Background : Dynamo Lighting / Charging System
I like to cycle when ever i can but the Scottish weather does not always make this possible or attractive particularly in winter. I place great importance on effective efficient lighting and in particular the idea of 'see and be seen'. I was never particularly happy with lighting systems available commercially. Removable battery systems had the nasty habit of running out in the dark leaving you unable to see or be seen! I decided to investigate bottle dynamo systems in the late 1990's although they were becoming particularly unfashionable. I also investigated high power battery systems and in the end purchased a 6V 10W/2.4W twin light system manufactured by Smart.
Those who dislike dynamo systems do so usually on the following basis:
1. The friction/rolling resistance of the dynamo rubbing against the tyre.
2. The low efficiency of the dynamo itself.
3. The lack of light when the cyclist is stopped at a junction or in traffic.
4. The incandescent filament bulbs in dynamo systems like all bulbs of this type are susceptible to over voltage causing premature failure.
I decided to design my own system which would address some of the objections but first a little more detail on the background to the anti-dynamo arguments.
Extra effort to overcome the dynamo
My view was that if the extra effort required to provide light while cycling was off putting then perhaps you should not be cycling anyway.
Dynamo Efficiency
Assuming a typical dynamo efficiency of 50%, with a typical full output of 3W from the dynamo the rider must in put 6W. A reasonably fit recreational cyclist should have no problems generating that level without any difficulty.
No lights when stopped
I agree entirely with this as i always felt somewhat vulnerable at junctions in poorly lit streets. Of course the solution to this was to have battery powered lights both front and rear in addition to the dynamo lights.
The lack of light when stopped has been addressed by a number of manufacturers over the years using a 'stand light' which remains lit when the cyclist stops. The stand light usually consists of a high output LED powered by a super capacitor which is charged by the dynamo circuit whilst cycling and then powers the LED when the cyclist stops. The stand light usually remains lit for 2-3 minutes. Of course if you are stopped for any time longer than this or if you do alot of start-stop cycling as in a city and you do not charge the super capacitor sufficiently you will have the same problem...no lights while stopped! So although the stand light partially solves the problem it does not fully solve it.
Over voltage - early bulb failure
When riding at speed, greater than say 15mph the output of the dynamo when the lights are switched on will be greater than 6V, the bulb rating. Incandescent bulbs like all electrical equipment does not like to be overworked and this will lead to early failure. Unless you regularly test the bulbs you may ride for a while after the rear bulb has failed. This would be dangerous and also has the effect of increasing the over voltage to the front bulb and thus reducing its life further.
Those who dislike dynamo systems do so usually on the following basis:
1. The friction/rolling resistance of the dynamo rubbing against the tyre.
2. The low efficiency of the dynamo itself.
3. The lack of light when the cyclist is stopped at a junction or in traffic.
4. The incandescent filament bulbs in dynamo systems like all bulbs of this type are susceptible to over voltage causing premature failure.
I decided to design my own system which would address some of the objections but first a little more detail on the background to the anti-dynamo arguments.
Extra effort to overcome the dynamo
My view was that if the extra effort required to provide light while cycling was off putting then perhaps you should not be cycling anyway.
Dynamo Efficiency
Assuming a typical dynamo efficiency of 50%, with a typical full output of 3W from the dynamo the rider must in put 6W. A reasonably fit recreational cyclist should have no problems generating that level without any difficulty.
No lights when stopped
I agree entirely with this as i always felt somewhat vulnerable at junctions in poorly lit streets. Of course the solution to this was to have battery powered lights both front and rear in addition to the dynamo lights.
The lack of light when stopped has been addressed by a number of manufacturers over the years using a 'stand light' which remains lit when the cyclist stops. The stand light usually consists of a high output LED powered by a super capacitor which is charged by the dynamo circuit whilst cycling and then powers the LED when the cyclist stops. The stand light usually remains lit for 2-3 minutes. Of course if you are stopped for any time longer than this or if you do alot of start-stop cycling as in a city and you do not charge the super capacitor sufficiently you will have the same problem...no lights while stopped! So although the stand light partially solves the problem it does not fully solve it.
Over voltage - early bulb failure
When riding at speed, greater than say 15mph the output of the dynamo when the lights are switched on will be greater than 6V, the bulb rating. Incandescent bulbs like all electrical equipment does not like to be overworked and this will lead to early failure. Unless you regularly test the bulbs you may ride for a while after the rear bulb has failed. This would be dangerous and also has the effect of increasing the over voltage to the front bulb and thus reducing its life further.
Solution
I designed a solution based on the stand light idea but rather than charge a super capacitor i chose to drive the stand light from rechargeable batteries. The rechargeable batteries have a capacity of >800mAH so with a stand light at the rear only of 20mA they would remain lit for up to 40 hours which is considerably longer than the 2-5minutes quoted by manufacturers using super capacitors. The battery pack uses 4 x 1.2V AA or AAA size cells so does not add a great deal of weight or bulk to the bike.
The system drives the front and rear lights normally and also charges the batteries used by the front and rear stand lights. The system is designed to start from a fully charged set of batteries and by recharging them on the move attempts to replace the energy used while stopped. Obviously over a long period of time the battery charge state will reduce particularly in cases of city cycling where there could be a great deal of starting and stopping so they will have to be removed and recharged. I have been experimenting with an on bike charge system which will charge the batteries at a higher rate when the normal front and rear lights are not lit. This should minimize the need to remove the batteries frequently.
System features
I designed a solution based on the stand light idea but rather than charge a super capacitor i chose to drive the stand light from rechargeable batteries. The rechargeable batteries have a capacity of >800mAH so with a stand light at the rear only of 20mA they would remain lit for up to 40 hours which is considerably longer than the 2-5minutes quoted by manufacturers using super capacitors. The battery pack uses 4 x 1.2V AA or AAA size cells so does not add a great deal of weight or bulk to the bike.
The system drives the front and rear lights normally and also charges the batteries used by the front and rear stand lights. The system is designed to start from a fully charged set of batteries and by recharging them on the move attempts to replace the energy used while stopped. Obviously over a long period of time the battery charge state will reduce particularly in cases of city cycling where there could be a great deal of starting and stopping so they will have to be removed and recharged. I have been experimenting with an on bike charge system which will charge the batteries at a higher rate when the normal front and rear lights are not lit. This should minimize the need to remove the batteries frequently.
System features
- Drives front and rear lights from dynamo.
- Charges batteries from dynamo while cycling replacing energy used while driving stop lights when stopped.
- Drives front, rear and side stop lights. As stop lights are ultra-bright LED's they are driven from constant current drivers.
- Low weight, compact design easily installed on bike.
- Uses standard readily available rechargeable batteries.
- User selectable battery charge rate.