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  1. #1
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    Possible to run e-bike motors off a generator?

    I want to build an electric push trailer. I'm a pretty big guy, and would like to use the trailer to haul a couple hundred pounds of gear along dirt roads and offroad to my campsite. I'm thinking I would probably need two 48v hubs for that kind of load.

    Because batteries can only hold a limited charge, I want to build a generator that can deliver the required power to drive the hubs, and charge the battery. I would not need a huge battery capacity, since I'll be able to run the engine most of the time. But I would need the batteries when travelling through areas where people might not appreciate the noise.

    Has anyone had success using a generator? I can buy a generator off the shelf, but I also have several small engines, from 3.5-10hp. And with a homemade setup, I'd be able to make the trailer like a go-kart, with the engine driving the wheels directly, in case something goes wrong with my electrical setup.

  2. #2
    Senior Member kalliergo's Avatar
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    Sure, it's possible. It's likely to be a fairly complex (and expensive) project. Gasoline generators aren't very efficient as electrical power sources go, of course. And I'm not aware of any portable generators that will give you 48 VDC directly (if you want to rig an engine and gearing to drive a wind generator, lots of them are 48 volts) so you'll have to deal with the losses involved in rectifying and transforming the current, the cost of the equipment to do that (a charger or chargers if you want it prepackaged). If you use dual hub motors, you'll want a controller that's capable of operating them synchronously. . . all in all, not an easy project.

    How far are you talking about traveling, between locations with access to commercial power, in what kind of terrain? And what is the usual condition of the road surfaces?

  3. #3
    Senior Member rscamp's Avatar
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    Connect the generator to a charger. Connect the charger to the battery.
    Rob

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    Senior Member kalliergo's Avatar
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    Quote Originally Posted by rscamp View Post
    Connect the generator to a charger. Connect the charger to the battery.
    That really isn't a very helpful response.

  5. #5
    Senior Member rscamp's Avatar
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    Quote Originally Posted by kalliergo View Post
    That really isn't a very helpful response.
    Well, it is short on detail, I'll give you that!

    It is helpful because it describes an approach to the problem that fully addresses the issues associated with adapting the power generation system to the electric propulsion system. The battery is the buffer that makes it all work.
    Rob

  6. #6
    Senior Member kalliergo's Avatar
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    Quote Originally Posted by rscamp View Post
    . . .it describes an approach to the problem that fully addresses the issues associated with adapting the power generation system. . .
    Perhaps, but the issues the OP faces, in actually implementing a dual hub motor pusher trailer, are rather more complex than charging a battery with a generator, as I suspect you may know, rscamp.

  7. #7
    Senior Member rscamp's Avatar
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    Point taken.

    However, this topic is better suited to a forum on more advanced vehicle topics than just ebikes, but here are some suggestions:

    First and foremost, keep it simple.

    - only go to a hybrid drive if it is absolutely necessary - with a trailer there is a lot of additional space for batteries and keeping it all electric reduces complexity considerably.

    - if a hybrid is necessary, use a series hybrid rather than a series-parallel

    - it is questionable if adding dual drive capability adds reliability - it certainly complexity to the finished system and adds design requirements that are far from trivial

    - consider repairability along with reliability - use more common COTS equipment that can be quickly swapped out as LRUs rather than making "snowflakes"

    - to address commutation timing for two motors there are two practical choices:
    - lock the two motors together with the correct timing, or
    - use two controllers

    - consider that this sort of vehicle probably requires considerable low speed torque for the weight carried and terrain - the drive system should be selected accordingly

    - look at the simulator at ebikes.ca to get a better idea what motor, wheel size and voltage may work better in this application
    Rob

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    Thank you for the responses. I did not realize the complexities of synchronizing dual hubs.

    Now that I think about it some more, I've probably overlooked a simpler solution. Take a regular e-bike, and connect it to a gas-powered push trailer.

    I would be able to switch on the electrical hubs when I need additional power to climb a hill, or shut the engine off.

    I'd have a hybrid in principle, but without the complexity of attaching two power sources to the same drivetrain. As long as the gas engine is strong enough to carry the established load across level terrain, plus deliver enough electrical power to keep the batteries charged.

    So my next question is how well do the hubs perform at charging the batteries? Are all e-bike hubs capable of recharging the batteries? And what are my options regarding batteries? Are some better than others? Would it be more efficient to install a small generator to charge the batteries?

    Keep in mind having a relatively large trailer allows me to think outside the box in terms of what battery to use. I'm thinking I need to find the right balance between charging the batteries efficiently, without over-charging them.

    In terms of performance I need a trailer that is capable of carrying at least 100-200 pounds of camping equipment. For the roughest terrain I would probably get off and push the bike, with the trailer in tow. And where necessary unload some of the gear. Similar to how one would portage a canoe around a waterfall. It would also be nice to have two electric hubs, so I can have the necessary performance in areas where engine noise might be an issue. If it would be possible to drive two hubs off the same battery that would be nice.

