To discuss the electrical issue with some textbook motor and generator theory. All so-called bicycle dynamos are really alternating current generators they have no brushes and they are identical to many electro-mechanical mains voltage timers motors such as used to be used in central heating timers. Some such as a hybrid stepper motor have two (four), three or five phases and operate at low speed. This type of motor or generator is called a single phase permanent magnet synchronous motor or generator.
Two addendum's at the bottom of this page;
- A bicycle dynamo light and battery manager with a speedometer design idea. It interfaces by USB cable.
- There are some reference to magnetism, motors as generators.
voltage will drop sharply. There are other factors and the voltage drops as the current increases in the real dynamo.
Lightly loaded the dynamo is the same as a tachometer and makes a good speedometer.
The patent is dated 1936 - I found it difficult to understand. I would appreciate your comment below.
Tests below show that after re-magnetisation that the dynamo behaves as a fairly constant current source and the open-circuit voltage output increases with speed. Therefore the diagrams are roughly correct.
The magnet will demagnetise if separated from the armature so if you remove the armature you need to replace it with a keeper such as another armature. A magnet keeper is a piece of soft iron that conducts magnetism very efficiently. Mu-metal that transformers, motors, generators and the screen on old colour TV Cathode Ray Tube use is ideal. The metal should not be bent or hammered because this hardens the metal and reduces the metal's desired qualities so you should minimise the amount of work you do on the metal.
Microwave oven transformer with high leakage inductance - pictured left.
Single-phase shaded pole induction motor - pictured right.
The motor's mu-metal will need some more cutting to make it useful.
To cut a piece of mu-metal and carefully bend it into a radius. In more detail like a C shape but with the ends overlapping. I had planned to make the metal strip with one end folded up so it could be pulled out but the magnet turns out not to be as strong as I was expecting.
The estimate of the dimensions from outside dimensions;
- BSA and others - many sizes not known.
- GH12 (1936-38), 111mm outside diameter (from pictures). 12V, 2.7W and 3W
- GH8 (1938-41), 90mm OD (from pictures), 8V, 1.2W
- GH6, hub dynamo, AG and FG variable gear hub-dynamos. 6V, 2W
- Estimate magnet internal diameter measuring inside the bolts is; 70mm. and width 24mm
- The length required of mu-metal required is the circumference; 210mm = pi.D.
- Therefore ensure there is at least 230 x 30mm mu-metal
I understand that all post-world war two Sturmey-Archer dyno-hubs and gear dyno hubs are the same and parts interchangeable. The external appearance changed from time-to-time though.
I have some mu-metal and have cut a piece 30mm x 260mm x 0.5mm - it looks messy because I used kitchen scissors and it would be better cut with a guillotine to make a magnet keeper for a GH12 hub-dynamo. My plan is to carefully bend into a C shape radius.
The magnet is brittle and is pressed into a soft metal enclosure with water excluding lip. There is also a cardboard washer protector shown with intellectual property details printed on it. It is not necessary to move the wiring and it is best avoided doing that unless there is an issue with continuity or insulation.
I have used a mole wrench to hold the shaft by the not threaded flat sides, a 15mm ring spanner for the nuts on the shaft, and a 5mm nut-spinner for the 8BA nuts that hold the dynamo section together (the 5mm socket I have is too fat). The magnet has 20 poles in this picture.
The bearing can be seen the adjustment can be made from inside or also adjustment can be made with the dynamo section assembled using the remote adjuster picture on the bottom left corner of the tray of parts. If you are not going to touch the gears section it is probably best not to touch this bearing or the remote adjuster. (In this case, the bearing and the bearing the other side does need grease and therefore adjustment otherwise oil gets to the bigger bearing inside and other parts).
Video shows AW hub disassembly and that the drive side bearing is set to 1/4 to 1/2 turn slack and the non-drive side is set after the drive side bearing to 1/4 turn of slack. There are some differences and I have shown a tray of parts for the dyno-hub with the dynamo side bearing disassembled.
One difference with the variable gear only hub - There is no press-fitting bearing grease trap so that a little lubrication from the variable gear will spread into the dynamo section. The rust is a little greasy consequently.
Note; It turns out that variable gear is complete and disassembly and assembly was straightforward. Do use the video or other sources for maintenance information. You should not need to disassemble as far as the video shows you but also look at the planetary gears for timing marks an AG or AW does not have them but some variable gear hubs do and they must all be aligned when you re-assemble the hub.
There is one spacer between the drive sprocket and the variable gear but the video above shows two sprockets and it is important to put them back as they were found. The sprocket needed to be put back the other way like the video and another bike that I have. In conclusion, if this dynamo were to be used on another bike the location of the spacer or spacers would need to be reviewed.
