Vampire Charger Is A Rugged Anything-to-5VDC Converter

USB sockets providing 5 VDC are so ubiquitous as a power source that just about any piece of modern portable technology can use them to run or charge. USB power is so common, in fact, that it’s easy to take for granted. But in an emergency or in the wake of a disaster, a working cell phone or GPS can be a life saver and it would be wise not to count on the availability of a clean, reliable USB power supply.

That’s where the Vampire Charger by [Matteo Borri] and [Lisa Rein] comes in. It is a piece of hardware focused on turning just about any source or power one might possibly have access to into a reliable source of 5 VDC for anything that can plug in by USB. This is much more than a DC-DC converter with a wide input range; when they say it is made to accept just about anything as an input, they mean it. Found a working power source but don’t know what voltage it is? Don’t know which wire is positive and which is negative? Don’t even know whether it’s AC or DC? Just hook up the alligator clips and let the Vampire Charger figure it out; when the light is green, the power’s clean.

The Vampire Charger was recently selected to move on to the final round of The Hackaday Prize, netting $1000 cash in the process. The next challenge (which will have another twenty finalists receiving $1000 each) is the Human-Computer Interface challenge. All you need to enter is an idea and some documentation, so dust off that project that’s been waiting for an opportunity, because here it is.

43 thoughts on “Vampire Charger Is A Rugged Anything-to-5VDC Converter

  1. If you’re wondering about the arduino nano there: it’s temporary. i’m going to set this up so that it uses a few LM324s as comparators instead. cheaper power wise.


    1. How do you figure out and limit the supply current so you don’t damage the source circuit? Is there any sort of detection that says “this source cannot supply enough current?”

      I ran into the problem trying to boost voltages up out of random batteries, that getting 500 mA at 5 Volts out of a 1.5 Volt AA battery requires more current than the cell can comfortably supply, which ends up just heating the cell and throwing away most of the energy stored within.

        1. could you compare the unloaded voltage upon connection to the loaded voltage at the start as a sort of handshake/test and assume if X load produces Y voltage drop you may be drawing more than the source should be supplying? additionally it seems like you could use this to infer some data like “this voltage is likely N cells of Y chemistry” or “the voltage is dropping at a higher rate now so we’re probably about drained on the supply side”

        2. What to use at least something like MPPT?
          It musn’t save the source always, but it can help to get the maximum of the power from it and because of this, it can prevent from taking too much of the current (because voltage will drop and power too…)

          1. MPPT will kill a battery, because the maximum power output is when the source and load resistances are equal, which means drawing enough current that the battery’s internal resistance is equal to the effective load, and 50% of the energy is wasted inside the battery.

            In practice, more than 50% of the energy is lost because the battery chemistry becomes inefficient. If you take an alkaline battery and run it at the maximum power point, you get about a quarter of the charge out, which is less than useful in an emergency because the rest of the circuit wastes energy too and you’re just burning up your flashlight batteries or your smoke detector batteries that you might want to have around, for little effect.

        3. Yeah, but the point is that you aren’t getting much charge out because you’re overloading the supply circuit, and thus wasting your emergency supply.

          If there was a way to detect how much current the source can supply, like measuring its ESR somehow, then you slow-charge a power bank with it, and pull the 5 Volts out of the power bank instead.

        4. Maybe you could add a little thermocouple on a wire that you could tape to the middle of the cell which would throttle down the charging current if the power source gets above a certain temperature?

    2. How about a universal USB to USB charging adapter that tests the port to see how much power can be drawn, and queries the device to determine its maximum power draw, then pretends to be the device’s official charger – supplying as much power as it can take, but no more than the source can deliver?

      I put a 3 amp USB supply in a truck but the USB ports with it don’t even have the data lines shorted at the connectors. Can’t fix that without cutting the molded plugs off and replacing them. Thus no phone or tablet will pull more than 500ma.

      I have a dual port cigar lighter adapter. One port is marked 1 amp, the other 2.1 amp. My Samsung phone pulls 800~900ma from the 1A port but treats the 2.1A port like a data port, only pulling 500ma. OTOH, my Samsung Tablet goes the other way. I also have various supposedly high power AC chargers, including one by Belkin, but my non-Apple phones and tablets will only pull 500ma from them. Could be they’re made to trick only Apple devices into using them for high power.

