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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. A bit late response... you can see your "attachments" by clicking on your avatar / username in the upper right corner (don't know if it shows similarly if you're using a phone) and selecting Content -> My attachments. As for replacing the images with imgur ones, you'll have to edit each of the posts using the images and replace them with a direct link to the imgur image (the link will be automatically embedded as an image in your post).
  2. esaj

    Mod the baterry pack of ks-14b

    At least in older wheels, 16AWG was pretty common. The high current spikes aren't occurring all the time, and so far, no-one has reported the wires themselves melting, usually if something melts, it's the connectors, or mosfets dying on high current spike / transient voltage spike or whatever. Compared to other parts (connectors, mosfets, the cells themselves), the resistance of the wire is hardly an issue at that size. If you take a look at the motor phase-wires on the motor-side, you might be shocked (depending on the wheel, but some of those are really thin to get them through the axle, compared to the battery wiring). http://www.powerstream.com/Wire_Size.htm Definition: ampacity is the current carrying capability of a wire. In other words, how many amps can it transmit? The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility. NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal! 16 AWG is listed as 22A for chassis wiring (and that's for conservative & for continuous current).
  3. No idea, but @US69 probably has more or less direct line to them, so he might know... I'd expect them to be at least aware of the issue at this point.
  4. To dig a little bit deeper, I did a simulation with 30mOhm and 70mOhm cells paralleled. It's a bit "make-shift", but the basic idea is to simulate a pair under 10A draw. So, I put two voltage sources in parallel, both at 3.6V (about the nominal of li-ion cells, typically 3.6...3.7V), one with 30 milliohm internal resistance, other with 70 milliohms. If you directly connect two voltage sources in LTSpice, that means "0 ohm" resistance between them, which would make it impossible for the voltages to differ, so I used two 100 micro-ohm (0.1 milliohm) resistors to simulate the connection between the cells. I then use an "ideal current source" to cause a draw of 10A through the pair. What the graphs show (nevermind that the current is shown as negative, LTSpice just "wants" to show it that way, as I need to put the current source the "wrong way around" for it not to cause the voltage to raise before the voltage sources ) is that the voltage of Cell1 (the 70mOhm one) is around 3.3897V, while Cell2 is at 3.390116V, so a slight voltage difference exists. What the current graphs (well, lines, this is just a DC steady state simulation) show is that the lower resistance (Cell2) is passing about 7A of current, while the higher resistance Cell1 only passes about 3A. Like said, this is a bit "make shift" -simulation, as in reality the current isn't steady (the motor's being "pulsed" on and off, causing both high and low current draw alternatingly, as well as there are capacitors on the mainboard to steady the voltage and supply the very high current spikes, plus the motor inductances and mosfets, switching frequencies, parasitic capacitances and inductances etc. play a role...), and plain voltage sources with internal resistances cannot simulate the behavior of a lithium cell correctly.
  5. I'll start with the usual "I'm just a hobbyist and you may want to consult a professional", but here's my take: A guy who builds battery packs professionally once said to me that cell matching is a waste of money, but, and this is the important bit, we were talking about brand new cells and matching those very closely (ie. buy 100 cells and pick out the 4 x 16 = 64 pieces that are most closely matched for building 4 x 16S4P). His opinion was that it rarely is of any use in the pack longevity or such, and is just money down the drain. But like said, this was in relation to buying new, unused cells of same make and model. Yes, the charger is a "dumb" CV/CC (constant voltage / constant current) power source, the battery management system (BMS) -board in the packs is (or at least should) taking care of balancing the cells. You need to have a proper BMS for the pack, that's the best safety for the pack. Not 100% sure what you're saying here, as from 10 pieces each, you could only build one 20S pack, so all the cells would be in series. Putting different types of cells in series is not a good idea, as the lower capacity / higher resistance cells would drop their voltages faster and even get damaged / reverse their voltage. Proper BMS should prevent overcharging and over discharging, but likely the latter would cause a cutout (the BMS cuts the power output from the battery). You'd still need 20 of each (to create 20 pairs) to get a 20S2P pack. I've never tried it, but people have put packs made from different cells in parallel, and said that it works just fine (basically if one or the other pack is at higher voltage level, it starts charging the other pack). Having cells of different capacity / internal resistance in parallel might cause some weird effects, at least the bulk of the current will run through the lower resistance cell, but as the parallel cells connected through very low resistance, they should "even out" the voltage... Possibly, if you're using used cells, the cycle life is already lower. Another thing to note is that not only does the capacity of the cell degrade over time, but the internal resistance also might go up. While the cells may work just fine under normal usage, they may drop a lot of voltage at high current draw, and it usually just takes one bad cell to ruin the entire pack, like the BMS cuts the power if one cell drops too low, or even if it doesn't, that one cell reverses or overheats and destroys the entire pack... On the other hand, it might just work fine? Safest way I can think of would be measuring each cell with an electronic load to see if they "behave" under higher load correctly, and discard any "bad" cells. Possibly, but maybe not. If you have separate packs (ie. batteries, 2 x 20S1P) with their own BMSs, even if the other pack conks out, you still have one pack that you can limp home with (but if you're drawing a high current out from the packs and one cuts out, all the load drops on the second one, which might also buckle under the pressure...). The moment the other pack starts sagging, the second pack will start to charge it (simultaneously with powering the wheel), which may or may not be too much for the pack. But this is all just theoretical hand waving without any real measurements to show Somewhat faster, but as said above, when the packs are in parallel, the lower resistance one will also output current to keep the parallel pack in the same voltage (at least at the output-level, what the individual cell voltages are at that point is "invisible" to the other pack). Basically, you wouldn't probably get as much capacity out of the parallel packs as their combined watthours (/amphours) should be. Depends on your wheel, high powered wheels can draw very high current during takeoff and acceleration, but they (usually) don't last very long. If the voltage drops too much (or one or more cells are in bad shape and drop their voltage enough), the BMS might cut out, or if it doesn't have undervoltage protection on the discharge side, then you probably end up with a dead cell sooner or later. No problem, but I underline that I'm not a professional, so I don't really know... Plus I might be a bit drunk now... As a hobby, building battery packs for your own use might be fun (and somewhat dangerous), but if you're planning on saving money, likely you won't in the long run. If you want proper packs, contact someone like 1RadWerkstatt and get them to make you proper pack(s) from brand new, high quality cells and BMSs.
  6. This is the fifth case in total and third with firmware 1.07 by my calculations. Correct?
  7. esaj

