Gas Electric Hybrid, Hypothetically

Discussion in '2-Stroke Engines' started by stoppit, May 6, 2009.

  1. stoppit

    stoppit Member

    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.

  2. s_beaudry

    s_beaudry Member

    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?
  3. stoppit

    stoppit Member

    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).
  4. arceeguy

    arceeguy Active Member

    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.
  5. duivendyk

    duivendyk Guest

    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.
  6. Flapdoodle

    Flapdoodle Member

    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:

    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: May 6, 2009
  7. stoppit

    stoppit Member

    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
  8. duivendyk

    duivendyk Guest

    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 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: May 7, 2009
  9. stoppit

    stoppit Member

    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).
  10. Happy Valley

    Happy Valley Active Member

    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.???
  11. duivendyk

    duivendyk Guest

    No not necesarily,the problem is really to find a generator which will put out the right voltage&current (power) to charge this battery with,in the 4-6 k rpm range preferably.Car alternators are an overkill, they can supply the 36V (with suitable modifications) and can run at these speeds, but can put out about 30/50 Amps easy their main drawback is that they are bulky&heavy look at one on your car,but they may be the only game in town.The other possiblity is to use a dc electric bike motor (not a hub motor of course).They can be used as a dc generator but the only way you can control the output voltage is by speed control of the IC engine which likes to be in the 4-6k rpm range (output is proportional to engine speed).Of course you can resort to pulleys&belts to match speeds,that gets mechanically messy,but we may have to.Locating one behind the other with a belt drive in between on the back rack is the best place.Fuel efficiency is not really a major consideration,engines are usually most efficient&durable at 3/4 load,running them at full power continuouslyis not a good idea generally, esp the low quality Chinese ones which I would definitely NOT mess with unless you want to tinker away forever.The best bets would be the Subaru Robin engines.Go to look under engines, the Subaru EH 025 or EH035 are well engineered and easy to start.Honda's are OK too.You did not answer me question about battery life,do you commute,or use your bike just for riding around?
    Last edited by a moderator: May 7, 2009
  12. Flapdoodle

    Flapdoodle Member

    There are car alternators that are the size of my fist, but a little hard to find. Honda N360 sedan comes to mind. Another source is motorcycle alternators. eBay is a good place to look for a used one. Some have built in regulators.

    Years ago I saw a Honda portable generator that was surprisingly quiet and about the size of a toaster.
  13. stoppit

    stoppit Member

    Mainly I'll be using this bike for recreation, daily commuting (about 2 - 3 miles), and if this hybrid idea works out, possibly road trips to visit anybody and anything within a 50 mile radius of an Amtrak station. I'm still having to jerry-rig a few things before the electric stuff is even running (can't very well start that until finals are over and done with).

    I saw a couple 900 watt generators similar to what you mentioned, flapdoodle. They were online and weren't too expensive ($300 - 700), plus all had dc and ac outputs (a big plus if I were to go hobo camping with this thing).

    Any thoughts on modifying an old army ammo box to house the guts of the generator (so it's detachable)?
    Last edited: May 8, 2009
  14. duivendyk

    duivendyk Guest

    You don't want some clunky heavy monster at your back,that makes the bike harder to handle and takes the fun out of riding.If we could come up with some generator you could mate to that 25 cc Subaru engine,200-300 Watts,36V/6 Amps or so, we'd have it made.The trouble with motorcycle generators is that they are 15 V or so and frequently amalgamated into the engine,you need to have a bolt-on type. With some electronics tricks up my sleeve I can get around the voltage limitation and charge a 36V battery.I remember that little Honda motorgenerator, I think it was in this power range.
    This project,if it ever comes to fruition,will of necessity involve a fair amount of crafting things by hand,do you have basic metal working tools, are mechanically oriented and have access to some kind of work shop?.
  15. stoppit

    stoppit Member

    As a student at the uni, I've got full access to a machine shop. Experience wise, I took shop in h.s., have done wiring in houses, p/a's, guitars/amps, never really worked extensively with metal (more woodworking). I can handle the likes of a drill press, filing, grinders, benders, with some efficacy, but haven't really futzed around with metal on a lathe or anything that complicated. I am at least a quick learner and know some people who do art with metal, as well as a few folks who are gear heads in the motorcycle/hot rod sense.
  16. duivendyk

