There's a lot of talking about actual available power using an hub dynamo !!
OK, here below some considerations and conclusions:
1. Hub dynamos are universally rated nominal 3W-6V: nonetheless voltage can reach as up to 50V at no-load and power can slightly be more than 3W at speeds over 20 km/h.
2. If dynamo output is directly connected over an ohmic load then transferred power is stricktly bound to be equal to U^2/R but if instead of a resistor you use a rectifier with a built-in or an external buffer battery then transferred power can well exceed 3W, in both cases indeed the battery will be able to temporarily receive more power than a static ohmic resistor. So if you have the e-werk output set for instance at 5.6V with connected a 10 ohm resistor you won’t have more than 3.14W (provided that you pedal fast enough!) but if instead of 10 ohm you use a 5 ohm resistor you will never have the calculated 6.27 W ... believe me !!!
Here below however some considerations:
1. From SON technical documentation I’m reading that both SON28 and SONDelux are rated 6V/3W.
2. I’m also reading that, on a 28" wheel, nominal output is reached at about 16 km/h with a SON28 and at 19 km/h with a SONDelux.
3. Both dynamos feature an efficiency of 65% (approx) at 15km/h with a 700c-28” wheel
4. Now looking at the power plot available in the SON technical documentation in correspondence of 16 and 19 km/h respectively for SON28 and SONDelux I’m reading an input mechanical power of 4.3W … that multiplied for the declared 65% efficiency factor it makes an equivalent transferred power of 2.8W, something less the claimed rated power, this fact not surprising too much however since load conditions are a very general "lights switched-on" !!!
5. Of course going faster available power shall increase accordingly
6. With a SON28 at 20 km/h we will have an input mechanical power of 5.2W … that, again, multiplied for the declared 65% efficiency factor it will make something like 3.38W … better than nothing !!!
7. Now it comes the e-werk, whose efficiency we might assume to be something around 70%
8. So the 3.38W available at the output of the generator at 20 km/h shall have to be reduced to a miserable 2.37W (3.38X0.7=2.37) … not too much indeed
9. CONCLUSION: dynamo + e-werk = overall efficiency < 50% !!!!
BRUSHLESS DYNAMO PROTYPE (in fase di studio)
SCHEMA SEMPLIFICATO COMPRENSIVO DI:
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