    KS18L OoO - Please KingSong Read This Topic

    Right, I was referring to this report: The user Asu6nik walked his KS18L by the trolley inside a shopping mall. After some 20 metres, the wheel stopped, locked in one position and resisted turning, it did not respond to button presses. After one hour, he was able to take it apart and disconnect the batteries. By that time, the whole case became very hot, the batteries inside were very hot and were making a quiet hissing sound that could be heard by pressing one's ear against the battery case, the sound resembled a boiling teapot. After letting everything cool off and reconnecting the batteries, Asu6nik had the wheel ridable again. The charge level dropped from 85% to 40% in the process. While the batteries survived, likely they did lose at least some capacity permanently after such an ordeal..?
  8. esaj

    KS18L OoO - Please KingSong Read This Topic

    Haven't checked the datasheets (I assume they're still using STM32F103?), but it could be that the PWM output is still pulsing at whatever duty cycle it was left at when the firmware crashed (ie. while the mainloop is in infinite loop / stuck, the timer interrupts are still firing). The internal resistance of batteries, cabling, connectors, fuses, mosfets and the motor phases themselves are likely very low, so you're probably right that it should have blown the fuses if the mosfets were left fully open, but other than the mosfets pulsing, I can't think what could limit the current further without frying itself in the process. Still, there's gotta be quite a lot of current flowing to heat up even the batteries themselves (someone described them as burning hot to touch? Or was it just the mosfets?)... KS16S uses 2 x 40A fuses (one per each 16S2P), don't know about the KS18L.
  9. 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.
  10. 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
  11. Maybe... at least you'll think twice before fooling around with the batteries
  12. 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...
  13. 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
  14. 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.
  15. 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.
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