Thursday, 18 July 2019

Bicycle Hub Dynamo maintenance

    Changed; 16/11/2020 to 10/12/2020

Pictured; Sturmey-Archer, AG - 3-speed dyno-hub, dated July 1953;  
3-speed wide variable gear hub and 6V, 2W generator.  40 spoke.

The first impression - the sprocket turns both directions without engaging and was floppy but after dismantling, reassembling and lubricating the gear hub is free running, it should feel loose which it does.  The case is bright chrome with some rust and the internals seen from the outside are dirty black dry oily and dry inside.  It has not been oiled adequately probably not assembled correctly and the toggle chain is missing - this dyno-hub's condition is unknown.

The dynamo - feels dirty but does not feel like there is any internal rubbing.  Turning the dynamo is definitely lumpy as would be expected as the poles line up but the magnetic force is quite high - which could mean the winding is shorted and/or the magnet is in a very good state of magnetism.   To be correct it is not a dynamo because it does not have a commutator, brushes and therefore produce direct current but it is a single-phase permanent magnet (alternating current) generator. 

Once the terminals were tightened there was good continuity.  Shorting the contacts makes the magnet detent force stronger (harder to over come) as should happen and indicates that the winding is not shorted. That is as far as I can tell over the friction from internal dirt at first but now that everything is put back together properly, lubricated the hub runs fine and appears to be in good order.

On opening the dynamo it becomes apparent that the magnetism is not particularly strong and it is quite easy to slide the winding assembly against the magnet.  The magnet is old for the time, probably AlNiCo type that would never have been particularly strong.  The air gap, as expected, is large by modern standards of motors and generators but that is because it uses the same high side-thrust weight carrying bearings as the wheel this lowers the dynamo's power a lot.  It turns out that the magnet was not fully magnetised but probably magnetised using a calibration procedure in order to set the required output current.

Pictured above right;  Stronger ceramic/ferrite type magnet from a 1950s or early 60s TV.

Summary - Mechanically the Dynohub was made like all Sturmey-Archer / Raleigh products of good quality materials, to be easily maintained and serviced over its almost indefinite life span.   I have read that Sturmey-Archer hubs were sold with a 50 year guarantee in 1950.

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 appendices at the bottom of this page;  
  • A bicycle dynamo light and battery manager with a speedometer design idea.  It interfaces by USB cable.  
  • There is some reference to magnetism,  motors as generators.
Graph - Expected current can be drawn up to the same limit irrespectively of the generator speed and then the 
voltage will drop sharply.  There are other factors and the voltage drops as the current increases in the real dynamo.
Small graph - With no load, the output voltage increases linearly proportionally to the speed of rotation.
Lightly loaded the dynamo is the same as a tachometer and would make a good speedometer. 

In a discussion on Facebook, I have been shown the patent below which claims a method of providing some voltage regulation rather than current regulation that I suggest above - load voltage regulation is claimed.  The magnet is machined in a way to form discrete poles so that the magnetism does not slip around and presumably be weakened more quickly.  The claim is also that the current reaches the desired level quickly - That would occur in any case by having a lot of poles and a high number of turns/volts coil.  The graphs with the patent do show some voltage regulation when loaded.  The description also mentions reactance of the winding being a limiting/regulating factor but I am not sure how this helps to model a generator?

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 V.
The losses in the dynamo are due to;
  • Bearing friction which is very small in the case of a thin oiled bearing.
  • Magnetising force - the power needed to change the magnetism polarity in the iron conducting the magnetism to the winding this is very small and might be 1% of the maximum power available for the given frequency which can be determined by looking at the B-H curve for the material.
  • Eddie currents in the iron conducting the changing magnetism this depends on how thinly it is laminate.  This looks fairly lossy because the metal is not thinly laminated but is just three laminations.
  • Copper losses are the losses due to the resistance of the winding when current is drawn either into a lamp or a short circuit and are;  I2*R which is; 0.45W = 0.32 x 5 in this case.
Magnet keeper to prevent demagnetising - if required;
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 an old colour TV Cathode Ray Tube use are 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.

 Colour TV, Cathode Ray Tube magnetic screening is made of mu-metal.  Microwave oven transformer
with high leakage inductance - pictured left.  Single-phase shaded pole induction motor - pictured right. 

Mains frequency transformers come apart into a bobbin with valuable copper wire, "E" and "I" section mu-metal.  I suggest cutting the mu-metal into strips and sticking it to some sticky tape end to end and side by side.  The microwave oven transformer with high leakage inductance pictured is welded and will probably be difficult to take apart, therefore look for another transformer.  Very old mains and loudspeaker transformers are not varnished so come apart easily for example.