  9. #9
    Senior Member rscamp's Avatar
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    This is simpler. On the down side though, I think the amount of regen you can get will be very limited and I'm just not sure if it is a good idea to push a bike with regen braking on - especially on hilly or slippery terrain. On flat, dry roads it is probably okay, but not ideal. You could forget and have an issue if it starts to rain and the road gets slick, for example...

    Direct drive hubs are capable of regen with the right controller. Geared hubs have one way bearings and are not. The amount of regen is generally fixed and in reality almost better for helping with braking than for providing energy back into the batteries. The traction the trailer can develop will have it's limits too and needs to be considered.

    Another practical consideration is you will need very dependable and responsive throttle control on an IC engine powered trailer!

    I'm probably not much of a judge as I don't know what you know and what you don't but I'm guessing you've got a fair bit to learn and become familiar with before you can attempt this with a reasonable expectation of success. There is a lot to know about battery options and characteristics, controllers and motor characteristics on the electric side alone. This doesn't mean you shouldn't start and attempt this (it might be fun!), but it does mean you'll need to do your research above and beyond what anyone tells you here and be reasonably confident it is going to work before spending $$$.

    You can run 10 motors on the same battery pack if you want. Just as long as the total current is appropriate for the batteries used.

    I go back to the previous advice and say keep it simple. I really think you are better off to make a strong ebike. Use two strong hub motors and either more batteries or a generator/charger combo to achieve range extension. Of course, this is just my recommendation...
    Rob

  10. #10
    Senior Member kalliergo's Avatar
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    I just checked back in to the thread. Rob has you covered now. I'd pay attention to his guidance. And I strongly second his advice to go with an ebike.

    I would only add that powering the cranks has major advantages over hub motors, especially in that it allows you to take advantage of your gearing and operate your motor nearer its most efficient RPM range. If you're rich, or just for ideas, take a look at the EcoSpeed system.

  11. #11
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    Quote Originally Posted by websthes View Post
    I want to build an electric push trailer. I'm a pretty big guy, and would like to use the trailer to haul a couple hundred pounds of gear along dirt roads and offroad to my campsite. I'm thinking I would probably need two 48v hubs for that kind of load.

    Because batteries can only hold a limited charge, I want to build a generator that can deliver the required power to drive the hubs, and charge the battery. I would not need a huge battery capacity, since I'll be able to run the engine most of the time. But I would need the batteries when travelling through areas where people might not appreciate the noise.

    Has anyone had success using a generator? I can buy a generator off the shelf, but I also have several small engines, from 3.5-10hp. And with a homemade setup, I'd be able to make the trailer like a go-kart, with the engine driving the wheels directly, in case something goes wrong with my electrical setup.
    websthes,
    Your idea is so much like mine it is scary. I also have met with a lot of resistance to my idea. Bikers fall into gas or electric group(usually.) Hybrid gas/electric is a new concept. The GM Volt is a good example. The gas motor only charges the battery and only starts when needed. Prius and other gas/electric hybrids both gas and electric propel the wheels. There are dual wheel hub kits available. I've seen some BMC dual drive kits. They are geared motors. My solution to the 48v problem is to build the generator with a 24v alternator. A pair of 24v 500w geared hub motors should give the torque I need to haul a fairly good load. As far as propelling the trailer, a third motor could be possible. I'm using a single wheel trailer that stays on the same plane as the bike. Imagine, 3 wheel in line drive. If this set up works reasonably well, I will consider using a PM alternator conversion for a wind generator. They can put out 90 volts at 2500 rpm(even less depending on the stator windings.) Yes, if your generator/alternator can put out the power, it could run the motors with the batteries serving just as a buffer. There is a relatively new product on the market: Ultracapacitor. Google it. There's a guy with a "Boost Pack" who starts his car. They are also used in Off road racing vehicles to elimanate the heavy battery. A combination of Ultracaps and LiFePo4's would be killer for this application.

  12. #12
    Senior Member DrkAngel's Avatar
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    Lightbulb Simple Hybrid eBike-eTrike

    Doable!

    Parts list:
    2 - 48V capable brush motors
    1 - 96V capable brush controller ... might be tough to find?
    1 - 96V "buffer" battery (109.2V full charge)
    4 - 30-50A rectifying diodes
    1 - 1200-1500-2000?w 110V AC generator w/4 cycle engine

    96V will run 2 - 48V brush motors in series - 48V through each motor but requires 1 - 96V controller

    Actual generator Voltage output may vary but many generators have voltage "trim" adjustments between 110-120V
    4 diodes will "full wave rectify" 110V AC into DC with a minimal <1V voltage loss ~109.2V DC

    Dependent on the size of the 96V battery, this might be classified a hybrid or a series hybrid.
    Last edited by DrkAngel; 11-13-13 at 10:04 PM.
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  13. #13
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    I would encourage the use of a gasoline generator that the engine was rated for very minimal pollution. I use both electric and gasoline motors to build human+other hybrid powered bicycles and there is a huge difference in how cleanly different small engines burn their gasoline. Also, consider something capable of running on E85 or better if you have access to fuel alcohol or propane or liquid natural gas all of which burn many, many, many times cleaner then gasoline.

