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The 170Wh battery of the cheaper model won't carry you for 20km, maybe 15km if you're light weight, and you can't ride as fast towards the end. As a rule of thumb, you can divide the watthours by 15 or 20 to get the actual range in kilometers, it varies depending on your weight, riding style, uphills etc though. And in case you were wondering, buying the cheap model and then upgrading the battery packs to the bigger option later on will likely be more expensive in total than buying the big battery-version directly. The batteries are usually the most expensive part of the entire wheel, except for the very small batteries, like that 170Wh, where the most expensive part is likely the motor. I wouldn't look at anything that's less than 680Wh (for 16S/67.2V) or around 800WH or so (for 20S/84V), especially for the more powerful motors, the small batteries (less packs in parallel) cannot even give out as much power as the motor could use and you'll hit range anxiety sooner or later.

You measure the charger unloaded (or specifically very lightly loaded just by the 10 megaohm or similar input impedance of the meter) to see that the maximum voltage is correct. Under load, it starts to drop the output voltage so that only a specific maximum amount of current (constant current mode) flows to the packs. Once the voltage has risen high enough to reach the maximum, the constant voltage mode starts, where the current will drop as the battery voltage gets closer to the charger voltage, dropping to 0 when the battery has reached the same voltage as the charger (which happens much, much later than when the LED changes from red to green in most chargers). The BMS-comment refers to what the charger voltage should ideally be. The balancing circuitry in the wheels is based just on slowly "bleeding" charge off the cell through a resistor once a certain voltage threshold has been reached (which could be up to 4.2V), so for the balancing to occur, the battery pack must be charged until it reaches high enough voltage for all the cells to "catch up" and charge to the same maximum voltage. For example, if your 20S-battery pack was charged to a voltage of 83V, you still don't know whether all the cells have charged equally (83V / 20 cells = 4.15V per cell), or if 19 cells were at the full 4.2V and the one was at 3.2V, or a mixture of these. The previous is a bit bad example, if there really was one cell that 1V behind all the others, likely that one cell would already have been so degraded that it should be replaced, but even much smaller differences cause some of the cells discharge faster than the others, causing extra stress on them and they will die sooner. But ideally the charger voltage should be high enough to fully charge and balance all the cells if left charging for long enough, which basically should be the amount of cells * 4.2V. Should, but, most wheels have some form of reverse polarity protection in their BMSs (apparently at least Gotways don't, some other older wheels like Firewheels don't). The idea is to protect the battery from a charger with reversed polarity (wrong type of charger) or external short circuit through actual diodes or mosfets. If there are BMSs that use diodes for this protection, they will have a "side effect" that the diodes cause a drop of their forward voltage (around 0.3-0.7V depending on type of diode even at low current) before the cells. Thus if you have a diode dropping 0.7V before the actual cells, and your charger outputs 84V, the batteries won't charge but to around 83.3V. I originally thought that the Firewheel charger was set to 67.8V (for 67.2V wheel) because there are protection diodes dropping around 0.6V in the BMS, but in reality it was just a badly adjusted / drifted charger. For your Gotway you can simply check that the charger's at 84V, since there are no protections. But, in case there were protections and you wouldn't actually know whether there are diodes or mosfets there, it'd probably be better still just to adjust the charger to the typical 4.2V per cell voltage, or at least not much above it. The only reason for higher voltage, while still avoiding overcharging which can cause a fire or explosion at worst, would be to ensure that the cells reach their full voltage when leaving it on charger for balancing to occur. But there you'd be better knowing the protection circuitry, or even better, being able to measure the individual cell voltages, it would be so much easier if the wheels had BMSs that report the individual cell-voltages (or even better, active balancing, but likely that won't be seen).

I'd at least like to think that the engineers designing the wheels do know what they're doing, but likely it's more a matter of far less stringent safety and quality requirements/culture in general and trying to save on manufacturing costs to keep the wheel prices low(er). Hopefully when pushing the envelope towards something not seen so far they do take their time and test things more carefully. Or just use @Marty Backe as a crash test dummy before real people

Yeah, it's a small miracle that nobody has (to my knowledge) died so far on a high speed crash... for the motors, it's really hard to say how much can they actually handle. In the e-bike world, people have "overvolted" the stock motors in the past for higher speeds, some could take it, others not. There's quite a lot of metal and mass on the motors, and the metal side covers should conduct heat pretty well, plus there's more or less constant airflow around the covers while riding, so it might be that it works just like it is with higher voltage and still using maximum currents... or not. The motor arcing voltages are likely pretty high, but how high, no idea. Several hundred volts? Less? More? There's more to it than the motor alone. Higher voltage mosfets tend to have higher internal resistance, which likely means more losses (and heat) in the mainboard to get rid of, which may require better cooling. Higher voltage "kick-backs" from the motor. Bigger capacitors for the higher voltages. Beefier step-downs to handle dropping the voltage for the mainboard electronics (12V or so for gate drivers, 5V for USB and such, down to 3.3V for the MCU, IMU and some other parts). Larger BMSs for more cells in series. Maintenance becomes more dangerous the higher the voltages go.

Another thing that came to mind is (if they're using the same motor), how much power can the motor handle continuously? With higher voltage, you use less current to produce the same power vs. a lower voltage. If the motor can handle the same duty cycles with higher voltage as it did with lower voltage, that means more total output power. If not, and they have to limit the power (average current, lower duty cycle) to keep the motor heating in check, it means that they're trading higher top speed for less torque (less current) for the same output power.

Slightly off-topic, but wasn't it revealed some time ago that GW's never had any "80%" alarm, just the typical speed- & battery-percentage based alarm that starts to go down once the battery is depleted enough? Can't find the topic right now, but there was a picture with different models, voltages and speed-limits... Edit: Here it is: Official values directly from Gotway: Don't know where the "80%" -thing originated.

