UL 2272

[lizardmech]

Has anyone else heard that this standard includes strict limitations on the number of cells allowed in series? If imposed on EUCs it could potentially impact riding safety as dramatically lowering voltages means current must be increased and motor torque must be reduced as thicker wire with less turns will be needed. There's various ways this can reduce safety, increased current means more heat from all the wiring, reduced torque and battery sizes increase the probability of faceplants. If it's true I don't think UL considered other types of self balancing vehicles exist beyond the small hover boards. 

It might be necessary to try and bring this up with UL somehow or else we may see many less safe EUCs produced in the future. To resolve the issue they could either clearly specify the standard is only for the small hoverboards with 8 inch wheels not self balancing vehicles in general. Or revise it so the battery pack requirements do not compromise rider safety.

[dmethvin]

9 hours ago, lizardmech said:

Has anyone else heard that this standard includes strict limitations on the number of cells allowed in series?

It probably does include limits, at least indirectly, because if the voltages got much higher than they are now then exposed parts could cause electrical shock to people and there is a whole new set of rules about that. Since the Ninebot Mini Pro has the typical 15s Ninebot configuration and already passed UL2272 we know that must be allowed. So I wouldn't get too wound up about it yet.

[lizardmech]

It's a problem if there's limits on P count as well. 15S2P is not enough in many situations. I'm skeptical of the standard in general when it was put together in such a short amount of time and they said they didn't take into account safety when in use. The majority of EUC injuries appear to be from issues related to dealing with large currents and thermal issues so designing a safety standard that ignores safety when in use and potentially puts users at greater risk is a little irresponsible. If you cut voltage and battery sizes the same energy to keep it upright still has to come from somewhere in the form of additional current which will mean more stress on conductive components and battery cells.

[esaj]

3 hours ago, lizardmech said:

It's a problem if there's limits on P count as well. 15S2P is not enough in many situations. I'm skeptical of the standard in general when it was put together in such a short amount of time and they said they didn't take into account safety when in use. The majority of EUC injuries appear to be from issues related to dealing with large currents and thermal issues so designing a safety standard that ignores safety when in use and potentially puts users at greater risk is a little irresponsible. If you cut voltage and battery sizes the same energy to keep it upright still has to come from somewhere in the form of additional current which will mean more stress on conductive components and battery cells.

On a related but more-than-a-bit offtopic-note, while in general I'm happy about the laws passed in Finland about personal light electric vehicles, what puts me off is the (seemingly arbitrary) wattage limit. The law says that the vehicles cannot have motors beyond 1000 watts. I guess they thought that this would limit the maximum speed they can achieve, the law separately states that 25km/h is the maximum allowed on bike lanes, although I don't remember if it actually limits the maximum speed the vehicle could achieve (in theory). But anyway, what they don't seem to realize is that limiting the maximum power of a self-balancing vehicle is a bad move, because you can still make a 500W motor that goes 50km/h, but simply doesn't have nowhere enough torque to keep balance...   Whereas you can make a 5kW motor that has very low top speed but lots of torque, thus being actually safer than a fast low wattage motor (in self-balancing vehicles). Rant over.

[Mono]

The most obvious reason why law makers want to limit power is that unlimited power can be easily abused. Whether 1kW is a reasonable limit is indeed debatable even if it seems already to acknowledge that self-balancing devices need more power than e.g. bicycles. According to my experience with a 500W motor and 80kg payload, 1000W should be fine, but I can see that it might not be with larger payloads. In any case, let's be honest that the danger comes first and foremost from speed generated from torque, lack of torque is only the secondary source.

[lizardmech]

I don't think power limits are a good idea, there's too many variables such as rider weight. Another issue is I'm not even sure the direct drive EUC motors actually reach their power peak when in use, peak power occurs at high RPM where torque is lower, direct drive EUC must operate around the low end of the motor power output because they rely purely on torque to stay upright. If you imposed a 1KW power limit there's nothing stopping someone making an EUC with a CVT or gearing system meaning it could access the entire 1KW at any speed while a 2KW direct drive model may never even manage to deliver 1KW to the wheel. Even a single geared model with 10:1 gearing would ruin any attempts to pick a power limt, low torque high rpm motors have larger range of RPM that is near peak output.

[Scatcat]

Standards bodies seem to prone to set standards without really digging into all aspects of the subject matter.

What would really be safer: a 20S4P-system with sufficient arching/electric shock protection, or a 10S8P system with twice the current? And if the second system was a safer option, then why does Tesla run their cars at ~400V?

The simple truth is that a high voltage system is the better option from a pure engineering perspective - given that the components used can handle the voltages, and that circuit tolerances and isolation are enough to prevent shorts and arching. Less current higher voltage generally means less heat generated and less power loss to Joule heating. Of course, and that is the reason for the limitations, higher voltage overcomes resistance much easier. Handling a high voltage charger or a higher voltage battery pack requires a lot more care. At a certain point you can fry not just the equipment, but yourself too if you make any stupid mistakes.

But to set a maximum voltage without looking at the safe use of the equipment under the actual conditions where it would be used is just bonkers. We handle 240V daily, and the wall plugs we use are designed to let us do that reasonably safely as long as we don't go dumb-dumber. Sure we have fuses and breakers to save our hides when we do go down the "intellectually challenged" road. But designing chargers and internal circuitry to enable safe handling is not rocket-science. A standard that required a certain level of safety measures at higher voltages would be much more relevant, and enable the designers of our equipment to use whatever voltage required.

That said, I can see why it is tempting to limit voltage. At a lower voltage the risk of some stoopid f--k electrocuting him-/herself is distinctly less. In my youth, having tried being one of those stoopid f--s myself, I can attest that high voltage is no picnic (Trying to fix an amplifier, my amateur self learned the hard way that high voltage capacitors keep their charge for longer than you might think, didn't need a blow-dryer for weeks )