Open source capactive charger resurrects an electric skateboard

mikey-sklar-on-electric-skateboard

Here’s [Mikey Sklar] posing on his new electric skateboard. Well, it’s new to him at any rate. He bought it used on eBay for $250. That may not sound like much of a deal, but these will run more like $800 retail. The savings comes because the thing would no longer charge. But it took him just an hour and a half with his capacitive charger to resurrect the flat lithium cells.

The first thing he did in trouble shooting the situation was to measure the voltage of the battery pack. It registered 5V, which is a far cry from the 36V it should supply. The built-in charger does nothing, as it’s circuitry isn’t designed to work in a situation like this one. But [Mikey] has a tool perfect for this purpose. Da Pimp is a capacitive charger which we’ve seen before. It succeeds where the other failed because it is able to adapt itself to the internal resistance of the battery, no matter what voltage level it starts at.

[Mikey] shows off the use of his charger in the clip after the break. His first test run was more than two miles without issue.

[http://www.youtube.com/watch?v=MLHjccKfltk]

Comments

  1. Per Jensen says:

    Wonderful simple circuit, however I wouldn’t want to be near when the Power mosfet fails shorted and there’s a Li-pack connected… Recipe for fire and explosions… Also, please be aware that all parts of the circuit is connected to live power, so you can get killed touching the battery and what it’s connected to. Many commercial battery chargers for electric drills work on this principle btw. My DeWalt charger is very fast, and contains no transformer what so ever, but it requires that the battery pack is very well insulated, or people gets killed.

  2. Sdfdsfds says:

    I thought the HaD community ripped to shreds his charger as being incredibly dangerous and poorly designed?

    There isn’t a single positive thing in the comments from the last article about the charger: no mains insulation, no safety cutoffs (time or voltage), poor layout, incoherent design…

  3. Chris C. says:

    The built-in charger doesn’t work by design, as a safety feature. It’s potentially dangerous to recharge a lithium cell that has become so heavily discharged. Irreversible electrochemical changes have occurred that may result in bursting and/or fire.

    Da Pimp works simply because it has no specific safety features for lithium cells. It allows you to do things that shouldn’t be done by the average consumer, and you assume any risk by doing so. It certainly has nothing to do with adapting to internal resistance.

    Lithium batteries have been discussed on HAD many, many times before. So I cannot overstate my disappointment that a HAD editor, who is exposed to knowledge like this on a regular basis, still doesn’t understand; and posts nonsensical explanations instead.

    • Super_Nurd says:

      If you take your browser on a journey to his site, you will find that “Da Pimp” seem to be more intended for lead-acid batteries, and although still a dangerous ordeal, it is significantly less risky than Lithium cells. A neatly put together hack in my opionon, but the creator should have stated more of the saftey risks (or atleast have stated that the user is at risk), also there really is nothing new to this, I remember seeing these quite often.
      screwdecaf.cx/dapimp

  4. Wizzard says:

    Also in agreement- Those cells are ticking time bombs. Literally.

  5. Peter says:

    What these guys said. He got away with it, *you* might not be so lucky. However, he had nothing to lose and as long as he took the proper precautions (for me, that would invove an outdoor, fireproof surface and a cut-off 55 gal drum) why not give it a try?

    In spite of the thrashing I got when commenting on safety in the x-ray thread, thinking about what could go wrong before you apply power is always good advice.

  6. fartface says:

    Exploding Lithium cells are fun! That is a neat design to cause explosions!

  7. tony says:

    If the nominal voltage is 36 volts, then that is ten cells. Five volts comes to 0.5 volts per cell. Dow Kokam has told me it is dangerous to charge a lithium cell if the voltage dips below 2.5 volts, let alone 0.5 volts. There is a very good reason the charger wouldn’t work. It is designed not to make things explode or catch fire.

    Watch for pack swelling. The off gassing causing the swelling is an indication the cell is going to fail. You do not want this.

    Discharge the battery with a small load and dispose of them properly. Then switch in some new cells

  8. ka1axy says:

    I’ve looked at the schematic for “Da Pimp”. Not to put too fine a point on it, but you’re basically connecting AC line to the output leads. That’s why he tells you not to touch them when the unit is on.
    Should you choose to build his charger, you should understand the safety issues involved (AC line voltage on the output leads) and take appropriate precautions to keep yourself and anyone else who has acess to the work area safe.
    The easiest and cheapest way to make “Da Pimp” *much* safer, would be to add an isolation transformer in front of it. If you can’t afford to do that, at least plug it in to a GFI.

    • Gary Niger says:

      Or, you know, you could just use the lab supply for charging that.
      Depending on whenether or not you’re willing to risk your lab supply dying in a lithium fire, of course.

  9. David says:

    Why didn’t he just use a transformer? This design is crazy.

  10. ThanhTran says:

    Apart from the dangerous charger (which shouldn’t be used to charge lithium batteries, and I would not use it), I’m puzzled at why his battery still worked after getting down too far, and it didn’t appear swollen or puffed. If I leave a battery pack on my plane or Hal overnight and forgot to disconnect it, next day it would be swollen up and become useless. All I can think of is that the battery pack has a built in protection circuit and it has some problems that prevent charging/discharging and it gives out only 5v. ANd maybe after kicking it with his charger, the protection circuit was resettled and thus it worked again? I’ve seen this kind of behavior on small lithium batteries inside cheap Mp3 player from China.

    • el_walto says:

      I’d have to agree. No way he got a 36V lithium battery sitting at 5V back to working. Or it now has very reduced capacity, and it will blow up the second time he tries to charge it.

      • Bebop says:

        Sounds right to me too. On board smart charger and battery circuit is holding things up. With any luck the cells aren’t too bad_____ Maybe they were run down **JUST** enough.

        10 Cells is a lot care for, my net books 6 Cell battery lasted a year before I got some warnings that a cell might be going bad. I would crack that battery pack open and monitor each cell closely. Get rid of the dangerous ones. Heed the warnings here on hack a day, look up lithium battery fire on youtube. Those things are like a volcano with thermite and a honey badger when they go off.

  11. Yasuo says:

    Looks like Dust2 in the background :D

  12. agtrier says:

    Weren’t we supposed to have flying skateboards by now?

  13. Sven says:

    I would be surprised if there was a protection circuit in that battery pack, it’s hard to design such a thing for the high currents found in motorized toys like this.

    It is also fully possible to be lucky and manage to charge a severely deep discharged LiPo, but just like running across a highway it’s not recommended.

    The safe voltages people usually state for Li* cells is something like 2.5-2.75V on the low side, and 4.2 on the high side. According to an article i read the actual voltages are more like 2.0V on the low side (sustained) and 4.4V high (sustained). Going outside this span _may_ damage the cells, but it’s not a certainty.

    I have managed to charge cells discharged to nearly zero, i just did it as a test, under supervision and in a fireproof enclosure, but they did take charge and they did work. They had a very low internal resistance when charging however, and an increased internal resistance when discharging. Note: I discharged the cells and threw them away afterward, i wouldn’t actually use cells that had been that deeply discharged.

  14. Nick says:

    Am I the only one that though this was les claypool on a skateboard?

  15. mefornow says:

    I keep coming here for insightful comments and all I find are nanny’s repeating each other. One person has said this is dangerous. Got it.
    BTW my years of hacking experience tells me that this is dangerous, and I need to tell you so, to show my years of experience.

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