Dynamos, Lights & Power On The Trail

Since becoming more interested in bikepacking and much longer distance riding the question of powering lights and a GPS unit has been one I have thought about. I use a Garmin Edge 800 which is charged via USB so I don’t have the option of simply carrying some spare AA’s. Additionally the lights I used previously for off road riding were Magic Shines, which although great value and great for an evening ride aren’t really known for there long run time. More recently I have got back into documenting my trips and so keeping cameras charged has also entered the equation. Keeping a phone charged is another possible consideration but it’s one that is a lot less important to me. More often than not there’s no signal where I’m riding and as such running my iPhone in air plane mode gets you multiple days of run time anyway.

One might argue that I had done alright so far using a USB battery pack and that wouldn’t be an unreasonable statement to make. However I have had to do a lot of a lot of managing of lighting as well as battery swapping, normally at the most inconvenient moments, and on several occasions become dangerously close to having to get the back up paper maps out because the Garmin has almost died. Sure it’s not a line I have actually had to cross yet, but if there is a way of removing that line completely, or almost completely, then why the hell not?

When I started to spec a bike that was more long distance orientated I decided to be bold, experiment a little and go for a dynamo hub. Of course it could have been an expensive error but after reading Rob Deans account of using the SP PD-8 several years ago, I was fairly confident that it would be the right way for me to go.

The Kit

Shutter Precision PD-8X (Dynamo Hub)


Unfortunately this is the best picture I have pre-build due to a hard drive failing.

Initially Shutter Precision only did one disc brake, full size hub in the 8 Series which was the one that Rob Dean wrote about, the PD-8. Being quick release only though represented a problem for me as I wanted to go with a 15mm through axle fork. I contacted Shutter Precision on the off chance that they might be planning a 15mm version and was stunned to hear that actually they were and it would be out within a couple of months. Unfortunately it was delayed for a while but finally it appeared in their catalogue and before long Intelligent Design Cycles, a Taiwan based supplier, were listing it for sale. This was months before any were due into the UK so I paid the extra shipping and risked the tax. I was lucky and in the end not only did I have one of the first that made it into the UK but I also had it at a great price. I built wheel myself lacing the hub the a Light Bicycle “Wider 29er Carbon Rim” with DT Swiss Competition Spokes. Those rims are absolutely awesome by the way, I really should write up a review.

Something to bare in mind with this hub is that the bearings are not user serviceable. You will need to send the hub back to Shutter Precision to have this done. As I understand it though this is an issue within the market place and that most dynamo hubs require special tooling and recalibration. You can find out more by reading this FAQ on the Intelligent Design Cycles web site. It may seem like a right hassle to have to take the wheel apart but you would have to do this to service the bearings anyway even if they were user serviceable. I estimate it will be something like once every 3-4 years that I will need to do this as the bike I’m running this hub on is one of three bikes I run plus I have a normal front wheel for it so I won’t be using it any more than I really need to. I think this hassle is comparable to servicing it myself once a year as I do with my other wheels. I have it on good authority that there is a service centre in Germany but I’m awaiting more details regarding that.

Exposure Revo (Dynamo Light)


I spent a while trying to decide on which light to go for. In the end I got down to going with the Exposure Revo. Mostly because of good customer service reputation, a number of good reviews and their pedigree in terms of the light of choice for the endurance community. The Revo is 800 lumens, which in today’s lumens wars sounds low but the reality is that this is perfectly fine for most terrain most of the time. On an average descent it’s always been good enough. The times when I have been reaching for the helmet light have mostly been when riding very tight and twisty single track or the occasional very technical decsent. The former of which would always make me want to have a helmet light and this would be the same how ever bright the bar light was. I think there is a lot of benefit to having a light that is pointing where you are looking, not just where your bars are facing. You might ask why bother with a dynamo if you are going to have a battery light anyway but I don’t generally run the helmet light continually and when using the middle setting of the Exposure Diablo you get a very long run time. Worse case scenario over a very long trip would mean needing to charge the Diablo but having a dynamo doesn’t make this a problem. It’s important to remember though that you have to have some sort of power regulator, like the Sinewave Revolution, between hub and light. Not doing this risks frying the Diablo internals as it doesn’t have the same built in circuitry as the Revo. In terms of brightness there have only been 2 situations where I have felt that the light wasn’t bright enough. Sometimes when riding with other people who have a super nova strapped to there bike their light can make your night vision less sensitive and as such make the light seem dimmer than it really is. The second situation is extended periods of hike-a-bike where you aren’t really getting anything out of the dynamo at all and you are normally trying to avoid tussocky ankle breakers.

Sinewave Revolution (Dynamo Power Regulator/USB interface)


With 2 AA sized batteries for scale… it’s small.

