Hooking up 12v 13w TV to exercise bike

Thread Starter

.paul.

Joined May 20, 2019
3
I'm considering adding a TV/DVD to my exercise bike. The TV requires 12v and 13w to run. I'm asking how to generate 18w at 12v dc from my exercise bike. I can get 12v bicycle generators that output 6w. These are the type that run from a bike tyre. I could probably run something similar from my exercise bike, but i need 18w output.
 

dendad

Joined Feb 20, 2016
3,006
I have seen a Fisher and Paykel washing machine motor mounted on an excercise bike. That is the way I would go. Then you just run a universal switch mode power supply on the 3 phase rectified output as if it was the mains voltage. This will produce high volts out so treat it like mains power!

Or you could rewire the motor and run like this......
 

Tonyr1084

Joined Sep 24, 2015
3,578
My point is that it isn't as easy as you might think. I've ridden bikes with those generators. They're like dragging a dead horse behind you. Two of them will be that much more difficult. And no matter what source of generation you use - the bottom line is you will get as much energy out of it as you are able to put into it (pedal) for as long as you are able. And you have to maintain a minimum (or better) RPM. The larger the exercise wheel the greater the torque required to spin the generator.
 
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Thread Starter

.paul.

Joined May 20, 2019
3
I have seen a Fisher and Paykel washing machine motor mounted on an excercise bike. That is the way I would go. Then you just run a universal switch mode power supply on the 3 phase rectified output as if it was the mains voltage. This will produce high volts out so treat it like mains power!

Or you could rewire the motor and run like this......
Thanks for the reply, but i want to keep this as small scale and simple as possible. I only need 12v DC.
 

Tonyr1084

Joined Sep 24, 2015
3,578
"Robert" was able to maintain approximately 700 watts for one minute. Your TV draws 13 watts. The video proves that Robert could watch a 53.8 minute TV show. He'd miss the end. Can you match Robert's ability?

700 ÷ 13 = 53.846.

If you're able to watch an entire show (one hour) you'll be competing in Olympic Bicycling soon. Even a half hour show is going to take a lot out of you.

Feasible? I'm sure you can pump the pedals for some period of time - depending on your level of fitness. Me? I think I'd last maybe 10 minutes. It might prove to be a good workout. But instead of a TV I'd power a fan to keep me cool.

Not trying to rain on your parade. Just preparing you for what may very well be the outcome.
 

Bernard

Joined Aug 7, 2008
5,262
A well conditioned biker should be able to maintain 248 W for an hour. I would pick item no 10-2521 from SURPLUS CENTER, 1/11 HP, PM,
12 V, 2820 RPM with 1.75 in. pulley riding on 28 in wheel . A belt drive might be better than friction?
 

MisterBill2

Joined Jan 23, 2018
3,874
My experience with bike generators has been that they have poor regulation, or none at all. So you may damage the TV running it on one of them. ALSO, the generators for bike lighting put out AC, and the TV wants DC, so you will need to do a bit of work on that part as well. So get a 12 volt brush type blower motor from a automotive heater/AC, and use that for the DC generator. But you will still have the brush noise without a good filter. Probably an analog voltmeter will help hold the speed constant.
 

crutschow

Joined Mar 14, 2008
23,348
How about using a vehicle 12V alternator?
Get one with a built in regulator.
The most efficient belt connection, is those that use a flat, toothed timing belt.
Adding a small SLA battery connected to the output will allow you to watch while you slow down or rest.
 

MisterBill2

Joined Jan 23, 2018
3,874
How about using a vehicle 12V alternator?
Get one with a built in regulator.
The most efficient belt connection, is those that use a flat, toothed timing belt.
Adding a small SLA battery connected to the output will allow you to watch while you slow down or rest.
That would certainly work very well, but the last timing belt I bought cost over $30, so suddenly the project is neither simple nor cheap.
 

mvas

Joined Jun 19, 2017
538
"Robert" was able to maintain approximately 700 watts for one minute. Your TV draws 13 watts. The video proves that Robert could watch a 53.8 minute TV show. He'd miss the end. Can you match Robert's ability?

700 ÷ 13 = 53.846.

If you're able to watch an entire show (one hour) you'll be competing in Olympic Bicycling soon. Even a half hour show is going to take a lot out of you.

Feasible? I'm sure you can pump the pedals for some period of time - depending on your level of fitness. Me? I think I'd last maybe 10 minutes. It might prove to be a good workout. But instead of a TV I'd power a fan to keep me cool.

Not trying to rain on your parade. Just preparing you for what may very well be the outcome.
Actually, the video proved that Robert can generate enough energy, 21 Watt-Hours, in approx 1 Minute,
which would allow Robert to watch a 1 hour and 37 minute show on a 13 Watt TV.

