I've searched the forum but have been unable to find any old threads to help me with my Dynohub. I was told I can check if the hub still works by spinning the wheel the placing a key on the screws: if it sparks, which it did, the hub functions. After connecting the wires, however, the lights do not illuminate. I read Sheldon and some other blogs, but the terminology alludes me. I do not anything about electrical maintenance. Can someone offer any feedback or links with diagrams that could help me troubleshoot these lights issues. Thanks all!

There are some wiring diagrams here:

https://hadland.files.wordpress.com/2012/07/sadbu.pdf

but i don't know if that'll be helpful. What light are you talking about? Have you checked the bulb(s)? Troubleshooting dynamo lighting systems can be a nuisance; you have to check every wire, every position of the switch, and so on.

Good to start at the source! Next check the ends of the wires where the bulb is. Same type of approach or use a test light. Keep in mind that you need two electrical paths. Think of it as to and from the gen. Some where in the circuit there is a break. The trick is to find out where it is. The obvious one is the bulb. Can you get it to light up with another source or use short wires from the gen to the two terminals on the bulb? If it doesn't light up, you can touch the ends of the wires while the wheel is spinning and check for a spark. No spark, bad wire.

It is a routine of finding where it works and where it doesn't to find the break.

It gets worse when the return or ground is the bike frame.

A common failure point is the contacts for the bulb and switch. Make sure these are free of corrosion. Test the bulb to make sure it isn't burned out. Then check all the wiring for continuity, and make sure the ground circuit is good as well.

Get a volt meter. You will find that there is voltage at the terminals on the hub, because your key already proved it. Move along the wires with the volt meter and find where the voltage does not reach.

The voltmeter also comes with an ohmmeter which is a continuity checker. I believe you can test a filament bulb, but I'm not sure. What kind of headlight are you trying to illuminate?

To add to what Tom said, get a voltmeter (DMM). You can get a basic cheap one at Harbor Freight. The one I linked will do everything you need (and more).

It includes an ohmmeter, which measures continuity and resistance. On a low scale (20 ohms), you should be able to measure the bulb resistance. The filament in the bulb should be a low resistance (probably 5 ohms or so). If it reads open, then the bulb is burned out. This is assuming a standard incandescent light bulb. An LED bulb is a diode, which conducts in one direction only.

Using the ohmmeter, you can also check the continuity and resistance of the complete wiring system. For example, you could measure the disconnected wires, wire to wire. An open reading will indicate a break somewhere in the system. Move on from there until you find the culprit(s).

I haven't checked the bulbs. How do I open the lamps to access them? Could they be replaced with a more powerful watt bulb or LED?

Perhaps, if you gave us some photos of the lights you're working with, we could address those questions.

A Sturmey Archer dynohub is rated 6v, 1.8w. Actual voltage/power depends on the speed the bike is moving. Sturmey Archer supplied bulbs that were optimized for that power source; using bulbs optimized for more powerful dynamo (most bicycle dynamos are 6v, 3.0w) will result in less light. LED's are of course a more recent development, and yes, LED bulbs are available. Unfortunately the lamps are designed around the original bulb, using a parabolic reflector to collect the light and direct it where you want it, and if the LED's light source is in the wrong place, the parabola will have the wrong shape for the purpose. So while you can replace the bulb with an LED bulb, which will give more light, it won't necessarily give better light.

I put an LED bulb in an old fashioned flashlight, the kind that used two D cells. The results were pretty poor, because the LED directs the light forward, and the parabola assumed that the bulb would spread light evenly in all directions.

I have successfully put modern LED headlights and tail lights on old dynamos but not old dynamo hubs. Two were the sidewall (aka bottle) dynamos, and one is the kind that goes where a kickstand goes. The results are every bit as I had hoped. Mechanical drag from these dynamos is greater than with dynamo hubs, but the light it produces is excellent. The advantages are cost, weight, and ease of installation.

[MENTION=73614]rhm[/MENTION]'s point seems to be that a modern LED headlight might not start producing good light until the power (wattage) reaches a certain point. I haven't worked with those old dynamo hubs, but these old dynamos I've installed seem to produce an excess of power. How much power do the modern headlights really need before they start doing a good job?

No. A lamp made for an incandescent bulb has a parabolic reflector that directs the light where you want it. if you replace that bulb with a different light source, even if it's more powerful (which an LED probably is), if the light source is not at the focal point of the reflector you will get less light where you want it.

I agree with your reason that parabolic reflectors and LED bulbs don't work well together. I'm asking you to clarify your point about LEDs optimized for 3-watt input. It appears that you are saying that the 1.8-watt output may be insufficient. Am I correct?

If the Dyno Hub only puts out 'X' W DC, thats all You got .. the Multimeter will tell .

Current ones Put out 3W6V, AC.. 2.4w front 0.6w rear, or 3w if no taillight load.



new LED headlights like B&M IQ2, the diode is facing down from the top,

its back attached to a heat sink..then re directed forward by the reflector

Yes, that is correct in some way, but I'm pretty sure it is incomplete. You'd be better off having it explained by someone who understands electricity better than i. Sheldon Brown has probably already f done so.

I do know that in Europe, where every bike has a sidewall dynamo, they sell 0.6w bulbs for the tail light and 2.4w bulbs for the headlight. It is common knowledge that if you burn out your tail light you must replace it immediately lest you overpower your head light bulb and fry that as well. I don't know if this is true. At any rate, those 2.4w bulbs are readily available and appear to fit Sturmey Archer lamps fine, but they produce a very weak light.

All the more reason to use a modern headlight. They have voltage regulation and won't burn out from excessive voltage. This is explained on Peter White's pages. I tested one of my sidewall dynamos and watched it put out 15v easily. Voltage is all over the graph. And these modern lights just don't care.

My wife and I took a ride at dusk last week. As often happens, I got pretty far ahead of her. I looked back and saw her B&M headlight screaming up the road to me. It is powered by a Sanyo BB dynamo. We haven't tested it in the dark yet, but as a be-seen light, it far exceeds my hopes.

I took the bike to a local guy who specializes in 3-speeds, and all he had to do was lower a large gold lever (I forget the name) that connected to the bulbs, and immediately the lights kicked on! After 56 years, the
hub still works!!! Who knows how old the
b s are, but I am blessed that they still illuminate
well! These bikes are resilient!

If the bulbs are not used and they don't experience vibration or high impact, the shelf life should be quite long.

That's good news.

You should see how many old three speeds are in my neighborhood in Manhattan. They've proven to be the most durable type of bike around, more than the old American one-speed coaster brake bikes with the fat tires.

The original bulbs on my 1955 Phillips still work, but not bright enough for me to find my way with.