You guys are still missing the point. All except Bob and, the - dare I say - sllghtly smug-looking Mr. Hevans1944....
What! My Hugh Hefner pose (minus the ubiquitous pipe and bathrobe) is only
slightly smug-looking? And the penetrating gaze behind the all-knowing eyes... what's not to be smug about? I thought this was pretty good for a "selfie" taken in my kitchen.
... (Who I think I may be senior to, unless he is trying to indicate that he graduated from college in 1944)
...
I graduated with a BEE degree in 1978. Since moving (retiring) to Florida last December, I have discovered I am junior to just about everyone else who lives here. I think the
average age is somewhere in the mid-80s. Younger further North, toward Tampa and Atlanta. Don't know about Sarasota, the Miami beach area, or the Florida Keys. But it does feel nice to be called "young fella" at age 73 instead of "old fart" like they did in Ohio. Despite all that, I have prob'ly forgotten most of what the current generation thinks it "knows" and the parts I do remember represent tried-and-true wisdom garnered (sometimes painfully) from the previous century. Either that, or just the musings and ramblings of an old fart. Your choice.
... Yes, he understood my question, and provided the answer by way of his photo. And that's all I wanted to know. It's obviously possible to employ mains power to start a car, but perhaps not practical, if the photo is indicative of the hardware required. ...
The photo is indicative of just one way to do it for a small engine not demanding humongous current. Larger engines will require a larger transformer and rectifier set. It didn't start out that way, i.e., to be a car starter power supply. And if you wanted to do this on a regular basis, say as part of a garage shop service operation, a bigger transformer and rectifier set would be required for reliability. Maybe something on the order of 200 pounds of transformer instead of 50 pounds. The steel-frame and wheels I added later probably adds another 50 pounds. The bungee cord is used to drag the thing around, sometimes through vegetation. I used to be strong enough to lift it, but am no longer able to do so. That is why I "guesstimate" the weight is around 100 pounds.
The device in the picture had another, earlier, life as the front-end to a low-voltage, high-current, DC power supply for a computer application. It consists of a step-down transformer whose secondary windings feed a high-current full-wave rectifier bridge. This produces full-wave rectified DC with lots of ripple at 120 Hz and lots of current... several hundred amperes without breaking a sweat or overheating. In New Zealand that would be 100 Hz, since IIRC your mains supply is delivered at 240 VAC and 50 Hz. The original application had several huge electrolytic capacitors to filter and smooth the ripple before applying the DC to a voltage regulator circuit. This is not needed for re-charging a lead-acid-chemistry automobile battery, or for starting a car engine.
... So, to ride this ailing horse a little further, I assume that the key is to transform the AC (which is 240v here in NZ) but is that the whole answer? Or are some heavy duty capacitors involved? ...
No
capacitors needed, but some heavy duty
rectifier diodes, mounted on a large-ish finned heat sink are absolutely necessary.
The heat sink on my device is cooled by convection air currents, but larger DC supplies use forced-air cooling, or even liquid heat exchangers cooled by refrigeration. Why? Because silicon diodes, which are just about universally used for high-power rectification of AC, all have a considerable forward voltage drop that starts at about 0.7 V and goes up with conducted current. At just 100 A that's at least 70 watts power per diode that must be dissipated. The only reasonable alternative is synchronous rectification using a semiconductor switch such as a MOSFET with Rds(on) in the milliohm range, or a bipolar junction transistor (BJT) operating fully saturated with a few millivolts of collector-to-emitter voltage. Even those will require cooling if currents can exceed kilo-amperes up through mega-amperes for really high power applications.
... I mean, jump-starting hearts comes to mind, if the rising whine of an about-to-be-deployed defibrillator that we constantly see on medical dramas ('Stand clear everybody!') is an accurate depiction.
Is that shocking (amperage?) achieved by capacitors?
It's quite "shocking," and somewhat dangerous to bystanders, since it must be applied externally through the chest wall with sufficient voltage to provide enough current to the heart muscle to be effective. There is a lot of electrically conductive tissue in between your heart and the skin of your chest. This tissue tries to "short out" the defibrillator paddles. And, yes, there is an energy storage capacitor involved, very similar in voltage and capacitance to that used with an electronic stroboscopic flash.
I, OTOH, have one of the latest state-of-the-art pacemaker/defibrillator implants. I wore it for several years without noticing anything. Then in January of this year it started "doing its thing," shocking my heart back to life. However, much lower amperage and voltage is needed when the electrodes are implanted in the heart, and I didn't notice the high-frequency audio whine from the charge-up DC-to-DC converter. I finally did an emergency room visit as result of the last episode in March. This lead to two open-heart coronary artery bypass graft (cabg) procedures. Seems an artery nicknamed "the widow-maker" was completely blocked and could not be stented. I was not eligible for a replacement heart, being somewhat old and definitely not rich and famous, but my heart surgeon was skilled and successfully stitched in two veins he removed from my left calf. He had harvested enough length to do four cabg procedures, but decided not to do that because I had been on the heart-lung machine for quite some time for the first two procedures. Even so, there was some evidence of "pump brain" or reduced cognitive ability immediately after I regained consciousness. This confused state rapidly went away, but I doubt I can still think as well today as I could fifty years ago, when I knew everything and was always the smartest person in the room.
Hop,
the amount of metal you have put into that charger...
next thing would be to build a tank
I needed some means to move it around because it was becoming too heavy to lift as I became older. The slotted angle iron happened to be available at a good price (free) and I could afford to purchase a few dozen 1/4-20 bolts, washers, and nuts to assemble it. The biggest cost was the wheels. I should have used larger diameter wheels, but the four I have work well on flat, smooth, surfaces like my concrete garage floor. The bungee cord makes it fairly easy to pull around. I have no desire to build a tank, but thank you for your support.
I hope
@portyforty sticks around for awhile. There are a lot of hobbyists here who could benefit from the support of an experienced IT person. If no one has said so yet, welcome to Electronics Point,
@portyforty.
Hop (AC8NS)