And of course, you can always attach more than one dynamo. You could use a hub dynamo normally and when you're coasting down a big hill, you can engage a sidewall dynamo. Not that it's a good idea, but it's possible. You could even have more than one sidewall dynamo. And you could have a BB dynamo!

I think that’s the takeaway from all of this - you either have to be pretty careful with your power needs or ride a long/appropriate time or find another power source. From those charts, it’s probably prudent to plan on something less than the 5W peak output and factor that against the time you can ride per day. If your needs are below that, you’re good.

Those charts are power output when running a fixed resistance. Modern USB chargers can put out to around 10W peak so 2A- enough to charge a smart phone at it's normal charge rate. Here's a good link to some info, in German so you'll need to translate https://fahrradzukunft.de/28/steckdose-unterwegs-7/
Using a Forumslader I can run a Smartphone running GPS, Strava, Facebook all day everyday, it struggles running a smartphone and a wireless modem, that's a little too much consumption and it'll go flat after a couple of days.

"As an example the Forumslader has 5 stage load matching, which is switched by a microprocessor, plus a voltage booster at low speeds to maximise output. "

Trevtassie, Is it possible to post a reference to the source for that? The most complex of the circuit diagrams I found for a version of the Forumslader had two values of serial capacitor, controlled by a relay. I wasted some time looking for more.

"Dynamos are constant current, usually around 500mA. "
If that were strictly true, it would be easy to extract more power. A frequency-dependent voltage source in series with resistance and inductance seems a better, and physically plausible model. However, I measured an almost 2:1 variation in inductance with wheel position (Sturmey-Archer GH6 Dynohub).

you can extract more power from a dynohub through various tricks. Constant current is just a convenient way of thinking about them, they are what they are. Nothing much constant about them, but thinking of them as a constant current source is a useful mental model

This model agrees with my experience and what I've seen from other sources; i.e. a voltage source that is proportional to the dynamo angular velocity, in series with a fixed inductance and resistance.
I've generated this sort of model for my 1st generation Schmidt by loading it with various resistances and riding at different speeds. With a large matrix of that data, it is possible to figure out the values that make the model match the data.
On the plus side, the measured value of dynamo resistance matches the model pretty much exactly.
I never tried to measure the inductance, so I can't comment on how well that might match the value derived from the testing over a range of speeds and loads.

I will say that riding up and down the street, over and over, with a meter strapped to your handlebars, is bound to get you some strange looks. I recommend a quiet back street. :)

Steve in Peoria

maybe the official english manual/assembly instruction of the forumslader helps, on the last page is a circuit diagram given. 5 condensators are shown, as far as i understand this.

Regarding the dyno hubs:
Here is an article about dyno hubs from Winfried Schmidt (the engineer and founder of Schmidt/SON) incl. electrical models. (Sorry, again in german from Fahrradzukunft.de, google translated)

As trevtassie has said (and shown in the link) (and has been said and discussed before by me), you can significantly increase the output of a dynohub. Hub dyno with 12 Ohm (equivalent to a 3W light system), Hub dyno with 24 Ohm and Hub dyno with forumslader. All links refer to fahrradzukunft.de

that is a good article! thank you!
I think I've seen the core losses modeled like that before, but I don't think I understand how the test data reveals the value.
My guess is that you must know how much mechanical power is being put into the dynamo rotation, and that is equal to the core losses when no electrical load is connected to the dynamo.
Is there another way?

Steve in Peoria

Reason for this are german regulations which require nominal output at around 15 km/h (Since Germany is/was one of the biggest markets for dyno hubs, as dynamo based lightning was legally required for nearly all bikes up to 2015 or 2017..). Those regulations are still based on incandescent bulbs and where never adopted to LED lights with their totally different light output characteristic. Some newer dynos (e.g., SON delux, Shutter Precision SP-9) do not meet the requirements at 15 km/h (with 26" or 28" wheels) and are (in Germany technically) only legal together with an LED light, so the authorities were a bit flexible in the last years...
There is a newer set of rules which probably will enter into force this year, maybe there will be changes to dynamo output requirements with respect to speed. There will be some changes regarding combined systems light the magnic lights.

