Onboard generator

Bitmugger

Active Member
Region
Canada
Can't see any chance in recharging it as you're riding it. No charger can charge faster than the battery can output, so you'll still deplete the battery. Plus I'd say the battery wouldn't last very long either.

To directly power the motor, skipping the battery, your bike would need a generator capable of around 50 amps output to sustain a steady 25-30amp supply (running it around 50% of available rpm)....These are not small and not light, and use a lot of fuel.

Its more something like this.... Its a good two man carry. Even if you had a Bafang M620, you wouldn't want to lump this weight around with you...

If my math is right you'd need like 48v x 20amps so about 1000watts of power delivered to the bike to run it well. Even with losses you could say a ~2000watt generator would run it....but given the engineering required to have a 120v AC generator make consistent smooth 54v DC power under a wide variety of loads that vary quickly and often, I think it's a tough hill to climb (pun intended).

Charging a spare battery while riding is more practical but I'd go with a trailer not your back rack unless you want noise, fumes and vibrations right behind you while riding.
 

TWB503

New Member
Region
USA
Ok if you're planning to run it while biking to power the bike that's a different kettle of fish. You'll likely want an inverter generator for that at minimum. I've not used an inverter generator but the typical AVR generators (the normal ones most people buy) struggle to supply a consistent constant voltage when the loads are variable. They don't spool up or down very instantly and you end up with surges and sags in voltage. They also inherently generate AC voltages so getting them to be 48v DC will require more electronics. ProTip: Generators with a 12v DC supplementary output can only usually push a couple amps through the 12v circuit (like 30-50watts). I was assuming you were going to run a 120v charger with it while stopped or at worst maybe had an extra battery already so would be charging one while using one.

I think you'll find using a generator to directly power your ebike motor (or attempting to charge/supplement your battery while it's in circuit) will be un-even and require more engineering/parts than you figure to smooth out the loads and voltages. Towing a genny to recharge batteries while stopped seems very practical to me and only requires one of those small 900w generators. On a trailer you might even be able to charge a battery while biking if you have a spare (based on your pics I think you do have at least 2 already and just need even more power). Lol.
The Westinghouse generator I use is an inverter
 

TWB503

New Member
Region
USA
If my math is right you'd need like 48v x 20amps so about 1000watts of power delivered to the bike to run it well. Even with losses you could say a ~2000watt generator would run it....but given the engineering required to have a 120v AC generator make consistent smooth 54v DC power under a wide variety of loads that vary quickly and often, I think it's a tough hill to climb (pun intended).

Charging a spare battery while riding is more practical but I'd go with a trailer not your back rack unless you want noise, fumes and vibrations right behind you while riding.
I have a 36V ~10A system, so when I’m accelerating, the motor uses about 420 or so watts. However the motor is not always on, so in an average hour, about ~300Wh of power is used(?). The generator can handle up to 1800 or so running watts, and i have 2 chargers, one 5A and one 4A. I can use both of them at the same time, but I could definately get by with just the 5A, which would offset the used power when I’m coasting or idling.
 

Bitmugger

Active Member
Region
Canada
I have a 36V ~10A system, so when I’m accelerating, the motor uses about 420 or so watts. However the motor is not always on, so in an average hour, about ~300Wh of power is used(?). The generator can handle up to 1800 or so running watts, and i have 2 chargers, one 5A and one 4A. I can use both of them at the same time, but I could definately get by with just the 5A, which would offset the used power when I’m coasting or idling.

I see your approach more now.

Am I right in thinking you are hoping to have a generator running and have a 120v AC charger plugged into it that outputs the 42v your battery expects and plug it into the charger WHILE riding the bike at the same time? If so that's interesting. I "think" the way the bike battery and BMS would handle it is if there's NO load on the battery (like when you are doing 100% of the pedaling) it might charge the battery and then when you start to draw on the battery it would briefly stop charging. But the display and/or lights on the bike might be enough to be a load on the battery and the BMS might not charge the battery. Or the BMS (or charger) might have current limiting on the charge circuit that would allow the trickle of juice coming in from the charger to go straight to the motor (when not charging) in which case you get the apparent "effect" of simultaneous charging and discharging at the same time. Thats a very interesting idea, but I am out of my depth on how you'd expect the battery/controller/bms/charger to react to all that.