AFAIK, for the exact same motor, and leaving out details like power losses at different currents due to internal losses (they increase in square, that is current to the second power times resistance), yes, I guess you could say that x% higher voltage gives x% higher speed, but in practice, the increase in speed won't likely be linear, but still faster at higher voltage. Of course at some point, the voltage will be high enough to cause a short circuit in the coils, as the wires adjacent to each other will "strike through" the lacquering or whatever it is the coil wiring is covered with and the entire thing shorts and likely melts... well, maybe not melt, the motor will just come to a sudden halt and you break your forehead on the pavement.

It's a good question, and I have no definite answer... basically both could be thought of as capacity, but the other gives the charge capacity and the other the power capacity, or something along those lines? People are more accustomed to seeing amp hours, because things like tablets and cell-phones use single-cell batteries, so the voltage is always the same, so you can just as well measure amp hours. Same for cars (at least as long as they use nominal 12V lead-acid batteries, for electric cars you of course look at kilowatthours). But when you've got devices using different battery configurations between models (different voltages), the amphours are misleading, because a lower voltage wheel will have a higher nominal amp-hour capacity, and using watt-hours gives you the "reality".

Yeah, saw that. I was actually talking in Discord today about electronics in general with dongie (don't know if that's his forum handle or who he actually is really ), and delved a bit into the dead ACM board Rehab sent me a couple of years back. It just now dawned on me that the weird 140+V @ 75V input (apparently) voltage-doubling node on the step-down is probably a voltage doubler so they can use a cheaper AC/DC -converter there (minimum input 85V) to make it work with the 16/20S packs while saving a bunch vs. using a proper DC/DC -converter... well, if it works...

Right, didn't consider it from that point of view, good point. Still, while progress is a nice thing, considering the f**k ups of pretty much every manufacturer in the long run, I have my doubts how good idea pushing the voltage up all the time is. I just hope nobody ends up electrocuting themselves.

If you take X cells with Y amphours, you always get the same amount of watthours regardless of the configuration, for example 100 x 3Ah cells: All in parallel: 3.6V nominal, 300Ah => 1080Wh All in series: 360V nominal, 3Ah => 1080Wh And any combination in between (2S50P, 50S2P, 4S25P, 25S4P...)

Hope they get the design right, as this requires even better components, higher clearances/creepages on the board etc. The voltages are even more lethal than before and if they keep this up, some regulatory body is going to start looking into the wheels. Don't know the "rules" that closely, but anything over 60V DC is already regarded highly dangerous and there are limitations to selling such devices to normal consumers. Then again, electric cars use several hundred volts (400V DC or something in Teslas?). AFAIK, they don't even use mosfets anymore, but IGBTs, maybe that's the next step for wheels.

There are some links in the first page of the thread about self-powering modules that also do current & energy measurement that cost about the same. Price-wise, any really low volume project just cannot compete with those, plus the Chinese seem to push the components much closer to their limits (the linked module in the above seems to use a linear regulator + a big heatsink, that voltage meter requires only about 1/10-1/20th of the power the BT-module + an actual display would need). I'm constantly on the fence about this, because I personally don't even necessarily need a Charge Doctor-like device (seeing that I already have a working CDv2), but the meter in general might be useful elsewhere... Then again, in my other stuff I likely won't need support for anything like 100V.

Yes, directly on the charger pins, make sure you have the multimeter wired correctly (for voltage measurement, if there are separate jacks for current measurement ) and use a high enough DC voltage range (Usually they're something like 2, 20, 200V for the basic meters, so use the 200V DC area). Unloaded charger should output the maximum voltage, 4.2V per cell, ie. 67.2V for 16S, 84V for 20S, 100.8V for 24S (assuming there are no actual diodes for reverse protection in the BMS). If it's slightly higher (like 0.01V per cell), it shouldn't usually be very dangerous, on a pack with healthy cells, the voltage is divided pretty much equally across all the cells in series, so for example 84.2V / 20S = 4.21V / cell, but going much above starts to stress the cells and in the worst case can damage them, so the safest bet is to stay around 4.2V per cell (some chemistries can handle overvoltage better than others). On some another topic, I think it was mentioned that KS uses 4.24V as the cell overvoltage protection threshold. The passive bleed-balancing should take care of slight overvoltage above 4.2V, albeit slowly. I found out that the Firewheel charger I was using with it was putting out 67.8V (for 67.2V packs) after I had already been using if for quite some time, that's 4.2375V per cell, and I know the pack didn't have any kind of reverse protection (so no diodes dropping the voltage) because I could power things directly from the charge port Apparently it didn't have any overvoltage protections either, because I'd often take the wheel "hot off the charger" and my rides start with a short straight bit and then a couple of hundred meters of downhill without issues, where the regenerative braking was likely pushing the voltage up even more... If the charger voltage's below the maximum battery voltages, the cells will never be fully charged (or some will and others wont, if they're out of balance enough), and depending how high the balancing voltage per cell is in the BMS, the cells might never get balanced and you won't get the full range out of the pack.

For a light-weight rider, the high power can actually be a bit of a problem, not having the body weight to throw around, getting the wheel to respond (especially if its on hard-mode) in an uphill for example can become problematic, as the high power can easily overcome trying to push the fronts of the pedals down and the wheel tends to stay level, not getting enough "feedback" to push up the speed. Then you either need to stand tip-toed on the pedals or try to grab it with your legs and force it to lean forwards. Some people have 3d-printed parts glued to the side they can grab with their legs to get the wheel to tilt forwards and force it to accelerate. I changed my wheel from hard to middle because of this, made accelerating uphills a lot easier and I noticed I like the slight "give" during strong braking.