Winfried Schmidt (founder of SON) is working/experimenting with hub dynos designed as a power source for all those new electrical toys. [Sources: 1. A interview/podcast (in german) with W. Schmidt; 2.Information from a owner of a LBS (local bike shop) with high interest in that area]

It is done via mechanical input. The linked test (from cyclinguk) is based on measurements published in fahrradzukunft.de (as stated there by referencing to A. Oehler and O. Schultz). In their first dyno hub test, the test rig is described in the second section, incl. the determination of mechanical power input. For the most recent hub dyno test from fahrradzukunft.de the same test rig was used.

I found the links in the last few posts very interesting. Thanks.

In the Forumslader instructions, I see five electrolytic capacitors. I would expect one to be connected for the reservoir/smoothing function after the rectifier,
leaving four on the AC side to cancel inductance. Assuming the common polarised parts, they need to be connected in series pairs. Those traces can be seen in the
board layout diagram. So my interpretation is that there are only 2 or 3 speed-matching stages. No visible relay, so it would be interesting to know how the switching is done.

Steve (steelbikeguy) wrote:
"I've generated this sort of model for my 1st generation Schmidt by loading it with various resistances and riding at different speeds. With a large matrix of that data, it is possible to figure out the values that make the model match the data.
On the plus side, the measured value of dynamo resistance matches the model pretty much exactly.
I never tried to measure the inductance, so I can't comment on how well that might match the value derived from the testing over a range of speeds and loads."

I did something similar, as well as measuring resistance and inductance directly when stopped. I have a poor selection of resistors, so not a large matrix.
The results match the higher of the the static inductance measurements, but the resistance came out 50% higher than the static value (6 ohms).
That might be due to magnetic/eddy losses, but I would not claim much accuracy for the measurements.

"I will say that riding up and down the street, over and over, with a meter strapped to your handlebars, is bound to get you some strange looks. I recommend a quiet back street."
I would not like to try that with the local potholes! I turned the bike upside-down and drove the tyre from the chuck of a variable-speed power drill, then a small grinding wheel
for higher speeds.

"I think I've seen the core losses modelled like that before, but I don't think I understand how the test data reveals the value."
I think I recall trying to match figures from a website (perhaps Steve's) using that two-resistor model. The results were worse (higher residuals) than the simple one,
with a clear systematic bias.

With the Forumslader it's definitely 4 stages, the capacitors can be switched in and out in different combinations, all switching is done by microprocessor controlled mosfets. The whole thing runs on 12V nominal, there are 3 x 3.7V batteries, there is a voltage doubler in there to increase the output voltage from the hub when it's less than 12V. With the smartphone app you can actually see the steps in output as speed increases.

If you consider 5V1A charging, Taiwan SPINUP bicycle dynamo USB charger F12W-PRO can achieve such charging speed.

If your mobile phone has a capacity of 3000mAh, then it can be fully charged in about 3 hours.

It claims to be waterproof, so you don’t need to worry about the weather.

US$499 for 1A ???? ouch.....

SPINUP dynamo are really expensive.
I only bought it because it included a dynamo and a USB charger. I have used products with poor charging efficiency before, and that is a waste of money.
For me, it is necessary to charge both USB 1A and lights.

Exactly. 5W of charging is bumping against useless for current electronics.

The solar panel that I’m testing is looking pretty good. 500g, $75. At 45N latitude (I.e. pretty far north) in early April, it puts out 11W in hazy overcast, ~3-5W in high overcast without even getting it perpendicular to the sun. Going to USB either on the dynamo or on the solar panel is a big hit on efficiency.

