five person pedal power generator help

[gestalt]

OK, so a pedicab friend of mine is part of a group putting together a DIY fest at ringer park in allston Massachusetts august 24th http://www.allstondiyfest.com. In years before they had a guy who brought a pretty nifty three hub motor powered generator to power a small stage. Well that guy isn't around this year so they asked me if i could help.

I don't have a surplus of hubbies but I do have a golden motor hpm5000b unused.

Model: HPM5000B -- High Power BLDC Motor Voltage:48V/72V/96V/120V Rated Power:3KW-7.5KW Efficeincy: 91% Phase Resistance (Milliohm): 6.2/48V; 12.0/72V; 36.0/120V Phase Induction(100KHZ): 68uH/48V; 154uH/72V; 504uH/120v Speed: 2000-6000rpm (customizable) Weight:11Kgs Casing: Aluminium Length (height): 126mm Diameter: 206mm Features: Compact design,Water resistent, Stainless Steel Shaft, Self Cooling Fan Applications: Electric car, electric motorcycle, electric tricycle, electric golf carts, fork lift, electric boat, etc

I figured I could take five doner bicycles that only need the cranks to work and weld them onto a frame that supports one long axle. Each bike would drive a cog on the axle which had a large chain ring that finnaly went down to the motor. Here's a pic of what I'm thinking.

The questions I would have would be

1. How burly, and what kind of three phase bridge rectifier would be needed?

2. How many deep cycle marine batteries would be needed?

3. What kind of charge controller?

4. Any good sources for a dc-ac inverter capable of powering a small stage?

There is going to be a benefit show thrown to raise money for this. As well as donations from organizers and some kind of crowd sourcing thing. There is a per diem fee work space that we can build it at and the current idea is that wheels will go on it so it can be towed by bike.

Any input would be appreciated.

 

[fechter]

Assuming you want to use a 12v system, 5 people x 300W = 1500W @12v= 125A

At 12v, you might not need to turn the motor very fast to get a lot of amps.

300W might be more than average people can do for a long time but Lance Armstron on steroids was rated somewhere around 600W continuous.

125A brige rectifier is going to need some cooling for sure. Going to a 24v system, current needs are cut in half. 24v inverters are available, but less common than 12v ones. 125A might overheat the motor, so higher system voltage will help there. 48V inverters exist too.

You could use a giant voltmeter that everybody looks at and instruct them to pedal less if it exceeds the desired set point (alternately 5 cheapie digital voltmeters, one for each person). Otherwise you'd need something that resembles a large brushed motor controller to use as a charge controller.

 

[Chalo]

I built something along these lines for a single rider, but there is no reason the system couldn't scale up.

I used a brushed DC scooter motor as a generator, but if you add a bridge rectifier, your system can work identically.

A 12V battery served as an energy buffer and a voltage setting device. I had two devices in between the generator and battery: a 12V electromechanical relay that switched on at some pedal speed corresponding to less than 12V, and a big power diode to prevent the system's battery driving the generator. I didn't trust the diode to keep the battery from leaking away, so I added the relay as a hard disconnect.

As you pedal, at about 8V the relay closes, and the voltage continues to rise with speed until it exceeds the battery voltage plus the power diode's forward voltage. At that point, juice begins to flow into the battery and pedal resistance rises rapidly against any increase in speed.

It works great. I added a plus/minus ammeter to monitor current into and out of the battery, and a voltmeter to allow the rider to ease up before the voltage rises too high for the battery. How big a battery is needed is more a function of the load than of the generator system. Bigger batteries can carry a bigger load longer without input power, and they provide a firmer resistance against overvoltage. But I'd expect one of my trusty Hawker Odyssey motorcycle-sized batteries to work just as well as a big truck battery for as long as it could carry the load. (The Hawker battery has power capacity similar to a big truck battery, but a smaller energy capacity.)

For your motor/generator, I'd gear it for a multiple of 12V and provide batteries, diodes, and relay to match the system voltage. It's just much easier to design the electrics for higher voltage and lower current, and the mechanical drive for higher RPM and lower torque.

I'd use self-aligning agricultural implement bearings-- pillow blocks or flange blocks-- to carry the shaft. I'd use probably a 1" shaft to reduce shaft flex and straightness issues.

 

[The fingers]

You could use a giant voltmeter that everybody looks at and instruct them to pedal less if it exceeds the desired set point (alternately 5 cheapie digital voltmeters, one for each person).

And add a guy with a switch behind the workline in case they fail to pedal fast enough. :lol: