Portable energy sources.

[Frank]

I don't know about being the best choice, but I found mini jet turbines to at least be an interesting idea.

Ah, sorry I missed this!

Yes, micro-turbines have come a long way and are certainly very interesting! I happened to live close to the people who made that a very real possibility: AMTJets.

Before those, micro turbines couldn't even push their own weight, literally. Mildly interesting for model planes, but not much else. Those guys put a microcontroller inside, came up with some very interesting materials and production techniques and a very clever computer program to run all that (with lots of fall-backs to prevent overheating at all costs and save on lots of weight and mechanisms), and made something that could push (at the start) about 1.5 times it's own weight. Interesting!

I've seen one in action on a bench, and it's definitely something. But we still have some time to go before they become a valid alternative: strangely enough, we have to scale them up a bit before they get there.

But I have been to some model plane shows, and they are superbly entertaining! There was a large plane shaped like a black triangle with two of the most powerful turbines, that did some fly-by's, just a few meters from the public. Scream!!!

The operator lost control during a high and fast turn, and it made lots of expensive debris, really fast. Happily that happened about a hundred meters from the public!

There was a pretty plain plane, shaped like an A10, with a single turbine strapped to it's back, that did a very slow fly-by, and went all-out when it was cruising right in front of me, about three meters distant. WOW!!!

I have dreamed about things like attaching 8 of those to a chair and go for an extremely interesting flight.

So yes, I think the technology to make all those nice things we talked about in this thread is available, we'll just have to wait for the investors and companies willing to invest in some serious factories to make them all happen. Electric cars, VTOL "cars", walking "cars", exo-skeletons, robo-helpers for in the home, very high capacity batteries and all the other sci-fi things all us geeks would love.





Edit: the maximum thrust those micro turbines can deliver is at the moment about 6 (!!) times their own weigth, for the latest models. An Olympus masses about 3.8 kg flight ready, and can push 23.5 kg at max thrust. Put 4 on a chair, and you really have a pocket rocket, that can even lift you straight into the air, as long as you're not too heavy!

 

[Basic]

The in-wheel motors are interesting for many reasons. (Reduce the space and energy loss in a regular transmission, and you can maybe make the wheel suspension simpler.) But the weight looks like a problem to me. You say that they a modern brushless motor is much lighter than older motors. But won't you still get a lot more unsprung weight than with a regular system?

 

[Frank]

The in-wheel motors are interesting for many reasons. (Reduce the space and energy loss in a regular transmission, and you can maybe make the wheel suspension simpler.) But the weight looks like a problem to me. You say that they a modern brushless motor is much lighter than older motors. But won't you still get a lot more unsprung weight than with a regular system?

Yes, you are right. That's the main problem with them. But then again, you don't need axles anymore, and you can use smaller and lighter brakes. So, they make the wheels a bit heavier when you use light metals, than when you would fit the all steel wheels still in use. And you can save some more by flipping the dampers and such.

All in all, you gain a little unsprung weight for an increase in efficiency more than 100% compared to current combustion models (as a percentage of the energy used that is delivered onto the wheel), and a torque at any RPM that far surpasses any combustion engine that can deliver more than three times that sustained power. But you should substract the production, delivery and storage efficiency for the electricity used from that.

 

[Sxotty]

Yes, you are right. That's the main problem with them. But then again, you don't need axles anymore, and you can use smaller and lighter brakes. So, they make the wheels a bit heavier when you use light metals, than when you would fit the all steel wheels still in use. And you can save some more by flipping the dampers and such.

All in all, you gain a little unsprung weight for an increase in efficiency more than 100% compared to current combustion models (as a percentage of the energy used that is delivered onto the wheel), and a torque at any RPM that far surpasses any combustion engine that can deliver more than three times that sustained power. But you should substract the production, delivery and storage efficiency for the electricity used from that.

I don't think that would necessarily be true, rotating weight is more of a problem then non-rotating weight. Of course that might mean that it is actually easier to stop if you use them to create energy a la hybrid, and the motor is slowing them down too, I guess it all depends how they do it.

 

[Blazkowicz]

in a post-oil world I think we'll have hydrogen internal combustion engines for the high end, maybe less efficient but more fun.

 

[nelg]

The in-wheel motors are interesting for many reasons. (Reduce the space and energy loss in a regular transmission, and you can maybe make the wheel suspension simpler.) But the weight looks like a problem to me. You say that they a modern brushless motor is much lighter than older motors. But won't you still get a lot more unsprung weight than with a regular system?

I also wonder if the lack isolation from vibrations and jolting would do to reliability. And what happens if you drive through a deep puddle?

