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Charging from dynohub

Old 03-22-14, 06:27 PM
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Charging from dynohub

Hi everyone,

I recently upgraded to a Schmidt dynohub and wondered how everyone went about charging their devices. I heard that dynohub charging causes added stress on batteries because the charge is always in flux. Should I get a cache battery instead of hooking my smartphone up directly? I am using a Sinewave Revolution USB charger.

Thanks
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Old 03-22-14, 06:51 PM
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I'm curious , looked anywhere else? or this the place, where you are dependent for all your info?
I am using a Sinewave Revolution USB charger.
can you share what your owner's manual says, for those that dont have your same Kit?
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Old 03-22-14, 07:09 PM
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Honestly don't remember where I got the concern from, maybe it was over at Thorn Cycles Forum. The Sinewave has nothing to do with my question, just thought I'd share my entire setup.
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Old 03-22-14, 11:28 PM
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I thought the literature says you don't need a cache battery to charge your phone. I bought one but haven't tried it out yet.
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Old 03-23-14, 08:56 AM
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I like the cache battery, it can be used to power up other things as needed.

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Old 03-23-14, 10:32 AM
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I've just added a Schmidt dynamo hub and Luxos U to my touring rig. Haven't used a dynamo in years, and don't have any experience with this one presently. However, in my reading, the cache battery was to keep constant power going to the device being charged-ie, an iPhone, which will give an error message everytime voltage drops below (3V?) It makes sense to me that it would stress out the device, having power fluctuations all the time-so therefore a cache battery is a good idea me believes.

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Old 03-23-14, 07:16 PM
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Ok thanks for the replies. My Android phone is less fussy over power sources than my Apple was. Might go without a cache and see how it fares.
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Old 03-24-14, 02:32 PM
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I'm fairly certain there is nothing in the battery itself that's bothered by fluctuating charge currents during a charge cycle. And I'm a EE (though not an expert on Li-ion chemistry and pathologies).

One problem is that your smartphone/tablet/etc has its own charger built in, which is stateful. That is to say, when you connect a DC source, it goes through a sequence of states as it verifies the source quality, then initiates pre-charge (in case one of the battery cells has a short), and so on. That state machine may well be confused by the dynohub output, so I would agree that a design incorporating a cache battery or supercapacitor is a good idea.

You also want max-power-point tracking (MPPT), which dynamically varies the load applied to the dynohub to extract the most power at any given instant. Good luck finding out if widget X supports this from the marketing literature! If you break open the widget and look at how it's built, you can sometimes tell if it is a linear or switching regulator as the presence of an inductor implies a switching regulator. This is a necessary (but not sufficient) condition for MPPT.

Unfortunately, as long as we are stuck with non-removable batteries, there are always going to be multiple voltage conversions in this kind of application: dynohub -> [cache storage] -> 5V USB -> battery. You are probably lucky to get better than 80% power efficiency end to end.

And now you know why engineers suffer paralysis when forced to pick which high-tech gadget to buy.
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