Dynamo hubs, USB converters, power banks, and phones

My bike has a SONdelux dynamo hub and I recommend it to anyone interested in distance riding, especially when self-sufficiency is important. I also ride with a power bank, and use my iPhone in lieu of a bike computer. A lot of cyclists dismiss using phones rather than dedicated head units, citing battery-life problems. If you use your phone exactly as you would use a head unit, battery life would be a problem, but you can use a phone differently, in a way that gives good battery life: leave the screen dark and rely on periodic spoken status announcements. For the kind of riding I do, this is fine. Both the Ride with GPS app and the Cyclemeter app can do this, possibly others. Even so, in a multi-day self-supported event, you still need to optimize your phone charging.

I have tried a few different mounting systems for my phone, and Quadlock, which makes the mount I am using currently, does offer a mount with a built-in Qi charger. I’ve tried it, it does work, but the mount is huge and charges less efficiently than the charging port. If you use one of these, you will end your ride with less charge than you started with. If you plug into the charging port, you can keep the phone at 100% charge.

You can charge the phone from the dyno via a USB rectifier (I have this, which is part of a kit with a dyno-powered headlight), or you can hook up a power bank in series and charge your phone and other electronics using pass-through charging. I’ve tried two different power banks at this point: the Nitecore and this Anker model. They both have the same capacity: 10k mAh. The Nitecore, attractively, is the smallest and lightest power bank with that capacity, but the Anker has a couple useful features. One is that it has a Qi charger on its body. This could be important if your phone’s charging port gets wet (this has happened to me on a long ride–it can take a long time for that port to dry out once wet): you can’t charge via the port when it’s wet, but with a Qi charger, you can still charge wirelessly. I also found that my bone-conduction headset draws so little power when it’s charging that the Nitecore pretends it’s not there, but the Anker recognizes it, and even has a special trickle mode. Note: I’ve got an older Nitecore. It looks like the new model also has trickle charging.

Both of these power banks do support pass-through charging, but they behave differently when receiving power from a dyno hub. If you are charging your phone via pass-through charging with the Nitecore, power is available from a very low speed–maybe 4 mph. The Anker requires a higher threshold to pass through the charge–maybe 9 mph–and on one day, I found that my speed was hovering around that threshold for a long time, so the phone was constantly entering and exiting a charging state. This is annoying if nothing else, and probably not great for the phone.

I also found that one of the iPhone cables I was carrying (I had a few) was fussy about its power source–it would not charge my phone when plugged into the USB rectifier, but it would charge from the power bank.

A smart setup might be to get two 5k mAh chargers (perhaps this), with one strictly receiving a charge from the dyno and the other discharging to power your other electronics, swapping the two as needed. This is slightly less efficient, but offers some redundancy.

Here’s a visual breakdown of the various charging schemes I discuss.

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