Pedal powered generator anybody?

4745 Views 18 Replies 5 Participants Last post by Qmavam, Sep 10, 2010

bigwilly312

Discussion Starter · Sep 8, 2010

Sorry if this has already been discussed. I have a dc motor generator that produces 12v at 150 rpm. I'm hoping to mate this to an Etek style brushed motor that produces 8hp at 48v. This would be in a small lightweight trike for personal transportation. I would set it up almost recumbent bike style except the pedals would turn the generator at about 8 to 1 or 10 to 1 ratio. That would send power to the motor which would then turn the rear wheel. My question is would this generator motor be capable of handling the load placed on it? Would a blocking diode make any difference on this load? If not, I am prepared to accept plan B. Which is to insert four 12v batteries and use the pedal powered generator to simply charge them as I go. I would use some sort of slider throttle on the batteries for speed control. Sorry I don't have all the tech specs but would this work? It's not free energy if I'm pedaling.

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rillip3

· #2 · Sep 8, 2010

bigwilly312 said:
Sorry if this has already been discussed. I have a dc motor generator that produces 12v at 150 rpm. I'm hoping to mate this to an Etek style brushed motor that produces 8hp at 48v. This would be in a small lightweight trike for personal transportation. I would set it up almost recumbent bike style except the pedals would turn the generator at about 8 to 1 or 10 to 1 ratio. That would send power to the motor which would then turn the rear wheel. My question is would this generator motor be capable of handling the load placed on it? Would a blocking diode make any difference on this load? If not, I am prepared to accept plan B. Which is to insert four 12v batteries and use the pedal powered generator to simply charge them as I go. I would use some sort of slider throttle on the batteries for speed control. Sorry I don't have all the tech specs but would this work? It's not free energy if I'm pedaling.

This would work fine, but I'm not sure to what effect. To charge a 12v battery you need more than 12 volts (more like 15-16). Also, you'd only be able to charge one battery, but you would be pulling from four, so one of the batteries is going to die sooner.

It would also depend on how much amperage this generator makes at that speed. You'd need at least 2 A to get an effective charge going, and even then you're talking a slow trickle charge, extending range a bit more than charging it up for another trip.

It seems to me the best way to hook it up in parallel; that is, the system is only 48v, but when you're pedaling, the pull on the batteries is not as strong, some of the current is coming from you instead. This avoids unbalancing the pack, the higher voltage and amperage needed to charge a battery, and it increases efficiency too. Taking the pedal power and turning it directly into motion would be more effective still, but that engineering could be more difficult.

Woodsmith

· #3 · Sep 8, 2010

If you want to pedal a generator to power a motor to power your trike you would have a series of efficiency losses in each conversion of energy.

You would have a better efficiency if you wer to just pedal a chain drive to the drive wheel(s) and forget the motor and generator. It would also save you a fair bit of weight.

If you want an electric drive then the system could work with a battery pack.
But how are you going to charge a 48v pack running a 48v motor when you are only generating 12v?

Again it may be better to have a direct chain drive with a motor assist.
Can your 48v motor regenerate?

bigwilly312

Discussion Starter · #4 · Sep 8, 2010

Each turn of the pedals would turn the generator about 10 times. Depending on how I gear it. I could get as much as 40 to 1 but fear that pedalling would be much to difficult under any load. 60 pedals per minute is a standard leisurely amount I figure. That would be 600 rpms for the generator. That would add up to 48v at just a leisurely pedalling frequency. So the main question is the load capacity. It is a fairly high wind turbine motor that recommends a 75 amp blocking diode. The diode is supposed to prevent current from backing up into the generator. Would this prevent or at least decrease the load factor? Without the batteries, the speed of the pedalling would determine the speed of the tribe. That would make for a much simpler setup obviously. I've watched videos with this motor and 48v appears to give about 50 mph. Not bad for a leisurely cruise.

