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esaj

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Everything posted by esaj

  1. True, it's probably easier to understand it as the time it takes to charge than a value of current. Still, in real-life circumstances, actually charging from empty to full in one hour would mean that the charge rate is actually far higher than 1C, because the amperage (and thus charging "speed") drops towards the end, as the charger voltage reaches the maximum and stops raising it. To keep going at 1C until the end, the charger would have to raise its voltage above the maximum battery voltage and then somehow "know" when the battery itself has reached the maximum value and stop abruptly. Thus even a 2-hour charge may be using close to or even more than 1C before the CV-phase begins. With the large capacity of most current wheels, probably nobody actually reaches the "1C" -values... imagine something like 20S/1600Wh pack at nominal 74V (3.7 * 20), that would be over 20Ah. Likely the charge port or wiring will melt, or the BMS components will die before that high current can be reached. Edit: Oh right, for the unitiated, the "C"-rate for charging speed is explained here: https://batteryuniversity.com/learn/article/what_is_the_c_rate
  2. I was looking at Brymen BM859s https://brymen.eu/shop/bm859s/ a couple of years back, seemed pretty good for its price, but then found a second-hand HP34401A (6½ digits bench meter) for 240€ with shipping. I then faced the same problem, how to tell how good it actually is (ie. how much it has drifted from last calibration, which was several years ago)... What I ended up doing was to buy precision resistors & voltage references, make boards for them with measurement points and power the references from a battery (to prevent any "noise" from a linear or, even worse, SMPS power supply) and see if the meter reading was within the tolerance of the part. I got down to 0.05% in voltages and 0.01% in resistors with no problem (using good probes, they're just as important as the meter itself, for example: https://www.tme.eu/de/details/pp-bm10a/messleitungen-komplettsatze/brymen/pp-bm-10a/# , I got horrible jumpings in the readings with cheapo Chinese probes ), beyond that, no idea. Good enough for me You can get 0.01% 5PPM/C (SMD) resistors in singles for around 1€ per piece for "common" values (I simply got 10, 100, 1k, 10k, 100k, 1M, 10M), don't remember what the 0.05% voltage references were, a couple of € maybe. After that, it starts to get expensive, 0.005% resistors are something like 20€ per piece.
  3. You can probably find a ton more just by a quick google search for something like lithium ion cell balancing , but here's a couple: https://www.batterypoweronline.com/blogs/why-proper-cell-balancing-is-necessary-in-battery-packs/ https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing Wheels don't seems to have "active" balancing circuits, rather they just bypass shunt cells that reach the full voltage, thus the "balancing" on the wheels works by charging it to full and then leaving it still on the charger for the rest of the cells to catch up (even after the charger light turns green to indicate "full" battery, there is still current running, many of the chargers turn the light green somewhere around 200mA). I use Charge Doctor to monitor this, and wait until the current drops to very near zero (10-20mA). I recall seeing a screenshot from the app of some wheel (Ninebot Z, maybe?) that showed the individual cell voltages, wonder whether they have an actual active balancing scheme?
  4. From what I know, this is true, the amperage is hardly a problem for the modern wheels with multiple packs in parallel. Some years back, most of the wheels had just one or two packs and there it could have become an issue. Nowadays, the limiting factor is the charge connector (such as a GX16) and the wiring, which can become very hot with high amperage, still, 5A for a GX16-3 or such should be within limits (the maximum given by manufacturers is 5A or 7A, depending where you look, and seems to go down the more pins the connector has). The newer plugs used on some wheels (don't remember the name, the rectangular one) are probably meant for higher amperage, and even the other wheels could be retrofitted with thicker wiring and multiple charge ports in parallel. I think 1RadWerkstatt used to sell a kit with 8A charger with two outputs (4A each) and secondary charge connector to fit in the wheel...
  5. Sorry for a slight thread hijack/off-topic, but looking at this board, I don't see many capacitors near the corners of the MCU (I'm assuming it's the U4 on the left side), and it's hard to follow from the low resolution picture where the lines go. Do you know the values of the capacitors feeding the VDD/VDDIO/VDDA -lines of the MCU? The reason I'm asking is that I need to add an STM32F0 -MCU to a board I'm designing, and the datasheet seems to suggest somewhat excessive amounts of capacitance for the power inputs: Even ST's own Nucleo-board has just 1uF + 100nF near the regulator, a couple of 100nF's combined for VDD's, and a single 100nF for VDDA with a ferrite bead to filter noise (apparently the capacitance on VDDA should be lower, because the VDDA-line must come up faster than the rest). Maybe they're just being conservative on the datasheet, but it's funny that their own dev-kit board doesn't follow their suggestions... And now I'm struggling trying to fit all the caps near the MCU on an already crowded board with strict size-limitations
  6. Nice renders, the pedals look a bit small, but maybe that's just because of the bulky shell.
  7. I'd be guessing that a high-power e-bike motor might be better, I've seen kits going up to 15kW (guess it's the peak power though). No need for so many magnets / coils as with an EUC, as the motor doesn't need as precise control...
