# Jump starting a car with a Cell Phone **URL:** \ **Category:** Factual Questions\ **Created:** [June 16, 2000, 1:54pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577 "2000-06-16T13:54:25Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [March 6, 2017, 6:09pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/21 "2017-03-06T18:09:46Z")
So these newer devices appear to be a miniature version of something like a [nautilus](http://www.canadiantire.ca/en/pdp/motomaster-nautilus-battery-pack-800-a-0111592p.html), only they use a light weight lithium battery rather than a heavy lead acid battery… and they’re not as powerful (6Ah/300A output vs 33Ah/800A output) or have as many attachment options. I’d consider them either pocket-sized back-up battery packs that could boost a not-too discharged car, or a cell phone battery back-up on steroids. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [March 6, 2017, 6:29pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/22 "2017-03-06T18:29:40Z")
> [@running\_coach](#): > > There’s a ton of 'em [on Amazon.](https://www.amazon.com/s/ref=sr_nr_n_3?fst=as%3Aoff&rh=n%3A15684181%2Cn%3A%2115690151%2Cn%3A15706941%2Cn%3A387679011%2Cn%3A1253955011&bbn=387679011&ie=UTF8&qid=1488804107&rnid=387679011) I have a Winplus and it works just fine. Recharges a laptop or cell phone multiple times, great for camping or power outages and yes, I have used it to help a stranded motorist jump start their car. The battery pack is about the size of my Note 3 phone but about 3/4 inch thick. Don’t need full sized jumper cables any longer. If the Winplus happens to be low on charge I can charge it through my aux power port or cigarette lighter port and then go jump another car. Battery pack, short jumper cables, charging and supply cables all fit neatly into a small case about 8 X 10 X 2 inches. I keep it under may car seat. ---
**Author:** ![znog84](https://avatars.discourse-cdn.com/v4/letter/z/13edae/32.png) [@znog84](https://boards.straightdope.com/u/znog84)\ **Post date:** [March 7, 2017, 7:33am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/23 "2017-03-07T07:33:52Z")
> [@Fubaya](#): > > These aren’t really cell phone batteries, they’re several times larger. They’re small battery packs that can jump start a car and also have a USB port that can charge a phone. Right. I’m not talking about a portable cell battery to charge your phone/jump car. I’m talking about your cell phone (I have a Galaxy S7 Edge), being powerful enough to start you car WITHOUT losing a lot of juice and still having power after you jump your car. And it would have a peripheral device with +/- cables and an app to initiate it. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [March 7, 2017, 8:55am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/24 "2017-03-07T08:55:22Z")
Reason# 11174 to have a manual. You can push start the damn thing and not worry about having to “jumpstart” and buy hideously expensive gizmos which do sweet fuck all. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [March 7, 2017, 12:57pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/25 "2017-03-07T12:57:26Z")
> [@AK84](#): > > Reason# 11174 to have a manual. You can push start the damn thing and not worry about having to “jumpstart” and buy hideously expensive gizmos which do sweet fuck all. you can’t easily do that on a modern car, even with a manual transmission. when you’re starting the engine from an “OFF” state, the PCM needs to see the engine crank through _at least_ two complete revolutions of the crankshaft before it’ll enable fuel and ignition. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [March 7, 2017, 1:12pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/26 "2017-03-07T13:12:37Z")
> [@jz78817](#): > > you can’t easily do that on a modern car, even with a manual transmission. when you’re starting the engine from an “OFF” state, the PCM needs to see the engine crank through _at least_ two complete revolutions of the crankshaft before it’ll enable fuel and ignition. Which bastard invented that and why?:mad: Please tell me his execution was long drawn out and painful! ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [March 7, 2017, 1:15pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/27 "2017-03-07T13:15:20Z")
I’ve jumpstarted my car using my cellphone to call AAA. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [March 8, 2017, 12:03am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/28 "2017-03-08T00:03:47Z")
Why does your car need to be running before you call AAA? ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [March 8, 2017, 12:09am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/29 "2017-03-08T00:09:17Z")