 

[ShootMyMonkey]

Please tell me you didn't just take the distance, divide it by speed and multiply by the motor's maximum power rating... please

Fine, whatever. I never intended it to be an accurate figure or anything -- the point was simply that it's a lot of energy even though the real figure is significantly higher than that (also the fact that 500 kWh fits pretty squarely with the average monthly consumption of a single-person apartment, so I deliberately chose convenient numbers)

in a post-oil world I think we'll have hydrogen internal combustion engines for the high end, maybe less efficient but more fun.

I seriously doubt that. The effectiveness of hydrogen combustion is really not useful by itself, though semi-useful in a mixture with other fuels. Either way, a hydrogen economy is going to end up being a fuel-cell thing.

I also wonder if the lack isolation from vibrations and jolting would do to reliability. And what happens if you drive through a deep puddle?

...or just about any road in the state of Texas?

But you should substract the production, delivery and storage efficiency for the electricity used from that.

Figuring that, you probably lose about half, I'd think. i.e. for 500kWh output energy put to pavement, it's worth about 1 MWh spent to get it there from the production phase.

 

[WhiningKhan]

Fine, whatever. I never intended it to be an accurate figure or anything -- the point was simply that it's a lot of energy even though the real figure is significantly higher than that (also the fact that 500 kWh fits pretty squarely with the average monthly consumption of a single-person apartment, so I deliberately chose convenient numbers)

Why would you assume that the maximum power output is used continuously? It isn't, obviously.

Speaking of energy consumption, last week my home was consuming electricity at a rate of about 10kW when I happened to take look at it (okay, it was -25 celsius so I was curious to see how much was being spent). So in these conditions, that 500kWh is used up in two days...

 

[ShootMyMonkey]

Why would you assume that the maximum power output is used continuously? It isn't, obviously.

If you equate average speed achieved for a given distance covered with simply constant speed covering that same distance (i.e. same work achieved). Assuming that you don't have fluid links or clutches anything that will keep the wheels spinning when the motor isn't working, and instead have fixed direct links to each motor, that means that maintaining x speed means the motor has to maintain the corresponding rpm (there's no option of only applying or intermittently applying enough power to keep the car moving). As mentioned before, you can be at very near peak power/torque output on an electric motor at very low rpm. Maximum output is simply a worst-case. If anything, I wasn't accounting for the fact that no motor is 100% efficient.

Besides which, nothing good can come out of assuming that any form of efficiency is possible. Especially if the whole point of the calculation is to have an upper bound.

Speaking of energy consumption, last week my home was consuming electricity at a rate of about 10kW when I happened to take look at it (okay, it was -25 celsius so I was curious to see how much was being spent). So in these conditions, that 500kWh is used up in two days...

Conversely, I can bring up examples where I've gone an entire month drawing only 120 KWh. Neither of which is all that representative of a nationwide average.

 

[Basic]

You got it all wrong ShootMyMonkey.
The rated power is for max accelleration. Otherwise you use significantly less. Just because a motor is capable of delivering a certain momentum (power) at a certain rpm, it doesn't mean that it always will draw that power at that rpm. If you don't load the motor, it will use less power. And if you drive at constant speed, you dont load the motor so much.

I've read that for a modern mid sized car, you need something like 15 kW to keep it at a steady 100 km/h (60 mph). At 30 mph you need a lot less. It should be less than half that.

Now if you do a lot of stop and go, you could get the 50kW peaks in the accelerations. But otoh, you'll get back a significant part of it when you brake.

 

[ShootMyMonkey]

The rated power is for max accelleration.

I'm pretty sure I've seen electric motors rated for both continuous and peak. The GM example I mentioned before, for example, is rated at 90-something kW continuous power, with a peak around 130, IIRC.

I've read that for a modern mid sized car, you need something like 15 kW to keep it at a steady 100 km/h (60 mph). At 30 mph you need a lot less. It should be less than half that.

For a modern car running on an ICE, there's going to be some effect due to gearing. 30mph and 60 mph could be the same rpm, though different loads. Load always has less effect on the fuel consumption than the rpm.

Now if you do a lot of stop and go, you could get the 50kW peaks in the accelerations. But otoh, you'll get back a significant part of it when you brake.

That's odd. I always thought regenerative braking was pretty much next to nothing in what kind of return you get. The only reason it works out for hybrids is because the actual battery capacity isn't much at all. At least if you compare to the output you get out of petroleum or a fuel cell, it's a drop in the bucket.

 

[Frank]

I'm pretty sure I've seen electric motors rated for both continuous and peak. The GM example I mentioned before, for example, is rated at 90-something kW continuous power, with a peak around 130, IIRC.

Yes, but that continuous power figure is the amount it can keep on delivering indefinitely without overheating and such, not the amount that is consumed when cruising. A free running electric motor consumes next to no power.

