Here’s How To Jump Start Another Car With Your Tesla Model 3

JUL 10 2018 BY MARK KANE 22

Sure, an electric car can assist a dead ICE car.

One of the Tesla Model 3 owners posted an interesting video using the car’s 12-volt battery to jump-start an internal-combustion engine car that had a dead battery.

The video shows the connection and the mission was successful… and here’s something that appeared in comments. Should you jump start the ICE with your BEV (Model 3 in this particular case)?

From the hardcore EV perspective… if the ICE is dead, do not resurrect it. Ok, just joking.

From a technical perspective, jump-starting an ICE car could be harmful to the EV – especially in the winter when there is a need for high amps for cranking. That puts stress on the 12 V battery in the EV (which is a smaller problem) and the DC/DC converter (which is a bigger problem). According to the comments, Tesla’s DC/DC is ready for 200 A, but surges could cause failure at some point and that comes at a cost.

The other issue could be confusion of the software that monitors the 12 V battery.

It’s an important topic because many EV owners will from time to time see ICE with a discharged 12 V battery. There is a safe way to charge the 12 V battery using the Model 3, but of course it’s not quick.

“It says if you must jumpstart with a Tesla you should let the Tesla charge the opposite car and disconnect before attempting to start. Thanks again!”

Let us know what the best practice should be and maybe there should be some training material released for us all to examine and understand.

Here is the discussion:

sss: You’re essentially starting your ICE from a motorcycle battery. You really don’t have access to the juice in the main battery. There’s only a DC-DC converter that keeps the 12V battery charged; it cannot supply cranking current. By jump starting, you are putting the DC-DC converter in jeopardy and also the 12V battery. Also, this will really confuse the software that monitors the 12V pack and could result in a fault. This has happened to other people trying to power their dashcams directly from the 12V battery.

Andrew Reinsma: I understand what your saying but it is still a regular full size 12V car battery with sufficient cranking AMPs to start an ICE. If you check the owners manual under what to do when your 12V dies in a Tesla you’re actually supposed to jumpstart it exactly how I did but in the other direction. It then states once the computer starts up you are to disconnect the external 12V source and put the car all back together. This is letting us know that the cars 12V inverter will charge the battery back up to full. If the car can handle charging a 20AMPh battery all the way back up from cold dead then the stress on an ICE jumpstart should be negligible.

sss: Andrew Reinsma the stress isn’t negligible, contact the service team and they will tell you that you aren’t supposed to jumpstart an ICE car with this battery. The battery is actually a very large point of failure on the car. Also if u really need to do this you would probably be safer disconnecting the battery from the model 3 The procedure to boost the 12v on a dead model 3 Is safe because the purpose is to get the main pack contractors to close and start charging the 12v pack. This is different than pulling current from the pack and the dc dc inverter trying to account for that spike.

Andrew Reinsma: sss I did a bunch of reading in on the topic since you commented and you are right. It’s not recommend to jumpstart but the cranking AMPs of the battery is 45 and the cars DC inverter is safe up to 200 AMPs. If I would have done this in the winter I could have hurt my Tesla. Thanks for your input. It says if you must jumpstart with a Tesla you should let the Tesla chrage the opposite car and disconnect before attempting to start. Thanks again!

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22 Comments on "Here’s How To Jump Start Another Car With Your Tesla Model 3"

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Or just buy one of those very small, excellent Lithium ion jumper kits. Mine has a built in flashlight, digital display, charges my kids tablet’s when we are parked, and jump starts gas/diesel V8 cars!

Basically this. I would rather risk a ~$50 jump pack versus the DC/DC converter in my car. No brainer.

Or just buy one of those very small, excellent Lithium ion jumper kits. Mine has a built in flashlight, digital display, charges my kids tablet’s when we are parked, and jump starts gas/diesel V8 cars!

Why an electric car needs a 12V batery? I didn’t get it…

Exactly – they should have transitioned to 48 volt by now 😉

But why they don’t use the lithium batery of the car? What is the purpose of having an 12V Lead batery?

To power everything in the car except the drivetrain. You need to 12V battery to power the computer and to energize the HV battery contactors to turn on the DC-DC converter. If you just left the DC-DC converter on all the time you’d have massive vampire drain problems.

Also lithium batteries can’t cope with freezing temperatures. So good old Lead Acid is still the best technology for the 12V. Once they have Li+ batteries or some other chemistry that is cold tolerant Pb batteries will enter the dustbin of history.

Ok! Thanks for the explaining!

Lots of reasons, which is why Tesla hasn’t transitioned. One of the simplest from a users point of view is that 12V accessory socket that so many of your things run off of.
48V? Why not 100V, why not the big battery’s 300V? Each has advantages, each has disadvantages, and the ability to kill you.