Were it a simple circuit, what would happen is the bike would draw on the highest voltage first (the charger), pull all the current it can from that until it has what it needs or until it pulled the voltage down to the level of the battery and then draw from both. This would mean your charger could be asked to give current beyond its maximum rating. But in a complicated ebike scenario with active electronics that have current limiting abilities and sophisticated BMS/Controllers I am unsure how that would all work in real life.

Interesting idea though....I want to see it now.
 

Bubba zanetti

Active Member
Region
Canada
City
Trail, BC
With your forward motion you could drive a wind turbine that constantly topped up your battery. An added benefit would insects torn to tiny, less bothersome pieces.
E7A51742-2D4C-4B00-B135-0A591BE418F8.jpeg
 

Mr. Coffee

Well-Known Member
Region
USA
City
A Demented Corner of the North Cascades
The big problem would probably be range, because with a second battery you'd have to stop and switch out the battery, which adds time to your trip (albeit only five minutes at most, which isn't really enough time to justify a 46 lbs generator instead, but oh well...). With a generator, the battery remains at a high charge (and since my bike pulls a constant amperage, since the battery charge is higher, it gets more power due to the higher voltage), and once I've gone long enough to burn all the fuel, i still have a full charge, which is good for about 20 miles. Plus, sometimes people (myself included) forget to plug in before they leave.
I will say that a second battery is probably more practical, but come on, that's no fun, is it?
(and also with a second battery you don't get the quick refuelling of the petrol generator, plus you're getting less range for the money [subject to disagreement]. But if I'm totally honest, i just think having a generator is cool, even if it's impractical)
If you are wanting to do this to just do it, then more power to you.

The price difference between a halfway decent generator suitable for charging e-bike batteries and a spiffy Bosch 500wH battery is less than $350, and that difference will be much smaller with less expensive e-bike batteries. And the marginal cost of electricity on the road is zero. While with a generator you are paying for fuel and maintenance of the generator, which if you are using the generator a lot those costs can add up rapidly.

The batteries fit in panniers just fine. And two 500wH batteries weigh in at about 12 pounds, as opposed to 40+ for a generator and fuel. Presumably if you need this kind of range day in and day out you are carrying other stuff so you will likely have panniers anyhow.

You are also likely to need oil, parts (in particular fuel filters and air filters), tools, and a fuel can to keep the generator running on a long trip.

From a practical standpoint, in theory in decent terrain I can cover 150 miles in a day with three 500wH batteries, and about half that in mountainous terrain. Unless I was committing to insanely ambitious days or riding the AlCan or through Ladakh it doesn't seem like hauling a generator is appropriate technology.
 

TWB503

New Member
Region
USA
I see your approach more now.

Am I right in thinking you are hoping to have a generator running and have a 120v AC charger plugged into it that outputs the 42v your battery expects and plug it into the charger WHILE riding the bike at the same time? If so that's interesting. I "think" the way the bike battery and BMS would handle it is if there's NO load on the battery (like when you are doing 100% of the pedaling) it might charge the battery and then when you start to draw on the battery it would briefly stop charging. But the display and/or lights on the bike might be enough to be a load on the battery and the BMS might not charge the battery. Or the BMS (or charger) might have current limiting on the charge circuit that would allow the trickle of juice coming in from the charger to go straight to the motor (when not charging) in which case you get the apparent "effect" of simultaneous charging and discharging at the same time. Thats a very interesting idea, but I am out of my depth on how you'd expect the battery/controller/bms/charger to react to all that.

Were it a simple circuit, what would happen is the bike would draw on the highest voltage first (the charger), pull all the current it can from that until it has what it needs or until it pulled the voltage down to the level of the battery and then draw from both. This would mean your charger could be asked to give current beyond its maximum rating. But in a complicated ebike scenario with active electronics that have current limiting abilities and sophisticated BMS/Controllers I am unsure how that would all work in real life.

Interesting idea though....I want to see it now.
You are definitely right in thinking!
 

TWB503

New Member
Region
USA
If you are wanting to do this to just do it, then more power to you.

The price difference between a halfway decent generator suitable for charging e-bike batteries and a spiffy Bosch 500wH battery is less than $350, and that difference will be much smaller with less expensive e-bike batteries. And the marginal cost of electricity on the road is zero. While with a generator you are paying for fuel and maintenance of the generator, which if you are using the generator a lot those costs can add up rapidly.