    I am by no means apposed to liquid combustion fueled power sources. But a simple choice in brand name can make the difference between producing less pollution then a modern gasoline car or more then a modern gasoline car with your set-up.

    As to home generator built set-ups I would like to point out that older model car alternators especially those from the late 70's early 80's period (new replacement parts from auto shop) are capable of producing substantially more voltage then they are rated for since they used the methodology of controlling the field coils power to control the output voltage and with some modifications to the voltage controller unit it is possible to produce anything from 6-120 volts charge from them just by adjusting the field strength (they are not permanent magnet generators but rather use an electric magnet field coil instead and adjusting the power supplied to that field coil adjusts the voltage that is generated).

  14. #14
    Senior Member DrkAngel's Avatar
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    Lightbulb Single 48V Motor From 110V AC Generator

    Single 48V Motor From 110V AC Generator

    A simple 2:1 wound transformer would work nicely and allow a single motor, brush or brushless, to run at ~54V.
    Combined with the rectifying bridge, (4 diodes), and buffered with a small 48V battery, should provide nice clean DC to the controller!

    4 Cycle-Stroke Generator?

    Why a 4 stroke engine?
    50% more efficient.
    No oil mixing.
    1 half the toxic pollutants of a 2 stroke!
    Sadly it does weigh and cost a bit more, but if used a fair amount should be more eco2.

    A generator meeting CARB compliance represents an additional degree of eco-friendliness.
    Last edited by DrkAngel; 11-15-13 at 07:17 PM.
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  15. #15
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    The trailer I am building is in the Aevon style with a suspended monoshock 16" rear wheel. We will probably runs tests with the rear axis connection as in the "Bob trailer", but it seems intuitive that a seat post mount will be the "friendliest." If you have ever hauled a bumper hitch vs. a fifth wheel trailer, you would understand the farther forward the trailer is attached to the tow vehicle, the more stable the ride. A fifth wheel travel trailer is considered so safe and stable that as long as there is an intercom installed, passengers may ride in the back. Besides, the seat post hitch is just so slick to connect and disconnect with a quick release seat post.

    The engine we are using is the newly CARB compliant 79cc HF motor. Hasn't been available in California for the last several years until the carburetor was updated. This is where it gets interesting. We are planning of powering the rear wheel. The question is, do we put a centrifugal clutch with a jack shaftnto the rear wheel, or do we just put a hub motor? The primary function of the gas motor is to run a 24v alternator to charge 2 12v batteries in series for the 24v motors on the bike. The most probable outcome will be a hub motor since that could be run in "stealth mode" on just batteries and still be able to propel a bike with no motors of its own.

  16. #16
    Senior Member dougmc's Avatar
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    Quote Originally Posted by DrkAngel View Post
    96V will run 2 - 48V brush motors in series - 48V through each motor but requires 1 - 96V controller
    I'm not sure this "motors in series" thing is a good plan.

    The resistance of an electric motor varies a lot -- the more the load put on the motor, the lower the resistance it provides. And if you have two motors in series, the lower the resistance one motor provides, the *less* voltage it will get and therefore the less power, when what normally happens to a motor that's got its own battery is that the more of a load it gets, the *more* power it absorbs.

    And if one motor is getting less voltage, that means the other motor is getting more voltage. (The current between the two motors will have to be the same, but the voltages will differ based on the load put on each motor, with the motor with less load getting more power. This might actually work on a tricycle where each motor drives a rear wheel, as it'll act like a differential, complete with the flaws of a non-limited slip differential.)

    Also, you'll only be able to get away with one ESC if the motors are brushed (yes, you did mention this, but it's worth repeating) -- if they're brushless, they'll each need their own controller (unless they drive the same shaft and you can guarantee that each motor will always be in phase with the other -- then you could get away with one 96V ESC and both motors connected to it -- but basically in parallel), and if the controllers can't handle 96V each, if you load down one motor, the ESC for the other motor will get most of the voltage, and could fry.

    Now, if the two motors both power the exact same thing -- they both drive the same shaft -- it might work, as their RPMs and loads will always be the same. But if they drive different things (especially through different gearings), strange things will happen.

    Personally, I'd suggest just going with the charger suggestion (though it probably can't use anywhere near all the power the generator can put out), but if not, just go for a standard 48V setup and make a high power switching power supply that takes 110VAC and outputs 50VDC (or whatever the battery delivers with no load when full) and put it into parallel with the batteries when activated. Though really, rather than that, I'd just put more batteries in the trailer and ditch the generator entirely.

  17. #17
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    Why not make the cover out of solar panels?

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