There are not many people, who can do what Robert did, in approx 1 minute.
Robert generated the energy 100 times faster than required for a 13 Watt TV.
In the real world, we do not have to generate the energy as fast as Robert did.
Most people can easily generate 13 Watt-Hours in 1 hour.
So no, we are not competing with an Olympic Cyclist.
 

wayneh

Joined Sep 9, 2010
16,102
The good news is that getting 18W from pedaling an exercise bike is completely reasonable. It'll add significant resistance to the pedals it and wouldn't be practical for normal bike riding, but it's OK for this application.

The bad news is that all such projects, including windmills, suffer some of the same design challenges:
  • Power varies with RPM, so regulation is required. Sounds simple enough but it's a huge problem when your load is roughly constant but the supply is variable. In your case it's not too hard to solve this problem with electronics. For instance a car varies the voltage to the alternator windings to maintain an output voltage. If "too much" power is available, the windings get less current and the output power of the alternator is reduced. We also have buck converters that can accept a wide range of inputs and efficiently deliver a steady output.
  • Cutout rpm. This is the RPM which must be reached for the system to produce usable power. If you're TV requires 13W and the electronics waste 2W, you need 15W before you can watch TV. You could ride all day at 10W and it ALL goes to waste.
  • Generators/dynamos need higher RPM than humans (or windmills) make. This means you almost always need some sort of mechanical advantage - gears or pulleys - to adapt the human to the generator. The bicycle dynamo accomplishes this by running a small wheel against the large bicycle wheel to get a significant RPM increase. Many similar projects use pulleys and belts, but that's not super practical for your project.
  • Storage. Without some storage, the load dies every time there's a drop in the supply.
These can all be (and have been) solved, but not without some cost and complexity.

One thought: There are e-bikes with regenerative braking, meaning they can capture rolling energy to put charge back into the battery. If you could get your hands on that part of the bike, it might be a nicely engineered solution.
 
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MisterBill2

Joined Jan 23, 2018
3,874
The good news is that getting 18W from pedaling an exercise bike is completely reasonable. It'll add significant resistance to the pedals it and wouldn't be practical for normal bike riding, but it's OK for this application.

The bad news is that all such projects, including windmills, suffer some of the same design challenges:
  • Power varies with RPM, so regulation is required. Sounds simple enough but it's a huge problem when your load is roughly constant but the supply is variable. In your case it's not too hard to solve this problem with electronics. For instance a car varies the voltage to the alternator windings to maintain an output voltage. If "too much" power is available, the windings get less current and the output power of the alternator is reduced. We also have buck converters that can accept a wide range of inputs and efficiently deliver a steady output.
  • Cutout rpm. This is the RPM which must be reached for the system to produce usable power. If you're TV requires 13W and the electronics waste 2W, you need 15W before you can watch TV. You could ride all day at 10W and it ALL goes to waste.
  • Generators/dynamos need higher RPM than humans (or windmills) make. This means you almost always need some sort of mechanical advantage - gears or pulleys - to adapt the human to the generator. The bicycle dynamo accomplishes this by running a small wheel against the large bicycle wheel to get a significant RPM increase. Many similar projects use pulleys and belts, but that's not super practical for your project.
  • Storage. Without some storage, the load dies every time there's a drop in the supply.
These can all be (and have been) solved, but not without some cost and complexity.

One thought: There are e-bikes with regenerative braking, meaning they can capture rolling energy to put charge back into the battery. If you could get your hands on that part of the bike, it might be a nicely engineered solution.
The solution for the variable energy delivery has already been suggested, which is a small battery, perhaps a 3 AH gel cell. The cut-in threshold and the speed increase are both handled by the speed step-up provided by driving from the big bike wheel to the small generator pulley. And that alleged regenerative function on e-bikes is rather fictional, at least in my experience with a cheaper E-bike. In fact, it was a total fabrication, an outright lie. So an alternator plus diodes or else a PM dc motor will do the job without much problem. The main challenge will be getting the high-traction surface on the generator/alternator drive wheel.
 

wayneh

Joined Sep 9, 2010
16,102
I suspect that what the TS is hearing is, "forget it". The ready-made solutions are all under 10W and beyond that, it's a fairly ambitious DIY project.
 

MisterBill2

Joined Jan 23, 2018
3,874
I suspect that what the TS is hearing is, "forget it". The ready-made solutions are all under 10W and beyond that, it's a fairly ambitious DIY project.
I would certainly not suggest giving up, since it is certainly a possible project. What we need is a picture of the exercise bike that the TS wants to add the generation ability to, since there is a wide spread of kinds. AND some of those bikes include a generator.
 

crutschow

Joined Mar 14, 2008
23,348
A flat-belt pulley vehicle alternator, could possibly be directly driven from a bicycle tire by friction.
Wrapping the pulley with electrical or duct tape might improve the contact friction.
The pulley could be held against the tire with spring tension.

A vehicle junk yard could be a cheap source for such an alternator.
 
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