# Bicycle Power Generator

Discussion in 'The Projects Forum' started by alliag, Dec 31, 2007.

1. ### alliag Thread Starter New Member

Dec 31, 2007
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So I am in the process of making a bicycle power generator, but am confused with parts of the circuit and what will be required.
I am using:
1. a 12V (3ma i thin) CIM motor as the generator, it will be hooked up to a bike trainer stand. PEDAL POWER IS FREE

2. I am receiving a bunch of 12v rechargeable large capacity batteries for free. Now i know the addition of more than one battery will increase the voltage as well. Will i be able to charge the batteries through the twelve volt generator?

3. Next i figured i needed a transformer to drop the voltage down (from the voltage equal to the amount of batteries i get) to 12v for the power inverter.

4. The power inverter will finally convert the DC TO AC current and allow me to run standard outlet appliances.

So the additional batteries are only important because I want longer use out of them before they deplete and need to be charged again. But im not sure this will work due to the lower voltage needed for the inverter. So if anyone has any ideas please let me know. Feel free to critique or improve the circuit .

2. ### Ron H AAC Fanatic!

Apr 14, 2005
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Put the batteries in parallel, not in series. Then you will still get 12V. Each battery you add increases the number of amp-hours you can get from them, which is what you want.
This way, you won't need a transformer, and this is a very good thing, because transformers require AC. They won't work on DC.

3. ### SgtWookie Expert

Jul 17, 2007
22,183
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If your CIM motor is 12V 3mA, you will have to do a LOT of pedaling before you even generate enough power to light up a single standard LED.

Pedal power is not exactly free, the pedaler is going to want lunch eventually

Batteries: If they are connected in parallel, the voltage will not increase but the current will.
If they are connected in series, the voltage will nearly double, as will the current. (There is some loss due to the internal resistance of the battery which cannot be eliminated.)

In order to charge the batteries, you will need to supply them with a somewhat higher voltage than their rating in order to cause current to flow into them. You simply state, "12v rechargeable large capacity batteries" without mentioning the technology of said batteries. Lead-acid batteries are quite common, and can be charged at fairly high rates. Of course, you're not going to get that high rate using a 12V 3mA motor as a generator.

"Trickle chargers" have been used for a long time to recharge automotive batteries. They generally output somewhere between 1 and 1.5 Amperes, and they take a very long time to fully charge a typical automotive battery; sometimes a full 24 hours or even more (depending on depletion and battery capacity). If you're generating 12v at 0.003 amperes - well, you're not going to make much progress. You'll need quite a supply of sandwiches for the pedaler, though.

4. ### mrmeval Distinguished Member

Jun 30, 2006
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And lunch comes from the environment which is solar powered.

Wow

I eat my sunshine filtered through various life forms.

5. ### alliag Thread Starter New Member

Dec 31, 2007
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awesome thanks for all the help guys, ill keep you posted on the progress.

6. ### alliag Thread Starter New Member

Dec 31, 2007
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So i need help with one more thing....since the motor will be directly hooked up to the battery, i know i need a diode to prevent back charging on the motor....where can i find a diode big enough to handle 12v and a max of 100 amps of charge created by the motor.

7. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Ahhh, 100 AMPERES?

How in the world do you plan on getting 100 AMPERES at 12V from a motor that you previously stated as being rated at 3 milliamps? That's an increase of 33,333%.

I think you're a miracle worker

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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657
He's also a team of horses. 1200 watts is about 1.6 horsepower. That would probably stop his bike even if he were going downhill.

9. ### beenthere Retired Moderator

Apr 20, 2004
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I was in a science museum that had an exercise bike driving a generator. I was playing football at the time, but found it really hard to keep a 100 watt lamp lit for more than a few minutes (maybe 2).

10. ### alliag Thread Starter New Member

Dec 31, 2007
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first of all the 3 mA was a mistake...i was looking at the wrong specs and did not realize what i wrote. i know it doesn't make sense. The motor specs say its peak amperage output is 100 amps, it does not necessarily what i will be able to put out. As far as biking ability, I am an actual cyclist, i ride for two teams and am in very good shape...it is not odd for a cyclist to average 100 plus watts during an entire race. I am rusty will my electronics knowledge and thats why i came here, so help, rather than criticism would be appreciated.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Sorry, alliag. We like to have fun here, but it shouldn't be at others' expense.
I would use something like this. It's good for 20 amps, which I doubt you can exceed. If you think you need more current capability, there are other parts available, as well as other vendors. This is just one I found at Digikey.
Can your battery handle 20 amps charging current?