For a modern car running on an ICE, there's going to be some effect due to gearing. 30mph and 60 mph could be the same rpm, though different loads. Load always has less effect on the fuel consumption than the rpm.

Yes and no. Heavy load, like with fast acceleration consumes some orders of magnitude more power than cruising. But there is a lower limit to the amount of gas a combustion engine needs to keep on rotating. So, when cruising and using a combustion engine, lower RPM is much better. But an electric motor can be just as efficient at any RPM, as long as it's designed that way.

That's odd. I always thought regenerative braking was pretty much next to nothing in what kind of return you get. The only reason it works out for hybrids is because the actual battery capacity isn't much at all. At least if you compare to the output you get out of petroleum or a fuel cell, it's a drop in the bucket.

Well, yes, as long as you use the regular generator. Lots of losses that way, and just not very efficient. But with the motor/brake/generator all part of the wheel and all the same mechanism, it can be quite efficient.

 

[Xmas]

I'm pretty sure I've seen electric motors rated for both continuous and peak. The GM example I mentioned before, for example, is rated at 90-something kW continuous power, with a peak around 130, IIRC.

Err, "continuous power" is the max power that can be sustained over a longer period of time, while peak power can damage the motor. It should be easy to see that the power consumption of an electrical motor is equal to the electrical input which can be controlled by a simple variable resistor.

 

[WhiningKhan]

If you equate average speed achieved for a given distance covered with simply constant speed covering that same distance (i.e. same work achieved). Assuming that you don't have fluid links or clutches anything that will keep the wheels spinning when the motor isn't working, and instead have fixed direct links to each motor, that means that maintaining x speed means the motor has to maintain the corresponding rpm (there's no option of only applying or intermittently applying enough power to keep the car moving). As mentioned before, you can be at very near peak power/torque output on an electric motor at very low rpm. Maximum output is simply a worst-case. If anything, I wasn't accounting for the fact that no motor is 100% efficient.

No offense, but you are not making any sense. The fact that whatever type of motor provides the maximum torque at a specific rpm in no way implies that it must be outputting the maximum power whenever it is running at that rpm. Maybe you are thinking too far and forgetting the basic physics?

Regarding Basic's notion of power required to maintain speed - if a certain output power from engine is needed, the same requirement applies to any type of engine, let it be electric or ICE. Gearing or whatever does not introduce more power to the equation, all the power there is comes from the, duh, power source. If ICE can keep vehicle's speed steady with let's say 15kW _output power_, why would electric motor need multiple times more? Where do you think the energy goes?

 

[Frank]

With most DC motors, the voltage controls the speed. When free running, the induction (field induced resistance) is maximal, and the current running through it is nealy zero. When you increase the load, the voltage will drop, and you need to reduce the resistance of the circuit to supply more current, which increases the voltage. At heavy load or near 0 RPM, the impedance of the circuit is near zero. That means that the current becomes as high as it possibly can get, generating lots of heat.

In short: you regulate the speed, and you supply as much current as needed to keep it constant. The current is what consumes power and heats things up.

While you can regulate the voltage, that's pretty hard to do without converting any excess energy into heat, which is terribly inefficient. To do it right, you need to limit the power by switching the circuit on and off very fast and regulate the overall power by changing the duration of the pulses. A switching power regulator uses a coil and a condensator to smoothen those pulses into a regulated voltage. But that's still not efficient enough for a DC motor at low RPM or under heavy load, as the motor will try to consume all the available power and become really hot.

A brushless motor works by having a microcontroller generate just the right pulses at the right time, so it uses the coils of the motor as the energy limiter. It's basically used as a switching power supply without the condensator. So it's as efficient as we can make it, especially under very changing conditions, and especially at near zero RPM. That's why you can get rid of the clutch and gearbox as well.


Edit: It's the difference between the large and heavy power bricks that get pretty hot, and the very small, light and cool switching power "plugs" you see more and more nowadays.

Edit2: for AC motors, you need to generate one or more sine waves with variable frequency. That's really hard to get right. So, while AC motors by themselves are more efficient than DC motors, it's a pain to regulate them. That will be much less efficient than when using a brushless motor. And they are just as bad as regular DC motors at low RPM. And while it's easier to use them as generators, it's harder to make them into good, variable brakes.

 

[Frank]

Btw, another difference between a regular and brushless motor is, that with the brushless one the whole casing of the motor rotates, not just the axle. Which is exactly what you want from a motor that is built into the rim of a wheel.

 

[Frank]

To get back to the original question: does anyone knows of some interesting portable power source or storage that is close to market? I would really like to see all the things that are made possible by that!