Can a Leaf give a jumpstart to ICE?

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BuckMkII

Well-known member
Joined
May 6, 2017
Messages
258
Location
Seattle
Sorry for a question that has undoubtedly been asked and answered many times, but search didn't immediately turn up the answer: A guy at work asked if I could give him a jumpstart. Neither of us had cables, so he had to wait 15 minutes until the campus cops came and bailed him out. Had we had cables available, would it have been a good idea to jump his truck?

This was a full-sized pickup, so it wasn't a matter of a tiny four-banger, either. Would that change anything?
 
It should work if you follow the correct procedure and use a chassis ground instead of the negative battery terminal, which has a sensor on it. I'm not sure though how well the Leaf's DC-DC converter can handle the brief but high demand, and if the Leaf is off the 12 volt battery is too small. What I suggest, though, is that you carry either an inexpensive lighter socket to lighter socket kit, or a lithium portable jumpstarter.
 
I have jumped 3 vehicles, one of which was a big Ford diesel truck with glow plugs and it was 0F or -17C. I just had #4 cables, connected them and tried and the diesel barely cranked. So we let it sit for 3 minutes and tried again and it started.
 
BrockWI said:
I have jumped 3 vehicles, one of which was a big Ford diesel truck with glow plugs and it was 0F or -17C. I just had #4 cables, connected them and tried and the diesel barely cranked. So we let it sit for 3 minutes and tried again and it started.

Was your Leaf in Ready mode, or off?
 
The Leaf was on , ready to drive. I think the #4 cables with 16 foot leads made it so it could instantly jump the truck, but at the same time they limit how much power they can pass over to the other vehicle. I do have another set of 4/0 cables but haven't used them with the Leaf.
 
Good to know. I remember jumping a couple of V-8 engines with my little Civic Si many years ago, but I didn't want to say the Leaf could do it, with no caveats.
 
Jump starting any vehicle from any vehicle can be dangerous. I always tell people if your unsure, don't do it. I have seen cracked 12v batteries and melted jumper cables from hooking them up backwards, not a good thing.
 
Over the last 4 years, I personally have successfully used my 2013 MY to jump at least 4 separate times on 3 different vehicles (one vehicle twice in a week due to a failing car battery).

First couple times I mistakenly used the leaf 12V negative terminal, but it didnt cause any problems. I can definitely hear the DC inverter kick on a few seconds after the batteries are linked with cables.

I've found it take upwards of 10-15 min when jumping a ICE with a old / failing car battery.
 
The portable jump starter battery is a good choice--I have used them (both sealed lead acid and lithium ion) numerous times. Good jumper cables (wires not smaller than 4 AWG) are also a good alternative--Leaf's DC-DC converter should work as well as any alternator.

Please do not try those ridiculous 12-volt power plug to 12-volt power plug cables because the wires in the dash are too small and many cars (Leaf included) must be on for the power socket to be energized. If you try it, there is a good chance of blowing fuses, melting wires, or damaging power distribution modules and very little chance of actually starting the other car.
 
Please do not try those ridiculous 12-volt power plug to 12-volt power plug cables because the wires in the dash are too small and many cars (Leaf included) must be on for the power socket to be energized. If you try it, there is a good chance of blowing fuses, melting wires, or damaging power distribution modules and very little chance of actually starting the other car.

I've never actually used one, but carried one for years. Are you saying this from experience (yours or others) or are you guessing based on the wire gauge? I ask that because the instructions clearly say to leave it connected for 10 minutes or more, until the light on it goes green. They are supposed to work like a faster trickle charger more than jumper cable. That would also warm the battery, which is why the AA battery powered lighter units that were sold for a few years also sometimes work. I think they are fused, although I'd have to check again. I agree that they are of limited use if only because both cars must have active 12 volt power ports for them to work. The downside to the lithium battery jumpstarters, of course, is that there is always a small chance that they will burst into flames and destroy the car and anything nearby. :shock:
 
The leaf 12v system can put out far more power than what a normal pair of jumper cables can move. Just the voltage drop going over the normal 6 or 8 gauge cables most people use will limit current to well below a safe limit.
The DC-DC converter puts out far more power than a normal car alternator can at idle.
I have 00 cables those come close to being able to send what the leafs DC-DC converter can make for the 12v system a shprt distance over to another vehicle.

The car 12v cigarette lighter should be on a 10 or 15 amp fuse. If you try to jump another vehicle that fuse will pop.
Just use jumper cables.

Or you don't like the person asking for a jump just tell them the leaf uses a 380v electrical system and it won't work.
 
