Obviously yes, these are the "chargers" we have been talking about in this thread.To those who have done this: do you use anything (charging device/circuit) between the dynamo and the phone/battery pack?
- If the dynamo output is too low nothing happens.What happens when the battery voltage of thd device is greater than the dynamo output voltage... does the dynamo then become a motor, and the battery attempt to drive it? (Just a diode would stop this, but that would drop 0.6 volts which could make a big difference to the charging efficiency, USB is 5V, dynamos are nominally 6V.)
- If the dynamo output is ok charging happens and the charger maintains a certain and safe current and wattage to load the phone or powerpack, amount depending on the dynamo output (which depends from your speed) and the losses in the charger.
- If the dynamo output is too high better chargers limit the current/amount of electric power while some of the cheapest ones may simply fry your phone.
One of the issues is that many phones do not like the idea of charging being constantly switched on and off (like it happens in city traffic) and bombard you with a pop up message on the phone's screen each time that you have to tap "ok" to start charging. Which is annoying and means that you have to have your phone within reach and you have to be able to see the display to allow reliable charging.
To avoid a lot of the niggles you could charge a powerbank, acting as a buffer battery, that then charges your phone. Two troubles with this approach: For one losses in dynamo, charger and powerbank aggregate, so you will end up with way less charging power in comparison to charging the phone directly. Secondly only a fraction of powerbanks is able to be charged itself and charge a device (like your phone) at the same time. Some do exist but they are hard to find. So in most cases you have to charge the powerbank first and then only later are able to charge your phone. As charging a bigger power bank via dynamo is close to impossible a small powerbank will do for this purpose. Some of the better chargers (like i.e. the Forumslader) do offer an included buffer battery as standard or optional and with some this buffer battery may even be "precharged" at home.
Maybe have a look at the articles that linked to earlier in this thread to get an idea what is possible, what is not, what constraints and issues there are and what the advantages and disadvantages of the different chargers are for different usage scenarios. What you better should not do is to connect your dynamo hub directly to the power-input of your phone w/o a charger in between. This will not end up well.