    duivendyk Guest

    OK you're in excellent shape as far as the mechanical stuff is concerned,tell me more about this "battery management system",is the charger part of it or do you hook the charger up to it,also how big (heavy)is the charger itself.It's possible in principle to generate 120V ac from a motor driven gen. and go through the charger to charge the batt.This gives you more gen. options.These LI batteries need to be handled with some care (I'm not all that familiar with them),for instance you must not fully discharge them,or they'll croak.They are also quite expensive,so circumspection is prudent.Going thru the batt. management would be safer.
    Last edited by a moderator: May 8, 2009
  17. Flapdoodle

    Flapdoodle Member

    I would be afraid the ammo boxes would not allow sufficient cooling, and they are a bit heavy. Had two 30 cal boxes on my Yamaha Enduro as lockable saddle bags.

    Decades ago my dad and I made a portable gen using a B&S lawn edger engine, a car alternator, and separate regulator. The frame was pop riveted aluminum angle from the hardware store. Some panels were diamond pattern aluminum mash, and a rudimentary control panel with meter. My brother has it now and still uses it.
  18. stoppit

    stoppit Member

    Well, here's some of the info on the battery management whatsit:

    BMS(Battery Management System):
    Over-Charge Protection: 3.85V per cell - 46.2v ( 12 cells )
    Over-Discharge Protection : 2.3V per cell - 27.6 (12 cells )
    Max Discharge Current: 25A
    Max Charge Current: 5A
    Short Circuit Protection: Yes
    Balancing: Yes
    Battery Pack:
    Dimensions: 14" x 2 3/4" x 6"
    Weight: 10 Lbs
    Voltage: 36 V
    Capacity: 10 AH
    Cycle Life: 1500+
    2 Amp charger

    from the website I bought the battery: "The intelligent charger ... is engineered to regulate charging once the battery is fully charged. It will shut itself off when your battery pack reaches a full charge, but it is always a good idea NOT to leave your battery pack plugged in all the time. Just unplug the charger when the charger light is green." here's the Battery Website
  19. duivendyk

    duivendyk Guest

    That looks pretty good.Good news (maybe),I surfed around and the thought struck me that the electric lawn mowers might have motors(generators) that operate in the 4-5k rpm range and might be in our power range.I found a potential candidate !.It's the motor from a CUB battery powered electric lawn mower.It runs of 48V which means that it can run as a generator at 36V+ (the gen output V is about 80% of motor V,they did not give the rpm but others (24V types ran at about 4.5k rpm),as do most types gas powered mowers .The EH 025 has enough torque to drive it and should be able to easily supply the charge current and may be more.In theory you ought to be able to charge through that batt. management gizmo plus supply the excess directly to the motor,but there might be some tricky aspects to this.In any case the thing is now to extract that motor from someplace (or at least info) without being held for ransom.CUB used to be IH (Int Harvestor and is supposed to make good stuff (according to CUB at least, which is heartening).I latched onto 'Partstree'.com they deal in for outdoor eqt,had nothing on CUB CC-500BAT (NOT EL!) that is a corded 120 V ac. affair,they wanted a mere $250 or so for what looked like a 0.5 hp 3500? rpm induction motor for that EL
    thing.Which is at least $100 too high.So I figure they'll want an arm&leg for the 48V dc motor.The only thing I don't know is what speed this thing runs at, but there is plenty of voltage reserve (12V).I found a CUB dealer in this area Farmservice (you can find them on the CUB site).Take a look around on the web or take a real life sneak peak.
    Last edited by a moderator: May 8, 2009
  20. gppeej

    gppeej New Member

    Cool thread guys. I have wondered for a while if a small RC airplane motor could turn a small dc motor backwards to create usable charging. I like to imagine a tiny little set-up that could even be slaved to the throttle to make noise - less at idle and more at WOT. They make RC motors from 5cc up to 50cc, and even 110cc boxer style motors. Most are very light.

    Something like this:|66:2|65:12|39:1|240:1318|301:0|293:1|294:50

    Notice the RPM from 1400 to 9000 and a weight of 1215g! that's only 2.7 pounds. But, I wouldn't know what alt/gen/motor would be best for these apps. Good luck.