The sockets are no problem. Anything that run on them you can charge in your home of a 120v outlet with an adapter anyway…so that’s not it.

But then you have to do a DC-AC conversion which is complex and getting anything with reasonable wattage is expensive. The vast majority of devices today, and I’d wager ALL devices you’d be using in a car, are going to be using low voltage DC internally. Going from a ~300V DC battery to 120V AC to be converted back down to ~5V DC by the devices is just hugely wasteful.

The reason is and HAS ALWAYS BEEN, the auto industry has standardized on the ’12 volt’ (6 cell) system – from 1953-1957 in the states (Ford of course always being the laggard), and from 1962-1967 in Europe (VW and OPEL being the laggards there). The OLD GM had the ‘great brain’ idea of coming out with a new ’42 volt’ (18 cell) system – really 36 volts but of course GM can’t even stick to common naming conventions two decades ago, to help implement things like electric power steering, except Parts Manufacturers decided to avoid that silly logistics nightmare, and just run electric power steering systems (as I have in both my EV’s also, obviously) on the plain old 12 volt system. A higher voltage these days might theoretically be a better idea, but it is far easier for dealerships and auto parts stores to only have to worry about replacement parts for a single voltage. Its called “Standardization of Parts”, something pioneered in the USA over 200 years ago and it is still a great Idea. I think ELI Whitney eventually even got a patent for the idea – although it was certainly an obvious idea to many before… Read more »

Well, it doesn’t absolutely HAVE TO have a 12 volt battery since the VERY OLD roadsters didn’t have one. EV’s COULD get along with just using the dc/dc converter, and have a motorcycle sized battery in the thing, but apparently manufacturers have decided that the plain old ubiquitous 12 volt battery isn’t very heavy, doesn’t take up a lot of space, and it is a good value compared to a motorcycle battery, seeing as it has to have 6 cells anyway.

I use the relatively large battery to advantage during power failures, when I run small household loads off the car, and if they are small enough, I don’t even bother turning the car on to recharge the 12 volt battery since I know it is not going to be a problem until hours later. Most outages are not that long.

(⌐■_■) Trollnonymous

My next project is to replace my 12v FLA with a 40A LiFePo4 pack.

I’ve already given plenty of ICE cars jump starts. The key is to connect the batteries together and wait a minute or 2. Give the dead battery time to accumulate a bit of a charge so when they try and start, the drain comes partially from the juice in their battery and part from yours. You don’t want you battery to take the brunt of the surge.

So, while some are complaining about the use of the Model 3 battery and if it should be used. My problem is that the author really isn’t following battery charging procedures correctly.
You should never hook the charging cars +12V last. The -12V is always last.
And the -12V should NEVER be connected to the battery, it should always be connected to chassis ground.

As the author indicating “there should be some sparks” is the reason why you hook the -12V to chassis ground last.

Car batteries are not sealed, the outgas some pretty nasty and flammable gasses. Sparking near flammable gases, well, need I say more?

As to the impact of charging to the Model 3. The starting systems of newer cars is very different than those from 1960. You’ve got vehicles that stop and start at a traffic light, the load requirements are significantly lower than they used to be. That’s why some of these lion chargers work. You don’t need 300 CCA anymore.

The gassing should just be pure oxygen+hydrogen — not really nasty, but definitely very flammable 🙂

I don’t see why they’re worried about the Tesla DC/DC converter……. (although this is the first I’ve heard that it is pretty big at 200 amperes – The Volt is supposedly 160 and the BOLT is 130 amperes). Why didn’t they just leave the car off while cranking it if they’re worried about it?

Everyone says to make the NEGATIVE connection away from the battery as the LAST connection since the sparking will be away from it then. He didn’t do that, so I wouldn’t say this is the approved method.

VERY DANGEROUS UNDERTAKING ! ! !….. “If You Pause The Video” you Can see that He comes Within a Fraction of an Inch from “Grounding Out” the Positive Cable On the Steel Body Bolt Under The Plastic Cover* The Bolt is Partially Hidden By His Thumb As He Moves The COVER Up & Out of The Way To Attach The Positive Cable…. If That Cover Presses That Positive Cable Clip onto that bolt and Makes Contact with it., “IT GROUNDS OUT” It will Arc and it “Will WELD ITSELF” to that Body Bolt* and The Results Will Be Devastating. If You Value Your Safety & Your Tesla…..NEVER DO THAT ! ! ! !

The proper way to connect cables was shown EXCEPT: On the good battery, you want to first connect the positive cable, and THEN you connect the negative, preferable to the vehicle ground strap rather than the negative stub on the battery. This is to prevent the “sparking” that was mentioned in the video. You do NOT want sparking because battery gasses are flammable, an in the rare case, they explode on the spark.

Hey, the video that this article is about is no longer available, here’s a link to a new video showing how to jump start another with a Tesla Model 3

Thank you!