In the spring of 2017 I purchased a Bush+Müller USB-Werk, as part of an update I was doing to a Rivendell Atlantis, which I had recently purchased, and which had been equipped with a SON-28 hub and two Haolgen lights. I also purchased a B+M IQ-X light — this was just before Peter White announced (in April 2017) that the USB-Werk and the IQ-X were incompatible.
Since then I've used the USB-Werk fairly successfully on two bikes — mostly my Rando bike, but also my commuter bike. I have female 3.5mm x 1.35mm plugs on both bikes, and simply put the USB-Werk into my handlebar bag. I had some problems with the output being intermittent, but put that down to defective wiring on the bike, or in the device. (I had a Magellan Cyclo GPS that eventually refused to charge at all, even when plugged into its wall wart.)
However, recently the "intermittence" seemed to have happened more often. On a recent three-day tour, I could not get any power out of the USB-Werk at all, and was forced to rely on a 10 Wh battery, which barely made it through the three days. What's frustrating about this is that when I run a test with a voltmeter in my shop, everything works fine; it fails only when I'm on the road.
In at attempt to diagnose which connector is defective, I bought a couple of $4 digital voltmeters and a bridge rectifier circuit, and cracked the case of the USB-Werk so that I could solder them directly onto the circuit board inside, eliminating the connectors from the system.
USB-Werk, with voltmeter showing the 5V output (from the Cache battery). There is a second voltmeter on the other side of the wooden stick that shows the input voltage. Because the input is AC, and the voltmeter reads DC, this reading is actually the output of the bridge rectifier circuit that you can see under the elastic band on the left-hand-side of the USB-Werk.
This arrangement, zip-tied to my handlebars, let me monitor the input and output voltages not only in the shop, but also while riding. What I found is that in the shop, with the bike in a workstand, I could spin the wheel and see the input voltage rise to about 6V. Once the Cache battery had time to charge, the output would rise to 5V and stay there. When I took the bike for a ride, I would initially see the same 5V output, but after about 15 minutes of riding, the output would become intermittent. (These voltmeters don't register below about 2V, so I don't know if the output voltage drops to 0, or just to below what the voltmeter can register, but either way, it's useless for charging a device.) After another 5 or 10 minutes, there is no more "intermittence": there is consistently no detectable output.
I had hoped that by cracking the case, I might see an obvious loose connection, or some other evidence of a failing component. I did not, but I'm going to post photos here of the internals, in case some more-knowledgeable BF member can learn from them. The two cache batteries are 150mAh LiFe cells.
USB-Werk circuit board and batteries
USB-Werk circuit board (front)
USB-Werk circuit board (back)
LiFe batteries