This is a regulator for a 6V/3W bicycle generator system.
The purpose is to switch to rechargeable batteries when
the generator is idle.
In addition, the device limits
the voltage across the bulbs when the generator operates at a high speed.
As you can see, the circuit is purely electrical. In the presented design, the switch has been moved, compared to the
original to a location where the switch better functions under different circumstances.
I kept the regulator on the bike for 2 years during which the circuit operated fairly satisfactorily.
Thereafter, I moved on to
an electronic regulator optimized for
the operation with a hub dynamo.
When the main switch is in the on position, and the generator is not
running, the bulbs are fed by five reachargeable batteries. Either NiCd or NiMH batteries may be employed.
A running generator
feeds the relay, which switches the bulbs to the generator in place of
the batteries. Excess voltage across the generator is used to recharge
the batteries. The Zener diodes are for protection. The batteries
can be further recharged through the charger jack. I have used a 7.2V
Radio Shack Battery Charger for the purpose.
As is seen, the circuit, generator,
and lights share the ground. All unmarked diodes
are 1A Schottky. D1 is some generic all-purpose 1A diode.
The low-current polarized DPDT (double-pole double-throw) relay
was purchased from
Since many relay manufacturers start their
lineup with such relays, you might be able to get one from
The relay's line of action goes horizontally across the
figure. Different connections and colors are for my own
All elements may be nicely packed onto a 1_3/4"x1_3/4" circuit board
and placed, with the 5 AA batteries, switch, mounted LED,
and the charger jack,
in a 1_5/8"x2"x2_3/4" aluminum box. I have used 800mAh nicads
from Radio Shack, which I soldered in series. Currently, higher-capacity NiMHs are available.
I mounted the regulator box on my wire basket. Using reflector holders,
it could be mounted on the frame.
I have used a FER 2001 generator and lights with a halogen bulb in
the front and with a regular bulb in the back. The regulator
ensures that motorists see me at an intersection while I'm
standing. The device genuinly gives me more security and the
drivers respect me
We do not have any hills here, so I cannot assess the operation
for a steep climb. A possibility is to include a trimmer
resistor in series with the relay for adjustments.
The schematic shown above is the most conservative, letting
the generator to take over whenever there is a slightest
sign of life from that generator. As the system performed
reliably, I decided, eventually, to tip the balance more
towards the batteries. Thus, I reduced the capacitor value from 330uF
to 75uF (the capacitor affects the delay in the reaction
of the regulator) and I put a resistor of 270ohm in series
with the relay (the resistor affects the threshold at
which the generator takes over). The particular values
would, generally, depend on the relay and on the taste, and should
be experimented with. In my case, the batteries now
take over when the light driven by a generator dims significantly.
to share with would-be designers:
The use of Zener diodes for protection, when dealing with such
large inductances as that of a generator, or of a charging
transformer, is absolutely
essential. Without the diodes, you will fry the delicate relay poles
in no time. Capacitors are useless for
Finding a right charging adapter turned out to be quite
tricky. I tried a number of them using the generous
Radio Shack return policy and buying individual
adapters from different outlets.
Do not count on the different relay poles to fire simultaneously.
Solar cells can deliver a respectable charging current in bright sun.
However, the current becomes abysmal under cloudy winter skies.
Around here (Michigan) these cells offer no alternative to a generator.
Standard battery holders are not practical on a bicycle.
The batteries easily pop out.
Another Regulator Version
Someone has asked me for a version of the simple regulator with a full-wave rectification, for a dynamo with separated ground, without the option of charging with an AC adapter, given that batteries could be taken out and charged outside. The schematic and comments are given here.