Hi, I'm a little new to electronic wiring, but I have some high-school experience and I need some help with a project.

I have a bike that has a generator tire that powers two lights (a front and back light). The two lights are 6 volts each and wired in parallel. They are powered by a generator tire on the front, and the generator tire can output up to 18 volts at a high speed. The problem is that there is too much variance in the power. Going uphill the lights can dim too significantly, or if I'm stopped at a light they turn off entirely.

I want to add a 9 volt battery to the wiring so that it will provide constant power to the lights, and then charge the the battery with the output from the generator tire. I've been doing some digging on various sites on how a setup like this would work, but I'm coming up a little short on the specifics of what I would need to add to the wiring to include the battery. All I really know right now is that I should probably use a NiCad battery, and that I need a way to trickle charge it when it's not being actively used. Can anyone point me in the right direction?

 

I would suggest that you use a six-volt rechargeable battery and a DC-to-DC converter from the generator. The converter would accept a varying input voltage from the generator and output a near constant voltage of about 6.2 to 6.5 volts to keep the battery charged. Using a nine-volt battery would cause the light bulbs to burn out rapidly.

Check eBay for DC-to-DC converters. Most ship from China and cost less than $10.

 

I think the output from the generator tire is AC not DC. When my multimeter is set to DC it will have a positive then negative value varying, and when set to AC will provide a constant positive value. Does that change the solution at all?

 

Absolutely does change the situation. You will need a bridge rectifier immediately after the generator output terminal to change the AC to DC before sending it to the converter and/or battery.

If your generator is like the ones of my youth (LONG time ago) it only has a single terminal and "grounds" to the lamps through the bicycle frame. If this is true of your generator then you will also need to isolate the generator from the bicycle frame (sheet rubber between the clamp and the frame) and run an insulated wire from the generator bracket to the rectifier. Note that output polarity of the rectifier and input polarity of the converter and battery must be correct.

 

Sorry, I'm going to need a little more help again. It looks like there are two types of bridge rectifiers. A "Full wave" rectifier and a "half wave" rectifier. Which one will I need. It also looks like rectifiers are rated for watts and amperage, so I would want a 6 volt rectifier because it's going to a six volt battery or something higher since the generator it is converting from can potentially be up to 20 volts?


Edit: Also, this generator tire has two terminals a positive and a a negative, so I don't think I'm looking at the problem you described where the bike frame grounds it.

 

A bridge rectifier by its very nature is a full wave rectifier. You need one with a voltage rating at least twice as high as the peak-to-peak AC output of the generator; higher is better. I don't recall ever seeing a rectifier rated for wattage but yes, they are rated for amperage. I would suggest a 100 PRV, 15 ampere bridge as it is WAY oversize for your needs, electrically speaking and also dirt cheap. 15A, 100PIV Square Bridge Rectifier-MPJA, Inc.
(I have no interest with MPJA other than as a satisfied customer. Radio Shack and many other on-line merchants will have a similar rectifier.)

Are the terminals on the generator actually marked + and -? That would denote that it is a DC output. Do you have two wires going to both the headlight and taillight?

 

The rectifiers I was looking at all have a voltage and amp rating. See for example:

http://www.radioshack.com/product/index.jsp?productId=12681237

You are right, the terminals are not marked + and - . I can connect to the positive output and then use any metal to ground it, and it will work correctly. However, the wire is insulated and no part of it actually touches the frame of the bike. It's designed to plug the negative into the other terminal on the tire. I just confused it with a negative terminal.

So just to be clear on this whole thing:

Run the positive terminal through a rectifier, then connect the rectifier to a six volt DC to DC converter. Then connect the positive and negative leads of that to the positive and negative terminals of a six volt battery. Then have two more wires from the positive and negative terminals, and connect that to the positive and negative wires on the light wiring. Do I have that all correct?

Edit: sorry, I linked to the wrong thing.

 

If the generator is AC it does not have a positive terminal. It may have a terminal that is grounded to the equipment but that is technically not negative either because the polarity on the terminals changes many times per second.

