Artland Rock das Rad
From PedalPower.cc
Bob Giddens (pictured singing) of USED Bicycles and Artland Country Club has sponsored one of the first pedal power sound systems in mainland Europe.
Contents |
System Overview
The system operates between 24V and 30V and uses a 24V inverter to provide power to a speaker system that runs on standard 240VAC power.
Power Bikes
4 Yuba Mundos that have been outfitted with e-bike rear hub motors are used as power bikes. Each bike has a rectifier (RS part 395-3238) that converts the 3 phase AC input from the motor to a DC output for sending to the Power Box.
Power Box
The power box contains 4 bicycle power inputs, 1 36V e-bike battery input, and one 24V DC power output.
Each bike input passes through a 30A current sensor and a relay (RS part 418-6215). The relay can turn off the input if the current or voltage exceeds preprogrammed maximums.
The ebike battery input passes through a 36V to 24V DC to DC converter (RS part 445-9793). The converter is adjustable for an output of up 30V output. However, it is set to 24V, so as to act as a backup source of energy in situations when a baseline voltage needs to be maintained for keeping on equipment such as mixers, projectors, recording devices, etc.
Power from the bikes and DC converter is combined in parallel into a positive (red tape) and negative (blue tape) rail. Attached to the rail are two parallel sets of two series 16.2V 58F Tecate super capacitors, for 32.4V 58F of total capacity. The positive lead to the capacitors has a 40A fuse.
Power Monitor
An Arduino Mega2560 is used as the power monitor and safety cutoff controller. In the present design, a regular Arduino Uno could be used, since only 6 analog inputs are currently needed.
The Power Monitor Arduino source code is available at the PedalPower.cc github repo
The power monitor uses six analog ADC (analog to digital converters) inputs to measure overall system voltage and individual current on the 5 power inputs. It uses two digital outputs for turning off the bike input relays and the converter output. The power monitor circuit continuously reads the voltage of the system and will turn off the 4 bike relays if the system voltage goes over 30V. It also continuously monitors the current input from the 4 bikes and the DC converter. It will turn off the converter if the current exceeds 12A, which is the converter's specified maximum.
The Arduino firmware maintains a running average of the voltage and current. The arduino's chip, the AVR ATMega328 supports floating point math, which allows for good averaging capability, but it's slow. Instead, the averaging is done using integer math, by first multiplying the raw ADC values by 10, so as to preserve some level of precision. When the averages are retrieved, then they're divided by 10 to get the decimal value. It's not as precise as floating point, but much faster. Here's the running average function:
int averageInt(int val, int avg){
if(avg == 0)
avg = val;
return (val + avg * (AVG_CYCLES - 1)) / (AVG_CYCLES);
}
AVG_CYCLES represents the number of samples to average over. This helps to smooth out the ripples and jitters in the voltage and current.
The code has a function for sending out the raw binary averages for collection by a host computer. An app running on the host can then use this data to display a status window for projection, and a live data feed for upload to http://pachube.com.