The motor's mu-metal will need some more cutting to make it useful.

The Plan to make a keeper - if required;
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. 
  • Sturmey-Archer
    • GH12 (1937-44), 111mm outside diameter (from pictures). 12V, 2.7W and 3W
    • GH8 (1939-44), 90mm OD (from pictures), 8V, 1.2W
    • GH6 hub dynamo (1944 - 83), AG and FG variable gear hub-dynamos.  6V, 2W (reduced to 1.8W subsequently I believe).
      • 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.

Picture - Making the keeper;  Find a glass jar of about the right diameter,
wrapping it in a rage then bending the mu-metal around the jar.
The kitchen scissors are described as cut anything up to tin plate and
are more suitable than the tin snips on the right.  A hammer, anvil
(use a vice with care) and a file to clean up the cut edges.

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 variable hub gear and other bicycle parts are made to loose tolerances so that no moving parts should feel stiff or tight.  That is they tolerate grit and dirt with the minimum of harm wear.  The frequent oiling is necessary to lubricate and to flush out dirt.

By comparison the synchro and servo, gear-heads and tacho or syncro resolver pictured right are expensive precision components used in precision instruments.  There is virtually no slack or stiffness in them.  They were supplied in the tightly fitting plastic pack shown and were made in the 1960s by Vartec.  These components can be stacked end to end and they fit firmly.  Synchros and servos must be used in a clean and dry environment.
Syncros and servos were developed for use to calculate gun ranging during World War 2 one of the lectures at college I attended was one of those war times boffins who worked on gun ranging.

Disassembly of the dynamo section;
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.

A dynamo hub bearings and the variable gears can be serviced without separating the magnetic parts.  In this case, the magnet moves around the winding freely and the inside looks clean enough so a keeper may not be required.  Although the amount of cleaning will be limited either way.

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.

I have wiped to clean the surfaces then rubbed them all with grease.  I have also pushed the coil a little way out of the magnet it moves too easily it should be difficult to move, indicating that the magnet has weakened over time.

The bearing can be seen the adjustment can be made from inside or also the 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).
Note that the GH6 front wheel fitted type hub dynamo bearing adjustment is carried out from the non-dynamo side.  See;

Inspecting the variable gear section bearings, greased and adjusting;
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 oil trap so that a little lubrication from the variable gear will spread into the dynamo section.  The rust seen in the picture is a little greasy.   The hub should not be greased other than a little to hold the balls in place so that it can be assembled.  This is a little different to the advice given in many videos.

Note; It turns out that variable gear is complete and disassembly and assembly is 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. 

Picture right; Broken old type indicator rod and toggle chain from an FW variable gear hub.  The indicator rod will fly out if you simply unscrew the toggle chain on hub made up until about 1950.  On such an older hub with an indicator rod unscrew the indicator rod so that the toggle chain the other side can slide out.

There is one spacer between the drive sprocket and the variable gear but the video above shows two spacers 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;

 1. With the bike wheel off the ground so that it can be spun freely;
  • 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 be supplied with too much current and fail.  Therefore, turn the wheel slowly at first to see if one or both lamps illuminate.
2. With the wheel removed from the bike and the bearings set properly;
  • 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.
  • 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 the force was different as described the magnet is magnetised and the dynamo is good or the magnet is could be weak.

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. 
If there is doubt about the lamp and the dynamo circuits test the lamp circuit with a battery instead of the dynamo.  Of cause, you can test with a multimeter rather than traditional methods but a multimeter in its time such as an AVO would cost more than a new bike in the 1930s.  The current from a resistance meter if connected to the dynamo may cause a small high voltage spark when you disconnect it (called back-EMF). 
The moving Iron test meter pictured right is probably 100 years old and had cotton covered wire with a small probe tip.  It works AC or DC but the scale does not say which it is calibrated in.  Notice that the body of the meter is live, I have not carried out any measurements with this meter.  It would have been much less costly than a multimeter but it was not a cheap instrument.

The second tool rematerialising the magnet;
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.





AL-0030-02B S1 is closed briefly then opened to re-magnetise the dynamo.  When S1 is closed the current starts to rise in the dynamo winding represented by L1, 5.5H (measured and calculated roughly) and R1 5Ω (measured).  D1 prevents the circuit from creating a high voltage (back EMF), ringing (oscillating), arcing which will hurt you and damage the dynamo's insulation


RED = VoltsGREEN = Amps.
The Ground symbol shown is not earth but is a reference point for this SiMetrix simulation.  
20A pulse shown is probably the current required to fully magnetise the dynamo (guessing based on patent detail 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. 
Providing that the mu-metal can carry this amount of magnetism without saturating - which is very likely because motors and generators are usually assembled then magnetised after assembly.

