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esaj

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esaj last won the day on June 1

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About esaj

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  1. esaj

    KS18L OoO - Please KingSong Read This Topic

    This. I think the manufacturers should give the users an option the fallback to an older revision of the firmware if they see it necessary, sometimes the new versions add unnecessary limitations (for experienced riders) or if they find out a bug (regression) that wasn't on an earlier version, users should have to option to return to older version.
  2. esaj

    KS18L OoO - Please KingSong Read This Topic

    While the firmware bug is a really bad thing, wow, that's some robust mosfets and motor there. If it indeed is a firmware crash (like it looks), it has left one high- and one low-side mosfet open, running full stall current through the 'fets and the motor (as much current as the battery can give shorted over the fets and the motor) for an hour for that one guy, and everything still works
  3. Maybe... at least you'll think twice before fooling around with the batteries
  4. The documentary as a whole is interesting, but I've linked it directly to the part where they show tests done to bigger lithium batteries (crushing, overcharging, puncturing). Big fireworks! Also (earlier in the document, around 15:30) they show what happens when pure lithium gets in contact with water...
  5. esaj

    New Gotway ACM shell

    I can't read Swedish And don't know much anything about chemistry, just that acetone dissolves some plastics (not just ABS). If it dissolves the plastic and evaporates quite easily away, then it should work just fine
  6. esaj

    New Gotway ACM shell

    Btw, you could just go to the closest Biltema and get the >99% purity stuff for a few euros/60 kronor: https://www.biltema.se/bygg/farg/rengoringsmedel/aceton-2000030019 Lego-blocks are pure ABS. ABS is also sold as filament for 3D-printers.
  7. Updated the first post a bit again. Hopefully these are two isolated cases (one with the earlier firmware problem, one with maybe hardware issue in the 1st batch?). Still keeping this pinned so people are at least aware of the possibility.
  8. If you buy from an US reseller, such as eWheels (Jason), they'll take care of warranty repairs, if such are needed at some point.
  9. Yes, but as @TomOnWheels stated above, the second case occurred with FW 1.07. Separate issue or the fix doesn't cover all the cases?
  10. The wheels have what is called "regenerative braking". The wheel (and you) have kinetic energy when moving, and you build up "potential energy" when you go up a hill. Law of conservation of energy says that energy "can neither be created nor destroyed; rather, it can only be transformed from one form to another". What this means is that the energy "stored" in the motion (or "just" plain potential energy when coming down a hill) must go somewhere, it cannot just disappear. A more technical explanation is given here: https://electronics.stackexchange.com/questions/56186/how-can-i-implement-regenerative-braking-of-a-dc-motor Trying to explain it more in layman terms... isn't easy When you're braking (or coming down a hill, steady speed or braking), the kinetic energy spinning the motor is used to charge the battery by using the motor as a generator. The rotating motor causes a voltage ("back-EMF"), but this voltage by itself isn't high enough to cause current to change direction from "normal" motor driving. What the stackexchange answer is explaining is that the mosfets and the motor inductances (coils) form a "boost converter", a circuit which "pumps" the voltage up (if you're more electronically inclined, compare this to a boosting switching-mode power supply). During braking (when the motor is actually being slowed down by shorting the phases together), the magnetic fields of the coils are "charged". When the low side mosfet stops conducting, the motor "free wheels" a bit, and then when the high-side mosfet is switched to conducting, the collapsing magnetic field causes the voltage to raise to high enough level for it to become higher than the battery voltage, forcing current to flow in the opposite direction, and thus charging the batteries. After a (very short) while, there's not enough voltage to keep the current flowing "towards" the batteries, and the cycle must be repeated. But as the wheel is turning the mosfets on and off really fast (6000-8000 times per second), you won't notice that it's actually switching between free-wheeling and braking. EDIT: The 6000-8000 times per second -value comes from the PWM-frequency, which to at least some wheels is around there. It could be that the high- and low-side conducting are changed more infrequently, but anyone who has ridden a wheel knows that you don't feel any "twitching" during braking, and I can't exactly rig an oscilloscope on there while riding the damn thing to see what's going on With fully charged packs there's the risk of (at least momentarily) overcharging the batteries, although there are usually large caps in the mainboard next to the battery power lines, which will at least take some of the energy coming from the motor. Overcharging a lithium cell is very stressful for the cell, and can degrade it (and in extreme situations, destroy it). If the battery BMS has overcharge protection also on the discharge side (cutting connection from the discharge side in case of overvoltage), the battery won't be "there" to take the energy, and you'll likely fall. How much it charges is anyone's best guess. A lot of losses occur along the way (at least resistance of motor coils, mosfets and connectors & batteries), so part of the energy is "lost" as heat (yeah, it doesn't disappear, but changes into "unwanted" form of heat instead of just charging the batteries, thus the power "loss"). There are other ways to slow down an electric motor, like driving the coils in "opposite" (ie. switching it on after it has passed the magnet, attracting it against the direction of the motion) to normal motor driving (I think this was called "plugging braking"), it has been debated before whether wheels could use this method in some situations. The problem with this approach is that the battery and kinetic energy is then transformed only to heat, in the mosfets and motor coils, and it's very taxing to the motor, and could burn the mosfets or the coils (or PCB traces, wiring or connectors). Still, it's possible that the wheels could use this method in some more extreme situations (power braking). The "resistance" (opposition) to spinning faster is caused by the phases being shorted together. If you ever for any reason need to disconnect the motor from the mainboard, you can try it: with the motor disconnected from the mainboard, try to spin it with your hand. It should spin relatively easy at this point. Now, take two connectors coming from the motor and press them against each other. Now try to spin the motor. You'll notice it's much harder to spin the motor now. You could also put the motor spinning with your hand, then touch the connectors together. The motor should brake really fast. If it's "plain" regenerative braking, the motor is producing, not consuming energy. If it's the "plugging"-type braking, then it would be consuming. Pretty much all resistance does is mostly causing power dissipation as heat. The momentary power from hard braking can lead to somewhat extreme power being produced. I'm too tired to break open the physics books, but I'd say that a 100+kg of mass being decelerated very quickly can produce quite high momentary power. Enough to even burn the mosfets (that has happened at least in older wheels with heavy riders and strong braking). Unless you try to stop on a dime from fast speed coming down the hill, and your batteries aren't charged to full, at least the more modern wheels should be safe in this regard. I've had the "pleasure" of finding out about the BMS overcharge protection in discharge side & full batteries in a downhill...
  11. esaj