> [@Princhester](#): > > Why does your car need to be running before you call AAA? He drained his phone jumpstarting the car. Now that it’s running, he can plug the phone into the car charger and make the call. 😃 ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [March 8, 2017, 12:50am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/30 "2017-03-08T00:50:51Z")
> [@AK84](#): > > Which bastard invented that and why?:mad: Please tell me his execution was long drawn out and painful! :rolleyes: nobody “invented” that, it’s a consequence of distributor-less electronic ignition and fuel injection. the crankshaft position sensor reads a tone wheel on the crankshaft which has a notch to denote when cylinder #1 is at top dead center (TDC.) However, on a four stroke engine, that could be TDC after the compression stroke, or TDC after the exhaust stroke. The PCM needs to also pick up the camshaft position sensor(s) to verify whether cylinder #1 is on the compression or exhaust stroke. since the camshafts rotate at half the crankshaft speed, there’s why the engine needs to be cranked through two complete revolutions. now, with the auto stop/start systems becoming popular, those can “sidestep” that requirement because the PCM is not turning off or going to sleep. it “knows” where the engine is when it shuts it off at a stop, so it can fire the next available cylinder after a very short cranking period. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [March 8, 2017, 1:15am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/31 "2017-03-08T01:15:20Z")
> [@running\_coach](#): > > He drained his phone jumpstarting the car. Now that it’s running, he can plug the phone into the car charger and make the call. Well then why not just drive to the AAA? That way he wouldn’t need to call. ---
**Author:** ![UltraVires](https://avatars.discourse-cdn.com/v4/letter/u/ecccb3/32.png) [@UltraVires](https://boards.straightdope.com/u/UltraVires)\ **Post date:** [March 8, 2017, 1:43am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/32 "2017-03-08T01:43:14Z")
> [@Princhester](#): > > Why does your car need to be running before you call AAA? I believe this was a whoosh. The poster “jumpstarted” his car by using his cell phone to call AAA to have them come and jumpstart the car. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [March 8, 2017, 1:49am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/33 "2017-03-08T01:49:08Z")
> [@UltraVires](#): > > I believe this was a whoosh. The poster “jumpstarted” his car by using his cell phone to call AAA to have them come and jumpstart the car. Let’s eat Grandpa. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [March 8, 2017, 1:59am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/34 "2017-03-08T01:59:53Z")
> [@running\_coach](#): > > He drained his phone jumpstarting the car. Now that it’s running, he can plug the phone into the car charger and make the call. > > 😃 If it were an electric car it would be a perpetual motion machine. ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [March 8, 2017, 3:05am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/35 "2017-03-08T03:05:45Z")
> [@jz78817](#): > > you can’t easily do that on a modern car, even with a manual transmission. when you’re starting the engine from an “OFF” state, the PCM needs to see the engine crank through _at least_ two complete revolutions of the crankshaft before it’ll enable fuel and ignition. So, how far do you have to push it then? In my experience, you always had to push then through 5-10 revolutions of the wheels before you let out the clutch. Approximately how many turns of the wheel would equal 2 revolutions of the crank shaft? 😕 ---
**Author:** ![Section\_Maker\_Jupe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/section_maker_jupe/32/1424_2.png) [@Section\_Maker\_Jupe](https://boards.straightdope.com/u/Section_Maker_Jupe)\ **Post date:** [March 8, 2017, 3:31am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/36 "2017-03-08T03:31:56Z")
…depends which gear you try to jump start the car in…😃 I used to have a 1964 datsun 320 i…teeny truck…you could jump it just by walking alongside then slipping into the seat and use 4th gear…my 2000 toyota tundra however, I can barely push anywhere on level ground… the new auto stop/start systems are pretty alarming at stop lights if you dont know whats going on…(just happened to me):eek: thought the car had died ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [March 8, 2017, 4:38am UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/37 "2017-03-08T04:38:32Z")
