Jumping another vehicle

[TomT]

It worked fine for me with the Leaf off when I jumped a Lincoln MKX the other day. Just wait ten minutes or so to build a surface charge in the jumped vehicle... I simply feel more comfortable with the Leaf off in such circumstances... I used heavy duty gauge 2 jumper cables, by the way.

Putting high loads on the little battery without the DC-DC converter is not a good idea. In fact, The DC-DC is powerful and yet current-limited, and since it is liquid-cooled, it can handle high loads much better than most car alternators. Without having the LEAF in ready, you aren't going to get much across the jumper cables from the small battery alone.

 

[Ingineer]

It worked fine for me with the Leaf off when I jumped a Lincoln MKX the other day. Just wait ten minutes or so to build a surface charge in the jumped vehicle... I simply feel more comfortable with the Leaf off in such circumstances... I used heavy duty gauge 2 jumper cables, by the way.

Wow, most people don't have cables anywhere near that thickness! All the stuff they sell for consumers is 6-8AWG usually, but with really heavy insulation to make it look "heavy duty".

Keep in mind, you are performing rapid discharge of the little battery in this case, then turning the LEAF on to a low battery. This is probably worse of a shock load to the LEAF's charging system than just drawing the energy from the DC-DC in the first place. (and definitely harder on the battery!)

-Phil

 

[TomT]

Yes, I am aware of that. Of course, in a worse case scenario, I could just jump back the other way to start the Leaf! :lol:

I don't think that the 5 seconds of starting load is really going to drain the leaf's battery that severely. However, I should have mentioned that I DID leave the Leaf on when I was doing the 10 minute surface charge to the other vehicle.

Keep in mind, you are performing rapid discharge of the little battery in this case, then turning the LEAF on to a low battery. This is probably worse of a shock load to the LEAF's charging system than just drawing the energy from the DC-DC in the first place. (and definitely harder on the battery!)
-Phil

 

[Ingineer]

Yes, I am aware of that. Of course, in a worse case scenario, I could just jump back the other way to start the Leaf! :lol:

I don't think that the 5 seconds of starting load is really going to drain the leaf's battery that severely. However, I should have mentioned that I DID leave the Leaf on when I was doing the 10 minute surface charge to the other vehicle.

It's not so much a drain, as it is a possibility of damage. The small battery in the LEAF was likely not designed to see starter loads, and might be damaged.

-Phil

 

[nater]

The best way to jump a car from the leaf is to bring the Leaf to ready, then hook up the cars, and charge the battery in "jumped" car a bit, then unhook, then crank over the "jumped" car.

The second best option is to crank over the jumped car with the cables still connected. The 12v battery will absorb the voltage spikes in the 12v system. Also, the jumped car's battery will soften the blow to the Leaf's DC system as well.

Avoid jumping a car with the 12v battery in the Leaf with the Leaf "off."

Nate

 

[TomT]

And you have reached this conclusion how? Unless the battery on the jumped car is only a little low and not dead, and you leave them paralleled for a relatively long time, you will not likely build up enough of a charge to start the jumped vehicle via it's own battery only... Personally, I think the Leaf battery is completely up to the task.

The best way to jump a car from the leaf is to bring the Leaf to ready, then hook up the cars, and charge the battery in "jumped" car a bit, then unhook, then crank over the "jumped" car.
The second best option is to crank over the jumped car with the cables still connected. The 12v battery will absorb the voltage spikes in the 12v system. Also, the jumped car's battery will soften the blow to the Leaf's DC system as well.
Avoid jumping a car with the 12v battery in the Leaf with the Leaf "off."
Nate

 

[hpage]

If you're really concerned about that puny Leaf battery, check out the battery tray -- it appears capable of holding a significantly larger battery!

 

[scottf200]

If you're really concerned about that puny Leaf battery, check out the battery tray -- it appears capable of holding a significantly larger battery!

What is the ???:CCA and ??:AH of the LEAFs battery?

 

[nater]

Let me rephrase that, the SAFEST way is to transfer some charge. Not necessarily the most effective.

Nate

 

[LEAFfan]

It happens, also many MANY lead acid batteries explode when you make a connection to them, sometimes spewing acid all over..

I've had my other cars' batteries jumped many, many times and not once was there an explosion OR a spark. I was told a long time ago how to jump an ICE from an ICE. You connect the jumpee's battery terminals first, then connect the + or red on the jumper's car. THEN, connect the - or negative clip to the engine BLOCK, not the negative terminal of the battery. So IF it sparks, it will be away from the battery in case of fumes. When done jumping, just reverse the steps.

 

[wwhitney]

I'm a little confused because when you jump someone you are not charging their battery per se

As soon as you parallel two batteries, the stronger battery (higher voltage) starts charging the weaker battery (lower voltage).