  8. Just a sidenote, to everyone ordering the Chinese "Blue pills" (the "bare-bones STM32F103"-board) and ST-link copies: Original Nucleo STM32Fx -devkits that come with built-in programmer/debugger (basically they have built ST-Link V2 directly on the board) cost something like <10€ + VAT from Mouser for the "lower end" models with 32 or 64 pins, for the "higher end" -models it's something like 15-20€ with higher pin-counts/more memory/etc if you fear you're going to run out of I/Os (up to 144 pin versions) or memory. If you order stuff for 50€ worth, you get free shipping, and it arrives in a couple of days. Nucleo STM32F103RB: https://www.mouser.fi/ProductDetail/STMicroelectronics/NUCLEO-F103RB?qs=sGAEpiMZZMtw0nEwywcFgIZtmIQSvK4F7SgvqhUm0of%2Bpet9mJDudA%3D%3D All Nucleos: https://www.mouser.fi/Embedded-Solutions/Engineering-Tools/Embedded-Processor-Development-Kits/Development-Boards-Kits-ARM/_/N-cxd2t?Keyword=nucleo&FS=True&Ns=Pricing|0
  9. Most bench power supplies (I'm assuming you mean what I understand to be a bench power supply, aka laboratory power supply) have current limiting, ie. they are constant current / constant voltage (CC/CV) power supplies, although there are some cheap models that have no limiting. Another issue is the relatively high voltage required for charging (I think Airwheels use 16S batteries = 67.2V max). Typical bench supplies are low voltage that can go maybe up to 30V. Even my industrial-grade programmable rack-mounted power supply can only go up to 30V. I have a couple of CC/CV 0-100V / 1A / 100W linears for higher voltage usage. IF your bench supply can go high enough in voltage, but has no current limiting, I'd be very careful trying to charge lithium batteries with it, although it is possible, but you need to turn up the voltage SLOWLY, keeping the current at low amps (say, 2A or less), and adjusting the voltage up until you hit 67.2V, then just leave it charging (although do monitor it so you can cut the power in case of trouble). Not something I'd definitely try unless you're familiar with how li-ion charging works and the risks involved, especially since I have no idea if the Airwheel BMS has reverse protections or such.
  10. esaj

    Downhill Issue

    The motor acts as a generator when you brake, instead of using power from the battery, it "converts" the kinetic energy to electric energy and recharges the battery.
  11. They're usually shrink-wrapped along with the BMS, but the "configuration" inside can be different from one wheel to the next. Here's an old picture of unwrapped Firewheel F260 pack: The FW pack configuration was an unusual one, I don't think any other wheel has similar... there are two packs (the other one with the blue wraps can be seen underneath the unwrapped one) with a single BMS just in one of the packs, and all the balance & charge/discharge -wirings for the other pack running between. Each pack is actually 8S2P, which are then connected in series to make a 16S2P for charging and discharging. Still, this is similar to what you'd likely find inside most packs. There's a a cardboard (some might use plastic) insulator between the two rows of cells, and each two cells right next to each other are in parallel. I didn't tear it further, but there's a factory wrap around the cells themselves, as the entire outer casing is the negative terminal, not just the bottom. In the below picture you see a couple of positive-terminal insulators to prevent the terminal from coming into contact with the edges (which are part of the negative terminal): If there's a tear or a dent in the pack itself, or in the cells (of course you won't see them through the outer wrap), I'd be wary of it. A hard knock on the pack (or the pack moving inside the battery compartment and hitting something) could cause such, but from what I've seen, the packs usually sit pretty snuggly in their compartments and won't have space to move around. Ninebot One (C/E) had a design fault where plastic "edges" (probably to make the part stronger) on the battery compartment cover could cause damage over time to the wrapping, possibly even the cells. The big issues are either cell puncture (probably immediate fire), the internal electrodes pushing against each other (internal short circuit, the cell will at least heat up considerably, if not catch fire/vent) if the cell has a dent, or the welded tabs on the positive terminal making contact with the outer edge (negative terminal, external short circuit). 18650 internal structure Welded tab has punctured the wrapping and made a short circuit, in this case it was when the guy was dismantling the pack, apparently only made a huge spark and burnt the wrapping, but if in a pack it would stay there, then there'd be trouble. Other than that, based on what I know, voltage changes are a good indicator of cell health, if one cell or cells in parallel (two or more cells directly in parallel will always have the same voltage) have lower voltage than the the rest, it's an indication of wear and tear (they discharge faster, possibly also recharge faster). Slight changes (something like around ten millivolts or a little more, 10mV = 0.01V) are probably just normal, that's what the balancing's for, but if the voltage of some cells drop much further from the others (or raise above them), there's something going on. Either the cell(s) has/have "aged" faster than the rest, or there's some other internal damage, like dendrite build up.