Instead of buying a "spinup" one could by the older "sunup" from the same company and save some money (maybe it has a little less power, efficiency is only at ~45%). The only advantage of the sunup/spinup is that one doesn't need a new front wheel, so it is imo only interesting if you don't have a dyno hub, but then the pedalcell system is still considerably cheaper and gives more power...

One of the pluses of the Forumslader Dynamo to USB jigger is that it can take a 12V (16-24V open circuit) solar panel and use that to charge the storage batteries. It can't do dynamo hub and solar at the same time however.

[MENTION=219896]JohnJ80[/MENTION], what are the dimensions of the solar panel, and I'm interested to know how you have attached (or will attach) it to the bike.

here’s the solar panel I have.

https://www.omnicharge.co/products/20w-solar-panel/

I’m working mounting out now but it looks like would fit nicely over panniers on the back. But if it works as advertised might not need to use it on the bike at all. 3 hours at 11W+ is 33WH which is roughly equivalent to a 10,000mAH battery capacity.

I think the key is a battery that can be charged directly by a solar panel. Solar panel voltage is all over the place and by the time you regulate
it down to USB, your efficiency drops fast.

Here’s the battery that we carried for two of us last year but we just charged if off of the AC mains when we camped at a camp ground. this accepts solar panel inputs directly and therefore charges very efficiently

https://www.omnicharge.co/products/omni-20/

I’m sure if I fooled around with batteries I could probably come up with a lighter solution even though this is pretty decent especially if your touring with someone else and can split it up.

I’m also sure that I’m going to see higher power produces in the summer and in lower latitudes especially for both of those conditions are present. I would guess that 45N latitude is pretty far north for most people and their touring plans.

The battery is rated at 1.4 pounds. Pretty good for what it does. Thanks for all that info. My friend in Northampton, PA just lost power because of high wind. Now the wind just arrived here. That battery could be handy in a power outage. I'm not ready to buy a generator for the house yet, so an Omni battery might be useful.

Yes. I live in an area where power can be unreliable. I also use this battery on sailing trips and it works well. But I’ve used it twice for touring now and it works well. We’re light weight in our touring gear at about 20lbs each for full camping gear including this battery.

I’m looking for the weight specs on a dynamo hub but I can’t seem to find them or at least it seems like they aren’t frequently published. I’d like to find that and compare weight against this.

[MENTION=219896]JohnJ80[/MENTION], I think dynamo hubs are typically around 500 grams, slightly less than this battery.

Thanks for that!

Adding in wiring and electronics for conversion, the overall weight difference for battery + solar panel is likely to be very small when compared to the dynamo setup but yet more flexible because it doesn’t depend on motion of the bike.

I also have a tiny 45W GaN based USB-C power supply that also works very well for charging that battery at the full 45W charge rate. So if the Omnicharge battery is completely flat, it would charge to 100% in less than two hours. A day’s usage of 35WH would be about 45 minutes of charging with that charger.

I think that the convergence of GaN power electronics, USB-C PD batteries, improved efficiency of solar panels, and USB-C PD charging makes for a lot of options that weren’t available even a year or two ago.

I have a couple Shimano hubs, they were already built into wheels when I bought them, I think they are the heaviest ones.

I have two SP hubs, rim brake model PV-8. I bought my first one in 2013, it was rated at 390 grams at that time. Mechanically, they have made a few changes so might be a few grams different. But you have to subtract the weight of the regular hub you no longer need.

My Sinewave Revolution is very light weight but it is ziptied to a bike right now, I am not going to remove it to weight it.

Hmmm, that is what Google is for. They say 37 grams.
https://www.sinewavecycles.com/produ...ave-revolution

Sinewave has no pass through cache battery, some devices do not play well with it for that reason.

I suspect that Son comes in between Shimano and SP for weight.

I agree that battery plus solar panel is probably about the same weight as a dynamo. Plus it's far more useful. But I keep thinking they were built for different purposes. I don't do extended touring these days, and if I did, I'm not sure what I would do for power. I do like my dynamo for lights, because I just get on and roll without needing to think about how charged my headlight is.