      There must be a way to make one USB port emulate all the different proprietary charger detection schemes for Apple devices, Samsung, and other Android devices – and fit it into a compact gizmo with a male and female USB Type A port and plug.

      One that only acts at a converter to make Samsung phones and tablets work with genuine and 3rd party Apple chargers would be nice. A not-Apple to Apple adapter would likely be warmly accepted by iDevice owners who chafe at Apple’s ripoff prices for chargers.

        1. And they also do not seem to work every time. A friend had an “intelligent” 2,5A USB charger and a Bluetooth Speaker with a 5Ah battery. It started with 1,8A on this charger only to drop down to 500mA after about 2 seconds. With my Samsung charger, which has shorted data lines it continued to pull 1,8A.
          So obviously there were some communication issues between the intelligent charger and the device.

      1. I had the same idea, but I don’t know how to determine the parameters from either the charger or the device being charged.

        e.g. Apple devices won’t charge at all, or won’t charge at their maximum value, unless the voltages on the D+ and D- are correct.

        But how do you determine what USB D+ and D- voltages the target device requires?
        One way would be to monitor the current being taken by the target device, and try various D+ and D- voltages and see what resulted in the highest current.

        But phone and tablets do not necessarily take the same current all the time. The smart charging circuits inside these devices, can initially start with a low current, and the increase it as the system determines the state of the batteries while charging.

        So any “enquiry” phase of the system would need to take long enough for the target device at each value of D+ and D- to allow for the max charge current to be reached.

        I’m not sure how many combinations of D+ and D- voltages there are, but the enquiry phase could take a while.

        BTW. Its possible that is not simply a question of supplying the correct voltages on D+ and D- lines… Its possible that the target system is detecting the actual resistance and not the voltage.
        If resistances, rather than voltages were need, then digital potentiometers could be used. But that adds a lot of the cost to the device, which would otherwise mainly consist of a microcontroller using PWM to generate the voltages, and some sort of current measuring device e.g a 5A Hall Effect chip.

        1. But to do this you would be breaking the EULA you signed for your Apple device and that just wont do.
          You must use an official Apple branded mains to USB charger and your vampire power solution needs to put out at least 90Vac 50hz to power that.
          If you do not, you will void your warranty.

          You cannot go willy nilly voiding a global megacorp’s charging method which are legally protected by patent.
          Are you some sort of intellectual property thief ?
          You should be in prison.

          Unles you pay the Apple tax you’re taking money out of the mouths of the children of these overworked employees.
          Shame on you. Shame.

    1. Right now I’m aiming for 1.5 low, 110AC high. 220 is too hard for me. The first one I made that worked was sent to PR right after Maria (where it worked for about a week, but it was a good week for it to be working, so it’s all good). At the moment I’m getting 3 low.

          1. 400V (between phases) is nothing special and not limited to industrial places. We have been slowly increasing the voltage from 220V to 230V while older equipment is hopefully scrapped before it overloads. This also also moved the between-phase voltage from 380 to 400.

          2. Better step that up even more to 415vAC (across phases) for Australia, with maybe a lower specced version for 240vAC – the common wall voltage (single phase). It used to be 250vAC in Western Australia (Perth) many years back. I don’t know if they ever changed it to bring it closer to everyone & everything else…
            And a low voltage of 1.1 volts DC. NiCd and NiMH are 1.2 when operating (under load), and less of course under higher load. A ‘carbon’ (alkaline) battery is nominal 1.5 volts, but deteriorates very rapidly under load.

            Doing both these extremes would be a pretty big challenge! It is commendable you have got it to go as far as you have.

      1. There are cheap modules that are intended to be used to convert AA to 5V 1A, and they work pretty fine from 0.8V to 4.5V. That range enables them to use even discarded AA cells that are not directly usable in devices and small solar panels when there is no direct sunlight. But using such module in wide-range converter will probably require some additional logic to protect the device in case higher voltages are used.

        1. An alkaline AA cell can be made to put out 5 Volts OR 1 Amps, but not both at the same time, because the 1 Amp at the output must turn to 6 – 7 Amps at the battery, and it simply cannot supply that much.

          In other words, you can’t draw 5 Watts out of a single AA. You can just about draw 1 Watt and that’s already killing it. For rechargeable cells, it works, but the typical single cell AA “emergency phone charger” doesn’t actually work because it kills the cell in 5-10 minutes before it has actually put any meaningful charge into the phone.

