Comment by amluto
5 days ago
This discussion is all about vehicles with large batteries, but how about hybrids? With light enough and efficient enough motors, all kinds of designs might become practical:
- Toyota-style hybrid drives could be a lot lighter, and they don’t need large batteries.
- e-bikes with tiny batteries?
- Hybrid aircraft? What if there was a battery large enough for takeoff and landing, a small motor (or pair for redundancy) for cruising and to recharge the battery, and motors and fans or propellers wherever is best from an aerodynamic perspective.
- Power tools.
The size of this motor is moderately interesting, but the power density doesn't really matter for most of the things you just mentioned. Almost every one of them is limited by the amount of batteries you can put in for both weight and power output reasons.
What do you mean? Modern LFP cells have quite high power density. LTO is even higher.
An e-bike with a 100Wh battery and a 300W motor would be extremely useful if it were light enough: you could carry it up stairs, onto trains, etc easily, and it would give plenty of boost to navigate traffic for short distances and make it easier to go up hills. The idea would be that most of the energy would come from the rider. 100Wh of modern LFP cells doesn't weight very much, but you still need to carry around the motor and the structure to support the motor.
In an airplane, you need a lot of power to take off, and weight is a big deal.
As the other poster mentioned, they're not even on the same planet as the current power density of the combined engine + fuel in an aircraft.
There are two things you are missing in these examples:
1. The motor won't scale down to a 2lbs and a few hundred watts. That's just not how it works.
2. The weight of the battery pack is partially about energy density, but it is also about the ability to discharge, which takes more batteries to make up for it. Let's say you wanted one of the motors in the article giving your device a "boost" of 500hp (sure, we can scale it back, but roll with me), your battery needs to output 400kW instantaneously. If it was a 48v pack, which is 13 cells in series, they would need to deliver 8,333 amps. Most cells are rated for something like 20a, so you need to put more in series to get the voltage high enough to get that to a reasonable number. A 400v car architecture is 112 lithium cells in series for example.
This is before packaging considerations, the increase in complexity of the base system, etc. When you look at the overall system, you're just not gaining that much. Cars are actually uniquely good for hybridization and electrification.
I'm super excited to fly an electric plane, but a lightweight motor isn't what's gonna make that possible. My current plane carries 561 kwh of energy in a 100 pound/ 17gal gas tank.
Even if you say the engine is only 30% efficient, I am still carrying an absolute shitload of energy compared to what I could get out of 100 lbs of lithium batteries.
The actual motor only weighs 84 lbs.
So I have a weight budget of 184 lbs (call it 200 just to be safe), and current capability is a peak output of 50hp (37 kw) and a cruise endurance of 3 hours at 40 hp / 30 kw. So just to math it out, lets say I will need about 90kwh of battery to come close to my current gas capabilities. At an extremely generous 5 kg per kwh, I need a battery that weighs more than my entire airplane's max gross takeoff weight. The weight of the engine is completely irrelevant when the battery weighs 450kg.
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I have a trek ebike and it's fairly light if I take the battery off. Could easily carry it up stairs. I don't think the motor is the problem
My first thought too.
While I see Toyota-style hybrids as designed for efficiency, there's also the performance hybrids like the new Porsche 911 T-hybrid where an electric motor spins up the turbocharger to eliminate lag while another integrated into the gearbox adds power. There is no "EV mode" so it doesn't need a large battery.
Arguably the most important characteristic of a sports car is light weight, so lighter motors would be immediately useful there.
> Toyota-style hybrid drives could be a lot lighter
The hybrid electric motor in a Toyota is already pretty comparable in weight to the motor in TFA, but obviously much less powerful. You can see the main hybrid motor of a RAV4 at [0]. If memory serves both the Camry and RAV4 hybrid models are only 2-300 lbs heavier than their gas counterparts.
0: https://youtu.be/O61WihMRdjM?t=120
Guess Lamborghini uses them:
https://yasa.com/news/yasa-and-lamborghini-high-performance-...
Technically a hybrid but probably not what you had in mind?
There's indeed a huge number of applications where lower weight electric motors could be useful.