I was able to test the function of the variable gear by screwing an old thread type thin 1.5mm spoke into the toggle chain place and see that the variable gear operates properly. The dynamo and gears have not been road tested on a bicycle.
Magnet keeper - if required;
You can push the keeper or another winding, as a keeper, in from one side and thereby push the existing winding out for inspection and cleaning. See TEST 4 below if you need to take this step which shows a procedure and measured outcome.
Testing the dynamo;
- GH 12 - I believe the circuit is two 6V filament lamps in series rated at 150 mA. Short one lamp to see if the other lamp illuminates then short the other lamp this will determine if there is a simple lamp failure.
- GH 8 - I believe the circuit is two 4V filament lamps in series rated at 250 mA. If the circuit is the same as the GH 12 then the test is the same.
- GH 6 - The circuit is two 6V filament lamps in parallel rated at 100 mA and 200 mA. If one lamp fails then the other lamp will supplied with too much current and fail. Therefore, turn the wheel slowly at first to see if one or both lamps illuminate.
- Turn the shaft and notice the dynamo detent force - which feels springy sort of lumpy and is very light. It does not matter which direction the wheel is rotated in the output is alternating current in any case.
- Short the dynamo output with a wire.
- Turn the shaft and notice the dynamo stronger magnet resistance force - which feels springy lumpy but is significant.
If there was no difference then;
- If the force is week then the winding may be open circuit or the magnet is demagnetised.
- If the force is strong then the winding may be short circuit but the magnet is good.
This is the same process that happens with a computer hard disk. A high pulse of magnetism is applied to the hard iron material to magnetise it. Such a pulse will also switch a magnets polarity north and south poles. This is done with the dynamo fully maintained and assembled then briefly connecting a high current from a voltage power source to the armature.
It turns out that there is no need for a particularly high voltage so the risk of the armature winding insulation breaking down and failing does not exist.
The Ground connection shown is not earth but is a reference point for this SiMetrix simulation diagram. RED = Volts, GREEN = Amps.
20A pulse shown is probably the current required to fully magnetise the dynamo (guessing based on patent above and the B-H curves below). The dynamos output will be a higher current than rated but well within the dynamos capability. These magnets have a wide tolerance in magnetic strength consequently the increase in the dynamo's output will vary.
The winding may fuse so a shorter current pulse would be beneficial. Increasing to 350V rectified mains would allow the pulse to be reduced to 0.4 seconds when the dynamo was newer the winding would have withstand this voltage. The winding needs to be dry but the insulation may have deteriorated over time and applying a high voltage to the winding may cause it to fail?
Allow the small detent force (the magnetism) to pull the armature to align the poles ready for the pulse of current to re-magnetise. You can test the magnetism by turning the armature to feel the lumpy pull of the magnets to the armature sections. This detent force is much bigger if you short circuit the armature and doing that will confirm that the winding has continuity and is not short circuit.
It turns out that a much lower voltage should have been used and a variable power supply so that the magnetism can be steadily increased until the dynamo produces the correct current. The magnet is used in the linear region in a similar way that sound is recorded on tape by a tape recorder. That is the magnet is not magnetised to saturation in the same way that hard disks, permanent magnet motors and generators usually are.
Alternatively use a car battery charger;
The car battery charger is connected to the dynamo, the dynamo shaft can move freely so that the magnet poles align when the pulse of power (magnetism) is applied.
Next step is as before switched on for one or two seconds then switch off. Take care to switch off quickly so that the dynamo winding does not heat up. Do not disconnect the dynamo whilst the power is switched on because a high voltage, called back-EMF, will be generated that will put the winding under stress unnecessarily. See diagram below;
It turns out that it takes a few seconds for the current to build up and the armature to move.
Video - Car battery charger used to re-magnetise the dynamo.
A digital multimeter does work if you keep the hub turning steadily for a longer period. The bulb lite up white indicating that the current was 470mA as the light bulb is rated.
WARNING THIS MEASUREMENT WAS TO IMPRECISE TO BE CONCLUSIVE. BUT THE METHOD IS THE CORRECT METHOD EVEN IF THE VOLTAGE WAS NOT HIGH ENOUGH. Adding the capacitor doubled the current to show 50% but on testing the dynamo showed no further increase in the current output. This is good because that indicates that dynamo is fully re-magnetised.
To properly test this procedure and voltages suggested the dynamo needs to be fully demagnetised. I could connect the winding to the mains 230V AC this should be adequate. But that is risky and I am not going to do that.
Tests 1; With the dynamo clamped by the shaft with a vice and string wrapped around the hub body then pulled;
Open circuit V, Short circuit I, 12V 6W Lamp
Slow; <10Vac, 440mA, <4V
Fast; 20Vac, 470mA ~6V
Very fast; 30Vac, 500mA, 8-10V
The dynamo's output is as originally expected nearly constant current regardless of speed and an open-circuit voltage proportional to the speed of rotation.