Qmavam

· #5 · Sep 8, 2010

bigwilly312 said:
Each turn of the pedals would turn the generator about 10 times. Depending on how I gear it. I could get as much as 40 to 1 but fear that pedalling would be much to difficult under any load. 60 pedals per minute is a standard leisurely amount I figure. That would be 600 rpms for the generator. That would add up to 48v at just a leisurely pedalling frequency. So the main question is the load capacity. It is a fairly high wind turbine motor that recommends a 75 amp blocking diode. The diode is supposed to prevent current from backing up into the generator. Would this prevent or at least decrease the load factor? Without the batteries, the speed of the pedalling would determine the speed of the tribe. That would make for a much simpler setup obviously. I've watched videos with this motor and 48v appears to give about 50 mph. Not bad for a leisurely cruise.

I don't think your legs are strong enough! Let's say your system is 80%
efficient, and you only want to get half the power your motor will deliver.
That's 4 hp out, with an input of 5 hp, how long can you put out 5 hp?
The motor is designed to put out 8 hp continuously, (I hope).
You could probably get 12 or 15 hp on a peak demand.
Put in some batteries, then if you want to pedal to supply some
charge to the batteries you can, but it won't be much.
I think it will be a strange sensation to pedal your fastest and not
have the bike speed increase.
MikeK

bigwilly312

Discussion Starter · #6 · Sep 8, 2010

You could be correct. I envision this as a good way to exercise while saving the planet as well. So, at the very least, this is very possible in some configuration. I needed to know that before taking the plunge into the wallet for this Etek motor and whatever else is needed. With an onboard pedal powered generator to charge the batteries, a person could think about using it in a 2 seater trike or maybe even a regular passenger car ev. Have you ever heard the expression "nobody rides for free"? You do your normal driving and your ride along companion does all the pedalling. You could greatly extend your driving range and maybe your wife will shed a few pounds in the process. Sounds like a win win to me

I just hope my wife doesn't read this.

Qmavam

· #7 · Sep 8, 2010

bigwilly312 said:
You do your normal driving and your ride along companion does all the pedaling. You could greatly extend your driving range and maybe your wife will shed a few pounds in the process. Sounds like a win win to me I just hope my wife doesn't read this.

Ya, my wife might shed a few pounds and your wife may not be happy
with you riding with my wife!

MikeK

rwaudio

· #8 · Sep 8, 2010

bigwilly312 said:
Each turn of the pedals would turn the generator about 10 times. Depending on how I gear it. I could get as much as 40 to 1 but fear that pedalling would be much to difficult under any load. 60 pedals per minute is a standard leisurely amount I figure. That would be 600 rpms for the generator. That would add up to 48v at just a leisurely pedalling frequency. So the main question is the load capacity. It is a fairly high wind turbine motor that recommends a 75 amp blocking diode. The diode is supposed to prevent current from backing up into the generator. Would this prevent or at least decrease the load factor? Without the batteries, the speed of the pedalling would determine the speed of the tribe. That would make for a much simpler setup obviously. I've watched videos with this motor and 48v appears to give about 50 mph. Not bad for a leisurely cruise.

I have a feeling that you are leaving current out of the equation, 48v by itself is 0 watts 0 hp 0 in any measure of power, you also have to consider the current required to make that power, to get the theoretical 8hp (ignoring losses) you want that is roughly 8x746 = 5968watts/48v = 124 Amps

As per wikipedia on human power an average person can develop 200watts for over an hour. An elite cyclist can generate "an instantaneous maximum output of around 2,000 watts" the 200watts for an hour is far from the 5968 watts required for your 8hp and we haven't even considered losses in the system.

