Electric bike with generator - Range Extender.

Hi All,

Just thought I'd join the forum and mention the project I've been working on - So here's my first post.

Around Christmas time, I rescued an old petrol bike from a pile of rubbish and rebuilt it, and it's quite a nice bike, but wanted something electric without the range limitations of batteries, so I built my own small-size generator after a few experiments and proof-of-concepts and finally built a prototype and tested it.

The generator was made by coupling a 300w motor to a small 4-stroke engine and using this both to start the motor ( pull start still worked ) and to produce power. All the flanges and shaft components were 3D printed in ABS. 300w isn't much, but the legal limit here in Australia is 200w, so it seemed enough.



After that, I needed an electric bicycle and so set about making one with a 500w 48v kit downrated to 24v.



Testing on the bench seemed to work OK, and so I developed an autothrottle controller to adjust the engine output power to maintain a particular voltage out of the generator, allowing for charging the batteries while in operation. Two SLA batteries provided the power for the motor, and the sink for charging. As voltage from the battery dropped under load, the engine power is increased, with a 1v hysteresis around 24.5 to 25.5 volts ( at least for the test setup ) - This allowed some charging of the battery while providing enough surplus power for the bicycle.



I cleaned up the battery holders, and used a framework of ABS brackets and 1/2" nylon straps to hold everything together. The batteries are in solid and don't move and the transistors of the controller heatsink into the bike frame as well.



A picture of the CAD diagrams for the battery holder components -



That was the MK I. I did ride around on it and finally collected some good operational data on it. The mileage was about 51km/l ( about 130 mpg ) including charging the battery while riding, but eventually the generator failed as it wasn't actually able to deal with the sorts of currents it was supposed to be designed for - Still, I got some good results and the combination of electric and petrol was perfect. No charging needed, can autostart and noise is directly related to power. The volume would go up slowly and then come down instantly that I released the throttle, though being electric, the batteries took up the slack in between. Also, the torque was available from standstill, so I didn't have to worry about pedaling to start - just throttle up and off - Also much better torque up hills.

Anyway, so far I am really happy with the outcome and am working on the MK II version, which should be even lighter, and have the capability to run full battery charge as well as power the bike, while running lights at the same time.

Regards
David.

Hi Agreen, Bluegoatwoods,

Thanks for the comments and questions -

I ran out of images to post in the first post - it was 5 only and I needed 6, but it has to go through a moderator at first - Here's the pic mounted -



The generator is just on the rear rack, and it's pretty easy to remove without any tools - just unclip and disconnect. It's a completely selfcontained unit. The servo I built adjusts the throttle depending on the battery voltage so as I run at full power, it throttles up slowly, then back down quickly when I let the throttle go -

The plastic parts in the drivetrain held up pretty good, but the first generator wasn't able to take the power, and some coils shorted out... So then the motor was pushing hard, and the motor controller picked up on the loss of power, and drove it even harder to compensate, and then it got hot, so the temperature was transmitted through the generator shaft and into the pins in the drivetrain, which got them to the point that the plastic could deform - so the plastic seems OK as long as the temperature is dealt with -




Anyway, the generator was cactus after that, so I needed to replace it - This time I've gone for a brushless motor, with good airflow and am driving that airflow under power from three separate sources - One centrifugal blower, a centrifugal compressor and an axial fan. It has airflow over the coils and over the housing at all points, and the original unit is rated at 80A continuous, so the 10 to 20 amps I am taking up are well within it's range.



The electric side of the bike got an upgrade while I was waiting for the new generator for the MkII design - it's been boosted -



I included a 600w inverter ( Boost converter ) that lifts the voltage to keep providing power to about 36 kph, within our local 200w limit. It's current limited and back-emf takes care of the rest, so I only set it for a single power output. So I can run under economy mode ( 125w ) or boost ( 200w ) and with the petrol engine, don't have to worry about range. Economy is about 51 kpl ( 130 mpg ) with charging the battery and propulsion - so it's pretty good. Also, it's technicaly an electric bike, so I qualify under EN15194 for up to 250w as well - though I still need to get that confirmed in writing.