Test 2; Reverse the polarity of the magnet
- Connect up as above and pulse the power on/off so that the poles align.
- Reverse the polarity of the power supply.
- Clamp the dynamo stationary then power on/off.
- Un-clamp the dynamo so that it can move freely then power on/off.
- If the magnet polarity had changed the dynamo should not move but it did move to a new alignment.
- I also tried with a 20V DC power supply unsuccessfully.
The magnet is not fully saturated and therefore a little more power could be obtained from the dynamo.
- Connected a 35VAC to the dynamo - this was not adequate and the dynamo remained magnetised but the magnetism was reduced.
- The current output but showed the current was reduced to; 380-400mA after the demagnetising experiment. Then re-magnetising and increased to 400-440mA subsequently.
WARNING - The test suggests that the dynamo's current output will be higher than rated initially and remained the same after three days and is unlikely to diminish over time. The dynamo needs to be de-magnetised then re-magnetised but at a lower amount of magnetism. Alternatively left as it is with higher power output.
Test 4; Replacing the winding with the magnet keeper
Pushing the keeper in and whilst pressing the keeper into the magnet to ensure the magnet has minimal gaps and magnet path is as good as possible.
Winding removed - the fingers of the iron are tapered - this is unusual I do not
know why this has been done but it would limit the magnetism progressively.
- The keeper has been made long enough to be used on larger diameter GH8 or GH12 dynamos.
- Test voltage peaked at 30Vac as before and the short circuit current varied between 370mA to 420mA slow to fast.
- The tapped fingers of the coil may be to do with proving some voltage regulation mentioned in the patent. I do not have enough equipment to test this.
Conclusion - re-magnetising and electrical;
The magnet material has a tolerance but evidently, the magnet was not originally magnetised to its saturation but even so still has very good retention of magnetism. With readily available fixed voltage second-hand equipment power supplies it is only possible to re-magnetise a dynamo to give maximum output about 400mA AC in this case.
Older style block power supplies have very loose regulation so it should be possible to wire a number in parallel in order to achieve the desired current rating and because of there loose regulation the current would be shared fairly equally.
- Total = 4.4V (white) = (Diode 0.4V) + (White LED 4V) and
- Total = 2.1V (red) = (Diode 0.4V) + (Red LED 1.7V).
- AC; 5.5V = 4.3V + 0.6 + 0.6. Surplus power returned to the wheel.
- Therefore the output voltage is; DC 4.7V = 5.5V - 2 x 0.4V. (<5.5V no load)
- Extra power wasted by the triac (z01 ST) <360mW = 1.2V x 300mA. (compared to <2W for a zener diode shut regulator)
I have not evaluated any of these.
A method of overhauling the dyno-hub that I used;
Sturmey-Archer - Dynohub history
GH12 (1936-38) - Dynohub
Magnet and magnetic material characteristic B-H curve. B = Magnetic force and H = Amp turns the current in the wire and the number of turns of wire if there were no losses in the magnetic circuit.
https://www.coolmagnetman.com/magfund07.htm There may be a security warning visiting this website but the site is very good.
AlNiCo Magnet (aluminium, nickel, cobalt) material B-H curve shows the magnet can be magnetised at a lower degree of magnetism.
At very high temperature the material will de-magnetise called the curie point. When the material cools again the magnetism can return. This way is not used to magnetise the magnet. The magnetisation is usually done after assembly with the material cold with a strong pulse electromagnetic field;
History of modern magnetic material;
Pandemic cycling and bicycle selection going-forward + Starting to ride a bicycle again.
Raleigh Lenton sports bicycle + General maintenance advice, technical and history.
Addendum; Motors that will also generate power;
- 1970's Impex 350mA, 5V/winding 48 step stepper motor.
- 1950s Induction motor (variable reluctance) - is not magnetised but will magnetise when connected to an AC power and spinning. The capacitor provides a phase-shifted supply and sets the motor direction. This motor will become a generator when spun a little faster than synchronising speed and put power back into the supply. If disconnected the motor stops generating power safely. But if capacitors are connected across the windings and the rotor has remnant magnetism some of these motors will build up magnetism and start to generate power when spinning.
- Permanent magnet brush motor - will produce direct current if spun.
- 1980's Astrosyn stepper motor; 24 step, 16V, 80ohms (200mA)/winding - this has a very much more powerful magnet than the 1970s motor and is a more powerful motor although it is smaller.
- Central heating timer permanent magnet motor - this is like the dynamo in construction but turned inside out.
- Hard disk stepper motor 8 pole - this will also generate but the voltage is so low that it would have no use.
