Please help me understand this in the motor sim tool

[qwerkus]

I'm trying to understand the various implications of using a 48V vs 36V Battery on the same motor. The motor simulator from ebikes.ca is very handy. Here is a screenshot of the same motor laced in a 20" wheel running on 36V vs 48V. I understand most of the infos on the graphs - like the obvious higher max speed of the 48V system but I don't get the efficiency difference at low speed: why is the 48V system @28% throttle up to 15% more efficient than the 36V system @full throttle between 5 and 10km/h ? While this doesn't really matter on long commutes, it can make quite a difference if there are many stops and gos.

 

[scianiac]

It's just how you have the graph setup, any motor will be more efficient when driving less power like this. The auto throttle is mostly useful to compare things at a steady state speed and anywhere outside the set speed it's an unfair comparison because on that graph the 100% throttle motor is less efficient at a lower speed but only because it's putting out way more power. While at the set speed point they are putting out the same power and you can see they are the same efficiency, because it's the same motor and battery voltage doesn't have much effect on efficient when compared fairly.

Just adjust the speed to a lower speed with the auto throttle on and then compare how efficient they would actually be at steady state at that lower speed. Or you could set them both to full throttle and compare how efficient they are when accelerating from a stop where.

Now in reality the higher voltage battery may be very slightly or a bit less efficient. Mostly due to the higher speed and faster acceleration. Which is to say if you can go faster and accelerate faster you are more likely to do so and that will have a large impact on efficiency.

 

[qwerkus]

Thank you for your reply. I set both motors to 25% throttle to achieve the legal 25km/h here, and now the curves looks much better. Interestingly enough, there is virtually no difference at all between 36V and 48V if you implement a speed limit in that setup. Maybe a few mAh lost due to the increased resistance of higher amps on the 36V motor, but nothing noticeable.

I also ran the sim with the slower winding, and found very little difference, apart from the fact that @36V it would not fully reach the 25km/h when laced in 20".

My conclusion is that if in doubt, go for a faster winding and apply a higher voltage. It makes little to no difference a low speed, but offers you the possibility to go faster should you want/need to.

 

[neptronix]

Consider throwing a grin all axle or shengyi sx2 ( fast winding ) into that simulation.. both will have improved efficiency over the RH212 on flat ground.

Motor speed ( in RPM ) can greatly influence efficiency.. DD motors typically do better, the faster you spin them. The shengyi likes being spun at very high speed more than most geared motors i've seen.

 

[wturber]

My limited experience with my two ebikes is that for most general use purposes the practical differences between different system efficiencies are dwarfed by differences in how the bikes are used. If you are doing long distance touring or are in some situation where every watt/hour really does matter, then these small differences might be practically relevant. But as a practical issue, these differences are generally hard to notice. I think battery sizing and how that affects battery drain down at higher amp outputs is probably more noticeable.

 

[neptronix]

Why not both..
- by oversizing your battery for the load, you can take a 10% efficiency loss down to <1%
- by optimizing the motor choice, you can get another 5%-10% efficiency versus not
- by optimizing your aerodynamics on an upright, you can actually get a 10% efficiency gain versus being mostly upright

Talkin' bout a 20% increase in range overall versus a totally unoptimized and typical situation.. the longer the distance you travel, the more this matters.

 

[qwerkus]

Why not both..
- by oversizing your battery for the load, you can take a 10% efficiency loss down to <1%

Check.

- by optimizing the motor choice, you can get another 5%-10% efficiency versus not

Unfortunately not possible.

- by optimizing your aerodynamics on an upright, you can actually get a 10% efficiency gain versus being mostly upright

Check - going cwlb.

Talkin' bout a 20% increase in range overall versus a totally unoptimized and typical situation.. the longer the distance you travel, the more this matters.

Only problem left ist the motor; I can't change it. 34 Poles DD hub weighting around 4.5Kg. Not sure which motor in Grin simulator comes closest.

On a sidenote, I have a front sx2 laying around here laced into a 16in wheel and would not recommend it. You are correct when pointing out the very high speed of the bldc inside, yet at high speed mine produces an annoying whining noise which makes it a deal breaker. Very quiet at low to normal speed though.

 

[neptronix]

Why can't the motor be changed?

Yeah no geared motor will do well in a 16".. 20" is pushing it already.

 

[qwerkus]

Why can't the motor be changed?

Yeah no geared motor will do well in a 16".. 20" is pushing it already.

Only model with integrated igh still in production.

 

[E-HP]

If it's the same motor, and only the battery voltage differs, then the higher voltage motor run at partial throttle will have the same performance as the lower voltage motor run at the same speed (whether full or partial throttle), since what is flowing through the phase wires is the same. There is no efficiency difference when running at the same speed.
The simulator has an oddity at full throttle. If you back down the 36V throttle even a little bit, the efficiency curves converge right away.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[neptronix]

Pretty much all controllers run a different duty cycle at <100% throttle which is less efficient, so this can skew the results of one system versus another.. if the simulator models that, it's a feature, not a bug!

 

[E-HP]

Pretty much all controllers run a different duty cycle at <100% throttle which is less efficient, so this can skew the results of one system versus another.. if the simulator models that, it's a feature, not a bug!

Maybe not a bug, but odd. Even with the same motor and battery, the efficiency curve close to full throttle changes dramatically. It shifts at the speed/rpm where the torque curve takes a dive. The shift appears to occur at the inflection point of the torque curve, though occurring near full throttle.

If you slide system from b left to right, you can see as soon as system b hits the dropoff of the torque curve, the efficiency curve toggles to match the full throttle system. In playing with the simulator, the inflection point of the torque curve triggers a few things, but is felt most with the sudden dropoff of acceleration, which is why I want that point to be beyond/faster than I normally ride, so I have hard acceleration through the full rpm range that I do ride at. I like higher voltage for more acceleration than for speed.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca