I'm just pondering if I need a dynamo.

Outside of powering lights, and maybe charging a phone, what other uses do they have?

Personally, the biggest use is increased safety. Knowing that you have an indefinite source of lighting at anytime (as long as you can pedal your bike) is huge. LED lighting technology has made it possible to have very good front and rear lights. Every year we are seing better dynamo-based headlamps hitting the market.

Other uses besides charging phones? I have read about some long distance riders doing timed events who have used dynamo hubs (with an appropriate USB headlamp like the Luxos U or one those special USB doohickies) effectively to charge the batteries of their Di2 electronic shifting when they start running low. Same thing with charging GPS batteries on bike tours, etc.

The reality is that most people can get away with charging devices at night or carrying a power bank. But with more and more people going "off-the-grid" with bikepacking or getting into randonneuring, along with the increased dependency on small electronic devices, it doesn't take much for some to see the merits of a dynamo hub.

yeah, I like having dynamo lights always available. I'm not sure what else you would do with them other than charge things or power lights

I suppose that it's just a matter of time before the gadgetry range expands. I'm thinking car cigarette lighter 'esque stuff.

since it's easy enough to get a usb output, just about anything can be powered from it. It's never going to be enough power for your laptop

Peltier cooler for my water bottle please.

If you are unsure, it is likely you don't need one, but that still doesn't make a dynamo extremely nice to have.

As Chris and unterhausen have already mentioned, it is nice to have light at all times of day, without worrying about how much battery you have left. And as they have said, with the right equipment, you can charge your gadgets. I've been using a Luxos U headlight for a few years now, and have been able to keep a Garmin Edge GPS and a GoPro camera charged with it. I've charged phones on occasion, too, but on a ride I normally keep that powered off and tucked away for emergencies.

If you're into the type of riding that will keep you away from a power source longer than your battery lasts, having a dynamo comes in very handy.

My European bike has an old fashioned dynamo which sits on the side of the tire. It works fine and I just got two brand B&M LED lights which are really bright. But it also adds some additional resistance. I personally only use it at night and have some flashing battery powered lights during the day.
But i would love to upgrade to a hub dynamo. They have a lot less rolling resistance and are "on" all time. Right now I don't have any other use than the lights but there are dynamo powered lights out there which have USB connectors so that you can charge a phone or other small gadgets.

I vote water bottle cooler. Keeps your water bottle cold on those long commutes during the day.

Charging a cashe battery and you can use higher current drawing devices . computers?

removable batteries for the charge 1 run the other option

generally only having 3w, 6v available , you cannot run devices and charge them at the same time.

It is neither easy nor cheap to get USB (5v DC) from a dynamo hub -- YET. It will be soon. In the meantime, unless you have a pressing need, use a dynamo to power your lights. There are a few gadgets out there, but the good ones are not cheap yet. The B&M light with a USB output looks great, but it was $180 last time I looked. Not easy to justify for many people. There are add-ons you can get which plug into your hub and provide a USB jack, but they're kludgy, require your own wiring or mounting to an extent, and aren't very proven.

Bear in mind that dynamo hubs are rated at 6w output. There are some useful things you can run on that, though you'd be better off if they have internal batteries of their own, since the output of the hub varies a lot. You certainly are not going to be generating enough power to provide any kind of cooling, not even a beverage. It's not nearly enough power for a laptop, either. If you have stuff that can't be run or charged with 6 watts, you'll need to recharge once you get to an AC power source.

The Luxos U is excellent, and only $110 + $23 flat shipping (for the whole order) from Germany. At that price (and their cheap prices for Shimano dynamo hubs and built wheels), I outfitted two of my bikes with dynamo/Luxus U setups for the price of one at US retail.
It's the cheaper than any other dynamo-to-USB solution, and it's a crazy powerful light as well with a very wide beam.

As Tom (@noglider) points out, dynamos don't provide much power. FYI, it's not 6 watts; "standard" dynamo output is 3 watts at 6 volts, and that's variable based on speed.

The best alternative use of a dynamo has already been stated: charging device batteries. You can trickle charge a USB backup battery that can store lots of mAh, and use it later to charge any device.

The Euro is low compared with the US dollar, so maybe that explains that low price. Good to know!

And absolutely, it's 3w, not 6w as I said. I don't know of many 3w devices and fewer that can survive on highly variable power, so all I can think of that you can do is charge a battery. This means a dynamo won't free you from carrying a battery if you have something to power other than a headlight.

I don't think a water bottle cooler would work that well, but I'm not going to do the heat transfer calcs to figure it out

Yes, the SPECIFIED power output is 3 watts, but that is a guaranteed minimum at a specified speed that is legally required for sales in Germany. The actual output is higher. BQ has published tests on dynos several times that show how high the output of different dynos can be, and at what speed. It's not at all surprising that we can connect multiple gadgets to the better dynos at least.

For a low speed rider (all those town bikes that are used in German cities and towns), the 3 watt limit describes the reliably available power. For a faster rider, a lot more can be had.

It would take some pretty fancy electronics to limit the power output to 3 watts at all speeds - I'm sure they are not included in the generator.

Besides, the 3 watts is intended to ensure that conventional filament bulbs can always be powered to a minimum level. Modern light sources (LEDs) are much more efficient, and I'd be surprised if the full 3 watts is actually needed by a modern LED head/tail setup.

the power the LED at a Minimum doesn't 'need' is (I suspect) where they redesign the LED and A Heat sink

to run hotter and be brighter to use that power available above the minimum .

The three watts rating is what you get when you connect the (once upon a time) typical filament bulb. I suspect most of the dyno lights run about this power(I think the old cyo was 700mA to the LED), but you can get over 10W with the right circuit.
Dynamo LED Light Systems for Bicycles (electronic circuits)

I am pretty sure there is some current limiting in most of the German dyno lights. I have been rather surprised when I took one apart, they seem to be more complex than the average battery light. I took a BuM tail light apart to make it work with the Luxos, and it had a lot more electronics than I expected. Same with my Supernova headlight that died. I was wondering if there was any hope for resurrection, and noted that the tail cap was loose. No way was I going to reverse engineer that board, and I wonder if there isn't more electronics up front behind the emitters.

eta: the current limit no doubt is above 3w. Just as one example, the Supernova has a very noticeable switch to voltage doubling.

Whilst on tour, my front wheel charging system adequately keeps up with my iPhone, my Edge 800 and my Petzl Tikka 2XP head torch.
I've recently built up a dynamo hub wheel for my Extra-wheel trailer in anticipation of getting a Sony camera which can be charged via usb set up (E-werk and cache battery).
I'm still pondering the virtues of two different Sony cameras so have yet to decide on model (RX100 or A6000).
When not on tour and commuting I tend to use the dynohub to keep the lights on all the time and simply charge the toys from a wall socket.

A refrigerator is indeed a device requiring a lot of juice to run, too much to rely on a dynamo I assume. Even a small one for just one bike sized water bottle. But perhaps some sort of evaporative cooling system might be viable? The idea is basically that you have a small tank of cooling water on your bicycle, connected by a small pump and a hose to a sock of sorts, that you put your water bottle into. The pump is powered by your dynamo to slowly re-wet the sock, as the water currently soaked up by the sock evaporates - thus cooling of your drinking water is achieved!

This is a sketch I drew up just now of the basic idea . Obviously someone else who actually knows about electricity, pumps etc. would need to build the device, rather than me.

I bought a B&M Luxos U for my first dynamo light system, primarily because I wanted the ability to charge other devices such as my iPhone. I've had the light now for about 4 months and haven't used the charging feature yet. Here's why. I primarily got the light for bike commuting, and you can't use the charger and light at the same time, and I need the light while commuting. My main use of the charging feature will probably be while touring, when I would like to be able to keep my iPhone charge while also using it for navigation.

You didn't mention taillights but that is an important bonus with a dynamo light system, which may be assumed by most users. My battery-powered taillights were most likely to run low while riding because they don't need to be charged as often as headlights and it's easy to forget to do that. It is comforting to know that my taillight is always working with the dynamo system. The same could be said for headlights, as well, if you sometimes forget to charge your front light.

One other advantage of the dynamo light system is that there is no "penalty" for running your headlight on high. With a battery-powered light, the battery life is much shorter when it's run on high. In my case, I tended to run my battery headlights on medium or low most of the time to conserve run time. However, I run my dynamo light on high whenever it's needed with no qualms about the battery running low.

Tarwheel,
We have a SON dynamo with Led head and tail lights, I often switch off the headlamp (bright days) to give more power to the "plug" usb, that makes a big difference.
R