    100V MSuper X ... check it out!

    Thanks for the trust, but I'm just a hobbyist in electronics, and my word definitely shouldn't be taken as any sort of "gospel"... there are actual EE's (electronics engineers) in the forums who likely know far better than I do.
  12. Updated some details in the first post, let me know of any further info that comes along or if there are errors in the post.
  13. esaj

    100V MSuper X ... check it out!

    The cells can give out a huge number of amps, the amperages reported by the manufacturers are (maybe somewhat conservative) ratings for maximum continuous (like 10A) and shorter while (20A) output currents. Above these the cell may overheat and catch fire or explode, but if you short circuit a cell over a small resistance, the amperage will be HUGE. The protections on the cells (like the CID, "current interruption device") should trigger and cut the current, but they aren't always acting fast enough or even working. Still, you can get a hundred or more amps out from a single cell for a brief period, probably at least tens of amps for a longer while, but it can also go up in flames pretty quick. Sometimes they just heat up, maybe make some smoke, other times... Video description: "Charging at 30 amps and then short it" Very short-term transients can be really high just inside the circuits with caps discharging, I used 10 x 47000uF / 160 milliohm each caps in parallel for a spot-welder that goes way above 1000A for a short period (~1 millisecond), and that's in a controlled fashion with 5 x mosfets in parallel with "proper" gate driving (large current drivers, ferrites, fast turn-off -diodes, parallel TVS's to kill of transient voltage spikes from weld cable inductance) to start / stop the discharge. But still, the Gotway amps measurements likely is way off. The overcurrent protection in BMS only disconnects the output, it does not limit it really (so more like "on or off"). The mosfets in the BMS board cannot limit the current, they would overheat and burn, only either "allow it or disallow it", not much in between. Usually the BMS datasheet has times for how long it takes for it to react, so for a short while (micro- or milliseconds) it can allow as much current as the cells just can give. Some random BMS datasheet, over current protection delay time is 5-20ms, short circuit protection delay is 200-500┬Ás. Also note that this is for 4S (and any number in parallel) BMS, with working current of 100A and over current protection triggering at 300A +- 20A. The short circuit current is expected to be higher.
  14. esaj

    KS18L OoO - Please KingSong Read This Topic

    Still, most wheels work just fine, so certainly it's doable (but I don't doubt that it's hard to "get it right"). If the voltage spikes aren't "too long", TVS-diodes in parallel with the mosfets might help? If the spikes last a longer while, they might die or interfere with the motor drive... but most TVS's can take very high energy spikes for short time frames (like kilowatts).
  15. esaj

    KS18L OoO - Please KingSong Read This Topic

    You could still pull the handle "hard enough" by yourself. But like said, that was just theorizing, could be something completely different. There have been some mentions about the "led rings" having some issues with earlier FW? The peak currents usually occur when the motor starts turning (0V back-EMF), although they could get very high during fast acceleration, especially uphill. The typical PWM-frequency of the newer more powerful wheels seems to be around 6-8kHz, unless that has changed. Guess they use audible frequency to minimize switching losses in the mosfets, but that causes some wheels to emit a high-pitch whine. When the wheel is running at steady speed, not much current (torque) is needed.
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