LED Conversion for Dynamo Driven Bike Lights

It was at the end of December in 2016 that the short days, rapid sunsets and long nights finally prompted me into some kind of action. My Bertin C 37 had been converted to a randonneuse by the previous owner who had added vertical dropouts, brazed-on centerpull pivots, dual bottle cages, cable guides and shifter braze-ons on the downtube. Oddly, he had not added provision for generator driven lighting which was mandatory, along with fenders, under the randonneuring rules at that time.

The bike was purchased from Mike Barry at Bicycle Specialties in Toronto and it was there that a generator braze-on on the non-drive seatstay was added and the frame was drilled for internal routeing of the wiring for the taillight. Honjo fenders were added (to allow wire routeing through the rolled edge of the fender) and provision was made for a combined tail light/reflector on the rear fender. I assembled the bike with a Soubitez 6V 3W bottle generator and a matching front Soubitez headlight with 2.6 W screw base front halogen bulb and a 0.4 W rear halogen bulb. The front light was attached to the left side Mafac brake pivot bolt via a custom Mariposa tubular cromo bracket. The headlight wire went back to the lower head lug, through a hole drilled in the lug and frame and out the drilled bottom bracket, up inside the rear fender edge and into the generator. The fender stay attachment shown in the taillight photograph is a custom Mariposa style stay which uses cromo tubing and braze-on fittings to produce a rigid, stable and rattle free attachment for the plastic fender light/reflector combination. The single taillight wire goes from the generator to the inside of the rolled fender edge and down the fender to the taillight housing.

The result of all that plumbing was not impressive even if state of the art for the period. There was a warm, yellowish light puddled on the ground about 3 meters in front of the bike and a nice bright taillight. There was a reason all those old French randonneuse bikes had big, D cell battery powered flashlights on their front racks.

Visibility for this rider was poor at best and the lights and rear reflector really just acted as markers to let other road users know I was out there. It was obvious that a lighting upgrade was necessary regardless of the fact that I seldom ride at night anymore.

There has been a great deal of progress with LED based bicycle lighting in the last decade but much of the “modern” headlight and taillight designs are aesthetically incompatible(read: ugly) with older, classic bicycles. So, the obvious thing to do was to search out some kind of LED lighting which would be retroactively compatible with my current Soubitez lighting.

One of the great benefits of the older style of halogen/incandescent lighting was the single wire format with the circuit ground being through the frame. So, what I needed was a conversion to LEDs that was a simple bolt-on or screw in with LEDs being available on line.

A simple on-line search was immediately fruitful. Compass Bicycles in the USA offers a red LED rear light in 0.35 W with a built in stand light feature. As well, a front LED conversion light was also available through Bikeco in the UK.  The NL 432 LED was rated at 120 Lumens and was compatible with the 6V output of the Soubitez generator. One of the drawbacks of the NL 432 was the necessity of using a regulator to avoid overloading the front LED. It was possible to add a regulator to the circuit but to keep the conversion simple, I deliberately chose to use the Compass rear bulb. This contains a built in standlight function which avoids the need for a regulator and allows a simple plug in and ride approach to the bulb conversions. Bikeco offers both screw-in and push-in LED bases to facilitate the conversion.

On the Bertin, the conversion was quite straight forward. The front Soubitez headlight levers open and the reflector pulls out as it is a simple friction fit. The bulb/LED base pops out

of the reflector and the halogen bulb unscrews and the LED screws right in. Note that the Bikeco LED has a conical projection on the top of the LED. This is a collimnator which disperses the LED light from the same point relative to the reflector that an incandescent bulb filament would. The rear LED is not configured like this as there is no need to worry about focus as there is with the front light. The standlight  circuit is integrated into the rear bulb base and once the bulb is screwed into the base there is no other action to take. My installation was easy as the rear light lens unclips from the reflector housing, the old bulb unscrews and the new LED simply screws in as a replacement. The lens just clicks back into place when LED installation is complete. The result looks just like this:


Road Test:

Once the bulbs were installed, the bike was taken out and test ridden. Once the generator was activated, the two LEDs immediately came up to full brightness. There was no gradual increase of intensity as I experienced with halogen bulbs just immediate full function with no fall off in brightness even riding slowly at walking pace. The slight hum from the generator was the same as previously with the halogen bulbs.

