It would be nice if there was a thorough review of all the charging options out there. Before I bought any of my three chargers, I saw some reviews of cheaper ones that said they cut out at higher speeds, comments on lack of waterproofing, etc. When you look at reviews on a site like amazon, it is hard to know if those are representative or if those are mostly posted by unhappy people, in general I did not see any good discussion of the options anywhere.

I was a bit frustrated with the high cost of what I percieved to be an inexpensive device so I tried to make my own. After blowing out several of them on downhills where the over-voltage from the hub fried the capacitors I decided to just go ahead and buy them instead of make my own. A dynohub can put out very high voltage at high speed if there is no load applied to it, I measured over 30 volts (AC) downhill at 25 mph. Now, several years later I have accumulated three different USB chargers.

I will summarize the three that I have, as follows:

B&M Luxos U. I have the Luxos U on the bike I built up this past spring. It is a USB charger and headlamp combination. Some people complain that it is quite large, but I think it is just fine. Some people have complained about waterproofing issues on this light, their first generation had different wiring and suffered water ingress. If I was going to ride all day in the rain, I might be tempted to put a plastic bag over it. Or if it was sitting outside during the night, might put plastic bag over it. I like the light pattern, it is asymmetric, in that it is wider than high with a reasonably good cutoff at the top so you are not wasting a lot of light by shining it over the horizon. USB charger is attached to the handlebar with a remote switch to operate the light. It is the only charger that I have that has a built in cache (pass through) battery.

AXA Luxx 70 Plus is another headlamp USB charger combination, the the USB charger is in the mount. These are not sold in USA, I ordered it from an online seller in Germany. This was my first USB charger. I am unimpressed with the waterproofing (or lack of it) for the USB circuitry. No cache battery. I like the light pattern, it is asymmetric, similar pattern to the Luxos U.

Sinewave Revolution USB charger. It works very well but it does not have a cache battery. It is possibly the most waterproof of all of the chargers out there, I bought it for my Iceland trip where I expected frequent rain.

My frequent reference to a cache (pass through) battery is because some devices will not charge if plugged directly into a charger that lacks the cache battery. That battery smooths out the power flow. My Garmin 64 is one of the devices that won't accept a charge unless a cache battery is in the circuit. I have to use an external cache battery when I use my Sinewave or my AXA headlamp.

Maybe someone other than me should start a new thread comparing chargers.