I haven't been able to find anyone else who has complete the project - To be honest, it works so well, that if I knew before I started, I would have put a lot more effort into the first prototype, but it really just just a fun experiment at the time.

It can be stopped/started as required, can autostart on drain and autostop on full charge, can be used with stop-start while driving or can adjust the throttle from idle to power to meet the current level of power drain from the battery - there's quite a few modes of operation, since it uses battery voltage as the key to know how much power to put into the system.

Regards
David

I just realized I should probably mention weight -

The motor/generator together weigh about 6kg in the Mk I version and about 4.5Kg ( about 10 pounds ) in the Mk II version.

So, pretty lightweight, even compared to batteries. Actually, the batteries on the frame weigh more.

Regards
David

Update:

I did a first test of the new Mk II version of the system yesterday, with some good results, and rode around for over 2 hours on the generator alone, after the battery was depleted. The new system has multiple fans driving cooling air through the generator, and the generator was able to provide power without issue for the entire ride.

the update also brings a new design which only uses plastic in compression modes of stress, except one place where it's torsional tension, and as a result of that and the massive weight savings in the new design, the fittings are now complete to the point that I don't have to redesign it other than to achieve other goals such as further reducing cost, protect from moving parts, etc ). The fan that drives the cooling is also now 3D printed and seems to handle the work well.

The operational volume is way down, and the pickup on the generator as it starts feeding power into the system is so slow that it usually isn't noticeable except that after a few seconds it seems to be making a little bit more noise, and it's not until I throttle back that I hear the engine tone drop as it reverts to idle and I can hear the sudden change ( throttle down is almost instant ).

At around 4 Kg, or 10 pounds, this is a very light generator, and I'm not sure how much lighter I can go while using a conventional petrol engine.

I just quickly wired it up to some of the existing parts I had on the test setup to get it working and took it for a ride.



Overall, some great results, and it's still working well, so I'll leave it like this and continue to ride around on generator alone for a while, and build a new model with new parts so that I can work on it on a test-bench while I continue to use the existing one and collect more information - though at this point, the experiment looks like a success -

Total power output is around 200w at the moment, or up to 300w peak, along with powering some seriously bright lights for use at night. One of the better things I added now power isn't a problem was some high intensity LED headlights - Theoretically, the thing should be able to put out about a kilowatt or so, but I haven't tried it up that high yet. Still, it's proceeding well.

David

An update - Fuel economy is measured now over a full tank - Consumed 367.8 grams of fuel ( estimated weight 0.755kg/l is 0.487 litres ) and was over 1 hr 20 minutes, with a lot of heavy uphill ( maximum power ) and average speed of 19 kph.

That works out to 56km/l or about 133 mpg

Better than twice what the Prius can do ! Of course, I'm going a lot slower, and have no regenerative braking, flywheel or other tech, but then I'm just pushing a bicycle too.


Still, a good measurement and I'm onto the third generation of shaft adapter now - still made of plastic.

Regards
David

p.s. Earlier I put in 443.3 grams of fuel, but forgot that was gross weight including container. Fuel weight itself was 367.8 grams after removing 75.5 grams for the container.

xseler said:

Literally, that's a great example of 'Southern' engineering!! I also like how you defied the rules by going into the 'grey area'.....

Bravo!!

Click to expand...

Thanks xseler

I tore down the new generator today, after about 6~7 hours of use at full power and checked it, but it was all OK, so I put it back together and installed the new front flange and dust filter.

It was a good feeling to take it down and find it all still in good order, so I'll give in another 10 hours, then go for 100 hours.

At this point, it's quite happy at running 400W no problem, but I don't have anything to test it beyond that - It should handle nearly a kilowatt though.

I got a few good runs from it since changing out some of the parts in the autothrottle, and I set the voltage on the gen to charge the batteries while in motion now, so they finished up after a 1hr ride at about 80~85% charge - a good outcome.



The final Mk III version with the clip-on air filter to keep dust out.

Regards
David