  2. The fact that you are doing this potentially from an AA or AAA even, COULD be the ONE manually selectable item. Your device STILL adapts all voltage sources. Noone said squat about current, so you are 199% in the clear…!!! This is not a lame cop-out. It’s a totally legit thing to limit current. I even swap chargers for a fast or slow charge on a device. Just lable a switch, that… Fast, Slow. The details can be in the instruction sheet. Make no apologies. If you have a battery holder capable of many small cells, a sensor could determine to send 100ma per cell, or such… maybe it holds 6, but you put in 2. One thing… an optiinal small lithium w a small solar cell that will charge a.. 1000ma(?) lithium in say, a week if cloudy days, or 6 hours if bright sun???

  3. From the title I was hoping for something that could tap a random power line running through the desert. I think some are 25KV, but others are much higher. I’m not even sure this could handle a loosely coupled transformer from one.

    1. It can’t. I mostly wanted to send something to a friend in Puerto Rico right after Maria hit, that he could use to keep his GPS and phone running. It worked for about a week before crapping out, but it let him call his wife when it was important, so it’s all good :)

    2. I wonder if there’s some way to do that inductively from the ground, like how fluorescent lamps stood on their end will glow under a high-tension transmission line.

      Because if you try to tap a random 25KV line in the desert directly, you are going to add what used to be your body to the dust blowing in the wind.

      1. The inverse square law is working against you. You might be able to charge some small batteries but not much more. In a disatser situation if high tension lines are up not much use for stealing power from the ground, somone still has more reasonable voltages in their walls.

    3. I was under the impression the really big towers (in Australia at least) are in the order of 130KV….

      And then there’s the high voltage DC connection between the North and South islands of New Zealand. There was even an article on this site about it, but I can’t find it. Some stupidly high voltage used on that one. For some reason one million volts comes to mind, but that is just ridiculously high. Anybody know what it actually is?

  4. Hmmm… where I’ve noticed some 100-250v to arbitrary voltage power bricks take a while for the light to extinguish (i.e. laptop PSUs), I hooked a bunch up to a 30v source and found some of them powered up.

    The lowest voltage running was a 100-250v to 5v (4A) brick from RS stock number: 117-6126
    Whilst it is listed as 85v to 264v ac… the revision we’ve got at work start up at 16v and drop out at about 13v-ish where anything 15v and up will deliver about 2A without cutting out.

    This project seems to bring that minimum voltage from 15v to 1.5v…

    How the chip in the RS part does this is by a an internal constant current of 10mA through a voltage reference (presumably 5v) for the internal oscillator and feedback circuits. That way the internal 5v regulator draws a constant current in the range of 13v through to 260v-ish.

    1. Forgot to mention: the RS PSU (as do many others) take in DC…

      Some other PSUs have a half wave rectifier for the constant current supply pin and thus will need the positive and negative lead swapped if they don’t turn on at first… for the rest that don’t power on DC is because of a chopper circuit relying on AC.

  5. I think this is trying to achieve too many things at the same time and it would be reasonably bad at all. In reality, a user would be happier with
    1. a normal phone charger which will probably work from 80Vac to 250Vac.
    2. A step down/up to 5V converter which can take some voltages up to 50-60V should be doable, then any kind of cordless drill, lead acid battery from around the house is viable. I highly doubt such a converter could be a step up from a very low supply like 1V, but 3V (1 li cell) should be achievable, a LT8471 seems like the right part for this.
    This converter needs some smarts to figure out how much it can draw from whatever battery is connected to it which may not be that simple to achieve.

    Putting this circuit in a power bank is much better, you could charge the power bank battery slower and then your phone faster.

    1. This is a commendable idea. One device to do “big” (like mains outlets, AC generators, etc) and the other to do “small” (like batteries, be they truck batteries, or AAA cells of unknown chemistry).
      To make it ‘universal’, an electronic/electic latching push button switch that defaults to “big”. If no power comes out, the user pushes the button to switch it to “small”. And a fuse in case they accidentally press it!

      1. I would not even switch them at the input, dangerous if you apply high voltage to the small one. They could both produce a fixed voltage like 5V at the end and do the switching between them at this level.
        Again, even for the small switcher, you have contradictory requirements between something that could work with 50V input and something that should work from 1V input.

    1. Yeah. I built this for a friend in Puerto Rico where I know that they have 110V. If I can get it to take 240V stably, I’ll do an indiegogo (and publish better schems, dammit!)

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