The batteries fit in panniers just fine. And two 500wH batteries weigh in at about 12 pounds, as opposed to 40+ for a generator and fuel. Presumably if you need this kind of range day in and day out you are carrying other stuff so you will likely have panniers anyhow.

You are also likely to need oil, parts (in particular fuel filters and air filters), tools, and a fuel can to keep the generator running on a long trip.

From a practical standpoint, in theory in decent terrain I can cover 150 miles in a day with three 500wH batteries, and about half that in mountainous terrain. Unless I was committing to insanely ambitious days or riding the AlCan or through Ladakh it doesn't seem like hauling a generator is appropriate technology.
I think the big difference is that I already own a generator, so that makes things a lot easier, all I need is the mount.
Also... I always feel guilt when I leach power off places, even if it’s only like 5 cents. (0-100% is about 8 cents around here), so I kinda feel obligated to pay for my own fuel, even if its expensive
Full tank is ~$3.11, will charge the bike about 4.6 times.
 

indianajo

Well-Known Member
There are lots of developed campgrounds in the PNW (Oregon, Washington, and British Columbia) where a biker can stay for $10 per night and where you will be able to charge up.
Yeah, but I'd have to cross Illinois Iowa Nebraska & Wyoming to get there. Where the only sure plugs are at KOA's that stink of sewage. Will not be camping there.
I'm going to glue 2 magnets to a shaft in the bad gear ebikeling motor with a fan blade on the end. See what voltage & amperage I get. I already have several 3 phase rectifiers from dead VFS drives. Plenty of wind these days.
Per response to previous post, hanging a propellor out in a head wind while riding is stupid. I don't need electricity at all if there is no head wind. If there is, more drag is not what I need. Perpetual motion machine. But my hips limit riding to 4-5 hours a day, there are 19-20 more hours sitting still.
TWB,your broken battery mount is one more reason I mounted the battery myself. With 1/2" aluminum angle and 1/4" SS bolts. Not garbage PVC plastic .
 
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Tars Tarkas

Well-Known Member
If your goal is just to keep going, why not get a small motorcycle? That's essentially, although very inefficiently, with little regard for safety, what you're doing by adding a generator to your bike. You're going for a Rube Goldberg solution. That's why this is so funny. Can you do what you're talking about? Probably, (but why?!) There may be situations where mounting or towing a generator would make sense, like biking across the Serengeti, but I think those situations are very rare and not what you seem to be talking about.

TT
 

TWB503

New Member
Region
USA
If your goal is just to keep going, why not get a small motorcycle? That's essentially, although very inefficiently, with little regard for safety, what you're doing by adding a generator to your bike. You're going for a Rube Goldberg solution. That's why this is so funny. Can you do what you're talking about? Probably, (but why?!) There may be situations where mounting or towing a generator would make sense, like biking across the Serengeti, but I think those situations are very rare and not what you seem to be talking about.

TT
Can’t take a motorcycle on bike trails, have to get a license, possibly less efficient than my system (subject to disagreement), etc
 

Tars Tarkas

Well-Known Member
Of course I'm only expressing my opinion. As for bike trails, you may have a loophole that would let you get away with it, but I suspect you'll generate a lot of resentment from others on the trail by riding along with a running generator, making your bike a motorized vehicle, which, as you say, may be subject to disagreement.

And how long is this bike trail anyway, that you need constant replenishment of your battery?

TT
 

TWB503

New Member
Region
USA
Of course I'm only expressing my opinion. As for bike trails, you may have a loophole that would let you get away with it, but I suspect you'll generate a lot of resentment from others on the trail by riding along with a running generator, making your bike a motorized vehicle, which, as you say, may be subject to disagreement.

And how long is this bike trail anyway, that you need constant replenishment of your battery?

TT
Usually it just ends up me using bike trails as parts of my journeys. Usually I do about 10 miles on each trail for each leg of a trip?
Yeah... people will probably think I’m a cock for having an engine back there, but eh...
 

retiredNH

Active Member
Region
USA
Everyone seems to think this is a joke thread. This is why I do not enjoy using forums.
I’m asking a genuine engineering question because I want other peoples opinions on which method of this would be most effective, in theory. Will I actually end up building an on-board generator for my bike? Probably not. But I enjoy having things mapped out and knowing the reasons why certain things would/wouldn‘t work.
If you're serious, then you have a bigger problem than I thought. The problem is basic physics. Maybe with a few safety problems thrown in.

I think enough people have commented already on why this is a crazy idea. And why no one does it.