Bike Regulator
Bike Regulator
Lighting Links

Regulator for a Hub Dynamo

This is a regulator for a 6V/3W bicycle hub generator system. The purpose is to manage the powering of bicycle lights from the hub generator and from rechargeable batteries, to charge the batteries using excess power from the generator, and to provide intelligent charging of the batteries from an AC adapter, when needed.
For a blown up view of the schematic click here.
Regulator Schematic


The switch has three positions: charge-off-light. In the charge position, the bicycle dynamo charges five AA NiMH batteries if those are drained. If the batteries are reasonably full, then the circuit draws virtually no power. In the light position, if the dynamo's average voltage is below some threshold value, then the bicycle lamps are fed by the batteries aided by the rectified dynamo If the dynamo voltage is high, the lamps are fed directly by AC from the dynamo and the dynamo excess power is used to recharge batteries. The direct use of AC maximizes efficiency. Additional circuitry is provided for an intelligent charging of the batteries from an outlet using a 12V AC or DC adapter. Practice shows that that additional circuitry may be redundant. A flickering green LED indicates the activity of the dynamo in the charge mode and the fact that the light is fed by AC in the charge mode. A red LED indicates the fast charge state when the charging is done from an outlet.
Circuit Details
Circuit Board
Complexity vs Efficiency

Regulator on the Bike

Regulator on Bike Closeup
I have not invented any universal way of mounting the regulator on the bike. In my situation, the most convenient placement was on the outside of the front wire basket. Presumably, my next choice would be a front rack or the fork.

The bike is Trek 730. My dynamo is a Schmidt, the older model that is not user serviceable. The front lamp is Bisy and the rear is DToplight (without a built-in standlight). Bisy is an excellent lamp. In my tests I found it two notches above Lumotec Halogen, with one notch separating Lumotec and Sigma. The philosophy which I follow is to have wiring that is serviceable by hands.



The regulator and a hub dynamo make a formidable combination. My previous spoke dynamo and electric regulator combination was good but not as outstanding as this one. The light delivery is uninterrupted. When the bike slows down, the light just dims a little before switching to the batteries. I often find myself checking the green LED in order to figure out what the main power source at a given moment is. Usually it is the dynamo that powers the light but, aside from of course slowing down to stop, the batteries often take over when riding uphill, in heavy snow, or in a heavy wind with rain.

Following the initial phase, after I removed the circuit protection, I had no problems of any kind with water. Many times already the bike stood for a full day in the rain and the circuit operated normally afterwards. Moreover, hosing the bike does not affect the circuit operation. The setup was mounted on the bike in May '00 and worked formidably throughout the serious winter.

So far I had no real need to charge the batteries from the wall. (I did that on a couple of occasions just making sure that everything works.) Riding in the daylight one way of my commute seemingly suffices to keep the batteries full. The neutral position of the switch practically got no use either.

After the above circuit, I designed a new one without a relay. In that circuit, the managing of power delivered to the lights from the dynamo and battery is done seamlessly using semiconductors, as is the delivery of power to the battery. At the same time, large electric currents encounter no single n-p semiconductor junction on their way, that would lead to losses. Zener diodes for limiting the power from the dynamo at high speeds are eliminated. A PCB version of that circuit just got over bench testing and now will get tested on a bike.


Being a complete amateur in the circuit design, without a clue what an operational amplifier was at the start or let alone a MOSFET, I benefitted a lot from designs made public by other people and in particular by Willie Hunt, Joe Gorin, and Steve Bush. The two last designs and several more were posted on the Net by Alex Wetmore who does much service to the cycling community by maintaining several lists at his site. I gained much information from the bikecurrent list (presently at Topica). Frequently asked questions for the bikecurrent list are maintained, in the true sense of the word, by William Burrow. Most direct help I received from Steve Kurt who faxed me his own schematic for a regulator and generously gave various type of advice. For my Bisy lamp I am grateful to Andreas Oehler.

Other Regulators for Dynamo Lights

  • Steve Kurt's circuits for a hub: a budget circuit - PDF schematic and construction by Brian DeSousa, a more complex circuit
  • 12V Standlight by Wolfgang Bergter
  • Dirk Glander's circuit with a lead battery (similar to Steve Kurt's circuit)
  • Steve Bush's circuit for driving two headlights from a Schmidt, another two-headlight circuit
  • Wolfgang Strobl's stand-light
  • Phil Endecott's backup for dynamo lights
  • An LED backup
  • Construction of two LED stand-lights is discussed in the mid-year (7/8) issues of the German Elektor for 1995 (designed around LM324) and 1999 (designed around 555).
  • My electric circuit

  • The commercial stand-alone standlights, that I came across, most took regular batteries. Available from the US had been the stand-light by Soubitez. Produced in the second half of 80s, it had been sold, for a low price, by Velo Specialite in Canada. It took 3 regular AA batteries to which it switched, for about 20 s, when the dynamo got idle. With the 3 batteries, the light was dim but bright enough to get you noticed. Two more stand-lights, Union and Friwo, are mentioned in de.rec.fahrrad FAQ, but they cannot be found on Friwo's or Union descendant's sites. (A photo of the Union Standlicht-Akku 8510 electronic can be found here.) I am also aware of a stand-light that had been marketed by Asista, a German supplier of bicycle accessories, taking in four 1.5 V batteries. Again, though, this stand-light cannot be found on the Asista's site and it does not seem present in the German stores. In the Toommarkt supermarket chain in Germany, I came across a no-name stand-light similar to the Soubitez and, to the best of my knowledge, to the Asista; for its schematic click here. This is the only one of which the production appears to continue. My Comments.

  • The Ellipsoid Plus light by Sigma came with an integrated stand-light based on batteries rechargeable without their removal. The circuit bears similarity to my electric circuit. That light has been disappointing in my experience. A possibly sturdier lamp with a backup is The Bird by Spanninga. A Jenymo bottle dynamo (look for it here) has a built-in 110mAh backup. When the dynamo is mechanically engaged, the backup keeps the light on with the same brightness as when powered by the dynamo. Unfortunately, that dynamo has a slippage problem. A backup is promised in the Lightspin dynamo, but there seem to be problems with rolling that version of the dynamo out. Patent description for Lightspin indicates just a 4.8 V backup with not very efficient circuitry.

  • Front and rear lights by Busch & Muller have LED backups drawing power from supercaps. Rear backups are good but front have been dim. The new LED front D'Lumotec topal by B&M is supposed to come out in a version with a cap backup. Following B&M, other manufacturers came out with backed up rear LEDs, as e.g. Spanninga with a supercap. A Hella rear LED lamp has, on the other hand, a battery backup. A battery backup is also apparently going to be provided in a version of the front LED HL 2000 Micro Tech dynamo lamp by the Hella. Byka front lamp, produced in the past, had apparently a battery backup that could be modified.

  • A standlight built into the rear LED light, RedLed by Roschko, that can apparently also power the headlight for about 2 min after stopping, is now avalilable from Yellow Jersey.

  • To simply limit the dynamo voltage at high speeds using Zener diodes see the page by Jim Easterbrook. Note: Halogen bulbs generally require a limiter and a Zener limiter is normally built into the halogen lamps (a bad exception: Jos halogen). A limiter of this type can be moreover purchased from Reflectalite and from OEG Products.

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