electric bike motor control from a car alternator

Thread Starter

toby woodman

Joined Apr 15, 2024
4
I am building a hybrid bike, I want it to work similarly to a diesel-electric locomotive, if I can find a 1000w 48 volt brushless dc motor and use a 1000w max dc generator that outputs 48 volts, the generator would be spun using a petrol engine, to vary the speed of the electric motor, would I be able to just vary the rpm of the petrol engine turning the generator. also what high current switch could I use to disconnect the output of the generator from the motor. thanks
 

Ya’akov

Joined Jan 27, 2019
9,248
Welcome to AAC.

First, why do you want to use an ICE to run motors for propulsion? Yes, diesel-electric locomotives use that method but they are decidedly not bicycles or motorcycles.

Second, no—for many reasons it would be problematic to control speed by proportional control of the ICE. A dedicated ESC (Electronic Speed Controller) is the right way to deal with it, it also eliminates question your second question.

By the way, even if you wanted to use an ICE like this, the most sensible way would be to have it charge a battery, not to be the sole power source.
 

Thread Starter

toby woodman

Joined Apr 15, 2024
4
I don't really have a good place to charge batteries, and the price of good batteries that can handle the charge cycles are expensive, how could one control a brushless dc motor off a continuous 48 volt 1000w power supply.
 

Thread Starter

toby woodman

Joined Apr 15, 2024
4
Welcome to AAC.

First, why do you want to use an ICE to run motors for propulsion? Yes, diesel-electric locomotives use that method but they are decidedly not bicycles or motorcycles.

Second, no—for many reasons it would be problematic to control speed by proportional control of the ICE. A dedicated ESC (Electronic Speed Controller) is the right way to deal with it, it also eliminates question your second question.

By the way, even if you wanted to use an ICE like this, the most sensible way would be to have it charge a battery, not to be the sole power source.
this motor controller comes with the brushless e bike motor, could I plug the positive and negative output from the alternator into the wires for the positive and negative battery terminals on the controller, would it work?
 

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MaxHeadRoom

Joined Jul 18, 2013
28,780
In spite of the current ratings on automotive alternators, I would hesitate to run them continuous at their rated current,
I could only see peak and short term at some of the typical rating many have. ! :confused:
 

strantor

Joined Oct 3, 2010
6,817
If you have a good reason for trying to do what you are trying to do, you will get better answers if you articulate that reason. The people on this forum are like the technical people on any technical forum and if we don't see the point of the exercise then we don't get very engaged. If we see what we think is the point, and that point is a foolish one, we (collectively, not every individual) will not bother replying or if we do it will be half-hearted or maybe even downright unhelpful.

Let me tell you what this thread looks like from my perspective (and probably from the perspective anyone else reading): it looks like an ill-conceived attempt to improve efficiency of a machine by adding complexity that can only possibly (per the laws of physics) decrease efficiency. If that's not what the thread is, please clear the air.

The way a hybrid works to increase efficiency is by storing energy in a battery. No battery, no gain. A car (or motorcycle) only needs its published HP/KW rating to get up to speed. A 300HP car might only need 25HP to cruise at 60mph, but getting up to 60 (if you have a lead foot) is what the other 275HP are for. A hybrid car can have a much smaller engine because the electric motor helps it get up to speed. Smaller engine = better efficiency. The electric motor in a hybrid isn't getting its power from the engine, it draws its power from the battery. Once the car is up to a steady speed, then the engine works to recharge the battery. The battery also enables the car to recoup power from braking. (Technical people: yes, I grossly oversimplified and intentionally didn't discuss series/parallel hybrids. please read the room and don't drag the discussion into the weeds, KISS)

What you are talking about, a hybrid with no battery, is basically the world's most complicated, heavy, expensive, and wasteful bike chain. You're taking energy from the engine and transmitting it to the wheel by converting mechanical energy to electrical energy and then back to mechanical energy. Each of these conversions produces heat and causes energy loss. You bike will have less power delivered to the wheels and extra unnecessary weight of a motor and generator. There are better ways to get energy from the engine to wheel. Ways that transmit mechanical energy directly, with no wasteful conversions. Like, a chain for example. The same chain everyone has been using since forever, because it's a good solution. Way better than what you're describing. So what do you hope to gain by doing this? Please do tell.
 

PeteHL

Joined Dec 17, 2014
476
An ICE is more efficient if it is operating at a constant speed. So using an ICE running at a constant speed to generate electricity that operates the motor propelling the bike isn't a totally inefficient arrangement. I suppose this might be the motivation behind the diesel-electric locomotive. My vague recollection is that a diesel engine compared to 4 cycle engine is less suited to operating at different rotational speeds.
 

geekoftheweek

Joined Oct 6, 2013
1,249
One thing not mentioned is the effect of disconnecting a battery from the alternator while the alternator is charging which would in effect be the same as connecting a motor controller directly to an alternator, running the system at full load, then instantly letting off the throttle. It can be a disaster, but at the same time a lot of that will depend on how much power your motor is actually pulling from the system... anywhere from it's not going to matter all the way to your controller will be cooked after the first stop.

