Series Hybrid with Hubmotor

[tolly]

I read this early this morning and it got my little head buzzing .I dont know a whole lot abought these electric motors so if I am off the rail please help me out.I like it because it sounds like a great way to thumb my nose at the state of IL.Instead of a a small generator running a elec. bike motor a small weed wacker motor 23cc or smaller bolted or welded onto a car or truck alternator or a old car generator that puts out 12 or 24 volts than it would keep the a constant charge on a bank of small batt..I dont really know what these hub motors power needs are but if a alternator can power the ac in my truck my guess is it could drive a little electric motor.The alternator really dosent take much to drive it it just needs the rpms.

 

[skyl4rk]

I rode the bike today with the generator. I'm still getting to know the thing. I think that the generator helps but I don't think it puts out as much power as I had hoped.

The flexible coupling hub is creeping and moving over time, I will have to take it apart to fix it. The motor is running well, however it is somewhat odd to stop at a stoplight and have a loud weedeater motor running at very fast idle. I may try a hand operated throttle?

I am going to run the bike around a 4.4 mile course near my house, first with electric only, then with generator and electric. Then I can compare average speed and voltage level after the run. Maybe tomorrow, if the coupling holds out.

 

[skyl4rk]

Saturday, Sept 20
64F, dry

start T: 9:30:20AM start time
initial V: 53.4, from overnight charge, likely float charge still on batts, 52V more likely true charge
mode: battery power only, wide open throttle
end T: 9:44:00AM
end V: 47.9V, after 5 minutes had rebounded to 49.1V
4.4 mile course measured on Google Earth
4.4 miles / 0.2276 hours = 19.3 mph average speed.

Notes:
No gas motor use.
Saw operating voltages between 25V and 46V.
Really slow at end, slow up Police Dept hill.
Appears to be roughly 6V drop between no load V and top speed V, example, 51V no throttle to 45V full speed WOT.
The batteries are old and not in top condition.

 

[skyl4rk]

Saturday, Sept 20
73F, dry

start T: 1:40:00PM start time
initial V: 53.1, from 3:40 hours charge, likely float charge still on batts, 52V more likely true charge
mode: generator plus battery, wide open throttle
end T: 1:52:00PM
end V: 49.4V, after 5 minutes had rebounded to 50.1V
4.4 mile course measured on Google Earth
4.4 miles / 0.20 hours = 22.0 mph average speed.

Notes:
Saw operating voltages between 45V and 51V.
Made it up Police Dept hill no problem, lowest voltage seen was 45V.
Generally saw 48 to 50V at full speed, WOT, level ground
The batteries are old and not in top condition.

 

[skyl4rk]

Generator Only

I started up the generator then unplugged the battery pack. The gas motor was running at fast idle speed. It was able to move the bike slowly, under 10mph, better than walking speed but not much more. I saw voltages of 60V to 70V under no load, with the motor slowing way down and voltages of 20V to 30V under load.

I wanted to try the throttle but was unable to reach it while riding. I will try to set up a hand throttle. I believe that with the throttle, the gas motor will be able to provide at least a "get home" speed of 15mph, maybe more. In other words, if the battery is dead, the gas motor can limp home as long as there is gas in the tank.

 

[skyl4rk]

Analysis

Due to lead acid battery chemistry, range is determined by how far you can go before you reach a 50% discharge rate. 50% discharge is a rule of thumb that you can discharge a battery pack to without damaging the cells and can then recharge it again and again for many cycles. For a 48V system the 50% discharge point is 48V.

My old and no longer in prime battery pack charges up to approximately 52V (after the float charge is removed). The range of this system is how many miles I can run before reaching a 48V level on the battery pack (no load).

My experiment under battery power alone showed that I could run approximately 4.4 miles before reaching the 48V level. Starting voltage 52V minus end voltage 48V is 4V. 4.4 miles / 4V = 1.1 miles per volt drop.

Under generator and battery, the voltage dropped 2.6V over 4.4 miles. 4.4 miles / 2.6V = 1.7 miles per volt drop.

The range provided by the generator system is approximately 150% of the battery only range:

1.7 miles per volt drop / 1.1 miles per volt drop = 1.54

So with the gas motor running at fast idle, range is 50% better than battery alone. With motor control of the gas throttle, this may be able to be improved.

 

[skyl4rk]

Under battery plus generator, it runs between 2 and 3 amps, hanging around 2.8a generally at speed and WOT.

