Jump Start a Prius with a Prius?

Really you just need enough juice to prime the brakes and flip the HV battery relays. Prius to Prius is OK.

The problem comes when you are doing Prius -> Hummer or something with a rediculously sized engine or a severely discharged battery. This draws a ton of current from the system which is too much for the poor Prius in some cases. The other caution is polarity protection, reversing leads can be catastrophic in a Prius (or any car really).

I would just jump it normally. Turn on good Prius A. Then wait for the HV relay click sequence, wait for the ICE spin up after 7 secs. Then connect the leads from car to car. You can use the jumper posts under the hood or the actual terminal in the boot, your choice. Then get in bad Prius B. Wait a couple seconds, press the brake pedal and wait for that "mrawwwwwwwwwww" sound to stop which is the biggest current draw of starting a Prius AFAIK. Then press power and wait until its ICE has started before disconnecting.

 

I've done prius to hummer sized vehicle. there was an F350 v8 turbo-diesel, a classic 60's mustang, a tour bus/Winnebago, and a v12 diesel tractor/land mover... it all depends on how you hook it up and how long you wait. for the land mover it was a 20 min wait (24v system disconnected to charge in series of 12v).. the bus took only 5 mins or so. the F350 took about 3 or 4 mins... (at it's worse)...

then there was the power outage where i pulled 980 watts through my 12v to 120v inverter for about 7 strait hours... but that's a different story....

 

There is a lengthy thread elsewhere on the forums explaining the foolishness of the above actions. It has to do with how deeply the battery was discharged and how much the vehicle will pull from your system vs. its own battery when it cranks. Even just a shorted battery by itself hooked up to jump start can pull more than the Prius can dish out in bad situations.

And those sparks are normal but one of the enemies of the Prius. I reccommend you invest in a set of "smart" jumper cables. One purpose is that they prevent sparks, the other is that they have automatic polarity detection/protection. So you hook the two cables on one side to any terminal on one car and the other two cables on the other side to any two terminals there. It doesnt matter which is + and which is -. It also delays a second or two before making the connection preventing any arcing. Not really dangerous as far as combustion with the Prius (still a concern on older vehicles with vented batteries) but it is dangerous in terms of the kilovolts of arcing going through the most electrically advanced vehicle on the planet. For $10 to $20 depending on where and when you get them, it is really a no brainer. I would use them only for jump starting the Prius or other small loads because they are generally thin gauge and not really meant for more than charging a 12v. In a Prius that is the equivalent of jumpstarting though

 

Yeah...I agree with V8CobraKid. It's definitely possible to jump something like a Hummer with a Prius. It's just a matter of getting the 12v battery charged.

However, like Toaster mentioned, it can also be dangerous. If you were to try to start the Hummer with the Prius still connected, the Hummer would be trying to run off of the Prius's alternator, which is not a good idea...at all.

 

How does a mere 12V all of a sudden become kilovolts?

 

1) The Prius does not have an alternator.
2) If the vehicle has a deeply dead battery, it could be more current pull then trying to start it.

Dialectric breakdown of air is close to 30kV or 33kV per cm. Obviously is depends on many things but that is sort of a rule of thumb. If you see sparks, then it is crossing air. Even if it is 1mm (less than 1/25th of an inch) you are talking about 3kilovolts.

 

Well, I guarantee you that there is only ~12V (from the battery) available on the 12V bus before the negative cable is attached to the body (and should you doubt this, use a voltmeter and see for yourself.) Hence, the spark must occur when the gap is (1 mm x 12V / 3000V = ) ~0.004 mm.

 

After some coffee I agree it wont make kilovolts on that side of the 12v system. Only place that would be generated is the ignition coils. However I have seen battery terminals spark at a range of a mm or so and I have no explanation for that other than ginormous ESD... Perhaps I was shuffling around on carpet before hand, I do not know.

I withdraw my statement of voltage spikes. Over current is still an issue, and has been discussed at length before. I think the hood terminals are 100A links? Not sure on that though...

 

The 120A MAIN fuse is located adjacent to the positive 12V battery terminal. There is also a 100A DC/DC fuse at the output of the DC to DC converter.

Those owners who have been lucky using a Prius as donor for a jump start on another vehicle (besides another Toyota hybrid) should not assume that they will always be so lucky in the future. It really depends upon how much help the recipient vehicle needs.

If the recipient 12V battery is slightly marginal then only a small amount of boost current may be needed and the jump start attempt will be successful.

If this happens on a cold winter morning, the recipient battery is dead, and the recipient vehicle is started while the jump cables are connected (especially if the Prius is READY and the jump cables are not connected directly to the Prius 12V battery terminals) then there is a good chance that the Prius electrical system will be damaged in the attempt.