Electric Bikes - I'm sure you guys have heard this one before, but...

ok, there I was looking at my honda ex350 generator. it weighs 18 lbs, and puts out 350 watts. What if I mounted the sucker onto the rear rack of my CA schwinn izip? Some electronics would be needed to convert the 12v output to 24V, and with that 24v, you could have it recharge the battery, and also provide power to the electric motor to drive the bike. An argument could be made that the bike is still electric driven, to not contravene all existing rules about electric bicycles. This would then be a true hybrid in the sense that you no longer have to worry so much about the range of the electric part of the machine.

of couse a hunt on supplies could possible find a more suitable engine only, and match it with a 24/48v generator in a much more compact package.

If this bike was on the market, I think I'd seriously consider buying one.

waddaya all think?

btw, I just got back from 2 weeks in china, and electric bikes are big over there. Found hub driven huge battery suckers there for equiv of $200 cdn. at local shops.

Those little Honda's are great, and pretty quiet.

Still, that's not a lot of power density compared to today's batteries. My 15lb 20AH 36V LiFePO4 pack for example, even at 1C discharge, has a power density of 48 watts / lb (720 / 15), the Honda is only 19 watts / lb (350 / 18).

However, the Honda has the advantage of much faster recharge time and perhaps much longer run time.

Since you mentioned one of the advantages of using the genset is no longer having to worry about the range of the electrical part, I guess you would have to look at how far do you really want to go on a bike.

In an earlier post I reported a 52 mile range from my pack before empty; for me at least that's a very long bike trip. Most of my trips are 20 miles or less so there is no way I would trade the convenience of an electrical plug for a can of gas. For others who are into serious touring, your concept might have more appeal. My 2 cents.

BTW, if you get serious about it, I would consider using the 110V outlet of the genset to transform and rectify down to 24VDC. AC/DC power supplies are abundant and cheap; DC/DC switching supplies are less so. And you end up with one less transformation, all of which are less than 100% efficient.

uh oh, I just noticed the thread/discussion/debate about gas powered on one of the stickies, Sorry guys, I haven't been here for awhile. I should have put this thread in its appropriate place, though technically, the gas engine powers the generator not the wheels directly.

Misslexi:Thank you for your reply and information. That power density thing was not my point. I was wondering if there is interest in the concept of having a small generator on an ebike. I think it would take a lot more powerful generator to power the motor. I never thought of the resistance of people who hate ICE bikes (new term I learned in another thread today) I'm sure people could reduce the weight, use proper volt alternator with rectifier and make a very light package that could be sold as an add on to ebikes and make a bajillion dollars. ha.

An argument could be made that the bike is still electric driven, to not contravene all existing rules about electric bicycles...

I like the way that you think.

I see, you're considering it as more if a charger than a direct power source, sorry I missed that the first time. It's an interesting concept. If we think of it in net power terms, lets say my eBike is running at 1.5C off my 20AH pack on average, that's 30 amps. The maximum charge rate allowable for the pack is 5 amps, at 43.7 volts, or 218 watts. The genset is 350 watts and with conversion inefficiencies it's no doubt capable of that. So we are adding 5 amps to the system which you can either choose to think of as 5 amps charging and 30 amps discharging, or more simply 25 amp discharging (the gas engine is really just helping to power the electrical one). This means I'm pulling 16.6% less current from the battery (5 / 30) so I'll probably go 16.6% further on a charge if we ignore the weight of the engine, gas and oil. That's 60 miles instead of 52 miles.

That's still not a compelling case for me personally. Especially not to haul around another 18 lbs. I'd rather attach another 20AH pack at 15 lbs and extend my range to 104 miles, ignoring the pack weight again.

Some would argue an eBike is already a hybrid system, what I think you have in mind is a trybrid (tribrid?) system :)

Still, if you pull of the engineering challenges and get a prototype ready, I'll be a guinea pig :thumb:

Staton is working on a gas drive with a electric motor built in. http://www.staton-inc.com/Details.asp?ProductID=3317

ok let's see

sizetech: thanks, not many people do.

misslexi: No Fair bringing math into this discussion :) My major in school was fingerpainting. ok, so here goes. If 5 amps is 218w @ 43.7v, then when you draw 30a from your battery pack, then you must be drawing 1290w. Does your electric motor really require that many watts to run? I was assuming that a 350w generator would be able to almost or nearly power a 350w electric motor, I was thinking the generator could do the dual purpose job of recharge/power, but come to think of it, when the generator is running, it is hard to fathom that the little thing could power me on my ebike. btw I have no idea what the C in "1.5C" stands for. I assume it doesn't stand for Celcius. I am not asking for a crash course in electroncity. If you think this is all over my head, just say so, and I'll research and figger all this new fangled stuff on the net. I was just throwing some ideas around.

15rms: That stanton thingy is cool. Shows that I'm not the only one that is insane. ha ha. It doesn't fulfill one of my criteria which is to use the engine to power the electric motor, thus keeping the bike in the ebike category, hopefully. Also I sure like the price they have posted on the sucker. If it hits the market, I'm sure I'll be interested, price depending.

