Which got me thinking about a simple way of directly using mains power as a jumpstarter. Which is obviously not possible, right now, anyway.
Sure, it's possible... and right away, too, if you care to
spend the money for an appropriate transformer and rectifier. This is basically what the folks pushing electric automobiles want for those who buy into their concept. Just make sure your house and garage have
at least 200 A, 240 VAC service, so you can charge the battery bank in your electric car overnight and then run it for a few hours the next day.
For simply
starting an internal combustion engine, you need a lot of direct current at a lower voltage than that provided by the electric utility directly to your house. That's where a transformer comes in, to lower the voltage, and the diodes come in, to rectify the AC into DC. Others here have provided an intermediate solution (line powered battery charger plus a spare lead-acid battery) that doesn't require the brute force of a heavy step-down transformer and expensive 300+ A silicon diodes mounted on a massive heat sink, as my device does. Yet these other "solutions" still provide a "jumpstart" capability using mains power, just not so instantly at the push of a button. The key is to collect electrical energy from the mains in small amounts, and store that energy temporarily before releasing it into the starter motor to start the internal combustion engine. The traditional energy storage device is a relatively inexpensive lead-acid battery of appropriate size, but newer methods such as super-capacitors and lithium-ion batteries are available for anyone with deep enough pockets of cash.
An automobile electrical system does essentially the same thing as my roll-around device, my automobile alternator serving the function of the electric utility after the engine is running, and the automobile lead-acid battery being used to temporarily store the energy produced by the alternator. A modern automobile, equipped with all the gadgets and gizmos people seem to want, requires a considerable amount of current from its alternator, while needing a sufficient additional current capability to re-charge its battery in the presence of a continuous high-current load.
As
@portyforty well knows, in earlier days automobiles only needed enough continuous electrical power to operate the ignition system, exterior lights at night, windshield-wiper motors when it rained, a fan to circulate cabin air over a heater core under the dash during cold weather, and perhaps a Delco vacuum-tube in-dash radio. These electrical loads could all be easily accommodated simultaneously and continuously with a DC generator and a 6 V lead-acid storage battery, provided the running engine's revolutions-per-minute was maintained sufficiently high.
That all disappeared in the 1940s after World War II. Six-volt batteries were soon replaced by twelve-volt batteries; DC generators were replaced by AC alternators, with integral diode rectifiers to provide direct current. And positive-grounded electrical systems were replaced with negative-grounded. Manual transmissions were replaced by automatics, many of which did NOT allow the engine crankshaft to be rotated from the rear wheels, through the transmission, when the automobile was pushed from behind. Push-starting was a common means of getting a car started if it had a flat battery and a manual transmission, because the ignition system received enough voltage from the residual magnetic field in the DC generator (whose shaft was rotated by means of a v-belt and pulley with the engine crankshaft when the car was pushed) to start the engine.
With all the "improvements" in automobile technology, it became necessary to carry "jumper cables" and depend on others to get a car with a dead battery started again. And then there were those who also depended on others to
have a set of jumper cables... or a spare gas can... or a tire jack... obviously these erstwhile drivers were no Boy Scouts, who are always prepared. Me, I have membership in American Automobile Association (AAA) so help is just a phone call away... unless my cell phone battery is dead or I am out of range of a cell tower.
The last automobile I encountered with a six-volt electrical system, was an old Dodge that my fraternal Grandfather owned. He kept it in an unheated detached garage at the home to which he retired in Morristown, TN, parking his car next to a bank of finned selenium rectifiers mounted on the inside of the outer wall of the garage. The "thing" was about the size of modern oven door and perhaps twelve inches or so deep, wired as a full-wave bridge rectifier, connected directly to 120 VAC power through a nichrome heater wound on a ceramic core. The rectified DC output from the bridge was connected directly to the terminal posts on the six-volt battery to provide a "trickle" charge. I have no idea how Grandfather determined how much resistance to use in series with the line voltage, or how he determined when the battery was charged and a trickle charge was no longer necessary.
I do remember getting shocked off this contraption, standing on the dirt floor of the garage (probably bare-footed) one summer and "experimentally" touching an exposed bare wire with one hand. I was maybe ten years old then and fascinated with Grandfather's electrical "stuff," motors and Edison cells and the like he had "acquired" over the years. He always warned me to "keep one hand in your pocket" before touching any bare wires. Didn't mention anything about bare feet IIRC.
It was a tough way to learn about electricity, but Grandfather was an "old school," West (by God!) Virginia, deep coal-mine electrician. He apparently favored learning by trial-and-error methods for anyone too lazy to read books and learn from the experience of others. So from then on I checked out of the library and read everything I could about electricity. Edison became my hero and the model of who I wanted to become. That is, rich and famous, with a winter home and laboratory in Florida.
I finally got the retirement home in Florida, and my laboratory is a "work in progress," but it wasn't until years later, in high school, that I even heard the name Nikola Tesla mentioned and later learned about the intense rivalry between the two men. My allegiance immediately changed from Edison to Tesla once I learned "the truth," although Tesla did appear to become quite insane in his later years. Genius often appears that way. Mu ha ha ha!
I didn't repeat my "experiment" with the selenium rectifiers, although I have received numerous unintentional electrical shocks since then. After Grandfather died, his Dodge was claimed by one of my cousins and transported to Bristol, TN. The last time I saw it, it was sitting on concrete blocks, wheels removed, in cousin's front yard, located at the foot of a tall hill his house was built on. Easy to see as you drove by it. I guess he must have considered this some kind of memorial to our grandfather. Or maybe he was just waiting for an offer he couldn't refuse.
Earlier this year, I or my wife left the exterior car lights on overnight and "drained" the car battery. Attempts to recharge the battery with my luggable battery charger/starter failed, although I was able to get the engine started. There was just no way the battery would accept a charge. Voltmeter measurements indicated a shorted cell. I researched a Chinese import available from Autozone and replaced the battery, avoiding "sticker shock" by finding the price online, but still not liking the cost. The failed battery was a replacement purchased at Autozone several years ago, long out of warranty. This may have been the third of fourth battery this car has had since it was manufactured in 2002.
[Edit: In an earlier post I mistakenly said my truck and station wagon were vintage 2008.] The car now has more than 200,000 miles on the odometer, is beginning to show some rust, and will probably be replaced this year or next year. I drove an earlier vintage of the same model (we like Ford Taurus station wagons) until the front wheels literally fell off one day in a parking lot, spilling large steel ball bearings everywhere. Still, it doesn't pay to skimp when replacing the battery. No need to go overboard either, but we have had "good luck" with Autozone car batteries.
