Stepper Motor Voltage Doubler Circuit
Stepper Motor Voltage Doubler Circuit
Double the voltage from a stepper motor using two bridge rectifiers
general | electric circuit | educationA
stepper motor can be used in conjuction with
PVC rotor blades to make a very cheap
DIY wind turbine generator. Stepper motors can be bought new quite cheaply, but they can also be cannibalised out of old printers, floppy disk drives, and other sources.
NEW Learn more about stepper motors and find out how to identify their wiring reading our article stepper motor basics.
On the side of most stepper motors is printed the rated voltage and the current per phase. Often an excellent stepper motor will be discarded by the
renewable energy enthusiast because the rated voltage is below the voltage required for the application - for example, an excellent 6 Volt rated stepper motor would often be ignored by someone looking to make a
wind turbine generator to charge a 12V
battery.
In some cases a low voltage
stepper motor can be used as is since the high speed of rotation of a small wind turbine generator will send the voltage generated high above the rated voltage. However, in time the stepper motor and its bearings will be damaged by being spun much faster than it was designed for. Instead a simple
voltage doubler circuit should be considered.
Voltage Doubler Circuits and Wind Turbines
A
voltage doubler circuit does exactly that - it doubles voltage. The power generated by the
stepper motor does not change, therefore following
Ohm's Law it can be seen that the output current must be halved if the voltage is to double.
Using a
voltage doubler enables a useful voltage to be ouput at low rotational speeds with the disadvantage that the current generated at high speeds is lower than it would be without the voltage doubler.
However, wind speed distributions can be modelled with the
Weibull Distribution. This tells us that a wind turbine will experience low and moderate
wind speeds far more often than it will experience strong gales. Therefore using a
voltage doubler with a low voltage stepper motor wind turbine will result in more charge getting to the batteries overall.
Stepper Motor Voltage Doubler Circuit
Making a voltage doubler for a stepper motor is very simple because stepper motors generate
four-phase alternating current (AC) electricity. Therefore all we need is a couple of suitably rated
bridge rectifiers wired as per the circuit diagram displayed above.
The AC voltage from each of the two pairs of
stepper motor coils is rectified by a bridge rectifier into DC voltage and the two output voltages are then added together giving a total output of double the original voltage, but with a current equivalent to that generated by just one pair of coils.
nb. Don't forget that between 1 and 1.4 volts is
dropped (i.e. lost) in each bridge rectifier.
The two
capacitors are used to give a smooth output DC voltage. If the
voltage doubler is for sub-16V applications, then the following
1000uF 16V Capacitors available from the
REUK Shop will do the job.
NEW Find out lots more about the practicalities of making voltage doublers, triplers, and quadruplers with our new article
Making Voltage Doublers and Multipliers
Smoothing Capacitors
Suitably rated
capacitors can be used to smooth the output voltage to keep it fairly constant so it can be used directly in electronic applications as well as in battery charging. One capacitor should be placed across the positive and negative outputs of one
bridge rectifier, and a second capacitor used similarly across the outputs of the other bridge rectifier.
Find out much more about
smoothing capacitors here.
Buying Bridge Rectifiers
A range of
bridge rectifiers is available for sale in the
REUK Shop including
1.5 Amp bridge rectifiers which are perfect for use with small
stepper motors
, and
35 Amp bridge rectifiers which can be used with much larger stepper motors.
Article Last Modified: 10:45, 9th May 2007
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