Gas Electric Hybrid, Hypothetically

stoppit

Member
Local time
1:49 PM
Joined
May 5, 2009
Messages
30
Location
G-boro, NC
Here's the scenario:
Have: Electric Bike with hub motor, lifepo4 battery
Idea: Add small displacement gasoline engine (< 30cc) somewhere low and tucked out of the way in order to generate electricity/recharge battery, thus making your bike capable of going way further if the battery charge wears out.

Since I just got done buying the electric end of things for my bike, fundage is nowhere near what I'd need to actually do this yet. However, I'd imagine that a little 2 stroke would do the trick but what would be needed to keep the engine from overcharging the battery/pretty much everything else is a complete mystery to me.

If all goes well financially over the next year (and I figure out how to do this), I'll hopefully be posting pics of the hybrid about this time next year.

Thanks in advance for replies.
 
What is your idea for having the <30cc charging the batteries?

Will it run a small generator or such? Or use the engine itself to create the charge?
 
Not really sure, this is still all a pie in the sky kinda idea. Truthfully the <30cc was just a guesstimate, this was just a hair-brained idea I came up with earlier, but the more I think on it, the more I like it. The only other option I've thought up would be to buy the smallest portable generator I could and just have the battery charger plugged in. The problem is that I don't know (and doubt) that this would be the best way to go about it. It'd be better if the gas engine could supply some power to recharging the batteries while the rest goes towards running the electric motor on the back wheel. I've got a battery management system built into the battery, so it won't overcharge (i don't think).
 
You can probably do this for very little money. A used weed trimmer or leaf blower engine, and a homemade alternator to charge the battery. If you look on some wind and "micro hydro" sites, they have plans to buid direct drive permanent magnet alternators that can produce plenty of juice at low RPM's. Running the engine at lower RPM would reduce engine noise.
 
Do you want to charge while running?.What is power req. of hub motor,Voltage& current, what is battery capacity ,voltage&ah.Tell me more,I'm an EE.
 
I had a similar idea and have a spare used Weed eater and alternator for the project. This is a few factors as I see it:

1. A gas engine, alternator + batteries + electric bike motor comes to a fair amount weight wise, so it may be prohibitive on a two wheeler.

2. For me anyway I am not fond of the pusher design, but a three or 4 wheeler bike would be more to my liking.

I have had some experience modifying weed eaters for other apps. Note that there are two main drive types for cheap eaters: A flex shaft that resembles an oversize speedometer cable, and a splined solid shaft and set of bevel gears at the head. The engine rotation of one is reversed on the other type, so make sure it has the proper rotation for an alternator if that is the route you go .

I have shortened the solid type by making new splines using a Dremel tool and abrasive cut off wheel. The flex shafts have swedged ends that are square shaped. They are a booger to make a new square end on, but it can be done. See my notes on the shaft and throttle: http://www.flapdoodledinghy.com/motor.html

Most automobile alternators (I think) have a hex hole on the center of the pulley end to make removing the pulley easier. It would be simple to file a hex on the end of the solid weed eater shaft.
 
Last edited:
Do you want to charge while running?.What is power req. of hub motor,Voltage& current, what is battery capacity ,voltage&ah.Tell me more,I'm an EE.

Charging while running would be preferable but not necessary (would be more in keeping with the hybrid idea behind this). I'm an economist, not an EE, so if any of these numbers don't make sense, that's probably why.
Hub Motor: Crystalyte RoadRunner with a 36 volt controller, can run at a peak of 25 amps (i think, if i'm wrong, then please correct me on this)
Battery: eBike lifepo4 with battery management system built in, 10 Ah capacity, 36 v, has max discharge of 25 amps and max charge current of 5 amps
 
OK,your info seems reasonable,one thing I forgot to ask what is your running time typically on a charge,I would guess at 90-120 mins ,is that in the ballpark (affects charging rate we would want to shoot for).I'm rather number oriented and as an economist you should be too,but not prob. in the same way (M1,M2,money velocity,who knows what else).I think it's rather. tricky to come up with a system that passes eng.&econ. muster.Temptation is to overdo it engineeringwise&end up with RubeGoldbergian boatankerish monstrosity.Keeping it as low-weight&simple is v. important.
My guess is that a charging system would have to deliver 200/300 Watt or 6 to 10 Amp at 36V to meet the need,(closer to top end).A top-end system would give you virtually
unlimited (electrical) range,a bottom-end would prob double or even be triple your range.
Problem areas: the main stumbling block as I see it is to dig up a suitable generator.it does not matter all that much wether it is an ac. or dc generator (the ac can easily by rectified,that's no problem),it has to run at 4000+ rpm to permit direct drive from the gas engine and be able to provide the 36V/10 Amp).ALL generators have the attribute that their output voltage is proportional to speed so speed control=voltage control= charge control.
The power requirement means 0.4 to 0.6 HP (horse power) from the gas engine,1 hp = 740 Watts that is Volt xAmps, assuming 80% eff. from the generator,which in turn means an engine output capability of over 0.65 to 0.95HP .Engines this size are rated for output at higher speed at typ 6k. rpm not 4k.(power is prop. to rpm.)This means an engine size of at least 25-35 cc displacement.
Enough for now,please comment &ask questions before we get too far afield.,I don't know what your knowledge base is.
 
Last edited by a moderator:
Alright, so anything that is running at 6k rpm would generate too much wattage, if I'm understanding this correctly. Running an engine that size at a non-optimal rpm would affect fuel efficiency. I'm none too familiar with this engine business, so any suggestions as far as getting the rpm right (gearing it down might work i guess, but i don't know if the resulting friction would do to energy loss).
 
This general scheme of an ICE/Ehub has long been on my list of things to do.
I've been referring to it as a tribrid, pedal/gas/electric in an attempt to keep as much of the functionality of the original bicycle as possible while adding the ancillary assist components.....and keep it under, say, a hundred pounds.

That you said you've already have obtained the electrical components I understand. However, I've been attempting to source an Ehub with regen braking and a controller that would trickle charge a, hopefully smaller_than_usual battery pack and still maintain sufficient storage for general use.

One question I've wondered about is: would a small gas engine have enough oomph to both drive an alt/generator while at the same time supplying power to the drive train of the bike?

I've seen it mentioned here by some who have experience with this type of thing that while an alternator spins freely at rest, under load it requires a lot of energy.....suggesting perhaps it couldn't do both at the same time.???
 
Back
Top