Long story short an alternator's magnetic field will not break down fast enough when you instantaneously remove a load and it will cause a hundred volt or so spike which will probably damage any controller you have connected. Since you are aiming for 48V it may be substantially more. Even with a battery connected you may have damaging spikes as you slow down / let off the throttle. Automotive electronics are generally designed with those conditions in mind... a generic motor controller most likely will not have the necessary protections.

While it sounds like a neat idea (believe me the thought has crossed my mind before just for the nerd factor) it's really not practical. I do understand though wanting to do it!!
 

geekoftheweek

Joined Oct 6, 2013
1,249
An ICE is more efficient if it is operating at a constant speed. So using an ICE running at a constant speed to generate electricity that operates the motor propelling the bike isn't a totally inefficient arrangement. I suppose this might be the motivation behind the diesel-electric locomotive. My vague recollection is that a diesel engine compared to 4 cycle engine is less suited to operating at different rotational speeds.
A good part of the motivation for a diesel electric locomotive is the immense mechanical stresses of getting thousands of tons of freight moving. A traditional transmission would probably be the size of a standard locomotive itself, and would need periodic maintenance and rebuilds. An electric generator and motor(s) on the other hand will run exponentially longer with much simpler maintenance procedures.

A diesel engine is a 4 cycle engine. The main difference between diesel and gasoline is in how the air fuel mixture is ignited along with a few other small differences. They both share the same 4 cycles. Smaller diesels can turn just as fast as their similarly sized gas relatives with the right design, but typically they run slower because of longer piston strokes, larger pistons, etc. that require slower speeds.
 

LowQCab

Joined Nov 6, 2012
4,218
A Train NEEDS and WANTS serious WEIGHT to get traction on the Rails,
so a ~4.5-TON Generator is actually a bonus.
That's a lot of Iron and Copper-Wire, which equates to higher efficiency.

This scheme just doesn't translate well to a ~20-pound Bicycle.

A Centrifugal-Clutch, and a Bicycle-Chain,
can't be beat for cost-effectiveness, and fuel-efficiency.

BTW, most, ( if not all ), Train Locomotives have massive 2-Stroke-Diesel-Engines,
so do many Semi-Tractor-Trucks.
.
.
.
 

WBahn

Joined Mar 31, 2012
30,252
The thread starter apparently has gone AWOL.
Perhaps, but it's a bit too early to make that call. After all, it's barely been half a day since they started the thread and less than twelve hours since their last response. People do sleep, go to work, watch movies, and otherwise have lives that aren't centered on responding immediately to every post in their thread.
 

WBahn

Joined Mar 31, 2012
30,252
An ICE is more efficient if it is operating at a constant speed. So using an ICE running at a constant speed to generate electricity that operates the motor propelling the bike isn't a totally inefficient arrangement. I suppose this might be the motivation behind the diesel-electric locomotive. My vague recollection is that a diesel engine compared to 4 cycle engine is less suited to operating at different rotational speeds.
You are mixing things that are not mutually exclusive.

Both gasoline and diesel engines (as well as other IC engines) can be either two-stroke or four-stroke). All four combinations have optimal operating speeds, but can work over a wide range of speeds.

The big motivation for locomotives using electric drives is the need to produce high torque at essentially zero rotational speed and do so for an extended period of time. Electric motors can be designed to do this very efficiently and robustly. Engines need transmissions and, for zero speed torque, friction clutches or fluid power couplings. For the power output that a locomotive needs, these would be huge, expensive, inefficient, and maintenance intensive.
 

geekoftheweek

Joined Oct 6, 2013
1,249
BTW, most, ( if not all ), Train Locomotives have massive 2-Stroke-Diesel-Engines,
so do many Semi-Tractor-Trucks.
I'm no train expert, but according to what I found in a quick search locomotive engines are a mix of both two and four stroke, and current production is all four stroke (in the U.S.). Two stroke semi engines went out with emission regulations. There has not been a new two stroke semi engine in the U.S. in decades. (1995 was the last year for Detroit Diesel's 71 Series). Those that still exist are old timers who are keeping them alive and farmers who just need a truck to use a few times a year. It seems Europe has followed in phasing out two strokes in most areas due to emissions regulations from what I could find.

It does look like two strokes are still popular in ships.
 

Janis59

Joined Aug 21, 2017
1,856
RE: << I am building a hybrid bike, I want it to work similarly to a diesel-electric locomotive >>
There is one small problem - car alternator have power efficiency between 20% and 25%. You ought to find much better alternator, best if on permanent magnets.
 
As someone who has rode and continues to ride bikes and motorcycles for 60+ years….. I would love for the thread starter to build such a contraption, he would be learning many engineering disciplines.

But the handling of such a contraption would be atrocious.
The only place to mount a motor-genset would be on a grille on top of the rear wheel.
Placing that much weight in such a high center of gravity and on an un-sprung wheel, and with a motorized unit capable of reaching much higher speeds (as compared to a pedal-only bike), the ride could be quite hazardous.
 
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