I was assuming that a 350w generator would be able to almost or nearly power a 350w electric motor

In theory that sounds right. The thing is, a do-it-yourselfer could do far better in terms of propulsion by using a gas motor to drive the read wheel directly (using a friction roller), without sacrificing the recharging capability. The trick is realizing that a direct drive hub motor can also work as an alternator, as long as the controller supports regeneration.


btw I have no idea what the C in "1.5C" stands for. I assume it doesn't stand for Celcius.

In this context, "C" refers to the rate of current flow relative to battery capacity, in units of 1/hour (i.e. amps per amp-hour). Batteries are commonly charges at a rate of 1C, meaning a 1 hour charge. Discharging at 1.5C gives you 1/1.5 (= 2/3) hours of runtime.

Dudley, you are almost right about the power required to run my mid-drive motor. First the voltage I mentioned, 43.7 volts, is what's recommended to CHARGE the battery. This is not the voltage one is likely to see when discharging the battery. The nominal battery voltage is specified at 36 volts so the power used at 30 amps is more like 1080 watts. Even though it's a 650W motor, that's a conservatively low rating, and that refers to the actual power the motor can output. Now we dial in the efficiency of the motor which I think is around 80% on average and you can see why the input power to the motor is much higher than the actual useful power at the motor's drive shaft.

In the case of the LiFePO4 pack I use, the battery should never be charged at greater than 5 amps. That's 0.25C where 1C = AH capacity of the pack, 20 in my case.

Therein lies one major difficulty with on-board chargers regardless of their energy source; the inability to charge a battery in a meaningfully short period of time (with respect to riding time) because the battery cannot tolerate high recharge current. One battery system that may be well suited to an on-board charger is something like the DeWalt 36V nanophosphates. I think they claim a recharge time of 30 minutes on a 2.2AH pack which is 2C (I think).

Or you may want to incorporate the latest technology, the Super Capacitor (I'm not kidding), which will take enormous charge currents from the ICE; wow, I think we just invented the first Quad-brid!

unime: Thank you for the science lesson. The friction roller drive would make the ebike definitely an ICE bike. I would like to at least keep the argument that the bike is an ebike, by having the generator power the ebike motor. I'm sure it is much less efficient, but sometimes we gotta jump through hoops. That does sound very interesting to have propulsion drive the hub motor to recharge.


Misslexi:You've opened a big can of worms now with bring math into this. I never realized there were motors over 500w. You obviously have an air conditioning compressor motor mounted and can easily out run police cars. I on the other hand chose to stay legal and have a 350w currie motor. I believe you are right that charging ratio would be about 6 hours/1 hours use. The real gem may very well be using the generator as power to the drive motor. In my case of a 350w currie, I think I would need to use a size up generator. This follows the "if in doubt, use a bigger hammer" theory. So honda catalogue shows a EU1000ia @ 29 lbs (yikes) has 1000w, plenty to power the currie even after all the losses, and enough left over to do the charging chores too. And to boot, it's a four stroke, prob use as little gas as my ex350. I dont propose this to be primary power, but only backup in case the batts give out during a day. I for one do not have very predictable days. Could be that I may never turn the "backup power" on in weeks, but nice to know it's there if needed. Yeah Yeah, I could turn on the human thrust instead, but what if I don't wanna. The izip is already 80lbs with the 50lb sla pack. The 29lb genset should put the weigh in line with a D2 Cat. An imposing thrust challenge indeed. The acid test would be to smoke past the cop shop and see if I end up in the slammer.

I like your idea,but i'd consider towing everything in a child's trailer because it will help keep your bike feeling like a bike.

Plus for short trips, you can disconnect the trailer and run on human and battery power only.

SeizeTech is right on.

I was on a bike trail last week that has more do-this, don't-do-this rules than you imagine. Once I actually stopped to read one the rules signs, the first one got my attention: "No Motorized Vehicles Allowed". As a quick aside, the second rule also caught my attention "15 MPH maximum speed", I was doing 20-22 MPH most of the way :o. Anyway, it occurred to me they could consider my eBike a motorized vehicle, probably I will never hear from anyone if I stay within the speed limit (I will). That's when I thought about the child trailer thing as a pretty darn stealthy way to stay under the radar. I could even put my cute little bird dog in there as a decoy, she'd be riding "shotgun" for once :lol:

Back to your Honda 1000, a friend who camps a lot has one of those things, you can stand right next to it and have a normal conversation. He even used that thing to power a small air compressor for driving a nail gun, it groaned a lot but never tripped the breaker or shutdown.

Let's be sure on one thing here - this is a less efficient set-up than a gas engine alone because there is some energy lost in the conversion from gas to electric. Don't get out the calculator - it is a fundamental principle of physics that, when it comes to energy, you can't get something for nothing. In addition, you are carrying 18 pounds of extra weight which cuts into your range.

I'm trying to think what advantage this might have but I don't know what it is. If you want electric to start with and gas as a backup, you're better off putting a small gas motor on an electric bike. The gas motor is lighter and more efficient than a generator.

i agree. i dont think efficiency should be a motivator for an idea like this, it would have to over you some other advantage

I think the OP wanted keep it a true eBike rather than a gas one.

One could make the case that a gas motor used only as a battery charger implies the machine is still an eBike.

More of a legal classification initiative than an efficiency one for sure.