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Car battery jumpstart gadgets

portyforty

Nov 10, 2017
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All the jumpstart gizmos seem unnecessarily complicated.
I would have thought that a gadget could be built that somehow connects the car battery to the house mains temporarily.
I've never seen such a thing so I guess it's not possible.
Can someone please explain why this is?
 

ChosunOne

Jun 20, 2010
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Well, to begin with....the jumpstart device needs to be portable. Even at home, a fair number of people park their cars far enough from their house/apt that the device would need a L-o-o-o-ng extension cord, which would sometimes need to be strung across the street. Not all of us have garages/carports next to the house.

So a mains-dependent device might be practical for a limited market, but that part of the market who actually needs to use it, i.e., has cars they think might need the occasional jumpstart, is also going to need a device that works anywhere, not just near a mains supply.

That's just my considered guess. I'm not a marketing expert.
 

portyforty

Nov 10, 2017
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I take your point.But what I was really asking was: Is such a device possible? It seems to this layman that it should be a heckuva lot less complicated, and therefore cheaper, than the jumpstarters I'm seeing online. Personally, my batteries have only ever gone flat at home - light left on, door ajar etc - so it would be as easy as plugging in a drill or a saw etc. to service my flattened batteries.
 

kellys_eye

Jun 25, 2010
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It's called a BATTERY CHARGER and they already exist. Use an extension cord if you need to.

Those portable kick start devices are intended for those (rare) occasions you aren't close to an easy mains supply or even off-site completely where they come into their own. If it happens at home you can quite easily attach a charger for 1/2 an hour or so if need be.

Household mains supplies are 120/240V AC (alternating current) whilst cars need DC (direct current and at a low 12V) hence devices to convert the AC to DC are required. If you connected house hold mains supplies directly to a car battery you'd be witness to a spectacular explosion!

If you want an 'instant' kick start then it boils down to the amount of instantaneous energy availability. It takes anywhere between 70A to 180A (at 12V) to crank an engine. A mains transformer set up to achieve this would weight a considerable amount and the mains extension cord probably the same again itself.

Modern portable battery storage, whilst limited in duration, can deliver many 10's (or 100's) of cranking amps - albeit for only a few seconds - but enough to turn an engine over and get it running which is why many such kick starters are made from a simple 17Ahr SLA battery - cheap, relatively light-weight and incredibly power-dense for the brief period it's needed.
 

portyforty

Nov 10, 2017
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You're missing my point. I already said I know about portable jump-starters, whether they be powered by conventional car batteries or the newer Lithion Ion power packs. And I'm well aware that you can't connect 110\240v AC directly to a DC battery. I'm an IT guy and my workshop is littered with old adapters that convert 240v to 9v, 12v 14v - whatever various laptops require.
It's starting to seem to me that what I'm suggesting isn't impossible. But you're saying that there wouldn't be a market for such devices. I disagree, but that's not the point.
I joined this 'electronics' forum just now because I thought that someone who knew something about automotive electrics\electronics could say, 'No, it's not feasible because of X or Y,' or 'Yes, it's entirely possible'.
So far, no-one has said that. Perhaps I'm on the wrong forum?
 

debe

Oct 15, 2011
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You can buy battery chargers that are capable of supplying enough current to start an engine, but only for short periods.
 

hevans1944

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Perhaps I'm on the wrong forum?
Well, if you didn't understand @kellys_eye's explanation, maybe you are in the wrong forum.

I would have thought that a gadget could be built that somehow connects the car battery to the house mains temporarily. ...
It's called a BATTERY CHARGER. See post #4 above.

... I've never seen such a thing so I guess it's not possible.
You IT guys think you have seen it all, so if you haven't seen it yet it probably doesn't exist... riiight?

... Can someone please explain why this is?
Howsabout a quote from Forrest Gump: "Stupid is as stupid does."

I joined this 'electronics' forum just now because I thought that someone who knew something about automotive electrics\electronics could say, 'No, it's not feasible because of X or Y,' or 'Yes, it's entirely possible'.
Yes, it's entirely possible. I have built one. It weighs about 100 pounds and rolls around on four wheels in my garage. It plugs into a standard 115 VAC, 15A, convenience outlet. It connects to my car battery (when necessary) with about ten feet of rubber-insulated, heavy-gauge, four-wire cable attached in pairs to large alligator clips. It is capable of supplying sufficient current to operate the starter on my 2008 Ford Ranger with six-cylinder, 4L, engine as well as the starter on my 2008 Ford Taurus Station Wagon, also with six-cylinder, 4L, engine... but not both at the same time. And it charges automobile batteries nicely too.

upload_2017-11-10_8-14-34.jpeg
 

kellys_eye

Jun 25, 2010
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All the jumpstart gizmos seem unnecessarily complicated.
I'm assuming you're referring to all the additional functionality many such charger/starters offer?

Given the total simplicity of a jump start unit and the power that is otherwise 'sat there doing nothing' the manufacturers have added inspection lights, cigarette lighter sockets, volt meter, air pump (tire inflation), USB charging?? - all as 'added value' and, yes, they can be called 'gizmo's'.

There's no obligation to use any of the gizmo's though....

