JUMP STARTING DEAD PRIUS WITH A DONOR PRIUS BATTERY PACK?

Well for being an expert in High Voltage systems, one would think you would know the difference between 12v and a single traction battery pack which has a voltage of what 7.5v.

 

@ericbecky has done it before.

Proceed with extreme caution.

 

A battery with higher voltage can always jump a battery with lower voltage.

Energy will flow from the higher voltage battery to the lower voltage battery.

Kind of like how water runs downhill.

Of course there is a big difference in risk between working with HV compared to low voltage.

Have I jumped a HV battery with another HV battery using only a few strands of wire when stuck in an emergency situation? (No fuse, no switch, not diode, etc) Sure.
Did I wear 1000v inspected safety gloves, some safety glasses, and closely follow other proper safety precautions? Of course.

 

You can do it in whatever manner you want.
Some ways will just create giant electric arcs or kill you, and others won't.

When you say jumper cables, I assume you do not mean jumper cables like you might use with a car. Those seem way to unwieldy and too large. Too much unnecessary risk that they may touch each other inadvertently. But then again, if I were stuck alone in the desert and had to McGyver my way out of it maybe I'd take the chance? I'd probably stick something non-conductive between the positive and negative so that they don't touch

*** Kids, don't try this at home and don't blame me if you get harmed. **** This is simply me telling a story.
Whatever you do, do not mix up the polarity and do not Cross the wires. It will be bad, so bad, so really really bad, if you short things out.

In my case I was stuck on a guy's isolated farm property far from the house. I needed some jumper wires. He had a trash pile nearby. From it, I dug out some sheathed house wiring. 25 feet of 12-2 wire maybe? Inside the sheath was a black wire and a white wire. I carefully separated last 2 feet or so of each end of the sheathing so that the black and white wires could be isolated.
I stripped as minimal amount of insulation as possible off each end of the black and white wires but enough so I could make a small loop that would fit over the contactor posts and be captured by the post's nut. I did not want extra stray wire poking about!

Put on safety gloves.

Put on safety glasses.

Pulled the orange plugs out of each pack.
One pack was lower voltage.
One pack was higher voltage

Started at the lower voltage pack.

Connected one end of black jumper wire to the negative terminal at the battery side of the contactor.

Connected one end of the white jumper wire to the positive terminal at the battery side of the contactor.

Then went over to the higher voltage battery

Connected the other end of black jumper wire to the negative terminal at the battery side of the contactor.

Connected the other end of the white jumper wire to the positive terminal at the battery side of the contactor.

Inserted orange safety plug on high battery.

Inserted orange safety plug on low battery.

Now the circuit was complete.

There was more to this story but that is the general gist of it. Removing the the plugs first, and inserting the plugs last, makes sure that the wires are fully secured before you complete the circuit and unleash the full voltage of the pack.

Always remove the plugs before attaching , or unhooking wires from the HV battery.

I did not unhook the sense wires, but you certainly could unplug the sense wires from the computer as an extra step.

 

Ah, my bad on my earlier reply. I thought you were just wanting to jump the 12v battery with a single pack out of ah old HV battery. Now that I've seen further posts I understand what you were asking.

 

Quick question for you, How did you charge up the bench pack originally? How do you plan to charge up the bench pack up once it is depleted?

I assumed you had an external hv power supply.
***
In my explanation above, I purposely did not say anything about putting the car in Ready mode.

With the cars off, the higher-voltage battery would slowly deplete, thus raising the lower-voltage battery's voltage until equilibrium in voltage between the two batteries is reached.

Once equilibrium is reached I would remove both orange plugs, remove the wires, then reassemble the batteries. Never putting the car in Ready mode.

So the answer to your original question is "yes", a pack from your bench could charge up a dead pack in your Prius, if the bench pack is higher voltage than the dead pack in your Prius.

****
Attaching a second hybrid battery to the hybrid battery of a Prius and then putting it in ready mode in order to charge the second battery is a different animal. It increases the possibilty of errors and damage to components. I have certainly done it and it is a continuation of the farm field story. But I don't want to go to far off your original question.

 

If the dead-Prius battery is severely low, there is a chance the bench battery won't bring it up to operating voltage in one session.

You may have to unhook everything, go charge the bench battery up again, and then go back with it to the dead-Prius battery.
***
But now I think I see the variation of what you were asking in your original question.

I described basically refilling one battery with another battery.

But rereading your original question, you are wondering if you can (briefly) use a good battery alongside a dead battery in order to start the car and then have the car refill the dead battery.

Now that is a combo I haven't quite tried before.

I have only done it by connecting an HV battery that was in a running Prius to the HV battery of a dead Prius. Revving up the running Prius to fill the dead Prius pack.

I'd be happy to talk through your question more on the phone.
It may work, but of course there are some technical and safety caveats.

For example
- What voltage should the jumpstart pack be at before you hook it up?
- Will the voltage drop too low for the car to go into Ready mode when you put the two packs in parallel?
- At what point do you take the jumpstart pack out of the equation? (Remove the orange plug)
- How will the car react when the jumpstart pack is suddenly removed?

Interesting experiment with it's own challenges. I'm sure it could be made to work. It would be trial and error and a bit of luck. Each situation would bring it's own set of variables into play.

Definitely do not physically unhook the wires between the batteries until both orange safety plugs are removed.

 

Other options...
Remove the dead pack and bring it to the charger.

Bring the charger to the dead pack.

Or swap in the bench pack that is already changed, and then charge the dead pack with your charger.

 

Hi All,

Am a new member onsite. Having a HV battery issue here with my Prius.

Am based out here in Gauteng in South Africa. Our Dealer does not have a bench charger. I have not been able to find any option here for the charging of the battery out of the car.

So would like to know if Eric could continue his story on connecting the 2 batteries and charging the low voltage battery in the car.

I have dismantled and reassembled a number of these units with no issues.

We now have a vehicle that has been standing for a number of years. and we just cannot get it to run. If we swop out the HV batteries, it fires right up.

I stripped the orange HV cables from a donor vehicle to make up a set of "HV Jumper cables".

Now just need to understand what else I need to consider before I connect the 2 batteries and attempt to get the car "Ready"

Any help and advice would be appreciated.

Regards,

 

I sent you an email.
Hopefully you found it helpful.