jump start car with boost converter - Page 1
Forum section: electronics / beginners

author: ascot
author_rank: Contributor
timestamp: August 06, 2020, 06:40:53 am
content: any one know if its possible to jump start a car with a 9 volt battery and a boost converter

author: Psi
author_rank: Super Contributor
timestamp: August 06, 2020, 06:49:39 am
content: Jump starting means supplying all the energy at once from another battery, so the answer is no, not with only one 9volt battery. You'd need 1000 or so.But you could slowly charge the car battery over 12 hours. Pulling all the energy out of the 9 volt battery and putting it into the car battery using the boost converter to turn 9V into 12V.That would give you enough for cranking the engine over for 2-3 seconds.Usually a car battery is not totally dead flat, so you might get more.

author: ascot
author_rank: Contributor
timestamp: August 06, 2020, 06:59:03 am
content: a car only needs 2 to 3 seconds to jump any more you would flatten jump pack anyway

author: bob91343
author_rank: Super Contributor
timestamp: August 06, 2020, 07:08:11 am
content: There isn't enough energy in the usual 9 V battery to make a dent in the state of charge of a car battery. Do the math. The energy required to start a car is far more than resides in a little battery.

author: Psi
author_rank: Super Contributor
timestamp: August 06, 2020, 07:33:21 am
content: Quote from: bob91343 on August 06, 2020, 07:08:11 amThereisenough energy in there.A 9 volt battery is 0.5AhIgnoring internal resistance for a sec (since we can take as long as we need to do the transfer)The 9 volt battery can do 0.5 Amps for 1 houror 1 amp for 30minor 2 amps for 15minetc..or 300Amps for 6 seconds.That's at 9 volts of course, not 12v, but it's close.It's going to be less than 6 seconds because we need a little extra for 12V instead of 9V and we will lose some due to boost converter efficiency.But we can guess that there's going to be enough energy for around 3 seconds of 300A cranking if we can get it out of the 9V battery and into the car battery.

author: brabus
author_rank: Frequent Contributor
timestamp: August 06, 2020, 07:40:49 am
content: Quote from: ascot on August 06, 2020, 06:40:53 amYes, if the boost converter has enough filtering capacitance: some Farads may do the job.Secundarily, it obviously depends on the engine.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 06, 2020, 10:27:13 am
content: i dont think the OP want to kid himself trying to charge a 40AH 12V SLA battery from puny 9V pack overnight. 12V-15V wallwart is probably much more practical. charging in system (in car) may result the 9V energy will be used to deal with car's electronics and security alarm etc before anything goes into the weakened 12V SLA. instead of buying fancy supercap at much expensive price, its good idea to buy the ready made $40 jump starter + tyre pump... can charge phones, 5/12/15/19V supply, charge laptop and has emergency led lighting, pincher etc... almost all in one type power banksomething like (clicked)there are cheaper version if you are tight arse and dont need the pump... the 4S (iirc) Lipo inside is directly connected to jump start port (to car's battery) and can be replacable with normal RC lipo. good for few jump start attempts. ymmv.

author: mikerj
author_rank: Super Contributor
timestamp: August 06, 2020, 02:31:49 pm
content: Quote from: brabus on August 06, 2020, 07:40:49 amIt's still not "jump starting" the engine though. You can slowly move most of the energy from the 9V battery into the car battery (assuming no parasitic drain) which might provide a couple of seconds of cranking, but this is trickle charging, not jumping. You'd be far better off with a couple of D alkaline cells than a puny PP3 type battery but it would still be a slow charging operation.

author: ascot
author_rank: Contributor
timestamp: August 06, 2020, 07:13:40 pm
content: this is not about charging the battery its about jump starting. A typical car battery has 13.80 volts if it drops a small amount it wont start therefore with a boost convertersay 14 volts you would only be looking at kick starting starter motor. If you turn you engine over with full charge it starts instantly most time therefore if we hit it with 14 volts even for a second or two whats the chances

author: Benta
author_rank: Super Contributor
timestamp: August 06, 2020, 09:06:30 pm
content: Let's get back to reality, please.An average starter for a 2.0 petrol engine will pull around 300...400 A, a diesel 400...600 A. And you want to do this with a pocket-sized 9 V battery?The voltage on a fully charged lead-acid automotive battery will drop to 9...10 V while cranking, just due to internal resistance.There's a reason why the AA or AAA jumper packs have the size they have. And why jump start cables are so thick...

