An Illuminating Subject


Dynamo lighting:  who hates it?  Almost everyone.  But virtually all vintage bicycles, except those wondrous vintage Raleighs with Sturmey Archer’s dynohubs, use sidewall or bottom bracket-driven dynamo lighting.


Soubitez dynamo with Margil roller

Today, I was finally connecting the wiring on the Mercier Meca Dural’s lighting system  – a project I have been putting off because, well, I hate dynamo lighting. The bike’s own original fork-mounted dynamo had long ago been lost, so I set up this nice Soubitez unit, shown above, which is very light-weight and free-spinning, as compared to its slightly older counterparts, shown below.


1941 Radios dynamo


1950’s Ducel dynamo


1953 EDELKO SELF dynamo

Lighting set-up is a project that I would rate right along side fender line adjustment and front rack mounting:  patience and resolve can be sourly tested as one works through the glitches and conundrums involving wiring routing, bulb wattage, voltage mysteries, and the absolute worst:  cutting electrical wires and clearing their housing so that they can be spliced properly to carry the current through the system.

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There are very few resources which adequately discuss how to set up a sidewall driven (or bottom bracket driven) lighting system. For the uninitiated, setting up the wiring on these old systems can seem daunting.  The most important aspect of the set up is insuring that the dynamo is positioned correctly so that a straight line can be drawn through the center of the dynamo, down to the center of the wheel’s drop out.  This will insure that maximum efficiency is obtained from these already inefficient devices.  Another mystery can be the wiring set up. Every dynamo needs a ground.  For vintage steel bicycles, the ground often existed automatically via the presence of a “ground screw” which contacted the steel frame.  The above illustrations are courtesy of Glenn’s New Complete Bicycle Manual.  They show how to set up the wiring, and how to position the dynamo.  Fortunately, the wiring part of these old systems is very simple:  hook one wire to the front bulb, one to the rear, and both into the dynamo.  These old systems are 6 volt/3 watt power that can easily be upgraded to LED lighting. One can apparently blow out the lights if going at very high speeds.  I haven’t had that experience yet, though.


3 wires through the lug braze-on: shifter cable, brake cable, and dynamo wire.

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Routing the dynamo wires across the bicycle’s frame can lead to frustration.  If you are really obsessive, you can make the whole thing look magnificent (clearly, I am NOT in this camp).  Ideally, you wrap the lighting wires wherever they can be wrapped, in this case around the brake housing. This Mercier Meca Dural has wonderful lugs which include many options for cable routing, so I ran them through one of the openings, and brought the wiring up across its sloping top-tube, to the front fork where the dynamo resides.  In between, I wrapped the wires around the front and rear brake cables.

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Amazingly, after changing out the wiring with something new and replacing a burned out front bulb in the Luxor 65 headlamp, the system worked!  Testing this out on the road will be fun, as this dynamo’s drag is significantly less than other’s I have tested.


Soubitez dynamo on 1977 Jack Taylor Tandem


Soubitez dynamo on 1973 Jack Taylor Touring


Busch and Muller Dymotec 6


If you really are interested in dynamo lighting for your own bike, you could consider using the more efficient Dymotec 6 from Busch & Muller.  I’ve had one of these around in my shop, but haven’t tried it out yet.  It is definitely lighter than any vintage dynamo I have handled.  However, I will also say that Soubitez dynamos appear to have the least drag among all the vintage dynamos I have tested.  I have two of these – each mounted on my Jack Taylor bicycles  – a 1973 Touring model, and and 1976 tandem.  They still work very well after all these years.


I do love the engineering quality of these old steel dynamos.  They are very pretty, but very heavy.  And, while I still hate dynamos, there are lots of reasons to love them. They can be disengaged whenever you want, so are only creating drag when lighting is needed.  They aren’t that much heavier than a hub dynamo, and are simple to add or subtract to an existing bicycle, without the complexity of a hub dynamo.  So, if you like riding vintage bicycles, maybe you will like dynamo lighting.

Lighting. Damn it.

peugeot late 40's headlamp

I have not been a huge fan of generator lighting.  Part of the reason is that I am loathe to do anything that would reduce the efficiency of my pedaling efforts.  And, I usually only have to ride at night during the winter months when the daylight is scarce.  Since my commute is 30 to 40 minutes each way, battery powered lights work fine for me.  Guilt can be assuaged by using rechargeable batteries, and further assuaged by using a solar powered charger.

