Coin Cell Challenge: Jump Starting a Car

Clearly a believer in the old adage, “Go Big or Go Home”, [Ted Yapo] has decided to do something that seems impossible at first glance: starting his car with a CR2477 battery. He’s done the math and it looks promising, though it’s yet to be seen if the real world will be as accommodating. At the very least, [Ted] found a video by [ElectroBOOM] claiming to have started a car with a super capacitor, so it isn’t completely without precedent.

Doing some research, [Ted] found it takes approximately 2,000 W to 3,000 W at 14 V to start the average car engine. This is obviously far in excess of what a coin cell can put out instantaneously, but the key is in the surprising amount of potential energy stored in one of these batteries. If the cell is rated for 1000 mAh at 3 V, [Ted] shows the math to find the stored energy in Joules:

According to the video by [ElectroBOOM], he was able to start his car with only 6,527 J, and [Ted] calculates it should only take about 9,000 J on the high side from his research. So as long as he can come up with a boost converter that can charge a capacitor with high enough efficiency, this one should be in the bag.

[Ted] has started putting together some early hardware, and has even posted the source code he’s using on a PIC12LF1571 to drive the converter. He notes the current charge efficiency is around half of what’s needed according to his calculations, but he does mention it was an early test and improvements can be made. Will it start? If it does, this is some awesome Heavy Lifting.

80 thoughts on “Coin Cell Challenge: Jump Starting a Car

  1. I remember once teaching an electronics class, and one example of electronics math that I would trot out was an estimate of the total energy in an AA battery .. the results actually surprised mem. You can (conservatively) lift a car the better part of a meter off the ground.

    1. Hey yeah, Hackaday, you gotta clarify. Do we still qualify for the coin cell challenge if we achieve lithium-hydrogen fusion and power an Arduino off *that*? Also, are submissions from Guantanamo Bay accepted after the prototype levels a town?

    1. If it has 24V electrics, it’s probably not an average car anymore.
      A starter motor has to bring all the things that moves with the engine somewhere around 500rpm, where the combustion can run the engine. So it has to counteract the inertia of the engine plus its accessories, a lot of friction (mostly from the accessories and cold oil), plus the compression. It basically depends on the characteristics of the engine, but the bigger the engine, the more power the starter will need.
      Not to mention that Diesel engines require a lot of compression and most of them also require glow-plugs (on an average European car, it’s about ~1kW for ~5 seconds, a lot longer by cold weather).

      If you want to have an idea of the power/energy needed to start an engine, push-starting a car can give you some hints.

      1. You can feed a stock 12v starter 24v for extra speed/harder circumstances and I know someone who does this on recalcent diesel plant engines in cold weather with a 24v jump pack. Long term its probably a really bad idea, but for getting that machine running and earning takes priority over the risk of having to buy a replacement starter less infrequently.
        I feed the originally12v starter on my dragbike 24v because it has a hard time firing it up on 12 and its quite a common thing to use 18 or 24v for short duration purposes in those circles also.
        On something modern with electronics that can get very upset by higher system voltages, its probably a really bad idea though. I’m not in the financial position to have modern things to damage, and my friend presumeably knows the risk/cost benefit to his actions for his particular machines.

          1. its a late gpz1100 unitrack 12v starter cranking over a car slick and bar kz1000 funny bored to 1500cc with a permanently connected belt driven screw supercharger + mechanical fuel pump adding to the drag though only 10:1 cr. The rest of the electronics (megasquirt3+msx + a pic chip controlling some more bespoke stuff) are fed from 12v, but the starter solenoid gives 24v to just the starter to help its workload. Its not burned out so far, but the rest of the engine is likely to end up in a bucket after a couple of meetings anyway so I don’t need massive service life ability.
            The reason I still run a onboard starter, is my pit crew is my 13 year old boy, my 10yo daughter and my wife, so I cant really see any of them being happy to drag out then hang onto a external starter on the end of the crankshaft. Plus if it stalls after the burnout box I have just enough battery capacity to restart off the button a couple of times.
            Its also why I overvolt the 12v unit, because the 12v unit is lighter than a heavier duty unit by a few lbs and f=ma.

          1. Heh…you speak truth. Might as well add headlights and tail lights to that list, too.

            And as I speak from experience, it’s also fun when someone converts not only from 6-volt to 12-volt, but when they also (without knowing what they’re doing, mind you) switch from positive ground to negative ground and don’t bother changing anything. Granted, 1923 electrical systems can *mostly* manage just fine with that, but the ammeter does read “discharge” when charging, and the generator actively works against the battery. Fun stuff.

