Is an Ewerk type device required for Dynamo

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ConRAD
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Re: Is an Ewerk type device required for Dynamo

Post by ConRAD »

Going through some posts here as everywhere else I've got the perception that many people still tend to misinterpret the basic concept of "current setting" present on the e-werk. On the other hand I think that the double dial of e-werk itself (Voltage - Current) is somehow misleading by its own. When indeed I read of people saying that they can achieve 5W just setting for instance voltage at 5V and current at 1A there is obviously something wrong since most dynamos are rated nominal 3W, and the product of V X A under normal conditions can’t exceed 3 !!
In conclusion, IMO, current should be regarded so far not as a forced setting but rather as a limit, isn't it ??

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andrew_s
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Re: Is an Ewerk type device required for Dynamo

Post by andrew_s »

Yes, the current setting on an eWerk is the upper limit, and you won't get the requested output if you aren't going fast enough.

However, you are wrong to say that dynamos are rated at 3W.
3W is the case if you are powering a basic 3W (6V/0.5A) filament bulb, but if you power something else, such as an eWerk or an LED light (or even two filament bulbs), it's not difficult to get more power out.
Bike-Rich
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Re: Is an Ewerk type device required for Dynamo

Post by Bike-Rich »

Many thanks guys, found out a lot with the help of this thread.
Thanks for the pictures Conrad.

andrew_s wrote:
However, you are wrong to say that dynamos are rated at 3W.
3W is the case if you are powering a basic 3W (6V/0.5A) filament bulb, but if you power something else, such as an eWerk or an LED light (or even two filament bulbs), it's not difficult to get more power out.


That's a good point, but surely it is the battery that is allowing the extra power rather then a 'raw' dynamo?
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ConRAD
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Re: Is an Ewerk type device required for Dynamo

Post by ConRAD »

Bike-Rich wrote:... surely it is the battery that is allowing the extra power rather then a 'raw' dynamo?

Definitely yes !!

… indeed the only difference in the between an ohmic load and the e-werk is the built-in buffer battery present in the e-werk USB model or, if you prefer, the external cache battery connected to the e-werk itself; in both cases 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% !!!!

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Bike-Rich
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Re: Is an Ewerk type device required for Dynamo

Post by Bike-Rich »

That's cleared it up, very detailed and useful reply - many thanks Conrad. :)
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matt2matt2002
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Re: Is an Ewerk type device required for Dynamo

Post by matt2matt2002 »

At last. What I will take as the definitive answer.
Many thanks
Matt
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simonineaston
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Re: Is an Ewerk type device required for Dynamo

Post by simonineaston »

A quick virtual chat with BeeKeeper earlier this week-end prompted me to look for this topic on the subject of powering lights and charging USB devices at the same time, and I thought I would take the liberty of bumping it on account of it being a Jolly Good Read! :D
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
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