Less self-heating occurs with the dynamo is magnetised by a higher voltage. You can see that the slope does not diminish in the rate of rising and simply heat up as in the lower voltage case above. AL-0030-01C 350VDC, 0.4 Seconds to reach 20A.  The winding needs to be dry but the insulation may have deteriorated over time so applying a high voltage to the winding may cause it to fail. 

AL-0030-03B 230VAC with rectifier 0.7 Seconds to reach 20A. The simulation diagram in the link is different 
 to the circuit diagram 230VAC - Fuse - switch - circuit breaker - bridge rectifier - dynamo. Similar to the 
battery charger below plus a fuse, a circuit breaker but without the ammeter, capacitor or the transformer.


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.
    How it works is that it produces a high current pulse - standard physics stuff but I need to experiment to find out how high the current needs to be?
    The device may require a dangerously high voltage and can produce high damaging voltage if the diode were not fitted.

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; 
AL-0031-02B The car battery charger has an internal rectifier diode so another diode is not required.
Connect up then switch on for 10 seconds or so then turn off.  The setting of the low or high charge 
switch  and then adding the capacitor will progressively increase the current and therefore the 
resulting dynamo output after re-magnetisation.
It turns out that it takes a few seconds for the current to build up before the armature moves. 

What happens; The armature (generator winding) of the dynamo (generator) will move and the magnet poles (field) and armature segments will align or re-align as the current and the magnetism increases.

Video - Car battery charger used 
to re-magnetise the dynamo.
Ensure that the dynamo can move freely so that the poles can align.  A moving needle multimeter or these old 2 cells 3V torch with filament bulbs (2.2V 470mA pictured) does a good job of measuring the function of the dynamos.  Look at the colour of the light to gauge current.  The old capacitors are similarly rated 30V to 63V 2,000uF to 5,600uF and the larger one is older.  

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.

It would appear that although the magnet seems weak judging by the how much mu-metal sticks to the magnet but this type of hard iron magnet was going out of fashion in the 1950s and TV manufactures were using ceramic stronger magnets which are black rather than silver.  By holding the shaft in a vice - wrapping string around the housing and pulling voltage and current measurements are difficult to make.

With a digital multimeter, I measured up to 400mA short circuit, although the dynamo is only rated at 300mA.  The current may have risen to 480mA after re-magnetising.   Measuring the open-circuit voltage with a moving needle multimeter was a little easier at up to 12V increased to 20V after re magnetising.  Adding the capacitor to the circuit doubled the current in the dynamo winding but did not, as far as I can tell, increase the power output of the dynamo after a re-magnetising again.

Warning this method was too imprecise to be conclusive.  But the method is correct even though 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 so 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 battery charger probably does not provide adequate power to reverse magnetise the dynamo but it has increased the magnetism of the dynamo.  The circuit may be useful.

1. The magnet is not fully saturated and therefore a little more power could be obtained from the dynamo. 

2.  Because the magnet could not be reversed it is also likely that a dynamo which is completely demagnetised would not remagnetise fully without a much higher current pulse?

Test 3; Demagnetise the dynamo so that magnetising the dynamo test can be repeated.
  • 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.
This test failed to demagnetise the magnet.  I am not willing to use a higher voltage.

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 tapered 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.
The assembly did not need cleaning but I did wipe the parts with grease on my finger.  I am advised that the gaps between the magnet poles can be cleaned with a pipe cleaner.
Test 5 - repeat tests after at least 1 month since re-magnetising the dynamo
Slow; Vac open >17V (analogue),  Iac 370mA (digital)
Fast;  Vac open >25V (analogue),  Iac 390mA (digital)
The digital multimeter, as before, gave less reliable readings.   
I also measure the average current with the moving needle multimeter and a bridge rectifier and this gave a consistent 300mA fast or slow.  The true value; 330mA (RMS) the metre is 40 years old out of calibration and the needle did not have a long enough period of current flow to settle at a final value.

    Ipk = Iav / 0.637
    Irms = Ipk x 0.707 
    Irms = Iav x 0.707/0.637 
    330mA = 300 x 1.11  -  Warning although the analogue multimeter gives consistent results it most certainly is under reading and the current is higher.