There are a couple of problems with the power that is produced directly from the dynamo that have to be sorted out if you want to charge a USB device. There are loads of different power regulators/UBS interfaces that will do this and again it took me quite a long time to finally decide which I was going to go for. I went with the Revolution made by Sinewave. Unfortunately there is no UK supplier of these yet and as such you have to order it from America. They dispatched it very quickly but frankly UPS service was rubbish. It was sat in a sorting office in New York for seemingly days on end before finally making it across the pond. Anyway the device it’s self is extremely small, lite weight and fully water proof. As is, it comes with a striped back wire that is suppose to be wired into whatever plug connection that your hub uses.


Before the outer layer of heat shrink was applied.

I had the option of twisting the pair in with the Revo plug and having 2 wires wrapped around the fork leg. However I decided something a little more graceful was in order and set about trying to find a better solution. After some chat on the Bearbones forum one of the members mtbmarkymark told us about the set up he was running in conjunction with his Revo. He had managed to source the female connector that is contained within the Revo light housing, which he soldiered on to the Revolution input. This means that the Revo wire can be plugged in directly requiring only one wire running up the fork. As Mark had had to order a whole bag of these connectors he was happy to let a number of us have one and for the princely sum of £1 he put together a pack containing the connector and various sizes of heat shrink. Big thanks goes to Mark for this and for doing the leg work in sourcing the part.

Depending upon your device you could plug it straight into the Revolution but as I run a Garmin Edge 800 there is a small problem with this. When an external power supply is connected to the Garmin it beeps and tells you, the same happens when the power is disconnected or runs out. When using an external battery this is clearly a useful feature but when using dynamo power, having the device beep at you every time you slow down sufficiently for the power output to drop or start moving again quick enough for it to kick back in again, is pretty annoying.

7dayshop Power Bank


To solve this problem I’m using a USB battery pack that sits between the Revolution and the Garmin in the chain. The pack is able to be charged, while simultaneously charging, providing a constant power supply to the GPS. It’s worth noting that not all USB battery packs do this, I already had one that couldn’t so make sure you check this out before buying one. The unit I use is the 7dayshop Power Bank available from 7dayshop for the bargain price of £9.99. Using a battery pack in this manner has the added bonus of being able to charge other devices over night while you are not on the bike. On many of my trips the Garmin has used less power than that generated so even when I started the day with the pack only partially charged, by the end of the day it will be more charged than when I started. This of course is very dependant on the terrain you riding on and the speeds you are getting.

Workflow and cabling

So in case it’s not 100% clear from the description above I thought it worth spelling out the exact “work flow” of the set up during any given trip.

  • Plugged into the dynamo is the wire that comes with the Revo. This is permanently plugged in, so there is never any need to be fiddling around with the hub. The wire runs up the fork leg and into a top tube bag.
  • During the day light hours this is plugged into the Sinewave Revolution with the converted plug pictured above. The Power bank is then plugged into the USB port on the Revolution. From this you can then attach any device that you wish to charge. In the main this is my GPS unit but it could be a camera, phone or any other device that can be charged via USB.
  • Once a light is required I simply unplug the Revo wire from the Revolution and plug it straight into the Revo light. At this stage you can then continue to charge your USB device from the Power Bank or not, the only difference being the Power Bank won’t be continually topped up.

Long Term View

I have used this set up for roughly 1300miles and in the region of 25 nights out. After getting over an initial problem with my own crap soldiering I haven’t really had any problems. I did break a USB cable on one trip which meant I couldn’t both charge the battery and charge the GPS at the same time but this wasn’t really a huge problem. Something to remember is that the GPS does have it’s own battery so you don’t need to be charging it all the time. Mine lasts for about 10 hours and you don’t need to finish a trip with a full battery so you can always be using the Power Bank to charge your phone/camera as you are riding along. It took me a few trips to make this seemingly very obvious connection. I would say that I still “manage” my phone battery a lot, constantly putting it into air plane mode but I use it to take photos and normally there is no signal anyway so it’s not like I’m missing calls.

So as you can probably gather I’m a fan of dynamos now and can heartly recommend there use. The exact make up of the gear may depend exactly on you, what you want and your budget but the concept of using a dynamo to power lights, GPS and phone in an off road environment is in my opinion a sound one.


  1. velomore99@gmail.com' Jamorris011

    I’m trying to source the female connector that you soldered to the sinewave. Do you know the size/type I need to be searching for? Thanks!

    • composite

      I can’t immediately help you out there as I didn’t source mine in the first place. I could try to get in touch with the person that found them but I haven’t had any contact with them in some time.

      Alternatively you could maybe contact Exposure and ask them, it’s the same plug that they use in the Revo.

So, what do you think ?

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