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 06, 2020, 11:23:07 pm
content: Quote from: ascot on August 06, 2020, 07:13:40 pmwe know. but people have given you the most practical, easiest and fastest solution for you for a reason, but...Quote from: ascot on August 06, 2020, 07:13:40 pm...if you want to try it out, you can make the thickest boost converter possible and see that your 9V battery wil be shorted out to 0V. hint: internal resistance is too much or in other word.. small cell pack will not be able to supply anything near, even 1 tenths the required wattage (Joule/sec) to make a car jump start. thats why people reroute you to the "charging" solution. thats why you wont be able to see a magnificent spark when you short a 9V cell with a wire like a thick SLA can.Quote from: ascot on August 06, 2020, 07:13:40 pmvoltage is not only the measurement here. we've seen a dead 14V (or anything reasonable figure) battery when opened that cant even to light a bulb because of too much internal resistance (broken structures and materials) developed inside. energy stored and its internal resistance are the measurement you should look at too. you must have all three (including the voltage) to make a jump start, you cant have only one or two.

author: mikerj
author_rank: Super Contributor
timestamp: August 07, 2020, 09:11:05 am
content: Quote from: ascot on August 06, 2020, 07:13:40 pmSay your starter pulls 300A at 12v (pretty typical), and assume a boost converter with an efficiency of 85%. That means you'd need to pull around 470 Amps @9v from the battery, which should already show this is impossible if you have any experience with electrical cricuits.A brand new, quality alkaline PP3 size battery might provide 3-4Amps for a few seconds into zero ohms i.e. the maximum possible current it can provide. A NiMh or Lithium Ion based PP3 battery would likely provide a bit more current, but still at least an order of magnitude too small.TLDR: the chances are exactly zero.

author: Psi
author_rank: Super Contributor
timestamp: August 07, 2020, 09:34:06 am
content: It would be pretty funny seeing just how many 9 volt batteries you actually need to start a car.If you can get 5A from a brand new 9V without the voltage dropping below 6V then you'd need 120 made from two parallel banks of 60 cells in series to get 12-18V at 300A.I suspect an issue might be the initial current peak, it's probably over 1000A until the engine starts rotating.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 07, 2020, 12:06:15 pm
content: or maybe we see it wrong. the OP want to charge say 1A into 12V battery at 300-400 seconds to provide 400A at 1second to jump start. i've never tried, the normal china boost converter probably can do, and if he can find a 9V battery pack that can give 1A @ 400 seconds charging, then it might be possible

author: Circlotron
author_rank: Super Contributor
timestamp: August 07, 2020, 01:28:16 pm
content: You can jump start a car with a battery made from 1000 lemons.https://youtu.be/4f2wsQkQ71oOr 1000 AA cells.https://youtu.be/OS_lRZtR-d4

author: Psi
author_rank: Super Contributor
timestamp: August 07, 2020, 01:37:43 pm
content: Quote from: Circlotron on August 07, 2020, 01:28:16 pmDid you watch the video?They didn't start the car with 1000 lemons, they found out you'd need 66 million lemon halves to do it.The video with 1000 AA cells seems legit though,With series strings of 8 cells for 12V the 1000 cells is 125 strings in parallel.A new AA can put out 5A without much trouble so 125 x 5A = 625A @ 12V

author: Circlotron
author_rank: Super Contributor
timestamp: August 07, 2020, 02:03:03 pm
content: Quote from: Psi on August 07, 2020, 01:37:43 pmOops... I saw the video quite some time ago. Forgot the details.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 07, 2020, 03:27:14 pm
content: Quote from: Circlotron on August 07, 2020, 01:28:16 pmok now the 4S Lipo charger i linked earlier looks abysmalbeside the 1000 AA combined sized bigger than a normal SLA battery, and its one time use (non-rechargable) how much will they cost? assuming each battery is 10 cents so 1000 AA is $100. a normal SLA cost is about half that, not bad not bad

author: ledtester
author_rank: Super Contributor
timestamp: August 08, 2020, 12:49:38 am
content: Not exactly jump starting a car, but recharging a car battery with 12 AA's:http://www.electroboom.com/?p=602

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 08, 2020, 05:16:18 am
content: Quote from: ledtester on August 08, 2020, 12:49:38 amin the comment, one guy suggesting using 2x 9V connected directly. so it might be possible.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: August 08, 2020, 05:25:25 am
content: I just feel sorry for the surrounding electronics while this is happening.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 08, 2020, 06:15:36 am
content: A 500 CCA 12V battery will not start my car. I need at least 600. 700 is better. The CCA of a battery is the number of amps the battery will still deliver after 30 seconds in -18C (0F) weather and still remain above 7.2V.You probably don't even need the boost converter. The starter should be able to work with 9V. But it will suck that 9V battery dry almost immediately. I could only imagine how quickly the terminals on the 9V battery would vaporize. Starter motor cables can be as big as 2 gauge.