It's not a product that needs redesign/redevelopment/remarketing unless you can add some OTHER gizmo that sets it apart from all the rest - built-in cocktail cabinet and binoculars perhaps?
 

dorke

Jun 20, 2015
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Hop,
the amount of metal you have put into that charger...
next thing would be to build a tank;)
 

BobK

Jan 5, 2010
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You can jump start a car (with a depleted battery,) using 8 AA alkaline cells. But only by charging the car battery for an hour or two.

The batteries have enough energy to start the car, but not enough power.

A home AC outlet has enough power to jump start the car, but at the wrong voltage. You need a trasformer to convert the voltage. A transformer that can handle that kind of power weghs about 50 lbs.

A battery charger that works off the line voltage is more like the AA cells. It does not have enough power, but the energy can be stored up over time by charging the car battery.

Bob
 

portyforty

Nov 10, 2017
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You guys are still missing the point. All except Bob and, the - dare I say - sllghtly smug-looking Mr. Hevans1944.
(Who I think I may be senior to, unless he is trying to indicate that he graduated from college in 1944)
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.

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?

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?
 

kellys_eye

Jun 25, 2010
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The fact that a car requires 10's to 100's of amps to crank - albeit for only a few seconds - is the reason why a large transformer is required.

To obtain the same 'oomph' using a smaller transformer you're (sort of) correct in that heavy duty capacitors are required. But the 'heavy duty' is such a high value capacitor as to be called - a battery. Which is all a lead-acid (car) battery really is and which is why most portable starters use them (in their smaller version - or, more modernly, ni-cad or lithium equivalents).

The heart-starter principle is heading in the right direction except the power levels are considerably lower and for a much shorter duration.

PS - I love how Hevans starter set up has that 'dragged through a hedge backward' look!
 

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Bluejets

Oct 5, 2014
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Simple ? .....how about a spare auto battery maintained with "smart" trickle charger so it is ready whenever you need it. That takes care of the household part.

As for the capacity, take the aforementioned battery and a set of jumper cables that will deliver 600 amp plus without dropping the end-of-line voltage too much. This covers direct driven starters as well as the geared versions.

Included in that would of course be the necessary-these-days inline filter to eliminate problems associated with "jump-starting" current day computer controlled equipment.

Of course there is no protection against those that continually connect things backwards.

Then again, any of the previous replies all have their merits.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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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.:D

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)
 

(*steve*)

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Is there any good reason you couldn't make a switchmode power supply delivering (say) 200A from a standard 240V 10A outlet?

I've seen computer power supplies that have power outputs in this range. Presumably they are protected similarly to smaller power supplies and might go into hicup mode if asked to start a car. I can't see why you couldn't have a constant current behaviour.

However, the weight, cost, and complexity would vastly exceed that of a simple lead acid battery kept charged by a small charger.

If you incorporate the battery, you remove the need for all that complex power electronics, and probably 90% of the expense.

My recommendation would be to fit a 12V lead acid battery and a charger in a box. If you feel so inclined, you could take it to a car with a flat battery and start it. You could even use it unplugged.

Hey! it sounds like stuff that's already on the market.
 

dorke

Jun 20, 2015
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The "new era" is upon us.;)
The newest thing is the use of super-caps in car jump starters.
These caps are in the range of the hundreds of Farads and can store enough energy to start a car.

These miniature jump starters are small and lightweight about, 1kg !
They aren't very cheap 70-200$ depending on quality and properties.

The smart ones work like this:
The caps would be charged from the dead car battery ,
which may mostly be in the 10-11V area ,but it can be very low voltage as well, say 3V.
This is probably done by DC-DC conversion and/or constant current charging in the jump-starter itself.

In the case where there is no battery or it is totally flat at 0v ,
the jump-starter uses an internal "small battery" to charge it's super-caps up.

Here is an example of one at work.
 
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BobK

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Very cool. I bet you could also charge it from some D cells, just in case the battery was too far gone.

Bob
 

(*steve*)

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Yeah, there are a number of supercap with very impressive current capability.

And if you're not too concerned with maximum energy storage, very simple overvoltage protection can be used to stop charging once any cap reaches its maximum voltage.

But again, the solution is a very low impedance source that is (relatively) slowly charged from another higher impedance source.

This brings to mind electric vehicles. Pumping fuel into a car is a faster way to get energy into a car than charging a battery. Even if you could charge a battery that fast, you're limited by the available power. Most of the enhancements in speeding the charge of electric cars come from improved battery technology allowing faster charging. Running cars from capacitors had been suggested as an alternative due to the faster charging and discharging you get with them.

I have also heard of some experimental battery technology which relies on (from memory) an interaction between two liquid electrolytes rather than between electrodes or electrodes and electrolyte. The practical upshot is that you can charge the battery by filling it with new electrolyte, and the energy capacity is determined by the amount of electrolyte. I can imagine some future "gas station" having special bowsers to drain and refill electrolyte reservoirs before "reactivating" the used electrolyte.
 

hevans1944

Hop - AC8NS
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Very cool. I bet you could also charge it from some D cells, just in case the battery was too far gone.

Bob
You could probably connect the USB charging port to a small photo-voltaic solar array panel to charge the ultra-capacitors... during the daytime of course.
 
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