The motor is assembled then the magnet is magnetised by a pulse from a high voltage source. This type of construction is used from 24 up to 500 step hybrid stepper motors.
Microcontroller based bicycle dynamo light and battery manager with a speedometer. Design idea and exercise with STM32 microcontroller. With interface by USB cable for speedometer display.
- Manage two cell NiMH battery charging using a coulomb counting method. Therefore it is best not to remove the battery's in order to maintain the battery state of charge and capacity. Therefore use the USB port charging.
- On PCB bootloader switch for fast programming via USB port plus software debug connector.
- Software proposed functions;
- Switch to turn on Dynamo power to the USB.
- Switch to turn the lights on.
- Red/Yellow/Green - battery charge status LED.
- Blue - USB connected status LED.
- Manage maximum power transfer from a bicycle dynamo or alternatively with component changes a two, three or four-phase stepper motor.
The power diagram;
Could be based on an industrial motor control system similar to a factory or wind turbine but without a power dump;
A voltage multiplier boosts the input voltage enough to allow all power supplies to start
- L6201 ST 1-4A Motor drive bridge driver - 12V minimum therefore the dynamo would need to run at 10V AC out or the circuit would require a voltage doubler to start up from 5V AC but won't start up from 1.8-2.5V battery. Operates up to 100KHz.
- L6205, L6206, L6207 ST 8-52V (8-52V) 100KHz 2.8A with various protection and current control options. These operate down to DC due to the Vboost charge pump.
- L6225, L6226, L6227 ST 8-52V (7-52V) 100KHz 1.4A with various protection and current control options. These operate down to DC due to the Vboost charge pump.
- TLE9201SG Infineon 6A half bridge motor driver - only operates to 20KHz, 8 - 28V.
- L99MOD51XP, L99MOD54XP ST motor drive 3x half bridge drivers 6A, 7-28V.
- BTN8962TA Infineon Half Bridge motor driver - 30A, 8-18V or 5.5V-40V derated. Maximum frequency unknown and is oversized.
- DGD05463 Diodes Ltd. ISL6208, ISL6208B Reneses - Gate driver and discrete transistors. No significant frequency limit (500KHz) but requires more parts and is an expensive option.
For Vbatt (1.8V - 3.5V) to 5V bidirectional - TC78H653FTG Toshiba dual half bridge up to 2A, 1.8V - 7.5V, 500KHz.
Summary a power diagram;
The 1.8V to 7.5V dual half-bridge motor drive IC provides the option for a better power path with shortest paths to and from battery. It took a long time to find these parts for what I wanted to do originally and the solution based on power supply ICs is good and was found more quickly.
The final is likely to be based on input boost rail but using a bridge Power factor correction and power supplies will do the job well and silently. The dynamo could be boosted to >10W but this configuration has not been designed for that power level, unless the boost rail be output for expansion regulator included (similar to version 02D).
Version 01D - this does not have a boost rail and the input capacitor could be changed to multiple super capacitor type.
Version 03? - will be rationalised and use cheaper high volume parts.
List of files;
There is a spreadsheet list of files *.xls
--- Basic bicycle dynamo battery and lights manager ---
- AL-0002-01D Circuit and PCB's - draft. The design should fit in under 100 x 100mm.
- AL-0033-01C.ioc Micro-controller selector and configuration project file draft (out of date).
- Large capacitor required will not be adequate to prevent the battery needing to carry some ripple current so therefore life be shorted. A bigger capacitor could be fitted.
- This is a simpler solution and shows the basic function.
- THIS VERSION HAS NOT BEEN COMPLETED
---- The PFC or boost power supply front end optionally this can be software-driven ---
PCB size 150x100mm 4 layer components on one side. - to follow
- AL-0002-02D -- with boost or boost PFC front end for lower battery ripple current wider voltage range and output switch mode power supplies.
- AL-0033-02C.ioc -- Micro-controller selector and configuration project file draft. software to be finalised. STM CubeM.
- AL-0034-01A - dynamo battery lights manager Synchronous rectifier controller.wxsch SiMetrix 8.3 simulation.
- Does not require such a large capacitor because a boost power supply has been added.
- The PFC boost power supply is unnecessarily complicated and the simpler software-driven power supply option is a tidier solution. Therefore do not fit the components shown in the block and move the jumper option appropriately.
- The design and layout are not completed.
- AL-0002-3A -- with software-driven PFC front end for wider voltage range and more efficient power transfer. (to follow)
- More functions of the input power supply and synchronous rectifier have been moved into a larger microcontroller.
- PFC function need not be implemented. A simple loosely boost regulator is all that is required.
- Current regulators for LED drive instead of voltage regulators to improve efficiency.
- The lamp power outputs are simplified to work with LED lighting such as below.