series Hybrid discussion

[johnrobholmes]

I have been thinking about a series hybrid for the far future projects. I really like the efficiency and quiet operation of an electric drive, but the range is certainly a limitation with current batteries. Sure I could build something with a huge pack and go 200 miles, but it would be heavy!! It seems that getting a good generator and battery charger set could make the vehicle have infinite range as long as you could find a gas station here and there (I am thinking about a trip from Missouri to Georgia via ebike). Heck, they burn coal and wood to get power to my house, so it really isn't that much different burning gas to charge my packs up.


So my random thoughts are such:

Typical Ebike build, for sake of arguments lets call it a 55mph licensed recumbent beast with full fairing for best efficiency. What would 55mph sustained take wattage wise? What about 30mph
Enough range to get 100 miles on a charge in emergency
A generator and charger powerful enough to keep the bike running at 55mph without battery voltage dropping

So what would the gas mileage turn out to be? I know it would be higher than a typical gasser, as the generator would only run in the most efficient rpm range. From specs taken off the Honda website, if I were to use 20 watt hours per mile on a typical ebike I could get 300 miles from one gallon of gas ran through the EU2000i generator (ignoring charging efficiencies). I think I found my 5 year project.

 

[MitchJi]

Hi John,

So what would the gas mileage turn out to be? I know it would be higher than a typical gasser, as the generator would only run in the most efficient rpm range.

But its less efficient to run a motor to charge batteries, used to run an electric motor than to drive directly via gas.

 

[lawsonuw]

I believe that the HPV hour speed record is near 55mph. My guess is that would put the lowest possible cruising power at 300-400 watts. Back figuring from your 20Wh/mile efficiency goal and 55mph speed goal It looks your target cruse power is 1100 watts at 55mph. At about 3x the minimum possible power consumption, I think that's quite a reasonable power consumption goal. Now if you could fit a 5500Wh battery pack your range could stretch to 275 miles with no generator. 8)

Lawson

 

[johnrobholmes]

Hi John,



But its less efficient to run a motor to charge batteries, used to run an electric motor than to drive directly via gas.

Then why are typical mopeds and scooters getting less than 100mpg? It seems that if efficiencies were closer that we would see more 200mpg scooters.

 

[gogo]

What about utilizing the quick charge capabilities of lithium batteries? If you could charge during your rest stops, could you get away without an ICE?

 

[johnrobholmes]

With enough batteries, sure I could get away with no ICE. Just gotta make sure that I don't catch the wall wiring on fire charging up :lol:

 

[fechter]

I think a couple of people have tried it.
One advantage to the series hybrid approach is you can leave the ICE generator at home on short trips. I was planning to do something like that, but never got it built up enough to test.
Here's a mock-up with a Honda GX-31 engine.

 

[MitchJi]

Hi John,

So what would the gas mileage turn out to be? I know it would be higher than a typical gasser, as the generator would only run in the most efficient rpm range.

But its less efficient to run a motor to charge batteries, used to run an electric motor than to drive directly via gas.

Then why are typical mopeds and scooters getting less than 100mpg? It seems that if efficiencies were closer that we would see more 200mpg scooters.

My intention was not to claim you are incorrect. Only to state the opinion that the issue of relative efficiency is more complex than your original statement. Highway driving at or near the optimum rpm should clearly be more efficient by using the ice to drive the wheels. If you are correct for stop and go driving a series hybrid will be more efficient. So at a minimum there is probably a spectrum of driving conditions. On one end the pure ice would be better than series (not including plug-ins) and on the other end series would be better. The question would be where is the point on the spectrum where a series hybrid becomes more efficient.

The following email exchange I had with Andy Frank leads me to believe that a series configuration might not be the best option (assuming you can get an affordable CVT). Below is a Calcars (http://www.calcars.org) article from about two years ago that was written by Andy Frank:
http://www.calcars.org/calcars-news/693.html

Andy Frank in American Scientist: Plug-in Hybrid Vehicles for a Sustainable Future
Feb 22, 2007

This is a great introduction to plug-in hybrids. It also tells the story of UC Davis Prof. Andy Frank's own evolution in developing the modern PHEV.

I sent him the following excerpt with a question in an email:

The advantage of that approach becomes obvious when one considers how most passenger cars and trucks are used by private citizens. The typical driver travels less than 40 miles a day. Thus having a car with at least a 40-mile range on battery power alone would allow most people to use no gasoline at all on a daily basis if they could recharge their car's batteries at night by plugging them into an electric outlet.

A simpler propulsion system is needed to be competitive with conventional cars. One possible strategy is to use what is called a series configuration, whereby the engine is employed only to generate electricity, which is then used to charge the battery and to power one or more electric motors coupled to the wheels. That arrangement has the advantage of being mechanically simple, perhaps requiring no transmission at all. It also allows the engine to run always at maximum efficiency. But a series hybrid also has some important drawbacks. For one, it needs to include a separate electric generator distinct from the motor (or motors) driving the wheels. More important, it suffers from the inherent inefficiency of having to convert the mechanical power produced by the engine into electrical power and then back to mechanical power.

The best strategy, in my view, is to use a single electric motor coupled with a simple transmission that links both it and the car's internal combustion engine directly to the wheels, which is termed a parallel hybrid configuration. In particular, I believe that the key is using a continuously variable transmission, which does away with the usual fixed gears and instead allows the ratio between rotation of the engine and the rotation of the wheels to take on whatever value will allow most efficient operation.