  12. While I do realize there's a (small) risk, this is how I've been storing & charging my wheels for the last four years: There are smoke alarms and carbon monoxide alarm (we have fireplaces) around the house, but no sprinklers or such. I never leave the wheel charging while away from the house or sleeping (well, there was that one time that I forgot to unplug it in the evening... )... I'm not overly worried of either really catching fire though, although it is possible. EDIT: Oh right, there's about 1kWh worth of lithium-cells in the ground cellar under the kitchen (with its own smoke alarm)... at least one of them is 3S1P -pouch lipo without any protections. Maybe I should do something about those...
  13. In a nutshell, most wheel BMSs have a basic balancing circuitry, but they only work when the wheel is charged to full (there are better so-called "active" balancers, but I don't think any wheel has them?). It's not necessary to do every time, but over time, the cells will discharge to slightly different levels and then not all of them charge fully (or if it's a really crappy BMS, it could allow some cells to overcharge). The more deeper discharged cells will start to fail sooner than the others, and might even die. For more information, you could start with https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing and Battery University in general, they have lots of good articles about batteries: https://batteryuniversity.com/learn/ Li-ions don't need "conditioning" or be run all the way down before recharging, like some other chemistries which have the "memory effect" (such as NiMH). Li-ions can be "randomly" (meaning starting charging at some battery level and stopping before full) charged without problems, except for the balancing issue mentioned above when the battery consists of multiple serial cells, but it should be enough to do a full charge every now and then. To ensure that the balancing occurs, you should leave the charger on the wheel for a while even after the "light goes green" to show that the battery is full. The balancing occurs at very low current compared to normal charging, when the cells are nearly at their maximum voltage. The chargers are "dumb" bricks with constant current / constant voltage -output, meaning when the battery isn't yet near full, the current is regulated to some amount (constant current -mode, usually 2A for the basic chargers), so the output voltage is lower than maximum, and once the maximum voltage has been reached (constant voltage -mode), the current will start to drop as the actual battery voltage starts to raise towards the same maximum (less voltage difference between battery and charger over more or less constant resistance -> less current). The red/green -light on the chargers usually changes color somewhere around 200mA (0.2A) or such, but for balancing, you should leave it there longer. One last warning: I've heard of, had and re-adjusted chargers that give out slightly wrong voltage (typically too low, then the charger will never charge the wheel fully or balance the cells), so best check the output voltage of the charger to make sure it's correctly adjusted (a basic $10-20 multimeter is enough for this, they can typically handle up to 200V DC if not more). If it's giving too high voltage and for some reason the BMS doesn't have overvoltage protection on the charging side (I think all the "brand"-wheels should have the protection, but can't 100% guarantee it), then in the worst case it could cause a fire.
  14. esaj

    Bitcoin

    @lizardmech and @John Eucist were in the craze a couple of years back, but don't know if they still do it. I own a few shares in a BTC-trading company, but since it's not publicly traded, no idea of what the actual "value" is nowadays, probably less than what I bought them for They did have a 300% increase in revenue due to the price spiking back then and everyone trying to get their piece, but I haven't followed up
  15. Before damaging the wheel in any way, you could start off with putting the wheel (turned off) in a box with some form of heating which you can control. Keep it at, say 60 degrees Celsius (140F), and if nothing happens, ramp it up to higher. The point is to simulate a wheel sitting in a hot car in summer: "“When temperatures outside range from 80 degrees to 100 degrees, the temperature inside a car parked in direct sunlight can quickly climb to between 130 to 172.”" 172 Fahrenheit is about 78 degrees Celsius. I doubt anything happens, the cells aren't supposed to start thermal runaway until they heat up to something like 125 or 150C (about 250-300F).