 

I think I need a picture of your generator. I have no idea how you would "plug the negative into the other terminal on the tire."

This is what I am thinking of when someone mentions a generator bicycle lamp.

[ATTACH=CONFIG]2750[/ATTACH]
(Image courtesy of Shutterstock.com)

Notice it has a single conductor coming out of the bottom of the generator and that conductor goes to both the head and tail lights. The other side of the complete circuit is made through the bicycle frame and the clamp holding the generator in place.

Looking at another picture, this one a graphical representation of the generator it is clear that the output is indeed an AC voltage.

[ATTACH=CONFIG]2751[/ATTACH]
(Image courtesy of nordicgroup.us)

Although this representation shows both wires coming out of the generator in truth the most common method is to fasten the second wire to the generator housing. If you have two terminals check to see if they both have insulating bushings where they pass through the body of the generator. You can also do a continuity test between the generator body and the terminals. No continuity means that both terminals are isolated from the generator body and (most likely) the bicycle frame and you will have TWO wires going to each light from the generator. It might be two wires from the generator to the first lamp and then two wires from the first lamp to the second lamp.

You CANNOT use a simple (one diode) half-wave rectifier for your proposed circuit. Because of the way the generator is wired you cannot use a two-diode full-wave rectifier circuit. You MUST use a four-diode bridge rectifier circuit to get the proper voltage and also minimized the "AC ripple" that is inherent with single phase rectifiers.

Assuming you have a totally isolated generator output (no continuity to the generator housing) and two-wire connections to both lamps you would run two wires from the generator output terminals to the AC (may be marked ~) terminals on the bridge rectifier module and then take off the DC from the + and - terminals of the bridge rectifier. This DC voltage will be entirely dependent upon the speed of the generator, rising to maximum when going down steep hills and dropping to zero when you stop. By running the DC to a DC-to-DC adjustable power supply module the module will output a constant voltage to the lights within the constraints of the module and the input from the generator. By inserting a rechargeable battery (6 volt gelled lead acid) in parallel with the the module output and the lights you will have the lights work constantly (you will need to insert a switch to turn the lights on and off) and the generator will maintain the charge on the battery. It may be necessary to add a diode in one or both output leads from the module to prevent a back-flow of energy from the battery into the module's output when the generator's output is too low or non-existent.

Hopefully I won't get admonished by an over zealous moderator for the following links to a DC-to-DC module and a bridge rectifier. I have no connection to Suntekstore.com except as a satisfied customer.

LM2577S DC-DC Adjustable Step-up Power Supply Module - Free Shipping

Bridge Rectifier 50A 1000V GBPC5010 AC to DC - Free Shipping

The rectifier diodes you previously linked to at Radio Shack would be fine for the blocking diodes between the battery and the module output if needed. Six volt gelled lead acid batteries are sometimes available from the big box mega-mart homecenters. They are used in emergency exit lighting. They are also available from numerous on-line merchants.

 

It's not an external device setup on the tire. It's a generator tire:

[ATTACH=CONFIG]2753[/ATTACH]

The actual generator is housed in a container inside the tire itself. It has two terminals on the side of it, you can see in the picture here. The copper one is the actual AC output.


Yes, I understand which kind of rectifier I need to use, the one I bought is linked to in a previous reply, I just linked to the wrong one by accident, I updated it to the one I actually have. I just needed a run down of how this is all supposed to be connected.

 

Thank you for the clear picture! This helps us see what you're asking about.

I think this is what's been throwing us off. You've been referring to it as a generator tire instead of a generator hub or dynamo hub. We should be clearer going forward.

That said, and based on this picture plus other information in this thread, I'm guessing that you may have a Shimano DH-3D71 hub, with these features and specifications. Is that correct? If not, could you tell us the correct information?

In the meantime, to help you accomplish what you're seeking to do, do you think this regulator for a 6V/3W bicycle hub generator system might work?

 

I've never seen anything like that. I'm backing away from this topic.