Wayne

 

[keydiver]

I'm a little confused because when you jump someone you are not charging their battery per se ...

This is exactly how jump starting works, by charging their battery off of your system. The cranking amps are usually so high that there is too large of a voltage drop across the jumper cables for your system to directly crank their starter. That is why you need to allow a few minutes for their battery to get enough charge, so that most of the amps are being drawn directly from their battery, not yours.

 

[scottf200]

I'm a little confused because when you jump someone you are not charging their battery per se ...

This is exactly how jump starting works, by charging their battery off of your system. The cranking amps are usually so high that there is too large of a voltage drop across the jumper cables for your system to directly crank their starter. That is why you need to allow a few minutes for their battery to get enough charge, so that most of the amps are being drawn directly from their battery, not yours.

I get your points. I've jumped my share of vehicles in my life having cars in my youth that were not that reliable and because I lived in a cold climate where weak batteries REALLY showed up in the winter. Certainly I have connected the cars and let the source just run for a minute before turning the key in the target. But I've always used heavy duty jumper cables. Unless you sit in the source car and rev the engine to 1000+ RPM you can certainly hear/feel the source engine lull for a second as the target car turns over. ie. the target car is getting a fair amount of amps from the source.

 

[vkruger]

Is the DC to DC inverter ever off in the Leaf? I assume it is always on so the 12V battery will never go dead if stored for a long time in the shade.

 

[davewill]

Is the DC to DC inverter ever off in the Leaf? I assume it is always on so the 12V battery will never go dead if stored for a long time in the shade.

When the car is off for an extended period, the 12v battery gets charged every 5 days. It's perfectly possible to run the 12v battery down before that recharge happens...and then it won't because the car won't do anything when the 12v battery is dead.

 

[DaveEV]

However, I should have mentioned that I DID leave the Leaf on when I was doing the 10 minute surface charge to the other vehicle.

That's probably how I would do it to avoid any possible issues with the DC-DC inverter. (Hook up jumper cables, turn on LEAF, wait 5-10 minutes for dead vehicle to charge, turn off LEAF, try to start dead vehicle).

Typically voltage drop across jumper cables is high enough that you can't really pull that much power from the jumper vehicle. Does the LEAF have any sort of over-current-device to protect the DC-DC inverter? The Prius has a 100A fuse to protect the DC-DC inverter, but there have been reports that it doesn't always do it's job well enough!

 

[LEAFfan]

That's probably how I would do it to avoid any possible issues with the DC-DC inverter. (Hook up jumper cables, turn on LEAF, wait 5-10 minutes for dead vehicle to charge, turn off LEAF, try to start dead vehicle.

I don't believe that's what Phil said. You need to have the car on and in 'ready' BEFORE you hook up the negative cable to the DC-DC Inverter and keep it on until the other car starts. You could damage the inverter or your 12V otherwise.

 

[DaveEV]

That's probably how I would do it to avoid any possible issues with the DC-DC inverter. (Hook up jumper cables, turn on LEAF, wait 5-10 minutes for dead vehicle to charge, turn off LEAF, try to start dead vehicle.

I don't believe that's what Phil said. You need to have the car on and in 'ready' BEFORE you hook up the negative cable to the DC-DC Inverter and keep it on until the other car starts. You could damage the inverter or your 12V otherwise.

Yes, I (and TomT) know what Phil said - Phil is concerned about draining the 12V battery hence the suggestion to leave the car on when jumping. Frankly, I'm a lot more worried about damaging the inverter than the 12V battery - it probably costs 10x the battery to replace. If placing jumper cables on the car when off drains the LEAF's 12V battery low enough to cause a big surge when powering on, it's very likely the 12V battery voltage won't be high enough to power on the LEAF in the first place.

 

[Ingineer]

The DC-DC converter protects itself. It will perform voltage foldunder if overloaded, I've already checked.

There is also a fuse, but the only way this could blow is a reverse polarity event, or a diode failure in the DC-DC.

The only way you would likely ever damage your converter is by jumping a dead LEAF with a reverse-polarity power source. That would be a catastrophic event!

Be DOUBLE SURE when connecting jumper cables, that you get the polarity correct!

-Phil

 

[JPWhite]

The DC-DC converter protects itself. It will perform voltage foldunder if overloaded, I've already checked.

There is also a fuse, but the only way this could blow is a reverse polarity event, or a diode failure in the DC-DC.

The only way you would likely ever damage your converter is by jumping a dead LEAF with a reverse-polarity power source. That would be a catastrophic event!

Be DOUBLE SURE when connecting jumper cables, that you get the polarity correct!

-Phil

Thanks for all of your insight Phil. I now know how to jump other vehicles safely. Appreciate it.