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Old March 18th 17, 04:05 PM posted to rec.bicycles.tech
Joerg[_2_]
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On 2017-03-17 20:50, Frank Krygowski wrote:
On 3/17/2017 10:55 PM, jbeattie wrote:
On Friday, March 17, 2017 at 7:00:01 PM UTC-7, Frank Krygowski wrote:
On 3/17/2017 8:00 PM, Joerg wrote:
On 2017-03-17 13:53, sms wrote:
On 3/17/2017 12:58 PM, Joerg wrote:
On 2017-03-17 12:11, sms wrote:
On 3/13/2017 12:28 PM, Joerg wrote:

snip

You could stick in a Murata LXDC55FAAA-203
http://power.murata.com/data/power/LXDC55FAAA-203_data_sheet_E.pdf

instead of the zener and do a USB version also with only three
parts.
But I know that you love designing your own switchers.


$3.50? Mon Dieu! :-)

I got some of the Murata LXDC55FAAA-203 units from Digikey for
use at
work. I guess I didn't realize from the picture on the data sheet
just
how tiny these things are. Maybe I'll buy some more and try building
some dynamo to USB adapters.


Be carful with that 16V abs max input limit. When the load current
drops
this can easily be exceeded by a dynamo, big time. You could burn off
the excess with a zener diode or TVS (though _not_ MOV) but these
have
large tolerances and could burn out if not well heat sinked.

I think you need somthing automotive here, some circuit that can
stomach
50V or more.

I'd just stick a 15V 5W zener in there for the rare times that the
dynamo is exceeding 11VAC. If I were going to sell these I'd do
something more robust.


And then you have to cool that zener. And hand-pick one because of
tolerance. Also, those things are soft. Better to build an "active
zener" with a TL431 and a transistor. However, I'd prefer a switch mode
regulator that can handle north of 50V because then you can capture all
the juice generated on that long downhill section. I have a few of
those
when riding into towns west of here. On the way back, of course, it's
sweating and suppressed cussing because those 1000+ feet have to be
gained back.

If you're trying to charge USB devices, you should at least look at this
design:

http://fahrradzukunft.de/12/minimal-lader/

It seems to be much simpler than what you're considering.



A zener diode is not a suitable device to limit USB voltage. The upper
limit in the standard is 5.25V.

https://en.wikipedia.org/wiki/USB

He should have at least a TL431 with a transistor as a shunt in there.

Anyhow, that is not why I'd invest in a hub dynamo some day. I want it
to be able to supply my 8.2V power bus on the road bike and charge its
Li-Ion battery pack. The MTB has the same but that will unlikely ever
get a hub dynamo. The smart thing is to at least have poor man's MPPT
and for USB provide a decent secondary regulator, preferably switch-mode
as well.


I use this device:
http://images.wisegeek.com/standard-us-power-outlet.jpg


It's not very portable.


I had some on my road bike a couple of weeks ago. Along with other
electrical gear I bought for a rework session.

--
Regards, Joerg

http://www.analogconsultants.com/
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