> [@TruCelt](#): > > So, how far do you have to push it then? In my experience, you always had to push then through 5-10 revolutions of the wheels before you let out the clutch. Approximately how many turns of the wheel would equal 2 revolutions of the crank shaft? > > 😕 It’s less than one revolution of the wheels to get two crankshaft revolutions. A lot less. If you’re push-starting a mid-nineties Miata in second gear, you’re looking at a transmission ratio of 1.888 in second gear and a rear-end (differential) ratio of 4.10. That means the engine’s crankshaft completes about 7.75 rotations for each rotation of the wheels. (Source: [https://www.flyinmiata.com/tech/gearing.php](https://www.flyinmiata.com/tech/gearing.php) ) Assuming a 195/55R15 tire, you’re looking at a circumference of about 74 inches. That means you’re getting a crankshaft revolution roughly every 9.5 inches of forward vehicle travel. You’d have to roll forward nineteen inches—less than two feet—to get the required two crankshaft revolutions. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [March 8, 2017, 3:21pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/38 "2017-03-08T15:21:57Z")
> [@EdelweissPirate](#): > > It’s less than one revolution of the wheels to get two crankshaft revolutions. A lot less. > > If you’re push-starting a mid-nineties Miata in second gear, you’re looking at a transmission ratio of 1.888 in second gear and a rear-end (differential) ratio of 4.10. That means the engine’s crankshaft completes about 7.75 rotations for each rotation of the wheels. > > (Source: [https://www.flyinmiata.com/tech/gearing.php](https://www.flyinmiata.com/tech/gearing.php) ) > Assuming a 195/55R15 tire, you’re looking at a circumference of about 74 inches. > > That means you’re getting a crankshaft revolution roughly every 9.5 inches of forward vehicle travel. You’d have to roll forward nineteen inches—less than two feet—to get the required two crankshaft revolutions. yeah, but have you ever done it? I’m not saying it’s impossible; pickering over numbers is all well and good, but I think many of you underestimate how hard it is to push a vehicle in gear with the engine over-driven that far. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [March 8, 2017, 4:48pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/39 "2017-03-08T16:48:56Z")
You don’t push it while it’s in gear and pushing a car isn’t really hard, especially if you know how to get leverage on it, and it’s obviously simpler if it’s going downhill. I’ve push started a bunch of cars and some do start within what seems like a couple of feet. Some are harder. Some are practically impossible. At my last job we had a little 2 wheel drive Tacoma that we used to run errands and the battery went dead on me once. The parking space was slightly uphill so I stood in the door, pulled on the steering wheel and pushed against the door jamb with my back in order to give it a good shove rearward. Then I hopped in and popped the clutch to start it. I rolled it off inside the parking space. ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [March 8, 2017, 5:06pm UTC](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577/40 "2017-03-08T17:06:59Z")
> [@jz78817](#): > > yeah, but have you ever done it? I’m not saying it’s impossible; pickering over numbers is all well and good, but I think many of you underestimate how hard it is to push a vehicle in gear with the engine over-driven that far. Yes, I’ve done it many, many times. I was “pickering over numbers” because another poster asked how far you’d have to roll with the engine connected to the driving wheels in order to get two full crank revolutions. Ideally, you let the car coast down a hill in neutral to about 10-15 mph. You push in the clutch, select second gear (or at least I do) and then let the clutch out rather suddenly. You let the clutch out quickly because you don’t want to turn your kinetic energy into heat via clutch friction; you want it all to go to the crank. The car decelerates with a jerk as this happens and the car starts. This procedure is why push-starting a car is sometimes called “popping the clutch” or “bump-starting” the car. And it’s exactly the same thing as kick-starting a motorcycle, except that car engines are large enough that they need a little more energy than one’s leg can provide. But it’s only about 4-6 times as much, and a 3000-lb car rolling at 10 miles per hour has more than enough kinetic energy to start itself. Also, it’s worth knowing that, until fairly recently, cars usually didn’t start on the first or second engine revolution even when using the starter. Electronic ignition, fuel injection and (to a lesser extent) direct injection all help modern cars start just 1-3 revs after the starter is triggered. Carbureted engines need to develop enough vacuum to pull fuel through the carburetor, and that takes a few revolutions. So the requirement that modern engines turn through at least two revolutions before starting isn’t really a constraint compared to earlier engines. [Previous page](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577.md?page=1) [Next page](https://boards.straightdope.com/t/jump-starting-a-car-with-a-cell-phone/22577.md?page=3)