          2. Kyle,
            my brother changed his 1942 Ford to 12 volts and promptly burned out every incandescent bulb, e.g. headlights, taillights, turn signals (aftermarket), dash lamps…

          3. When I pulled my Model T’s taillight (well, brake light, really) not long after I bought it, it was a 6V bulb. Battery was 12V. Explained why it wasn’t working. So, somehow whoever did the changeover figured out the headlights, but forgot the brake light, ammeter, and generator polarity. Horn didn’t have a resistor, either, but at least with sparing use, those don’t burn out too quickly on 12V. Now it’s got a suitable resistor, so I don’t have to worry about that so much, and for the first time in years it sounds correct.

            But eh, you find weird “fixes” with old cars. Part of the hobby.

        1. This is a big issue most old school “booster” starters on the boost setting run near 24v on 12v systems. It’ll get an old school car up and running but it’ll absolutely destroy the electrics in a modern car. Especially in a no load condition.

          1. Every piece of electronics in a modern is designed to survive more than 24V for short periods of time 10-30s (depending on a manufacturer). Reasoning behind it is that cars are delivered with boats and 1 of 100 will not start because of depleted battery and since time = money when unloading a ship you don’t wait for car battery to properly charge on 14V.
            They hook it up to a cart with double battery pack(actually around 28V) start it and drive it off the ship.
            source(i worked as electronics designer in Automotive for 3 years)

      2. Just as a data point, 24V vehicles are not always big diesels. My 62 Mercedes Unimog is 24V but it is only running an 85HP M180 gasoline engine. Only takes about 200 amps or so for crankover which is lower than quite a few cars. 24V was used in that truck because it was military spec, but it can be started with 2x pretty average grade batteries.

        1. What he said, mogs are cool. I run a 101fc land rover as one of my other toys which also came in 24v versions (though mine is a 12v) because the british army standardised on 24v and the 101 was used as a mobile radar vehicle.
          On the 24v 101, it even has special shielded plug leads and spark plugs (they were petrol), to eliminate electrical noise from interfering with the radar operation and lots of other special electrical add ons and extra bits. Thats also why I’m quite glad I have the 12v, because all the special parts are difficult to obtain now :-)

  2. At first I thought there was an error because 1000mAh could never fit into a coin cell, however they do exist and are quite common too.

    Can anyone explain why LiPo and other technologies are much bigger at a similar voltage and much less capacity (I think about the 240mAh LiPo I have for my mini quadcopter which is already bigger than a coin cell)? I understand LiPos have a higher C rating, however, I thought size was only constrained by energy density and size.

    1. Several reasons that come to mind, all related, though there are others:

      The need to dissipate waste heat during recharge;

      the different chemistry (rechargables have reactions that can be reversed without damaging the physical or chemical properties of the cell, non-rechargables don’t);

      most rechargables, these days, tend to be designed for large current capacity, which means large surfaces in the cell to keep current density manageable. Too high a current density can damage the cell in several ways (heat, chemistry, undesirable side reactions, etc)

    2. One thing is, a primary cell can be discharged all the way to zero because you don’t care about damaging the cell, while the rechargeables have a lower discharge limit that stops you before you get all the potential energy out.

  3. I love the homemade terminals! The terminals are something that I am very unimpressed with in my cheap RAMPS board. I definitely intend to upgrade it sooner than later. Every board I find though is at least a little bit of a compromise. I am considering designing my own. If so… I may have to make power terminals like these!

  4. As nobody seems to have brought it up yet… The problem isn’t how much energy is in the coin cell, it’s extracting it from there. Those cells have been designed for long, slow drain. Trying to extract all the energy from them in less than a few hours at least, is going to significantly lower the energy amount. And once extracted, it isn’t going to last long in the supercaps either.

    So good luck there, it might be possible to find the sweet spot on the drain rate and get the 6~7kJ in the supercap to start the car, but I think that for any practical use, this isn’t going to happen.

    1. Drawing loads of current fast tends to make them over heat and explode.
      I’d recommend a couple of heatsinks. One top and bottom. May as well use them as terminals.
      Stacked 80 up wrapped in electrical tape years ago. 240vdc and plenty of punch if you let it bite your finger. Worked well for some home made vacuum tube experiments though.

    2. Probably because the other people actually read the guy’s project page: he’s planning on an overnight charge of the capacitor(s).

      Also seems you may be under the impression this is being designed for practical use. It isn’t. This is a technical challenge to see what’s possible, nobody is deducting points if the thing isn’t practical (actually, around these parts being impractical and kitsch might help in the judging).