Using a light bulb 2.2V 470mA and 12V 6W I perceive that the dynamo power has diminished a little.  The multimeters tests suggest reduced by 5-10%.  The moving needle multimeter did not fully settle because I was not able to keep the dynamo turning long enough but it gives the most consistent results.

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. 

My guess is that there is a fixed voltage, therefore, current used to partially magnetise the magnet in order to achieve 300mA dynamo output current. It is likely that the correct voltage is found and set for each batch of magnets.

The point about magnetising to saturation is so that the magnet would be as strong as possible but the material used has a broad tolerance.  This tolerance would have made the output power vary between batches of dynamos made. Much more power is required to magnetise the magnet to saturation but the amount of effort required to demagnetise the magnet is also much more so the retention of magnetism would be better.  It turns out that unlike tape recording the magnetism does not seem to fade but I don't know if when generating power might regenerate the magnetism slightly?

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.

Pictured right; Old heavy transformer type block power supplies.  These range from 12V, 1A to 1.5A so two in parallel should be enough to re-magnetise a dynamo.  Four in parallel, in series with another four in parallel increase the amount of the dynamo is re-magnetism.   That is 12V, 2-3A or 24V 4-6A.  Ensure that all are plugged in then switched on and off together.

Rectifier regulator and LED lighting;

You can scavenge for rectifier diodes from an old PC power supply the low voltage side diodes are usually more efficient lower voltage drop Schottky types.  Schottky diodes have a low reverse voltage rating of 20V or higher but some newer types are rated at over 100V this means that a low reverse voltage rectifier could be destroyed by the dynamo at speed if the lamp units are disconnected.  LEDs from a car head, side and tail lights - generally if one LED fails the whole set is turned off and a dashboard warning is shown is a legal requirement in order to avoid ambiguity.  A 10,000uF 10V or bigger smoothing capacitor and Zener diode which will give low efficiency, low flicker lighting but these suggestions below are a little better;
Dynamometer tests ( on a GH6 dynamo show, the dynamo's output reached 6V 300mA at 30KPH below this speed, that blog's LED lighting drew progressively less current.  For a 26' wheel which covers about 2M per revolution the output frequency would be 83Hz which would not produce any noticeable whereas 50Hz can is noticeable. 
  • Therefore half-wave rectifier circuit (1) and 2 but without capacitors may not notice flicker above 15KPH (41Hz).
  • The full-wave rectifier circuit (3 and 4) with the capacitors not fitted and would not noticeably flicker above 7KPH (41Hz).
Capacitor values are estimated based on simulation for <30% current ripple in th LED at a frequency of 20Hz.  Arbitrary White LED was chosen and scaled for RED LED in the LTspice simulation AL-0037-???.
 1) 100%  current;  Total = 5.7V = (White LED 4V) + (Red LED 1.7V). 
The LEDs will alternately illuminate with the generator's AC output.  At low speed, all LEDs turn off as the voltage transitions through 0V.  Together this may not look acceptable to oncoming traffic or pedestrians.
2) 50% current, Voltage drop;
  • Total = 4.4V (white) = (Diode 0.4V) + (White LED 4V) and
  • Total = 2.1V (red) = (Diode 0.4V) + (Red LED 1.7V).
Circuit 2 and 3;  If one Lamp is disconnected then the rectifiers will need to withstand at least 30V reverse voltage.  A Schottky rectifier rated at 50V or higher is required.
3) 100% current; Total 6.5V = (Diodes 0.8V = 2 x 0.4V) + (White LED 4V) + (Red LED 1.7V). 
The reservoir capacitors shown are much less necessary than they are in circuit 2 they can be of a lower value in circuit 3.
4) Voltage limited;
  • Input; 5.8V = 3.9V + 1.1V + 0.6V. Surplus power returned to the wheel. 
  • Output; 5.0V = 3.9V + 1.1V + 0.6V - (2 x 0.3V).
  • Therefore the output voltage full load 4.8V = 3.9V + 1.1V + 0.6V - (2 x 0.4V)
  • No allowance for temperature has been calculated but the voltage is likely to be 4.5V to 5.5V.
  • Extra power wasted by the triac (z01 ST) <300mW from a graph in the data-sheet.  Compared to <2W for a Zener diode shunt regulator solution.
Provides enough voltage to run a USB device but the voltage being nearer the minimum be too low for that the device to charge at a good rate at the same time not so high to exceed 5.5V maximum. 
Simple Lighting systems suggestions (AL-0035-01C)
The LEDs may flicker a little but I have shown various mitigation measure and I also suggest using scavenged parts.