The other reason may be that my few experiences with generator lighting involved very inefficient bottle generators on old clunky bikes that belonged to friends and that I would occasionally borrow to ride as a child (my own childhood bikes were generator-free).  While I was busy contemplating how the generator worked, I would get more and more fatigued trying to ride up the hill to my house.  These devices put way too much drag on the tire, so I banished them to my minds’ nether-regions for decades.

Adding fuel to my flame, generator lighting is also often part of the standard equipment on a production hybrid or city bike, with poorly designed too-bright optics, which are sold to the enthusiastic masses, who then point their lights straight ahead, proceeding to blind all oncoming traffic.  I cannot tell you how many times I have been blinded in this way, one time from behind by a rider who was naively drafting too close at dawn, with her big bright light aimed horizontally, and when I looked behind to set up for a 3 lane left hand crossing, her light literally shocked and blinded me to such a degree that I nearly lost control of my bike. And I could not see past her light to the traffic I would soon try to cross.  Needless to say, I missed that turn.

Recently, I needed to install lighting on a few bikes I was working on, all of which used sidewall driven generators.  That got me thinking about installing lighting on my Meral, since I have begun using it as my primary commuter. I thought long and hard about that, and researched the pros and cons of bottle generators vs. hub dynamos.  I even explored a new technology – the rim driven dynamo built by Velogical.

Soubitez sidewall dynamo

Soubitez sidewall dynamo

If you are not an electrical engineer, dealing with the set up of a bottle dynamo can seem challenging.  First of all, it is very difficult to find wiring schematics and instructions for sidewall-driven generators.  These, I learned, are not technically dynamos, which generate DC power, but  magnetos, which generate AC power.  The only vintage shop manual in my collection which had more than a passing mention of generator lighting was Glenn’s New Complete Bicycle Manual, which is actually one of my favorite manuals because it has extensive guidance on rebuilding internal hubs.

Reading through Glenn’s guidance (who, in my mind, I refer to affectionately as “Dr. Glenn”), it is not hard to accept the old saying that mechanics do mechanical things and electricians do electrical things, and never the twain shall meet.

In days gone by, pretty much all bicycles were steel, and could be grounded with a simple contact to the bare frame or some other steel component.  This fork mounted dynamo on the Peugeot Mixte 650b that I recently restored is a good example of that:

Ducel fork mount dynamo

Ducel fork mount dynamo

The horizontal screw at the mount point provides the needed ground for this system.  As I was setting it up, I didn’t worry about much of anything as I wired up the lighting to this dynamo.  Thoughts of resistors, amps, volts, ground wires, and wattage never entered my brain.  And, after I connected the wiring, everything worked perfectly.  In fact, this little dynamo puts very little resistance on the sidewall, and I had fun riding around on this bike with my lights blazing.

But, that is a vintage system which requires only 1.8 watts at 6 volts.  Enter the new times, where 3 watts and 12 volt systems are the standard. (Question:  what are watts and what are volts – don’t ask me!)

Do you need resistors, double wires, and ground wires?  How do you set up a new system?  As I mentioned before, I seriously considered setting up generator lighting on my Meral, and toward this end I purchased a front wheel which featured a Shimano Deore LX hub (model DH-T670-3N), mounted to a Velocity Synergy 650b rim matching my existing rims.

Shimano Deore LX generator hub

Shimano Deore LX generator hub

I sourced a headlamp and tail lamp from Harris Cyclery and proceeded to test the system prior to mounting to my bike, to make sure I understood the wiring requirements. Once I figured out how to make the wires connect properly to the hub, I was able to mount the wheel into my truing stand, give it a whirl, and watch the lights illuminate my shop.  I even generated enough power to engage the standing lights, which remain on when the bikes is not moving.  But what really shocked me was the amount of resistance in the hub whenever I switched the lamps to the “on” position.  I had already read about these hubs having their cones being too tightly adjusted, which turned out to be true, and had fixed that.  Yes, these hubs were adjusted way too tight from the factory.  After that, I expected to experience only modest resistance when engaging the lights.  Not so.  Not so at all.  So I mounted the front light and installed the wheel into my Meral just to see if I was panicking for no reason.  As it turned out, the resistance in these hubs with the lights engaged is totally unacceptable to me, and I immediately switched back to my original wheel and battery powered lights.

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I am still interested in rim driven dynamos, and in generator hubs which have less resistance than the Shimano hub I tested.  Those are spendy options.  So for now, I will happily re-charge the batteries for my lights on all my bikes, and sleep well at night.