Il problema dell'alimentazione elettrica per chi usa la bicicletta, sia nell'uso quotidiano che per viaggi di più giorni, sta diventando sempre più impegnativo. Serve sempre più energia elettrica non solo per illuminare la strada nelle buie ore della notte ma anche per alimentare il sempre crescente numero di dispositivi elettronici a cui non sappiamo più rinunciare. Questo sito vuole essere un primo passo per provare ad orientarsi nella non sempre facile scelta degli strumenti necessari per gestire in modo possibilmente autonomo le proprie necessità.

The electric power supply problem for people who like to cycle either in everyday use and along trips of several days, it's becoming increasingly challenging. More and more electricity is indeed required not only to illuminate the road in the dark hours of the night but also to feed the ever growing number of electronic devices that we can't live without. This site aims to be just a first step in the attempt to orientate the user in the not always easy commitment to choose the most appropriate tools.

Friday, 23 September 2016

Why not 6 W at 20 km/h ??

So far, after quite an interesting discussion, I came-up to the conclusion that sometimes “EFFICIENCY” might not be at all a top priority. What is most important is indeed the effective power that a certain AC/DC converter can draw from the AC side (generator) of a system and deliver to the DC side (load) at a certain speed. To make it clear once again: “if one device gets an input of 3.0 W at 20 km/h and has an efficiency of 80% and the other device gets a input of 3.5 W at 20 km/h and has an efficiency of 75%, than the second device is the better choice in spite of its lower efficiency”. 
To make evaluations on how good an AC/DC converter is, I personally do not even need very sophisticated laboratory instruments since I make all relevant measurements directly on DC side. To do that I use a real generator, a real AC/DC converter (the one under test) and an adjustable ohmic load made-up of calibrated ceramic resistors. 
Some people make use of very expansive electronic loads, but that's a different story ... 
In my case the wheel/generator speed is controlled and finely tuned via an asynchronous motor powered by a 3-phase inverter. At this point the test method is extremely simple: I adjust (sink) the load till to get the maximum transferred DC power to the load taking care of course that the voltage doesn’t go below a certain “low limit”. For instance for usb 5V voltage I’d set this limit to 4.75V. The results seem to be pretty reliable so far. The basic estimate criteria would be that an AC/DC converter is as better as bigger is the amount of ACTIVE POWER that it will let to flow from the generator to the load. The test system I use is THIS ONE, home made but pretty well performing. Here below a couple of sample plots based on a Shimano DH-3D32-QR hub dynamo and an e-werk respectively set at 4.9V (1st plot) and 5.6V (2nd plot). As you can see the e-werk at 20 km/h doesn’t seem to be able to transfer more that 2.75W. 
The third plot, worked-out by an indipendent lab, http://fahrradzukunft.de/, well confirms above data. 
But what's most important, is that it shows that at 20 km/h some alternative devices, such as Forumslader-V5 or Dynamo Harvester Plus, can definitely do much better arriving to deliver more than 5 W !!



Courtesy of  http://fahrradzukunft.de/
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