- GPS (Garmin Oregon 600)
- Phone (iPhone 5)
- Front light (Exposure Joystick) & Rear light (small USB light)
- Camera (Sony Rx100)
The phone was on air-plane mode for most of the time unless I was checking/sending texts from/to Cath.
I didn't plan to or actually ride much at night so the front light was mainly used on low mode at camp-sites and bivvies and would probably have lasted the whole ride on one charge. The rear light similarly saw little usage, usually early morning when heading out of town.
The camera was a different matter. While the documentation states that the battery will last for up to 200 shots that tends to be: power on, take lots of shots, power off. I was using it like : power on, take shot, power off. Most of the power consumption is in physically getting the camera ready to take a shot and then physically going back to storage mode. The actual shot uses very little power unless you zoom in and out a lot. This meant that I got about 40 shots before the battery was flat. In retrospect I'd have been better using the camera on the phone.
While I've long been a convert for dynamo hubs on commuter bikes I'd not been convinced of their usefulness off-road where speeds are usually much slower. There'd be no guarantee that I'd have access to power sockets cheekily or otherwise so I settled on using a dynamo hub to generate the power. Having forks with 15mm through-axle somewhat limits you to only a couple of models so I went for the Shutter Precision PDX-8 and Stuart Rider built it up into a nice wheel for me. There have been a lot of reports about the bearings on the SP dynamo hubs failing, particularly the through-axle versions, so it was a bit of a risk going for that rather than the Schmidt version. So far I've done over 1600km on it and it's fine.
There's a slight problem with using a dynamo to power devices like GPSs, Garmins in particular, in that when your speed drops or you stop to check you are still on route or take a photo, whatever then the device thinks power has been removed and a screen pops up asking if you want to stay powered on. Annoying especially if the default is to then turn the thing off if no button is pressed! Consequently my strategy was to charge a battery during the day then use that battery to charge the devices at night. Hopefully I could maintain speed to keep everything going.
A test ride, on my commute, showed that I could generate 500mAh at a steady 20kmh. I wouldn't be maintaining that speed as an average, more like 10-12kmh so at a rough guess I'd generate 300mAh (I'll have to do a ride at that speed to confirm this) for about 12hrs each day giving 3600mAh in total. Keeping my power consumption below that would mean that I would be effectively energy neutral in that I wouldn't need to search out power sockets to top things up. The 3600mAh figure is quite useful as that's generally around the capacity of standard 18650 cells which are used in powerbanks - these all have stated capacities that are multiples of 3500/3600mAh.
My setup thus consisted of the dynamo hub which was connected to an Igaro D1 converter which itself connected directly to a 10,500mAh battery (i.e. one with three 18650 cells). During the day I'd charge the battery then at night change the battery from "sink" to "source" and top up the GPS then whatever device might need it. Occasionally I ran the GPS directly from the battery. For this scenario I also had a single cell battery that I could charge, converters like the Igaro don't like to be left "open circuit" with nothing connected and you can fry the electronics if you take a long descent at speed. A bit of "on the track" testing showed that the system would begin to charge once I got to about 8kmh but would then continue charging even if the speed dropped to 5kmh. Obviously you aren't getting huge amounts of charge through at those speeds but it does show that you can keep trickle charging things at little more than walking speed.
I started with everything fully charged and for the four days that I was riding the event it all worked as planned. It helped that much of the first day was fast riding. Once I'd scratched and then met up with Cath we went touring in Brittany which involved gentler speeds.
During the six days of touring we averaged around 90Km a day with around 6-8hrs of riding per day. With phone on air-plane mode and using the GPS screen sparingly (canals tend to have fewer options for going wrong than roads!) I was power neutral in that I could have continued indefinitely without requiring mains top-up. Except ...
I recharged the camera! This obviously has a fairly hefty battery inside as I basically drained a three-quarter full powerbank in recharging it. I spent the next two days slowly increasing the charge in the powerbank and generally ekeing things out. In retrospect I'd have been better using the camera on the phone. I should have probably recharged it when we were staying in hotels in either Reims or Paris.
One day I ran the Garmin directly from the powerbank. In typically Garmin fashion in this mode the unit ignores all the power saving options you've set up! I think it assumes that an external power source will be something with "infinite" reserve like a lighter socket in a motor vehicle or something similar on a boat. Consequently the screen stayed "on" all the time running the battery down! The Oregon actually works in opposite ways when using internal and external power - when using internal power the screen auto turns off and you have to press the power button to turn it on but when using external power you have to press the power button to turn it off.
In conclusion. For rides where you are able to maintain even a modest speed then a strategy of charging a battery through the day then using that to charge your devices is likely to work. For something like the Highland Trail and Cairngorm Loop where speeds are much slower I think you are better simply taking enough batteries to recharge your devices and not bothering with the dynamo, maybe a plug to use in a cafe if you can get away with it.