The beam intensity was significantly brighter than the previous halogen headlight but I still would prefer more light. The stock Soubitez headlight cast a bright spot in roughly the same area as the previous halogen lamp and threw some light down at the base of the front wheel. The headlight colour is a bright white light and is easily visible from the front. The light intensity is sufficient around town and gives sufficient light to the front if one travels slowly. It would be readily possible to out ride the light. There was no diminution of the light after a half hour ride which indicates there was no over volting of the LED.

Caveat: Consider that my comments about light intensity and visibility are filtered through 70 year old eyes which have reduced night vision capacity.

The taillight was excellent. The red light was highly visible from the rear (easily from a city block away  under street lights) and the standlight was at full brightness for seven minutes with lesser intensity for another four or five minutes. Outstanding.


The conversion is worthwhile if you need a classic style lighting system for intermittent use. If you are regularly commuting in the dark, I do not believe that this would be sufficient for your needs. It would definitely not be adequate for fast riding or downhill use on a road bike.



Bertin Generator Lighting

In the past, Bertin utility and touring bicycles came with built in generator powered lighting systems fitted by the Bertin factory. Whether they were an everyday bike like the sixties Bertin C 10 shown si Bertin mixte ebay frto the right  or the C 31 shown to the left below, they all carried seat stay mounted braze-on Bertin C 31 80s 11tabs for a 6 Volt, 3 Watt Soubitez generator as well as some form of taillight and a headlight as well. (Typically, also Soubitez.)

The tail light might be mounted directly to the generator braze-on tab as it was with plastic fendered  Cyclotouristes such as the C 117 or the   C 132. This was then complimented by a reflector on the plastic rear fender. In other cases, such as the C 116, the C 28, 29 and 31 the taillight and reflector were incorporated as an  integrated, single unit on the rear fender.

One exception to these methods was the 1980s Bertin C 134 which used a Sanyo bottom bracket generator attached to a brazed-on plate on the bottom of the chainstays directly behind the bottom bracket shell.Bertin Randonneuse 4

The front lights of plastic fendered bikes would have the headlight hung from a TA rack or one of the in-house provided chromed wire racks supplied by Bertin. The stainless steel or alloy fendered bikes might have the front light on a TA rack or mounted to the upper lip of the front, metal fender. The two photos shown above give clear examples of each method of attachment for metal fendered bikes.

TA Rack with Light Bracket Ebay

Photo Credit: Vintage NOS Bicycle Parts (EBay)

For those unfamiliar with the TA rack, various versions were made. There was a plain version without the dropped rod for mounting lights used just as a bag support, there was a dropped rod version with a threaded sleeve attached to allow screwing on a headlight and there was a third version with a dropped rod with no sleeve which permitted clamp-on light fittings to be attached to the rack’s dropped rod. All 3 TA racks were designed to mount to the pivot bolts and the mounting bolt of MAFAC center pull brakes.TA Rack With Light Bracket

I have used the version of the TA rack to the left attached to MAFAC  2000 center pulls brazed on to a Peugeot PF 40 and it was a very stable and effective light mount and bag support. No matter which of the two standard mount systems were used, the wiring was single strand of  insulated  20 or 22 gauge copper wire (.75 or 1 mm). My current C 37 has 1.5 mm wire and I have no idea why, although everything works perfectly.

If you are an owner of one of the various Cyclotouriste models, as a recent correspondent is who has acquired a NOS frameset, you may be Bertin brake braze onconfused by the holes drilled in your bottom bracket and your lower head lug (See photo with wire to the left). Whether your Bertin is also NOS or a stripped down version oldie lacking its original equipment, the purpose is the same. These holes are there to permit the routing of the single wire which will carry current from the generator to the headlight. The Soubitez generator needs only one wire because the frame or fender acts as the return path for the current.

