PedalCell bicycle power source

The PedalCell is a new take on a design nearly as old as the bicycle itself – the bottle dynamo, running on the front wheel. PedalCell has used the latest supercapacitor technology and a high-output dynamo to create a charging system that beats the pants off hub dynamos in terms of power overall and especially at low speeds. Yes, it's more visually intrusive – but if you've already covered your bike in racks and bags it looks fine.

PedalCell launched in late 2020 after a five-year development process. At least one of the team is a literal rocket scientist, having worked on the SpaceX project, and the amount of electrical geekery that's gone into the PedalCell is huge for what is at its simplest a spinning magnet inside some wire loops.

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You buy the PedalCell from its US website for $320 including shipping. This means you're looking at around the £280 mark with VAT and duty applied. As import duty can be a grab-bag of which code the border force decide to apply, don't take this price as gospel.

The PedalCell comes in two parts: the dynamo which clamps to your fork or frame, left or right side, front or back, which then attaches to the charging box with an 80cm cable. That cable length is as measured from where the cable emerges from the clamp and starts its journey to the box. There's plenty of slack for fork-mounted installations, but if you have a large frame then it might not stretch all the way to the handlebar.

Of course there's nothing saying the box has to mount on the bars – there's enough stretch in the rubber ladder strap to fit on a 35mm frame tube too. You could also pass the cable through the port in a framebag, thereby waterproofing your solution while cleaning up the look.

This would be a sensible plan for bikepackers using the PedalCell to charge up battery banks – particularly ones then able to pass charge through to devices while being topped up themselves.

A few caveats: PedalCell doesn't recommend it for use on carbon wheels, and it won't work on Lauf or Cannondale Lefty forks where the wheel moves in relation to the upper part of the fork. PedalCell says that you can mount it on the chainstays in those cases.

The charger itself measures 75 x 30 x 55mm, with the aforementioned rotating-mount rubber ladder strap on the back, the 6-pin connector at one end and the two USB-C charging ports at the other.

The USB ports aren't waterproof per se, I'd say rain-proof to an extent. Let's face it, few USB ports are waterproof, and if you're after a solution that will survive torrential rain you need to be looking at mounting everything in a frame bag, and/or going for wireless charging as offered by the likes of the SKS Compit+ system.

Installation

Installing the PedalCell is a few minutes' work with the provided 4mm Allen key. PedalCell offers a tamper-resistant set of bolts and a special Allen key for $20. One theft-proofing option is to just remove the charger box, which might discourage people who know it's needed.

It's really important to align the dynamo so the rubber ring sits perpendicular to the rim surface when engaged. It has a bolt to change the dynamo angle to fine-tune this.

The dynamo is held against the rim by a strong spring, with a locking mechanism to hold it out from the rim when not in use or changing wheels. This can be operated while riding with practice and care. PedalCell advises the top speed of the unit is 40mph; I wouldn't recommend trying to disengage the dynamo at that speed. This ability to totally disengage the dynamo is a bonus over hub models.

The dynamo needs about 5mm of rim to contact, which should be fine even for low-profile disc brake-only rims. It will wear black anodising off rims, leaving a silver strip of about 3.5mm, which against a tyre is hard to notice but worth being aware of.

PedalCell claims O-ring life of around 2,000-3,000 miles, and provides two replacement rings with your purchase. A pair costs $10 plus shipping, so hardly an expensive maintenance regime.

An obvious concern with a physical rubber-on-metal interface exposed to mud, rocks and general road filth will be wear, but over a few hundred miles of bikepacking on gravel roads and muddy tracks the PedalCell O-ring performed flawlessly and still looks in good shape. Overall, the installation and physical robustness of the PedalCell can't be faulted.

Charge!

One of the USB ports is a constant-output 'priority' limited to 600mA (3 watts), the other is the 'high power' port that can do 2.4A (12 watts), but needs the supercapacitors to charge up first. Somewhat annoyingly, this port is identified by a tiny black-on-black icon of a lightning bolt – which is near-impossible to see in sunlight or rain. I rubbed mine with a white crayon to make it stand out. The 3W/600mA priority port stays on for 30 seconds once the bike stops, if the capacitors are full – so if you're using that port to power a USB light you should be good.

