you'll need beefy jumper cables for this).
    6. While car is running, connect the car's own battery back by reattaching it's negative clamp. Note that this will cause a spark and needs to be done with a gloved (insulated) hand, and that this is dangerous since you can shock yourself or cause an explosion with the spark.
    7. Disconnect the Jumper cables, negative then positive.
    8. Run the car until the car charges it's own battery.

    This would avoid having the other car's battery bring down the Prius system voltage while engaged.

    I'm not suggesting this since I've never tried it, just brainstorming here. In fact, there is a danger in that the other car likely depends on it's battery to act as a capacitor and smooth the spikes in voltage from of the alternator. It is possible the Prius battery may be too small to do that effectively, resulting in damage to the other car's battery.
  7. DOC

    DOC Junior Member

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    I asked a Prius mechanic whether or not one could use those "cigarette lighter" gizmos to jump-start another car. He said probably not, but wasn't sure.

    Regarding a Prius jump-starting a regular car, he indicated it probably could be done but the problem is that the Prius battery is not as powerful as regular 12 volt batteries on the road and so it just might not work.

    A general rule of thumb, however, is that if you are going to use your car to jump-start another car, during the period when your car is charging the other car's battery, be sure and have your motor running to not totally drain your own battery.
  8. RobertO

    RobertO New Member

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    I really believe that, for the time being, we need to err on the side of prudence.

    I routinely jump start folks in parking lots using heavy duty jumper cable connected to my Toyota T-100 3.4 Litre V-6.

    But not my Prius. Most shopping centers have a security team that may/may not have a portable jumper kit. Then there's AAA, or "somebody else".

    A few years back I bought a rechargeable jumper/battery kit from Costco for about 60 bucks. They still sell them. The newer ones have some "improvements".


    I kept it in back of my truck or Mercedes depending on which rig my wife was going to drive out of town. She never had to use it, but I did (on both rigs and manyh other cars and trucks) It will turn over a big displacement engine easily.

    Notwithstanding the weight factor, that may be your Good Samaritan "out" when driving your Prius and you come upon somewon in need of a jump start.

    Bob
  9. DaveG

    DaveG New Member

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    You'd have to have the Prius in power-on mode to make this work effectively. When it's in "on" mode, the 12v system can draw from the high-voltage system so there's no chance of it draining the battery (it would just use the generator to keep the current up).

    That said, I keep a big jumpstart-pack in the trunk of my Prius so I can jump other cars from that, in addition to providing me with a 110v inverter and a worklight. Works like a charm.

    I wouldn't be keen to jump another car off of the Prius itself, but if it was an emergency, I wouldn't have a problem with it.

    Dave.
  10. inventor00

    inventor00 Orange County Prius Club

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  11. tmorrowus

    tmorrowus Member

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    DaveG-

    Even powered on, the Prius is limited in the amount of power it move from the HV pack to the 12V pack. I believe the limit is in the neighborhood of 100W but that's just a foggy memory. At any rate, it's less than could be sucked out into a dead battery in the other car.

    Having said that, it's not likely to happen nor to be a problem, just something to worry about :)
  12. Bo Ru

    Bo Ru New Member

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    I jump started another car from my Prius the way you would do it from any other car: battery to battery directly via jumper cables, with the Prius engine running. (I tried using the jump start lug in the fuse box of the Prius, but this did not work.) (By "battery to battery," I mean the negative cables were connected to the cars' frames, as always with jumper cables.)

    Since the Prius battery is in the back of the car, it's a little more awkward to make the connections, but once you uncover the battery, it's the same as jumping from any other car. (Location of the battery is described in the owner's manual.)
  13. richard schumacher

    richard schumacher shortbus driver

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    You were lucky not to have blown a fuse in the Prius, or worse. The Prius' 12V system is not built to supply more than 100A; the cranking load in a conventional car could easily be 400A.
  14. Eug

    Eug Swollen Member

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    Well, that's good to know.

    I've jump started a sedan and a van using the Prius. In fact, for the van, it was just a few weeks ago, with my 7 year-old Prius battery.

    No problems, but maybe I'm just lucky.
  15. seilerts

    seilerts Battery Curmudgeon

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    This is best done by disconnecting the negative cable from the Prius battery in order to isolate it, and thus connecting the Prius-side negative jumper cable to the negative battery post. Then, if for some reason there is reverse polarity, the worst case is having a bad 12V battery in your Prius, rather than a fried inverter. The Prius DC converter doesn't supply nearly enough charging current to be helpful during a jump, so there is no sense in having the car in Ready, thus the battery might as well be disconnected. It's really best to not ever use your Prius to jump start another car, but understandably there are sometimes emergencies.
  16. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Both of these posters were lucky. If the recipient car's 12V battery is marginal and just needs a little help, then the Prius can provide sufficient power.

    However, consider a worst-case scenario where you have below-freezing winter weather, a large V8 high-compression engine that is hard to crank over in the best of circumstances, and a dead 12V battery. In that scenario several hundred amps of current may be needed. If the jumper cables used are high-quality, that demand will be placed on the Prius electrical system. (If the jumper cables are low-quality, then the recipient vehicle will not start.)

    - If the Prius is READY, then the 100A DC/DC fuse may blow due to excess load placed on the DC/DC converter. This will be pretty costly to replace as all fusible links in the main relay/fuse box are contained in one assembly.

    - If the Prius is IG-OFF but the dedicated jumpstart terminal is used, the 120A MAIN fuse at the 12V battery may blow.

    If the Prius is IG-OFF and the jumper cables are attached directly to the Prius battery, then the worst that would happen (assuming correct battery polarity) is that the Prius 12V battery might be stressed to the point that it cannot be recharged.

    Therefore, if you have an emergency situation that requires using the Prius as donor vehicle, it would be best to have the car IG-OFF and connect the cables directly to the 12V battery. Even better to disconnect a 12V battery cable so that the Prius electrical system is out of the loop.
    2 people like this.
  17. andyprius

    andyprius Senior Member

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    About a year ago there was a p/u truck stuck at the gas station and they asked me for a jump. I patiently explained to them that my car is not equipped to jumper another battery, I could not do it. They resorted begging, crying and finally gave up. I think they were high on something after a all night binge. I recommend not doing it.
  18. Superbrownman

    Superbrownman New Member

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    ** I have tried this today and jump started a ford e350 van from 2005 and it worked...I jump started like any other car but pushed the gas pedal just enough to keep the motor running and it worked
  19. JimboPalmer

    JimboPalmer Nadir of Wrongness

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    If you jump start a Prius or with a Prius incorrectly, it will be a $4000 repair, so choose wisely.

    If you must jump start a Prius, use a Jump Pack, that halves the number of cables to attach incorrectly.
    Amazon.com: Schumacher XP400 400 Peak Amp Instant Portable Power Source: Automotive

    Then to jump start other cars, you hand them the jump pack and you have no risk.

    (The cigarette lighter is only connected if the car is Ready on every Prius I am aware of)
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