My question:

GM claimed that the Volt would get 50 mpg when running on the ICE so it doesn't seem to me as though running via a CVT will make a massive difference (please let me know if this is incorrect).

Assuming a PHEV with a 40 to 60 mile EV range most drivers would rarely get any benefit because most of their driving would be in EV mode. So for most drivers is the additional complexity and cost of a CVT configuration as opposed to a series configuration really going to be worthwhile?

His response:

If you read the excerpt carefully they also conclude the parallel system will be more efficient. In addition the article missed the fact that the loss of efficiency in a series system is even worse if the engine is kept at a constant output power, since then you would have even more losses due energy in and out of the battery!!

Yes you can optimize for one driving cycle or driving condition and get an impressive number with a series system but I guarantee you that in real driving the parallel system will do better. This is why both the Honda and the Toyota and I build parallel hybrids only and no serious players in the fuel efficiency game builds series systems.

In the medium and heavy duty area, series system have been used primarily because there is no parallel CVT available. However we now have such technology, Some parallel systems by Daimler and Eaton use discrete transmissions instead of a CVT because they don't have one large enough. They have not yet bought into our technology buit are considering it because the discrete transmission is a nightmare to control and good driveability is very difficult to obtain if you want good efficiency at the same time

As for the cost of a CVT, it is much less than one high power generator and controller using our technology. Thus the parallel system has one low torque motor and controller and a CVT versus two larger higher torque electric machines and two controllers in a series system. So the parallel cost is much lower and the performance better no matter which electric technology you have.

We have designed and built more hybrid vehicles than almost anyone and the reason for my statements are clear if you actually build the vehicles and drive them realistically. Incidentally, I have also shown that the parallel PHEV if properly constructed will be better than the parallel HEV with a small battery pack as well.

Incidentally, I have also designed and built many flywheel drive and hydraulic drive systems and compared them with parallel battery hybrid systems.

Of course he could be incorrect but he has done a lot of testing.
("One test is worth a thousand opinions")

 

[johnrobholmes]

Ahh, I see what you mean. Very informative reads, thank you. With a parallel drive the load can be changed from electric to ICE to keep the system at top efficiency. At higher speeds it becomes more efficient to use the ICE, and with stop and go the electric hails.


I saw T Boone Pickens speak the other day about the future of larger vehicles (and natural gas powered trucks). He did not think that hybrid cars would be useful but in special situations. "A battery cannot power a big rig", he stated. He also thought that another technology would make hybrid tech obsolete in the future, gut instinct.

 

[monster]

if a battery can power an F1 car it can easily power a big rig. you only need 7 seconds of power for regen braking.

 

[spinningmagnets]

Then why are typical mopeds and scooters getting less than 100mpg? It seems that if efficiencies were closer that we would see more 200mpg scooters.

When gas was $4/gal, there was a bunch of scooters bought in my town. I talked to quite a few of the owners. The 50cc scoots got 100-MPG, and the 150cc scoots got ~80-MPG. The small ones were really struggling, and the bigger ones had MUCH better accelleration. The Vetter site has guys regularly getting over 100-MPG from a 250cc. the streamlined body had so much less wind resistance, they were able to use a different final drive sprocket.

Above 25 MPH, aerodynamics plays a major role

http://www.craigvetter.com/pages/470MPG ... 0Main.html

There was a federally funded study in the 90's from a university in Idaho that had a series-hybrid Taurus. During accelleration, the motor used the battery pack and also the generator. When just cruising, the very large generator powered the motor and charged the battery back up. It was a 2-cylinder liquid-cooled motorcycle engine, and I seem to remember that the generator kW capacity was about twice the motor kW. During accelleration, the motor would get warm, during cruise, it would cool off.

I am a big fan of a series-hybrid trailer in those applications where over 90% of the trips are short enough that the EV has adequate range without the trailer. This makes it a plug-in hybrid with an easily removable engine/generator

 

[johnrobholmes]

I was thinking of a trailer setup actually. Something where I would just bolt it on for the longer trips.

 

[spinningmagnets]

I like the idea of a series hybrid trailer too. I only mentioned the Idaho Taurus because the sizing info may be useful.

Whether its on-board or on a trailer, here's a discussion about them, may have a few useful links in there.

http://visforvoltage.org/forum-topic/hy ... -generator

 

[paultrafalgar]

Above 25 MPH, aerodynamics plays a major role

http://www.craigvetter.com/pages/470MPG ... 0Main.html
...
/quote]
That link doesn't work for me.

 

[spinningmagnets]

try this one:
http://www.craigvetter.com/pages/470MPG ... 0Main.html

Its just a link about the Vetter competitions, and what the winners did. Not much of the techniques apply to real world driving, but the aerodynamics info is good for anyone. They show pics of what university-study and competition mileage fairings look like for bikes, scooter, and motorcycles. If the link still doesn't work, Google Craig Vetter 470 MPG.

 

[dogman dan]

Having rode mopeds, small motorcycles, big motorcycles, and now owning a 150 cc scooter, I have to agree, areodynamics are a big factor. The cheezy mopeds often have no fairing, or ones that are pretty much decorative. The scooter I have now looks fast, but only if you aren't riding it :lol: . Once you are in the saddle, your head and body catch huge wind. On my old honda 125, I would get a top speed of 50, but if I laid down on the tank with my feet on the rear pegs, I could cruise on the highway at 65. It was fast enough then, when the speed limit was 55.

I think the generator trailer is the only way to go for series hibrid, even for cars. Why lug it on the short trips. Love the motor on the seatpost rack, that would be er,, stimulating to ride. 8)