That definitely would not be enough to jumpstart a car. IIRC starters draw hundreds of amps of current. The one in my car is fused for 200A. It depends on the temperature what it draws.

Anywho he probably just charged the batteries up, and then started it.

At 5 amps, this seems more like a battery charger than a jump starter.

On an unrelated note, I see Hack a Day has finally upgraded to capital letters! Congratulations!

I would also guess that those power adapters weren’t actually limited at 1 amp each. I don’t believe that that type of transformer + rectifier commonly has any current limiting built into it and probably is only “rated” at 1 amp meaning it won’t start a fire at 1 amp.

horrible use of old console equipment IMO… if this was a one time thing it wouldn’t kill you to knock on your neighbor’s door for a jump. if this is a reoccurring thing then it’d be worth buying a legit battery charger.

and definitely no where near enough amps to actually jump a car.

Well you won’t jump start the car straight off them, but what you can do is leave them pushing 5A into the battery for a while to give it a boost.

It might be enough to kick some charge into a marginal battery but that’s all – the starter motor on a big engine can easily draw 300A on a frosty morning.

Top tip when jump starting any car though is to leave them connected with the “donor” engine running for 5 minutes or so. You can jump start a HumVee from a smart car that way!

The power adapters may not be actively regulated, like many cheap power supplies, but they most certainly would have some sort of overcurrent protection, otherwise they would pose a safety hazard. It could be just a fuse.

That said, in this case the supply would be at 12V ideally, while the load (battery) has significantly less voltage, being mostly discharged. If the supply really did output 12V regardless of load, it would surely blow its fuse with the discharged battery attached. As [Fallen] said, batteries can take much more current.

I’m going to guess that this supply is current-limited, having an output voltage that is only slightly greater than the battery voltage so as to maintain a 1A current output. Only when the battery is ~12V will the supply actually output 12V and turn down its current.

Well now that his car is started/fixed, he will have a gasoline powered 12 volt source for his video game consoles which he ruined the ac adapters for. Can’t wait for the hackaday article on how many game consoles work off 1 cigarette lighter.

Those little jump boxes, with the internal rechargeable battery, are fantastic. I’ve used mine dozens of times, mostly to jump start other people’s cars without messing around with cables and awkward parking. Anyone with a fossil fuel powered car should have one sitting in the trunk at all times. As a bonus for gadgety types, it’s also a solid portable source of 12V, some even have built-in 120V inverters.

usually not the best idea to put a bunch of switchers in parallel (series is ok).

As others have suggested – not all warts are current-limited.

I found out the hard way, powering a device that drew more current than anticipated, with a wall wart that happened to be laying around in my parts bin. No fire, no damage, but about 10 minutes into the test, I smelled something funny, and it wasn’t coming from the device under test. Took me a while to realize it was coming from the area of the power bar, and that the AC adaptor got enough that the plastic casing had begun to deform.

Oops. Shut things down, waited for correctly-specced wall wart to arrive.

Upon disassembly, there was no fuse, just a small transformer and a couple of diodes. I suppose that in the event of a dead short, the transformer windings would have failed, and/or some solder would have melted, but I didn’t particularly want to find out the end-state of this particular unit’s overcurrent failure mode.

@ Zero, Justin, and learnedthehardway:

Obviously not all, due to learnedthehardway’s experience, but most linear (non-switching) wall-warts are deliberately designed to have a sloppy, poorly coupled transformer, so that even if the output is shorted, the transformer will not heat up enough to be a fire hazard. It will get uncomfortably hot, but not a fire hazard.
This is part of the reason why these wall-warts are falling out of favor, replaced by switchers. Linear wall-warts are deliberately inefficient so that they can not provide dangerous amounts of power on their output.

I’ve done this years ago with an old AT power supply. I didn’t realize it at the time, but a charger has to be at least 13.8 volts to actually charge a battery to 12 volts. IIRC, after a full day of charging, the battery only put out about 10.6 volts, which was *just* enough to get the car started.

Okay someone publish Biff’s hack, because that sounded about 300% more interesting than what’s happening in this one.

While not particularly exciting, in spite of some peoples’ doubts it’d certanly work. Lead acid batteries will act like capacitors if briefly charged – a minute or two of charging will let them kick out 100A at 12V

This is identical to your standard car battery charger +3amps or -1amp depending on your selection using a standard charger.

Ok, and not with a smart car, either.

“usually not the best idea to put a bunch of switchers in parallel (series is ok).”

I don’t think these are switching regulators, just your run of the mill transformer-rectifier wall wart.

They said they’re big and heavy, so there probably just plain old transformers.

Agreed @ most above. This thing MIGHT work once in the summer, with a potato hooked to the antenna for good luck. Otherwise, put a sheet of foil under the PSUs so it is much easier to clean up the melted plastic. Now THERE is your hack. My battery is rated for 400 “cold cranking” amps. 1-3 or even 10 amps would be so incredibly iffy. I guess you could use it to power the radio while you wait for AAA or a neighbor to wake up. Just pony up the $20 for a plug in starter or beat your wife and kids without mercy everytime one of them “forgets” to turn off the electrics of the car. Most people/things memories are about half as long as what you hit them with is a good general rule.
Anyhoo it was interesting to say the least and the type of hack that would have my wife watching me, shaking her head, with 911 dialed and waiting to hit send lol.

Could he not just buy a jump pack?

mjrppe I don’t think people are so much dissing this as saying it is scientifically unfeasable and possibly dangerous to everything involved. Then again that doesn’t stop most of us. I would have been more impressed with a proof than what was given.
Comment section-yeah that is where people put comments good or bad. Why not create your own hack instead of bashing everyone as you suggest. The best leadership is by example.

A final piece of advice my dad gave me when I was eyeing my first car battery. “Son, it ain’t the volts, it’s the amps that kill you.”

excellent! it made it! :)

i’m no techno-wiz, so i don’t know what’s /supposed/ to work. but this did! when he got that glint in his eye after learning that the battery was dead, i knew i had to get the camera… and stand way way back. my one regret is that i didn’t use video for you skeptics. absolute failure was on my mind as well; either something would spark and explode, or he would be stubbornly trying until someone could be reached.

i too don’t understand what some of you are saying. we don’t have a jump pack, or second car, or any other power source to start a car. but he did have adapters and it turned the engine over. probably won’t be doing that again, but now we know it works! :)

in case some of you are confused, he did not charge the battery with the wall-warts; merely turned the car over and disconnected everything.

carry on hackers!

Aside from what others have said, I’ll add some trivia.

In the winter if the starter is pulling 300A, and you have an average of 5 feet of cable running from the battery to the starter, the voltage at the terminals of the starter will be around 10 volts.

Now, lets think about jumper cables. Assuming 8 gauge wire 15 feet long (some are longer than this and I’m being generous on the gauge used), the voltage drop between the vehicles can be as much as 6 volts and that doesn’t count the wire leading to the starter.

Sometimes it’s amazing it even works when it’s done correctly…