Dec 31, 2007
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13. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
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From what I can glean on the Internet, for 2 motorcycle batteries in parallel, you should keep the current below about 4 - 6 amps. You also should have a voltage limiter.

14. ### alliag Thread Starter New Member

Dec 31, 2007
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what would be the need for the voltage limiter with an inverter...the one i will be getting will be a 12v (dc) to 110v (Ac) with a 300 watt max. If the parallel batteries keep the same voltage, wont i been in track with the necessary voltage.

generator> diode > batteries> inverter> appliance?

15. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
That level of current limiting is to keep the batteries happy while just charging. Minimizes production of internal gas, etc. If you're running the inverter as you charge, then the concern might be to limit the charge rate to a couple of amps over the inverter draw. Overcharged batteries get hot and suffer irreversible damage.

16. ### alliag Thread Starter New Member

Dec 31, 2007
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im almost there in understanding everything. If someone wants to be super helpful and quickly sketch the full wiring diagram (including the diode) that would be greatly appreciated. Thanks for dealing with me so far.

again the circuit elements are

motor (generator)
diode
batteries
inverter
regulator

and just to clarify i do not plan on running appliances while powering...i will be putting a switch on either side of the battery so i have a charging circuit and discharging circuit.

Dec 31, 2007
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bump......

18. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
OK, I don't think we're quite done yet with all of the considerations.

How many of these batteries are you planning on connecting in parallel to charge?

I've seen two in your photos - you mentioned earlier that you may be receiving a quantity of them. The two you've shown appear to be the sealed lead-acid type.

Are they all the same size/capacity? Do you have part numbers for the batteries so that they can be verified?

Have you tested each battery to ensure that they will accept a charge?

With lead-acid batteries, sealed or not, eventually individual cells will cease to function, oftentimes shorting out at the bottom due to corrosion of the plates coupled with sedimentation, or due to sulphation of the plates. If after charging for a reasonable period of time (using a wall-powered battery charger) then removing the charger, wait for several hours, then measuring the batteries - if they don't measure at least 12.7V, they are no good and should be recycled. If you attempt to charge batteries that don't pass that test, you will be doing a lot of pedaling but I'm afraid your efforts will be wasted.

I suggest that each battery should have it's own regulator. While this might initially sound a bit absurd, it's really the only way that you can ensure that each battery receives only the amount of charging that it requires. As batteries age, various anomalies arise in the individual cells depending upon a variety of factors, including overcharging, allowing to stand in an undercharged state, excessive heat, excessive cold, etc. However, each regulator has it's own "tax", that is, dissipation of energy by heat due to voltage dropped across it. It seems that what is needed are low-dropout regulators or switching regulators using MOSFETs to minimize loss by heat.

There also needs to be an indication of the charging state of each battery. This doesn't have to be a constant indication to save on power; it could be an LED that fires intermittently. Persistence of vision on a 1/12 duty cycle 30Hz LED would make it seem to be constantly illuminated.

Additionally, management of the cells while they are in use needs to be considered. A 12v lead-acid battery is considered fully discharged at 10.4V. Switching in the cell array could be handled by power MOSFETS such as IRF1404's, IRF1405's, IRF1407's which all have extremely low Rds(on) (milliohm range) Vdss of at least 40, and current handling capability exceeding their TO220 package design (130A to 169A). They're also ridiculously inexpensive, at under \$2 apiece.

Failure to take things like these into account will result in less than optimal performance from the system, short battery life, and lots of fruitless pedaling.

Anyone else have other caveats that I've left out?

Ideas?

19. ### Newton1Law Member

Aug 22, 2007
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Go to a junk yard or an automotive supply house and get an alternator from or for a 12 v DC car or truck. This will have all the diodes and voltage regulation controls internal to the alternator. Hook up your bike to operate the alternator and connect it to your batteries and your already to go.

20. ### Audioguru New Member

Dec 20, 2007
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Like the guy who used a small computer fan on his bike to charge the battery for lights at night. He didn't know that the amount of power needed to charge the battery plus power the lights would be like dragging a huge parachute around behind him.

If you average 100W during a race then you will need to average much more to also charge the battery, or slow down but still use the same amount of effort.