Under generator only, full load from hubmotor, between 4 and 5a.

Since the dc motor is rated at 5a, there may not be any more to be gained, even at higher throttle.

...

I made a simple throttle control. When running with no batteries, the generator puts out about 5a at a fast idle and while trying to accelerate. The motor rpm slows down when load is added. It barely moves the bike along at a walk speed or maybe a little faster. When the throttle is turned, the motor does not speed up, it dies out. There appears to be a lot of load on the gas motor, caused by the dc motor.

...

The system I built was put together cheaply to learn about how a hybrid system works. For real life use, make sure that the dc permanent magnet motor/generator has an amp rating that will power your hubmotor at a reasonable speed. Also, make sure that the dc motor provides an adequate voltage level at the gas motor rpm which you wish to run at. Make sure the gas motor has a good muffler!

I have not weighed the system yet, but expect it to be about 20lb, in other words, heavy. I tried to get by on the light side using a small dc motor. My system is a range extender but not a real hybrid system where you can get home on gas power alone. A useful system will be heavier than my lightweight system.

Is a hybrid system worth it? When putting together a motored bicycle, it is already far more efficient than most other machines. Does it really need a hybrid system? Probably not, when a gas only system will give you 100mpg easily and 200mpg or more with some hypermiling techniques. The noise of a gas motor ruins one of the biggest benefits of an electric system. Instead of a hybrid system, how about a spare battery pack?

It is definitely interesting to experience how the motored generator and the hubmotor affect each other under various load conditions. The gas motor is far too loud to ride under normal conditions (this is something that could be solved with a better muffler). It was an interesting experiment but I don't see it as being very practical. However, hybrid systems seem to be the future of automobiles, so it was interesting to see some of the design challenges.

 

[duivendyk]

The weak point appears to be the generator (motor) which is not really suited to the application (high voltage./low current),the internal resistance is too high, Small car alternators might show promise,at high enough rpm and full excitation you can get 70V plus out of them.Could be too heavy though.The question boils down to is money better spent on more sophisticated batteries with better energy /weight ratio than on a complex hybrid arrangement,I'm inclined to be rather sceptical in that regard

 

[skyl4rk]

I went for a ride again tonight. The generator system works fine, as originally expected it is a range extender. 150% range extension is pretty good. However after building it I realize what I really want is a true hybrid that is not limited to range. It has a number of weaknesses that could be upgraded: the weedeater motor is a high rpm, low torque motor, not really the right kind of motor. The generator seems to do the job but has a limited output that I seem to be maxing out. It seems to give its rated power or a little less. Well what did I expect?

I have been trying to work out some things to experiment on. First of all, I have a rectifier on the way and will try to run a motor off of rectified 120VAC, maybe with a big electric motor starter capacitor to shave the peaks a bit. I will start with extension cord power but the goal of this experiment is to see if a 2000W 120VAC generator could be used as the basis for a hybrid. This is based on the availability and low cost of these powerplants. I don't think I would use my hubmotor for this, I would want to upgrade to a motor rated for higher voltage. I need to experiment to check it out but I think it will be about 110VDC (pulsed) after rectification. I may pull the Bosch dc motor off of my generator system and try it out, see how it handles pulse dc. It is rated at 110VDC I believe.

Probably the best type of generator would be a 3 phase generator which is easier to rectify to dc. This would be like a car alternator. I don't know if they are available in the 1500W to 2000W range. I would suspect that is what is used in hybrid powerplants. I wonder if I could rewind or modify a car alternator to get 60VDC. I could make that work with my hubmotor.

There is a new law in MI that apparently grants a $7,500 tax exemption for a plug in electric hybrid. I wonder if they will accept a homemade version of a plug in electric hybrid.

The next build will be set up for hypermiling. The gas motor will go on only when there is a load on the electric system. While waiting at a light, it will be silent. When I press the throttle, the motor will start up and run hard to produce a lot of power. As I reach cruising speed and let up on the throttle, there will be a threshold where the gas motor turns off and electric power does the job. Then when I am coasting, no power will be used. This will allow me to do pulse and glide engine off coasting to save on gas.

I really wonder how Prius and Honda hybrids are designed. I think I am learning a bit about it but it is not so easy as to slap a generator on a gas motor. It takes a lot of engineering and experimentation to get the kind of efficiency they are getting.

 

[skyl4rk]

This looks promising:

http://www.windbluepower.com/ProductDetails.asp?ProductCode=DC-512&Show=TechSpecs