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Mozda Setup
Michael Mazgaonkar from Mozda Collective in Gujrat has superb renewable energy setup (wind+PV+batteries+mini grid) schematic of which can be found here. This is used to power lighting in schools and other economic uses. He is planning to add Pedal power generator to this setup based on Hugh Piggot's axial-flux-generator plans (originally meant for wind turbines but adapted to pedal power as described here.)
Need for converter
Average human can output 75W consistently on bike. Michael figured that at the current output voltage (48V) conduction losses in coils are about 20W, which is almost 30%! To reduce these, he plans to increase the output voltage to around 150V DC by having more turns per coil. To charge the battery at 12V, he needs a step down converter. It needs to have high efficiency (at least 80%), low cost(max 50$), and high voltage protection at input & output.
Previous design & its drawbacks
Michael had earlier worked in Spring 2006 with student group from UIUC to design a converter for lower voltages. The details of the project can be found here under title DC-DC converter for EWB wind turbine project. Unfortunately, despite satisfying all other tests for DC converter, above converter managed to get just 6-12% efficiency. Thus challenge before us lies in understanding root causes of low efficiency, and improving it. There is surely scope for doing so, as many other MOSFET based converters advertise 85-95% efficiency. We need to figure out how & at what cost.
Immediate task: Feasibility study
Michael is raising funds to buy state of the art but costly converters such as Outback MX60. This will give him the proof of concept about the loss reduction by increasing generator voltage. After that is done, only low cost converters such as the one we plan to build can replicate this efficiency gains in many villages. He needs us to evaluate VERY carefully the feasibility of such device under $50, and if we have capabilities & commitment to construct one. (this is because they ultimately need a working prototype, and till now his association with all student groups has not resulted in a working product ) This pre-analysis has to be done hopefully before Dec 15th. Hence the rush :-)
MPPT controller
To help out Michael it would make a lot of sense for us to build and understand the working of a MPPT controller. Tim Nolan [www.timnolan.com], has designed and built an MPPT from scratch and it would make a lot of sense for us to build it and learn the workings of the controller. The tasks that we have to complete are:
- Find a facility where we can build and test the MPPT
- Understand the components of the circuit and how to adapt to Michael's needs. This will be easier to do once we have a working understanding of the controller, but it would make sense for someone to go through the circuit and see if any redesigning is necessary before building a test prototype.
- Along the lines of the above task, it would help to have someone look at the input and output parameters of Tim Nolan's MPPT as is drawn on his scematic.
- A cost analysis of the components is required beforehand, so someone needs to take lead in this aspect too.
- Finally the last step before building the test circuit is to obtain the parts, someone can also look into this.
A lot of the tasks that we have to do are sequential so it might be hard to look for parts before actually understanding the circuit itself. So what would make sense is for people to make some headway independently and then report their progress here as they start making headway. ---- Amadduri 01:55, 20 December 2006 (EST)