So in short, you NEED batteries to make up the other 120 Amps since you will be able to generate about 4Amps at 48V with a lot of work.
(I'm sure you wouldn't need the full 8hp at all speeds, however during acceleration and high speed you will need most of that power)

bigwilly312

Discussion Starter · #9 · Sep 8, 2010

Qmavam said:
Ya, my wife might shed a few pounds and your wife may not be happy
with you riding with my wife!
MikeK

Sorry MikeK. I didn't mean to imply that your wife needed to shed a few pounds. That's certainly how it read though. I meant our wives in general. I'm starting to think the parallel suggestion seems like the way to go. I appreciate everyones help but still no answer to the blocking diode factor. Just wandering. If it's job is to block power from draining back into the generator, would it not block the load? Or some of the load?

rwaudio

· #10 · Sep 9, 2010

bigwilly312 said:
Sorry MikeK. I didn't mean to imply that your wife needed to shed a few pounds. That's certainly how it read though. I meant our wives in general. I'm starting to think the parallel suggestion seems like the way to go. I appreciate everyones help but still no answer to the blocking diode factor. Just wandering. If it's job is to block power from draining back into the generator, would it not block the load? Or some of the load?

A diode is a semiconductor device that only allows current to flow in one direction. There is a small voltage drop across the diode in the forward direction, between 0.2 and 0.7 volts depending on the type. The 75A rating is the amount of current that can pass through it safely, often this is a maximum rating that requires a suitable heatsink to achieve and it is usually better to stay away from the maximum for reliability. There will also be a reverse voltage rating which is the maximum reverse voltage that the diode can block. IE if the diode was on your generator the diode must block the maximum ripple voltage from the battery/motor system. So the diode will "block" a small portion of the power from the load if you want to look at it that way. There will be power disipated within the diode based on ohms law V=IR where v is voltage, I is current and R is resistance, P=IV is derived from ohms law where P is power, I again is current, and V again is voltage. The power lost/blocked/disipated in the diode can be calculated by the forward voltage drop of the diode times the current through the diode. So a diode with a 0.7 volt drop at 75amps will disipate 52.5watts, if the generator put out 48v as you had hoped the voltage to the battery would be 47.3v.

Sorry if it's a bit confusing and I jumped around too much it's been a long day I know how it works but I might not explain it clearly. Looking up diode in google or wikipedia might help you understand what it does and what it is used for. There are also many types of diodes with many applications and uses.

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bigwilly312

Discussion Starter · #11 · Sep 9, 2010

rwaudio said:
A diode is a semiconductor device that only allows current to flow in one direction. There is a small voltage drop across the diode in the forward direction, between 0.2 and 0.7 volts depending on the type. The 75A rating is the amount of current that can pass through it safely, often this is a maximum rating that requires a suitable heatsink to achieve and it is usually better to stay away from the maximum for reliability. There will also be a reverse voltage rating which is the maximum reverse voltage that the diode can block. IE if the diode was on your generator the diode must block the maximum ripple voltage from the battery/motor system. So the diode will "block" a small portion of the power from the load if you want to look at it that way. There will be power disipated within the diode based on ohms law V=IR where v is voltage, I is current and R is resistance, P=IV is derived from ohms law where P is power, I again is current, and V again is voltage. The power lost/blocked/disipated in the diode can be calculated by the forward voltage drop of the diode times the current through the diode. So a diode with a 0.7 volt drop at 75amps will disipate 52.5watts, if the generator put out 48v as you had hoped the voltage to the battery would be 47.3v.

Sorry if it's a bit confusing and I jumped around too much it's been a long day I know how it works but I might not explain it clearly. Looking up diode in google or wikipedia might help you understand what it does and what it is used for. There are also many types of diodes with many applications and uses.

Well sir, you are the man! I wish my temperal lobes could make out with your cerebellum. I could possibly gain some much needed knowledge perhaps. Thanks to everyone for your help. I will now get on my knees again and pray for alien technology to fall in my lap.

rwaudio

· #12 · Sep 9, 2010

Well don't give up, just keep learning and you'll be able to build something that works nicely. I've been contemplating building a trike as well but it would definatially be a parallel hybrid to assist traditional pedal power.

