Just investigating what happens when lights are used at the same time as AC/DC converters:
Preliminary considerations:
USB-werk, e-Werk@4.9V, Luxos-U, etc. etc., they all arrive to produce 2.7-2.9W at 20km/h
An e-Werk, the traditional one I mean, will be capable to give you more than above stated powers if set at voltage levels above 4.9V … BUT the immediate above step of 5.6V if intended to be used with a standard 5V-USB load is a bit too much and so far unsafe !!
Another consideration is the following: some AC/DC converters, like the Luxos-U, once loaded with an excessive load, generally say above 500mA, will exhibit a sort of LLV-Low Level Voltage shutdown that for the mentioned Luxos-U is 4.75V approx, in other words below 4.75V it simply powers-off !!
Well, 2.5W are generally more than enough to power a normal gps. Indeed power required by very popular gps devices can span between 0.35W required by a Garmin 60CSx at 0% backlight to a very demanding 2.6W (sometimes even more!!) of a Garmin Montana 600 at 100% back illumination. In other words be careful because power requirements of a gps commonly increases exponentially above 60% back illumination !!!
Let’s come to dynamo: a very standard dynohub marked 6V3W is normally capable to deliver almost 6W at 20km/h whether coupled with its “perfect matching” load. The rating of 6V3W is referred to a resistive load of 12 Ohm, but if you couple it with 30-40 Ohm you’ll easily get almost 6W.
Now let see the matching dynamo-converter issue: when you couple a dynohub to an AC/DC converter like an e-werk, it will be this latter one to determine the usable “transferred power”. That’s why some AC/DC converters will be capable to deliver only 2.7W and some other ones will possibly arrive to the double. It’s a pure matter of internal electronics design, a design specifically conceived to optimize dynamo frequencies (20-70 Hz), voltage levels, capacitors charging/discharging, mutual impedance coupling … etc. etc.
NOW, about the story of running lights in conjunction with an USB-werk:
- Well, this is of course the most critical issue to try to give an answer to. To try to give an answer though, I do prefer avoiding extravagant theories and rather totally rely on much more dependable lab tests. To this respect I made the following:
NOTE: all my tests have been done using my usual TEST BENCH (i.e. CYCLEEX) alternatively connecting an Halogen or a LED lamp
TEST_1: 20km/h, the B&M Lumotec HALOGEN or LED light are OFF, I adjusted the load to a minimum of 8.7 Ohm to allow the voltage to stay above 4.76V, THE TRANSFERRED POWER TO THE LOAD IN THIS CASE IS THEREFORE 2.6W 
Preliminary considerations:
USB-werk, e-Werk@4.9V, Luxos-U, etc. etc., they all arrive to produce 2.7-2.9W at 20km/h
An e-Werk, the traditional one I mean, will be capable to give you more than above stated powers if set at voltage levels above 4.9V … BUT the immediate above step of 5.6V if intended to be used with a standard 5V-USB load is a bit too much and so far unsafe !!
Another consideration is the following: some AC/DC converters, like the Luxos-U, once loaded with an excessive load, generally say above 500mA, will exhibit a sort of LLV-Low Level Voltage shutdown that for the mentioned Luxos-U is 4.75V approx, in other words below 4.75V it simply powers-off !!
Well, 2.5W are generally more than enough to power a normal gps. Indeed power required by very popular gps devices can span between 0.35W required by a Garmin 60CSx at 0% backlight to a very demanding 2.6W (sometimes even more!!) of a Garmin Montana 600 at 100% back illumination. In other words be careful because power requirements of a gps commonly increases exponentially above 60% back illumination !!!
Let’s come to dynamo: a very standard dynohub marked 6V3W is normally capable to deliver almost 6W at 20km/h whether coupled with its “perfect matching” load. The rating of 6V3W is referred to a resistive load of 12 Ohm, but if you couple it with 30-40 Ohm you’ll easily get almost 6W.
Now let see the matching dynamo-converter issue: when you couple a dynohub to an AC/DC converter like an e-werk, it will be this latter one to determine the usable “transferred power”. That’s why some AC/DC converters will be capable to deliver only 2.7W and some other ones will possibly arrive to the double. It’s a pure matter of internal electronics design, a design specifically conceived to optimize dynamo frequencies (20-70 Hz), voltage levels, capacitors charging/discharging, mutual impedance coupling … etc. etc.
NOW, about the story of running lights in conjunction with an USB-werk:
- Well, this is of course the most critical issue to try to give an answer to. To try to give an answer though, I do prefer avoiding extravagant theories and rather totally rely on much more dependable lab tests. To this respect I made the following:
NOTE: all my tests have been done using my usual TEST BENCH (i.e. CYCLEEX) alternatively connecting an Halogen or a LED lamp
TEST_2: 20km/h, the B&M Lumotec HALOGEN light is ON, I adjusted the load to a minimum of 41.5 Ohm to allow the voltage to stay above 4.76V, THE TRANSFERRED POWER TO THE LOAD IN THIS CASE IS THEREFORE 0.55W
TEST_3: 20km/h, the B&M Lumotec LED light is ON, I adjusted the load to a minimum of 24 Ohm to allow the voltage to stay above 4.76V, THE TRANSFERRED POWER TO THE LOAD IN THIS CASE IS THEREFORE 0.94W
CONCLUSIONS:
- with the headlight OFF you can rely on 2.6-2.7W roughly as expected
- with the headlight ON you still can rely on some power, depending on the type of light, halogen or LED ! As you can see from the above numbers, in either case you still might have enough power left to supply 0.35W required by a Garmin 60CSx if used at 0% backlight !!