Inside the box is a computer that controls which ports get how much power, depending on your speed, what's plugged in where, how charged the supercapacitors are and so on. The supercapacitors are rated for between half and one million charge cycles, and operate over a wide temperature range. So basically, plug your stuff in and ride. Let the box charge everything as best it knows how.

I went for a 5,000mAh battery pack that could pass the charge through to my iPhone, thereby ensuring both my phone and the battery pack were always charged. On multi-day rides I'd plug my Garmin 830 and InReach GPS communicator into the 3W port, as they took next to no time to charge back up.

This is where the PedalCell rubber hits the road – just how much juice can you get from it for a given speed, compared to a dynamo hub? The answer is 'lots' – way more than a dyno hub setup and, critically, at much lower speeds.

Now PedalCell has been in the wild for a while there are several independent test results, including this one from the German FahrradZukunft team. Their results show the PedalCell beating out the other dynamo-USB converters, which were all powered by a SON28 hub dynamo on a test rig.

The SON28 is £200 by itself; you then need to build it into a wheel, and then buy the appropriate USB converter (dozens out there, anywhere from £30 to £237) to make it useful for charging things. Oh, and they do a max of between 0.8 and 1.5A at best, and you usually can't run lights and charge USB at the same time.

Of course, if you're using the dynamo hub just for lights that's a different story as you don't need the USB device – fill yer boots. But these days most people are also looking for phone, navigation and other charging options.

PedalCell has published a handy Google Spreadsheet detailing expected charge rates for given wheel sizes and speeds.

So the dyno hub + USB converter route is both considerably more expensive and less powerful than the PedalCell – but is undeniably tidier. If a dyno hub fails, you're looking at a wheel rebuild – which, depending on how handy you are (or not), could set you back more money and time.

There's no right or wrong way to do on-bike power, just what's the best balance of cost, looks, power and maintenance for your use case.

In use

Out in the Highlands on my bikepacking rig, the PedalCell gave me good results as reflected in the various online lab test articles. A 35km ride with 500m of climbing at an average of 17.5kph over two hours gave an output of 1,300mAh into a battery – meaning a usable 885mAh output available later thanks to the loss in the charge-discharge process. For comparison, that's about a third the capacity of a newish iPhone – so six hours riding would give you a full charge. Or run a Garmin for about a week, my 830 taking just 350mAh to go from flat to full.

The PedalCell is pretty quiet when engaged – you can hear a low hum, but if you're riding over gravel or chip seal it pretty much vanishes into general road noise, especially over about 25kph with the wind in your ears. Certainly it's much quieter than I remember the milkbottle-shaped metal-on-tyre dynamos of my childhood.

On an overnight trip of 140km, the PedalCell gave me more than enough juice to keep my iPhone, Garmin and GPS tracker running with screens on constantly, with loads in the battery bank for recharging overnight.

> How to go bikepacking: A beginner’s guide to getting started

If you were desperate to charge your phone as quickly as possible it will always be better to plug directly into the PedalCell, thereby omitting the 20-30% loss converting from 5V down to the battery bank's internal 3.7V, then back up to 5V. It's this inefficient conversion process – in or out – that makes battery banks hot to touch while charging or discharging. That heat is lost power.

Another factor that can make a considerable difference to the results you see from any charging solution is the number, type and length of USB cables and adapters you use. Adding in one or two right-angle adapters – while making things tidier – can decrease the efficiency by decent amounts. So always use the shortest leads with the fewest connection points.

Current available from the high-power port does depend on speed and the time the PedalCell has been running. The charger is constantly negotiating the best USB charge current with devices like phones, and each phone and battery bank manufacturer seems to do this differently. Fundamentally, you just need to know that the PedalCell manages charging for you at the most efficient rate, and that that rate is roughly two to three times higher than what you'd get from a dynamo hub at the same speed. If you care, the amount of drag for a given power output is about half that of a dynamo hub too.

Conclusion

Overall, the PedalCell is a great bit of kit. The design is robust, looks good paired with racks and bags, and critically delivers a lot of power at lower speeds more associated with long-distance riding. Price-wise per watt delivered, it beats out any dynamo hub/USB charger combination, without the special skills or tools that building charging into a wheel requires. It comes with a two-year warranty too.

If you need to power devices on long rides and don't mind the look, it's hard to go past the PedalCell.

Verdict

Great way to keep devices charged, while being easy to fit and swap between bikes