Electric Bikes - 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.

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?

Connect the generator to a charger. Connect the charger to the battery.

Connect the generator to a charger. Connect the charger to the battery.

That really isn't a very helpful response.

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.

. . .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.

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

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.

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...

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 (http://ecospeed.com) system.