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esaj

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esaj last won the day on May 11

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About esaj

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  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).
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