  16. Yeah, the motor + bit vibration is what causes the too wide cuts, not the machine axes. If you look at it, the cuts are straight and the trace width is pretty uniform, so the axes are running straight and true... probably I shouldn't have used to word "tolerance" really, but 0.5mm pitch components seem to be near the limits of what I can do reliably. I ran another board today, with slightly different settings (slower cuts, first with 30-deg 0.1mm bit at 100mm/min, then again with 15-deg titanium 0.1mm bit to clean up). This time the traces are closer to 0.2mm: There's copper "slivers" left behind, but usually they're relatively easy to clean off or might just come off simply by rinsing the board under faucet with some water pressure. Next time I need to cut this small footprints, I might go just with the 15-deg bit + "lying" about the cut width in FlatCAM so that it runs in the middle of the pins to see if it gets close enough to 0.3mm. It's not the machines "fault" as such, or even a machine tolerance issue, just the runout on the bit + motor. Here's what the earlier board with 0.1mm traces looks like after assembly: The resistors and capacitors are 0603's, except for the bigger cap on the right side of the chip (0805). The sticky looking stuff in the cut grooves is flux I haven't cleaned off yet... I burned the mosfet of the original Woodpecker-board enough times before with a higher powered motor, so I don't use it anymore Mine's currently running with Arduino Uno + CNC-shield with Pololu-drivers (set at 1/16th step) and a custom-made spindle driver. Tempting, but if I can save enough from what I get paid for this project, I might be going for the all-steel frame CNC next...
  17. https://www.1radwerkstatt.de/epages/80603321.sf/en_GB/?ObjectPath=/Shops/80603321/Products/Charger Chargers from 100 W to 1500 W in all voltages Output voltage according to customer requirements (one week delivery time) Current chargers in stock Chargers of the highest quality Aluminum casing Line filter on the input side Circuit protection, overvoltage protection, overcurrent protection, temperature monitoring in the charger If desired, the charge termination to 80% or 90% thus a substantial increase in the lifetime of the battery According to data sheets, a previous charge (80%) results in a battery life of up to 3 times. The battery should be fully charged every 20 to 30 charges with the original charger, as only the balancers work and minimum balance differences are compensated. This is not necessary for batteries (for example original Ninebot) without a balancer circuit. (These batteries have limited durability by saving this necessary balancer circuit)
  18. I haven't read that topic, and probably explained it badly and got too much caught up in the details. Yes, if you try to ride "too fast", you will fall. It's just that it seems that modern wheels no longer deliberately cut the power to the motor, rather just plain physics at work. Even while the mainboard logics / battery BMS doesn't cut the power, the motor cannot produce more torque after the speed (motor RPM) goes high enough, due to the voltage produced by the motor itself raising to high enough value to "overcome" the voltage of the battery / mainboard capacitors. The wheel will just fall forwards as it can't keep balancing anymore (cannot accelerate fast enough to "catch" you). Overlean and high power spike demands of bumps can still cause a fall. In an overlean, the battery cannot give out enough current to produce high enough torque to pull the wheel back upright. Even if you're running at a steady speed on level ground, if you go fast enough, the sudden bump can similarly need "too much" torque to keep the wheel upright, or if you're already close to the end of the torque-curve and try to demand more speed (acceleration) by leaning forwards.
  19. On top of this and the V10's (This is a single incident, but apparently the problem was more common place with the early V10's, enough to warrant for the company to recall wheels / send water-proofing kit for the packs to the owners), there's at least one Ninebot One fire reported recently: Someone made a mistake in changing a tire and blew up their pack: Also, Marty made a video of someone's ACM that caught fire after a crash, somewhere there was a picture of some other Gotway burning up on the street, and @meepmeepmayer reported of a KS18A that burned partially. Back in 2015/2016, there was at least one newspaper article of a generic catching fire while charging, but likely there were more cases than just that one. Probably others I've already forgotten about, and there might be reports in the forums floating that I haven't even read... Plus there's a lot of riders outside these forums, so it's not like we even hear of every incident. Still, likely an actual fire or explosion is relatively rare, I'd hazard a guess that most of the times the batteries die a more silent death.