LeftieBiker said:
Please do not try those ridiculous 12-volt power plug to 12-volt power plug cables because the wires in the dash are too small and many cars (Leaf included) must be on for the power socket to be energized. If you try it, there is a good chance of blowing fuses, melting wires, or damaging power distribution modules and very little chance of actually starting the other car.

I've never actually used one, but carried one for years. Are you saying this from experience (yours or others) or are you guessing based on the wire gauge? I ask that because the instructions clearly say to leave it connected for 10 minutes or more, until the light on it goes green. They are supposed to work like a faster trickle charger more than jumper cable. That would also warm the battery, which is why the AA battery powered lighter units that were sold for a few years also sometimes work. I think they are fused, although I'd have to check again. I agree that they are of limited use if only because both cars must have active 12 volt power ports for them to work. The downside to the lithium battery jumpstarters, of course, is that there is always a small chance that they will burst into flames and destroy the car and anything nearby. :shock:

I have seen several cases of wiring or power port damage from defective cellular phone chargers, electric heaters/fans, and other devices that should not have exceeded ratings of the power ports so I am concerned about something that connects a charged battery to a discharged battery through those ports. Consider the energy required to start an engine vs. how much could safely flow through one of those little jumper cables and it is clear that it would take at least 10 minutes (assuming the wiring in the dash could handle the current) to get enough energy transferred to crank an engine for 6 seconds.
 
Consider the energy required to start an engine vs. how much could safely flow through one of those little jumper cables and it is clear that it would take at least 10 minutes (assuming the wiring in the dash could handle the current) to get enough energy transferred to crank an engine for 6 seconds.

That's the minimum suggested connection time. The things are also supposed to restrict current flow to under 10 amps. But hey, I don't endorse them - I'm just curious.
 
I am strongly against those power port "jumper cables" because the failure modes of 12V batteries in my climate are either complete failure of a cell or failure of intercell connectors. Both of those failure modes are sudden and the battery cannot absorb charge or supply starting current so trickle chargers are worthless. It takes good jumper cables (minimum of No. 4 AWG copper if short length; No. 2 AWG or larger if longer) or a good portable booster battery (either sealed lead acid or lithium ion) to start the engine and a really good alternator to keep engine, lights, and accessories running long enough to get to a place to buy a new battery.
 
Around here, the trigger to buy a new battery is usually on the coldest days (like the recent "polar vortex" -20's Fahrenheit). In that case, you'd prefer to warm the battery by trickle-charging: if the battery was discharged (e.g. dome light on) and is now frozen solid, then doing a normal jump-start could cause it to explode. If it was just cold, then a 10-minute trickle will usually warm it enough that it is able to start the car on its own.

You know those re-usable heat pads? I've wondered if you could make a sleeve for the 12v battery, which is filled with supersaturated sodium acetate. When you need to prewarm the battery (e.g. when leaving the ski lodge after a weekend parked at 0F), you could hit a button under the dash, and the sleeve would quickly heat to 130F and prewarm the battery. When you drive the car, the car would heat the solution to 200F, melting it back into a liquid.
 
With an inexpensive converter, your EV can also power some lights and appliances when the power goes out.
 
LeftieBiker said:
Please do not try those ridiculous 12-volt power plug to 12-volt power plug cables because the wires in the dash are too small and many cars (Leaf included) must be on for the power socket to be energized. If you try it, there is a good chance of blowing fuses, melting wires, or damaging power distribution modules and very little chance of actually starting the other car.

I've never actually used one, but carried one for years. Are you saying this from experience (yours or others) or are you guessing based on the wire gauge? I ask that because the instructions clearly say to leave it connected for 10 minutes or more, until the light on it goes green. They are supposed to work like a faster trickle charger more than jumper cable. That would also warm the battery, which is why the AA battery powered lighter units that were sold for a few years also sometimes work....

While a pack of AA would probably suffice for the few seconds it takes to convince a LEAF to close the main contactors (and thus power the DC-DC converter), I'm having a hard time seeing it as a viable alternative to starting an ICE. Alkalines have a hard time even keeping up 1A discharge for more than about 15 minutes. For a grand total of 4 watt-hours delivered. Good quality NiMH AA like Eneloop can do about 4A for a good while, getting closer to their nominal 2WH per cell. Speciality NiMH can go 10A but have lower capacities. Best case will probably net significantly less than 20WH total into the 12V battery. I can't see that helping with cranking. Although with the ever-increasing dependence upon computerized systems perhaps some ICE cars face the same low-voltage dilemma as LEAF; where there might be sufficient cranking amps available but not enough voltage to make the computers happy; in which case maybe the little pack could accomplish something.
 
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