No allowance has been made for temperature and component tolerance (worse case design).

DC-DC converters & LED drivers;
A variable voltage or LED driver from 5V input evaluation boards-
I have not evaluated any of these.
PAM2841SR boost LED driver 2.7V to 5V in. There is an evaluation board for this IC.  Note that the input voltage must be lower than the LEDs (in series) voltage drop so that the IC can regulate the current.
There many other manufactures and types such as PAM2803, ZXLD1321 operates 1V to 3.3V at least.
ST buck-boost type use with circuit 4;


By combining the voltage pre-regulator above and then using a cheaper semi-regulated function block should be cheaper than using the evaluation boards above solution.

Picture right;  Surface mount LEDs - A Printed Circuit Board can be made with a footprint pattern like the reverse side but as if you were looking through the parts from the top.   Design the board with components on one side only.  Place very small dots of solder paste on to the pads (it should look as if you have not got enough solder paste on the pads).  Then place the LEDs and other parts on the PCB you don't need to fit all parts at the same time or be overly careful to align them properly surface tension will cause the parts to pull to align (or miss-align).  Place the circuit board on a suitably pre-heated hotplate to solder all the parts.  Using tweezers to correct any parts that go out of alignment or tombstone (stand up).  Use pliers to remove the board from the heat.  The board will go brown because it has been overheated and for too long but your circuit will function fine - heating and cooling need to be done quickly without jarring the PCB.

No PCB need to be designed and ordered if you unsolder the parts off of an old circuit board, cut the tracks as necessary and place your desired circuit and wires this works well.   Alternatively you can buy some stripboard or Vero board and do a similar thing with that but you probably will need to reduce the power rating of some parts such as LEDs in order to prevent them from overheating due to the lack of solder pad, copper area for heat-sinking.

Picture left - Stipboard or Veroboard can be used for prototyping of finished one-off design.  The prototype may be a mains power supply with switch-mode Lead-acid battery charging?  This type of prototyping can be good to see how a function works but usually, the function does not work so well unless it is not demanding.

Alternative - Bicycle dynamo light and battery manager  ---  See Addendum at the bottom of the page and also see;  electronics-design-project-bicycle

Links and references;
Tests of modern Hub dynamo efficiency's;

GH12 (1936-38) - Dynohub
GH6, hub dynamo, AG and FG variable gear hub-dynamos.
Note that the GH6 front wheel fitted type hub dynamo 
bearing adjustment is carried out from the non-dynamo 
side.   Unlike the AG variable gear dyno-hub.  

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. 
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;
Another bicycle dynamo project I am unsure about the data and the project was not completed but there is a useful dynamometer graph for a dynohub;

Other links;

Pandemic cycling and bicycle selection going-forward  + Starting to ride a bicycle again.

Raleigh Lenton sports bicycle  + General maintenance advice, technical and history.

Appendix; Motors that will also generate power; 
  • 1970's Impex 350mA, 5V/winding (4) 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 (4) - this has a very much more powerful magnet than the 1970s Impex 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.
Picture of a high number of steps, stepper motor. The shaft is mild steel and can bend easily so the coupling to the shaft must be flexible.  The construction is different from the dynamo with the two rotors are North and South poles of a central magnet so that the teeth then present alternate poles as the rotor turns.

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.


Appendix; Bicycle dynamo lights and battery manager;
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 on a tablet for example. 

The dynamo will output up to 20V when the bike is ridden fast I understand.   If we assume the dynamo will deliver 300mA then the output power is 7W but we can probably count on getting at least 5W. In order to get the maximum power from the dynamo, the current taken needs to be regulated so that voltage does not drop and thereby causing the power taken to drop below maximum.

AL-0036-02B Power diagram based on motor control to operate at low-frequency boost switch-mode using the inductance of 
the motor.  The bike needs to be moving at a good speed in order for enough voltage (>8V peak) be generated to start up the 
power supply in this simple design.  Most function blocks and parts are not shown and part values are not correct.  Expect the 
dynamo to whistle when running in the same way that the inverters and motors in a modern electric train whistle.  The 5V and 
Vbatt operate as a power in or out.
  • Manage battery charging.  Therefore it is best not to remove the battery's in order to maintain the battery state of charge and capacity learnt.  USB port charging either direction and data link.
  • Tilt sensor used to reduce the power taken from the dynamo using parameters set by the cyclist such as from a tablet computer connected. 



  2. Thank you for publishing this. a lot of effort went into what you have photographed and written.