Unfortunatially there's that stupid "law of conservation of energy" that says you can't create or destroy energy only transform it. That and "gravity" really can make our lives difficult sometimes.

I hear ya on the alien technology, I would like a new "battery"

bigwilly312

Discussion Starter · #13 · Sep 10, 2010

I just have two more questions. Is it possible at all to have the pedalling speed activate the batteries to then send power to the motor? Say I pedal up to a 12v to 15v range and then battery #1 is engaged and so on. I'm just trying to avoid using my hands for anything other than steering. I don't know maybe a floating throttle that's based off the voltage sent to the charger. Also all brushed motors just need voltage applied right? This Etek style motor sight keeps suggesting speed controllers.

G

· #14 · Sep 10, 2010

I hear ya on the alien technology, I would like a new "battery"

Lithium will do nicely. It is the NEW battery.

G

· #15 · Sep 10, 2010

Check out this site. Just follow a similar lead and go for it. It works and maybe you can create something like it.

http://humancar.com/

Watch all the video on this cool concept car that actually works. Human powered electric drive vehicle. No large battery packs needed with this one.

bigwilly312

Discussion Starter · #16 · Sep 10, 2010

gottdi said:
Check out this site. Just follow a similar lead and go for it. It works and maybe you can create something like it.

http://humancar.com/

Watch all the video on this cool concept car that actually works. Human powered electric drive vehicle. No large battery packs needed with this one.

That's what I'm talking about! Thanks for the info. To get past some energy hurdles might require us to do more than set there while talking on a cellphone and drinking a slurpy. Maybe the best untapped power source is us.

rillip3

· #17 · Sep 10, 2010

gottdi said:
Check out this site. Just follow a similar lead and go for it. It works and maybe you can create something like it.

http://humancar.com/

Watch all the video on this cool concept car that actually works. Human powered electric drive vehicle. No large battery packs needed with this one.

That's pretty freaking cool. I hope it comes around to production, but in the mean time I think DIY is the only way to actually get something in your hands. The Aptera, this thing, all seem to be perpetually around the corner. :/

My one concern would be with an accident. Seems to me that pole could mess up your internal organs pretty badly.

rwaudio

· #18 · Sep 10, 2010

gottdi said:
Lithium will do nicely. It is the NEW battery.

How about a pack the same size as my gas tank with even 1/4 or 1/2 the range of the ICE version. With 20C charge/discharge rating, not to mention a source from the "grid" to charge at that rate.
Ya that's dreaming

However I will probably be buying TS 200ah cells for my Porsche, and I'm sure I will be happy with them.

Qmavam

· #19 · Sep 10, 2010

bigwilly312 said:
Sorry MikeK. I didn't mean to imply that your wife needed to shed a few pounds. That's certainly how it read though. I meant our wives in general. I'm starting to think the parallel suggestion seems like the way to go. I appreciate everyone's help but still no answer to the blocking diode factor. Just wandering. If it's job is to block power from draining back into the generator, would it not block the load? Or some of the load?

I was just trying to be funny about the wives. (maybe it didn't work

I would think a generator would be a load if the output voltage is lower than the battery voltage. But it seems to me it will not be as simple as you want to make it. You would probably need a regulator for the generator. I think alternators are better at low rpm (research that) and they have built in diodes.
You sound like you want to run the motor without a controller, again I think you are trying to over simplify.
Everything you want to do can be done, but you need to keep reading and learning to see how it can be done.
I have seen some projects using motors and controllers used in R/C cars,
planes and helicopters that look good. The prices are cheaper for the R/C units. That might be a starting point.
I followed this group a couple of years ago when I wanted build an electric gokart. I picked up enough to build the cart shown here.
http://www.youtube.com/watch?v=5MKjbXltAew
I have since installed the deep cycle batteries and just recently put on a
new motor. I finally let the smoke out of the old one.
MikeK

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