 

Until the last picture, I thought this was one of those old vintage bikes. The last picture I see a quick release, and a rotor (disk brakes).

In all honesty, If it was myself, I would simply go with an aftermarket battery powered light and forget about the generator hub. As you mentioned light output is a problem. Adding a charging system to run a battery will a pain when it comes to water and waterproofing. These also add a fair bit of drag on your tire, making you work that much more.

It's been a while since I have messed with low voltage AC circuits. If it was DC, I would suggest looking at a simple capacitor bank which would help stablize the voltage a bit. It won't solve the shutting off when you stop, but it would help balance the power feed to the lights.
Are the lights a bulb or LEDs?

 

The generator hubs aren't common, but they are out there as commercial, ready-to-install products. A bit pricey, perhaps, but much nicer than the rub-on-the-tire kind you and I are used to.

The regulator, OTOH, is a grad student's DIY project.
Interesting topic, not the least of which is learning that the generator hub does, in fact, produce AC!

 

Um... Might have had a brain fart

OP, can you recheck your output and confirm it's AC or DC?
Thinking back to my LED rollerblade wheels back in the late 90's early 2000's, they simply had two magnets (axle and bearing casing).
If I'm thinking correctly, a couple capacitors in a waterproof housing would be enough to even out your power supply to the lights.

 

I think, if you check it out, that the schematic and the text for the regulator for a 6V/3W bicycle hub generator system confirm that.

 

I still think Furds solution is the simplest. The DC to DC converter would handle the regulation. If he just wanted to try capacitors maybe s full wave rectifier ahead of the capacitor. (Guessing only).

 

Yes, that is my tire!



Lordy lordy, that's my bike! Mine is a Raleigh Detour Deluxe, just like in that picture. I guess it doesn't matter what you want to do, someone's done it on the internet. [edit: whoops, that isn't a Raleigh. The paint job and frame is just similar. Got overexcited there]

I'm sure that the regulator he has here will work, although I'm not great at reading circuitry diagrams. Also, in his picture he's replaced the front light with two lights on either side of the basket, I'm not looking to replace the lighting system on mine, just supplement it. But, since the lights I use are 6 volts, the same as his, that shouldn't matter, correct?

 

Nor am I. Hopefully, another member will stop by who can help out with that.

AFAIK it shouldn't.

Glad it's starting to work out for you.

 

No that is your hub. Tire is the rubber part on the wheel that has a hub in the center. Correct terminology avoids confusion.

 

Murp, sorry. It's hub yes.

 

It'll take a BIG hamster to reach the pedals!

 

It really looks like one terminal of the generator is "grounded" to the bicycle frame. That will severely complicate matters but not make it impossible. I would still use the bridge rectifier feeding into the DC-to-DC converter and from there to the battery. From the battery run wires to a switch and from the switch to the lights. You WILL have to modify the lights so that they receive power ONLY from the two wires and have no electrical connection between the light bulb and the frame of the bike.

 

IMO I know this is DIY but that system is complicated.

I would either set up a seperate batery light system with a switch that you can turn on or off to suppliment. Not connected to your existing. They are pretty cheap.

But if it were myself I would go LED. Doing a quick search these last 50 hours on a charge on and 115 hours flash. ( 3AA each get the recharable type) Less then $20 bucks.

I would probably then figure a different use for that hub.

Bell Radian Bike Light Set (Black/Red): Amazon.com: Sports & Outdoors

Just my opinion.

 

What sort of voltage drop should I be expecting of the rectifier? When the hub is outputting 7 volts ac, it isn't giving me more than .6 volts dc.

 

None. It could be higher since the 7 volts is the mean voltage not peak inverse but wait for Furd to confirm.

 

Neveremind, I hadn't grounded the AC properly. I'm getting comparable voltage levels now.

 

A full-wave bridge rectifier will output about 65% of the peak input voltage. (I can't remember if it is 0.6333 or 0.6666.)

If you are "grounding" on the AC side then you need to be VERY careful to avoid any grounding on the DC side.