The C37 Generatorgenerator itself has a spring tensioned connector/terminal at the bottom (see photo) where the wires to the headlight and  the taillight finish their cable runs. The wires are inserted into a hole in the generator terminal and spring tension clamps them when the fitting is released. The wires (I twisted mine to reduce snagging) emerged from a hole I drilled in the fender (these are aluminium Honjos) where they were either taped to the inside of the fender or were tucked into the curled fender edge (mine are tucked in).

The left wire began at the head tube lug and was fed into and down the down tube then out of the hole in the bottom bracket, into the fender, taped near the edge or tucked into the curled edge, then out of the hole in the fender. The right hand wire began by being fed through the hole near the bottom end of the fender, tucked into the fender’s curled edge or taped to the fender until it passed through the fender hole adjacent to the generator braze-on. Both are then attached to the generator terminal as shown. On plastic fendered bikes such as the C 117 the separate taillight mounts directly to the brazed-on stay tab with a wire going directly to the generator terminal. The headlight wire can be attached with electrical tape inside the rear fender after it emerges from the hole in the bottom bracket and is then attached at the generator using the spring loaded brass terminal. The black cap on the generator is a soft rubber cover for the hard plastic generator wheel. It stops the generator wheel from damaging the soft, thin sidewall of skinwall tires.

Your bike’s headlight can be a period correct piece like my Soubitez or one of the new varieties of halogen or LED headlamps. The Soubitez headlight shown here was wired for another application hence the 2 wires but it is otherwise identical to the one fitted to my C 37. It is Headlight # 1Halogen Bulb Basecurrently set up with a halogen bulb as is the headlight on my bicycle.

The original lights were supplied with standard incandescent bulbs (screw threaded base) and were retrofitted with halogens. In the left hand image the round bulb is OEM, the pointy one is halogen and the brake pad is for scale! The halogen gives a brighter but yellow-white light compared to the incandescents. LED conversion bulbs are available (I will be trying them in future) and are available through the Lake Pepin Tour site here (US) or through Reflectalite (UK) here.

Bertin Mariposa light bracket Power is directed on the basis of 2.4 Watts to the headlight and .6 Watts to the taillight. With halogen bulbs, exact capacities must be observed but LEDs allow more latitude in application. With incandescent and halogen bulbs, the front bulb must be 2.4 Watts and the taillight must be .6 Watts to avoid burning out the bulbs by over voltaging them. To the right is a photo showing the headlight setup on my   C 37 including the custom,Bertin - Jim front brake tubular cro-mo light bracket for the Soubitez headlight. Further details of the bracket and the wire run are shown to the left.

The taillight set up on that bike includes an integrated light/reflector combination bracket. This entailed drilling three holes in the fender. Two allowed for the alignment tab and the attachment screw and the third allowed the passage of the light wire into the fixture. The .6 Watt bulb screwed into the socket and compressed the copper wire ends making contact and Bertin - Jim taillightcompleting the circuit. If you  have a       C 117 or similar with plastic fenders then a reflector will be mounted here instead, especially if your are using Milremo or Bluemels fenders.

However, if you are fitting ESGE/SKS plastic fenders, these have a laminated construction with an aluminium core between a lower and upper plastic layer. With these fenders a combination fixture like the one shown can be fitted. I am uncertain as to whether it needs to be wired or can be powered through the alloy inner layer.

As an aside, you should be aware that fenders with mounting brackets inside the fender  tend to channel water out and over the fender edges casting more spray than fenders with exterior brackets as shown on my black C 37.

As always, since you are the builder/restorer you must make the decision as to how accurate you wish to be in your work. Period correct with dim incandescent bulbs is no fun on the road at night but just fine for a bike that is a wall hanger. You may wish to compromise and keep the look of the bike period correct but sneak in halogen or LED bulbs which boost performance. Alternatively, you may decide on a whole new, LED based system altogether. For further details and elaboration, I would recommend Peter White’s excellent site as well as Compass Bicycles although they do tend to emphasize hub generators.