  20. I don't think the more modern wheels shutoff at high speed anymore. Older wheels (say, 2015/2016 and before?) did that, either because the BMS cut off the power when the current rises too high, or the mainboard logics did that for whatever reason. It's not the gyroscope switching off as such, either the logics stopping the motor drive altogether and leaving it powerless or entirely losing power to the wheel due to BMS switching off the discharge-side, but like said, I don't think any modern wheels do this anymore. I probably should revise the first post at some point, speed-related cutouts could be nowadays better described as the motor back-EMF (voltage generated by the turning motor itself, it acts as a generator) rising too high and then not having enough voltage on the battery/mainboard-side to drive current through the motor. The motor torque drops linearly with speed because of this, and when the back-EMF equals the battery voltage, the current, and thus torque, becomes zero. Of course on an actual riding situation, it's more complex, as the needed torque changes a lot, and the battery voltage goes up and down depending on how much current is flowing.
  21. I'm certainly not against solar, in my opinion it should be used a lot more in places where there's sunshine all year around. As for providing energy on a global scale, it's a no-go, not as the main form of producing energy, need to have backup. Here's the sun's radiation energy over a year where I live: On the left is average kilowatthours per square meter over the entire month from January (1) through December (12). On the right is the annual average amount of solar radiation power in different cities in Finland, I'm in the middle (1127kWh / m^2 / year). These are before the losses due to panel efficiency. Most of the energy is needed between November (11) and end of March (3), as that's when its coldest. Incidentally, not much sunshine during that time either. On winter days, the consumption is usually something like 60-100+kWh (when it's really cold, electric heating). I was offered a 3kW system installed for 12000€ (which is a rip-off price, really) a number of years back, with no energy storage. That's about 3-4 month median income (before taxes) in Finland. Probably could get such for half that price, still not really cheap IMO. The inverter needs to be replaced after around 15 years (but it's only 500€), the panels have warranty for at least 80% of nominal power output up to 25 years. After that, who knows...
  22. Cars etc. moved to here:
  23. I don't remember where the 20% figure originally came from, the only source I could find right now was this: The world's electricity consumption was 18,608 TWh[citation needed] in 2012. This figure is about 18% smaller than the generated electricity, due to grid losses, storage losses, and self-consumption from power plants (gross generation). Cogeneration (CHP) power stations use some of the heat that is otherwise wasted for use in buildings or in industrial processes. In 2016 while total world energy came from 80% fossil fuels, 10% biofuels, 5% nuclear and 5% renewable (hydro, wind, solar, geothermal), only 18% of that total world energy was in the form of electricity.[16] Most of the other 82% was used for heat and transportation. ( https://en.wikipedia.org/wiki/World_energy_consumption ) But that contains other than just transfer losses, so probably the actual losses in transfer are smaller. But, currently power isn't being transferred that much over very long distances, so building up a very large solar array in somewhere like the Mediterranean won't help that much in Northern Europe, and trying to transfer it (as electricity) over thousands of kilometers is likely a no-go with current technology, because of the losses in the transfer. Of course, if it could be used to produce some (clean) form of energy that was more easily transferable (gases, liquids...), then it would work much better.
  24. I personally haven't had a car since 2002, but my GF does... I think we clock in about 1000-2000km per year (that's about 600-1200 miles). At least that's what I think, she's had the car for over 10 years, it had way more than 200000km on it when we got it, and nowadays has about 240000km. Most of the time I travel by walking, bicycle, bus or by EUC. Train or bus for longer distances. Ship or airplane going from country to country, but I've only flown about as many times as I have fingers in one hand in my life The suns radiation power at sea level is something like 1kW per square meter. The current good (and expensive) panels have something like 20-25% efficiency. If you have a tracker turning all the panels to face the sun, you can make about 250W (0.25kW) per square meter on high efficiency panels (at best). To produce 1MW, you need closer to 4000m^2 of tracking panels (about 43000 square feet). After that come all the other losses in the system. And that's where the sun shines all year around. Powering a house is one thing, the highest power we use during winter (-30C / -22F) is probably less than 5kW on average. Powering a grid that charges umpteen cars charging along with everything else all around is another thing... Especially farther away from the equator. This is the problem, almost 20% of all electricity generated in the entire world is lost in transfer these days, and the plants are close the where the power's being used, not in a middle of desert in the other side of the country. I'm not that "sure we can figure it out"... but of course (hopefully) could be proved wrong.
  25. The largest nuclear power plants in the world are something like around 8000MW. So the largest plants could charge around 8000 such cars at once. How many people will be riding these? 8000 cars at once, 5 minutes each, there are 1440 minutes per day, so around 2.3 million cars charged per day, assuming all of the power of such plant is used to charge those. Most plants are much smaller. I hear you, but there are problems with generating enough electricity. Solar power works when you're closer to equator. What about up north from here, where the sun doesn't rise at all for almost 2 months during winter? No geothermal or waterpower available either, and there's not enough wind all the time.
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