      1. When I mention “practical”, I mean taking less than a month to extract the energy. Those coin cells are designed for VERY low currents. As a wild guess, I’d say you can extract around 2~3kJ out of the cell at the middle point between the internal resistence heating the cell up and the supercap leakage snuffing it. And to do that might take a few days of extraction. Overnight, I think it will mostly cook the cell.

  5. What if you don’t step-up that 3volts from battery with not-so-efficient switcher but instead connect battery directly to cap, then to another cap, then another, untill you fill them all. Ofcourse some current limiting would be required as battery’s capacity would be severly reduced if discharged with high current. Then after process is complete connect all caps in series to get required output voltage and utilize their charge.
    BTW, I don’t think that would work either, as above commenter said, you have problem that you can’t draw too much current from battery or it will have significantly reduced capacity, and on the other side you can’t allow supercap’s leakage current to eat-up charge you accumulated. So basically you have two requirements for process : to be very slow and to be very fast.

    1. This. Just a big heavy switch that moves the capacitors between parallel and series connection.

      Nominal discharge rate for these coin cells is just 1mA, so it would take 1000 hours to get all the energy out.. so yeah, there are bigger problems than just stepping up the voltage.

  6. oh, jump starting. i had first thought the goal was to zap a push-to-start (ignition) button. the second thought was for a goal of increasing the distance of RF-style activation of remote-start.

    1. Doesn’t need to be that special. I built a 500 Farad (yes full 500 farad) bank with 6 Maxwell supercaps (purchased from Mouser IIRC) that was capable of starting very large engines no problem. Since then, even larger capacity caps have come out in the same form factor as what I used.

    1. I wouldn’t have made fun of you. It’s also entirely possible to just build a bigass cap bank and use no battery (for jump starting anyways). My 500 Farad bank is now for exactly this, and even after sitting for almost a year, it still has a large amount of voltage left in it.

      1. You could use pyroelectric batteries.

        https://en.wikipedia.org/wiki/Molten-salt_battery
        >”Thermal batteries use an electrolyte that is solid and inactive at ambient temperatures. They can be stored indefinitely (over 50 years) yet provide full power in an instant when required. Once activated, they provide a burst of high power for a short period (a few tens of seconds to 60 minutes or more), with output ranging from watts to kilowatts.”

  7. Reading about over voltage on cars reminds me of an interesting over voltage meltdown and a valid lesson. Driving a Camry at night on which I had previously repaired the Bosch alternator, the lights flared up like lightening, the instruments went wild, there was a smell of burning electrics and the car died. During subsequent repairs, I had to replace most of the relays as they had melted into a permanent on or off state, all lamps and the complete instrument cluster. At first I though invisible lightening or a strong magnetic pulse from a nearby research institute had done the damage.

    Somehow, the on board computer survived but the alternator sounded funny. When starting up after the repair, the battery started cooking and with its load disconnected, the alternator was producing in excess of a hundred volts! Reason for meltdown found but not the cause.

    It finally transpired that the steel sealing plate of the rear roller bearing had become detached and shorting the field slip ring to earth putting maximum volts to the field coil. Under such conditions the alternator did what alternators are supposed to do it producing the maximum possible volts.

    Moral of the story; do not replace the rear roller bearing of an alternator with one that has steel sealing plates. It can cost you dearly. Rather use one that has a plastic sealing plates!

  8. Won’t there be an issue with how fast the voltage will drop in the super capacitor once you start pulling power?

    The starter might not work so great once you hit 9v and below regardless how much theoretical power you have left.

    You might have enough Joules of power, but do you have them available at a continuous voltage high enough to turn the starter over for that brief duration?

  9. At what point does the energy storage solution become cheating though? This guy is doing it all electrically, but would it be cheating to use a mechanical route?

    Can I use a coincell to power a tiny pump/screw that drops lead shot into a box with a sealed bladder full of nitrogen at the bottom? Then use the gas pressure to do my “work”? The storage mechanism would be large, and expensive, but the dissipation of energy stored as gravitational potential is effectively 0.

    I remember reading about an electrical grid that used excess power to pump water up into an artificial lake instead of dissipating it. Sometimes mechanical storage can be useful.

    1. Pretty sure there is no such thing as cheating for the purposes of this contest, it’s sort of intentionally over the top. As long as the power comes from a coin cell, it’s all fair game.

  10. I don’t think it would be cheating to use the coin cell to charge a LiPo or similar (define “empty” though) over a long period, then use the now-charged LiPo to quickly charge the SuperCap and then start the car. It sounds like the efficiency loss doing it this way would probably be less than the self-discharge of the SuperCaps over a longer period of time.

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