Belt Alternatives: flat, leather, fabric
We came to quickly appreciate, however, just how difficult it is to procure supplies in a country such as Nepal. Very, very little is available, and that which is tends to break easily. The constraints on our engineering efforts turned out to be much stricter than we first realized. In fact, we came to believe that finding reliable sources of supplies in Nepal is the biggest challenge facing anyone trying to build a sustainable product. It seemed as if every alternative energy project we came across was importing at least one key part for their device.
For alternative belts, we managed to find a flat belt from a local hardware store in Teku, a belt made of nylon backpack webbing from Alpine Sports in Thamel, and a thin leather belt designed to work on a sewing machine from a store in Tebahal. Rather than drive out to the ghatta with these belts, we first tested them on a "simulated ghatta" in our lab/living room. We mounted the rear wheel of a Chinese-made bicycle on a frame that we had been using to test local bicycle dynamos. This stationary bike served as a kind of ideal ghatta - not only was there no wobble in the rear wheel, but we could control the wheel's speed as well.
|
|
|
|
Belt Alternatives: flat, leather, fabric |
|
From our tests, we concluded that the car belt was the best kind of belt we could find to use in Nepal. Neither the backpack belt nor the leather belt could turn the generator's pulley; they both slipped right around it. The smallest sized flat belt we could locate turned out to be 1" wide, too wide to fit onto the bike wheel. Also, the material was joined together with a metal clasp, which was too stiff to turn around the small diameter of the generator pulley. Although our "A" size car belt (the smallest width available) seemed a bit heavy, it was indeed the best option. Belt length was another variable with which we experimented. From our limited testing, we found that there is a significant difference in required tension, slippage and wobble when we increased our car belt size about 50%.
We spent about 3 days looking throughout Kathmandu for a dc motor larger than 18W. We had absolutely no success. 1- and 3-phase induction motors are readily available for all kinds of purposes, and no one seems to have a use for big dc motors. We tried looking for bigger radiator fan motors, but discovered that trucks and other large vehicles use mechanical fans (driven by the motor) to cool their radiators. The only other dc motor of reasonable size that we found was a windshield wiper motor, again from the local taxis. This motor had a similar power output as our fan motor, but was harder to work with. We briefly considered rewinding one of the available dc motors, but discovered that rewinding shops can only rewind ac motors.
|
|
|
|
Ceiling fan with induction motor exposed |
|
AC induction motors are available en masse in Kathmandu. We found a promising 300 W, 960 RPM induction motor for about US$30. We had heard from several sources that an induction motor could, with the aid of a few capacitors, be converted into an induction generator (which would then require a diode bridge or other rectifier to charge batteries). However, we did not meet anyone with first-hand experience, and had heard that such devices can have a relatively narrow window of suitable rpm for operation. We decided to practice on a cheaper induction motor, a US$15 ceiling fan motor. This motor was designed to run at ceiling fan speeds (slow) and use 70 W. After some trouble getting everything disassembled however, we decided not to use an induction motor as a generator. Not only were we unsure we could get one working, but it seemed quite possible that there would be difficulty working at the many ghatta sites in Nepal. Not only do speeds vary from ghatta to ghatta, but they vary with the season as well (hence an expensive voltage controller would also be a requirement.)
Still in search for a large dc motor, we sought to buy a starter motor from a car. Swayambhu Shakya, a local auto mechanic, however, persuaded us that a starter motor is engineered only for very short periods of use. Extended use would wear it out very quickly. Plus, it was expensive. He convinced us that an alternator - already specifically engineered to charge batteries - was clearly the part we wanted. We gave up our search for the perfect dc motor and turned our attentions to alternators.
Key Lessons from this Search:
|
|
|
|
