On 2017-03-13 11:55, Jeff Liebermann wrote:
On Mon, 13 Mar 2017 11:06:18 -0700, Joerg
wrote:
A dynamo is essentially a current source where you can let
the voltage scoot up until a point is reached where the current drops
off so much that the total power begins to drop. Like MPPT for solar
generation.
Not exactly a current source. More like a resistor (coil resistance)
in series with an easily saturated inductor[1]. The problem is that
the bicycle dynamo operates over a range of frequencies, while the
typical solar charge controller operates at a fixed frequency. The
inductive reactance of the dynamo winding appears at variable series
resistance that increases as the dynamo goes faster. There are also
substantial differences in operating frequency between bottle and hub
dynamos:
http://www.pilom.com/BicycleElectronics/HubDynamo.htm
"Hubs rotate at a much lower frequency than bottles, and
though they have more poles to somewhat compensate, they still
end up delivering a much lower frequency. At 15 km/h, the
B&M Dymotec6 bottle dynamo (8 poles) outputs 168 Hz AC while
the Shimano DH-3D71 hub dynamo (28 poles) outputs only 28 Hz
at the same speed. At 8 km/h, a 28 pole hub is down to 15 Hz,
which causes visible flicker of the light"
However, in your link they say, quote "Hubs don't go into saturation
easily so that at moderate to high speed, they develop a higher voltage
than bottle dynamos, assuming they are not loaded with the typical 6 V /
3 W lights. To see whats possible, I ran a Shimano DH-3D71 at 136 km/h
in a test stand. The voltage generated was sufficient to ignite a
fluorescent tube and subsequently drive it at 55 V and 500 mA".
55V at 500mA. This is encouraging.
Highe power at high voltage also works with bottle dynamos. I have tried
with a Soubitez and a Ruhla dynamo, never a hub dynamo though because I
never had one.
Also, the dynamo iron and number of turns are selected so that the
dynamo saturates at some point near the operating speed and load. The
idea is not so much to regulate the AC output, as it is to reduce
mechanical resistance at higher RPM's.
I could make 12V filament lighting glow like halogen at high speed.
I tried to build an LTSpice model that simulated a real dynamo and
failed. I couldn't make it act like my bottle dynamo bench tests and
various online graphs. Maybe I'll try again this week. I'm suppose
to be on a (medical) vacation right now.
It's best to try that out on the bench, using a rechargeable drill and such.
[1] SON dynamo driving MOSFET bridge:
https://www.flickr.com/photos/kurtsj00/8480800746/in/photostream
http://www.candlepowerforums.com/vb/showthread.php?355392-Spice-code-for-dynamo-output
"CPF is currently closed for maintenance".
The author uses 0.1Hy in series with 2 ohm at 30 Hz. When I swept the
30 Hz over a 10 to 50 Hz range, it didn't look much like a dynamo.
--
Regards, Joerg
http://www.analogconsultants.com/