Product Review: SPIN UP F12W-PRO Bicycle USB Charger Dynamo from SunUp Eco (2)

Material (case)Aluminium
Material (USB charger)FRP (Fiber Reinforced Plastic), Aluminum
Working temperature-25°C ~ 65°C
Speed limit70km/h
IP ratingIPX4

Read Part 1 and Part 3 of the Review

The Challenge of Making a Front-Mount Bicycle Dynamo

Before the release of F12W-PRO, two rear-mount bicycle dynamos (R12W and R03W) in the line of SPIN UP have been in the market for some time. Turned out it is quite challenging to develop a front-mount model. While there are many buffers, including the saddle, the pads on our cycling pants, and even our butt, to absorb the vibration coming from a rear-mount generator, for a front-mount one, the slightest vibration could easily find its way to our more sensitive fingers via the fork and the handle bar. On the other hand, any noise from the generator will become more noticeable from affront than from arrear, thanks to the structure of our ears. It may sound trivial, but all these small nuisances will turn into major annoyances during long rides. But a rear-mount bicycle dynamo may not be an ideal choice – I wouldn’t want a generator on the rear wheel because all my electronic devices are on my handle bar. I don’t want to run a long wire from the rear wheel to the front.

Therefore, in seeing the need of a front-mount model, Mr. Yang and his team had been working on minimising the noise and vibration of the generator in the past 3 years until F12W-PRO was all set and ready to meet its users.

How Intelligent Power Management System (IPMS) works

As mentioned earlier, SPIN UP F12W-PRO is the first bicycle dynamo with Intelligent Power Management System (IPMS). Depending on our riding speed and the level of power available in the built-in reservoir battery (a lithium ion battery), the IPMS operates in 4 different ways in order to maximise energy efficiency.

In the first scenario where the reservoir battery is empty or near-empty, and our speed is not fast enough to generate the required output of 5W, any energy generated from our cycling will go straight into the reservoir battery first. It means the charging will not start if you plug in your phone at times like this, not until there is enough energy stored in the reservoir battery.

In the second scenario where our speed is still not fast enough to generate the required output of 5W, but the energy level of the reservoir battery has passed the required minimum, the IPMS draws energy from both the built-in reservoir battery and the generator at the rate of 2.7W and 1.7W respectively, making up a total output of 4.4W, which will surpass the minimum requirement of most smartphones and thus kick start the charging process. Although it is not impossible to tap more power from the generator, the development team decided to limit it to 1.7W for better cycling experience. My guess on the technical reason behind it is that they don’t want the generator to create too much undesirable drag during climbs.

In the third scenario where we are cycling at a medium speed of 15-17km per hour, the generator will happily churn out electricity at the rate of 5W, which, after going through the rectifier and the voltage regulator, is converted into a stable supply of 5V1A that can be fed directly to the USB port and then to your phone or other electronic devices. The reservoir battery is left untouched.

In the fourth and last scenario where our bike is traveling faster than 18km per hour and the energy generated is more than 5W, while keeping on pushing out a stable 1A current to the USB port, the IPMS will direct any surplus energy to the reservoir battery for later use. But again, to avoid creating too much undesirable drag, the maximum energy output is limited to the rate of 6.6W.

To minimise the possible harm and annoyance caused by our electronic device being charged having to stop and resume charging within a short interval, say every time we stop to take a sip of water or in front of a traffic light, the reservoir battery will power the USB port solely for around one minute before it goes off.

When both the reservoir battery and our electronic device are fully charged, the generator will only generate enough energy to power the onboard computer and circuits and thus bring the drag level to minimum.

For those who is also in need of a powerful front light, the additional wire branching out from the upper end of the cable, which is ready to be connected to a front light, will be handy. A Dynamo LED light set that includes a front light and a rear light is also available on the SPIN UP official site.

What Makes SPIN UP F12W-PRO So Special

Most of the other bike dynamos available in the market only have 3W of rated power. It’s good enough to light the bike lamps, but they have to rely on a power bank to collect trickles of energy before it can be used to charge a smartphone, which usually requires a supply of 1A. This really made SPIN UP F12W-PRO, which can feed energy directly from the generator to your electronic device without having to route through the reservoir battery, stand out from the crowd. Apparently, the time it will take to charge your device will be a lot shorter and the energy loss that will inevitably occur during the charging process will be far less.

Lithium ion batteries are very efficient, but still, a certain amount of energy will be lost when you charge the battery, and a certain amount of energy will be lost when you use the battery to charge a device. Under lab conditions, the total energy loss will amount to around 5%. This will increase to about 10% in the actual working environment, which is still pretty low. However, the cell voltage of the battery is around 3.6V~3.85V. Therefore, in order to be able to charge the battery with a 5V power source, a step-down circuit to convert the voltage from 5V to 3.6V~3.85V is required to be built inside the battery. Then again, in order for the battery to be able to charge a device of 5V USB standard, a step-up circuit will be required. The efficiency of these circuits are around 90% for one trip at best. So, the total energy loss for charging, storing and retrieving power with a lithium ion battery adds up to around 30%.

To confirm this, I got myself a USB meter to take readings of a pair of old and new power banks. I want to find out the amount of energy required to fill them up from zero and the amount of energy they can return. 

The round trip electricity loss is found to be ranging from 27% to 40%. This is the amount of energy you can avoid losing by charging your device directly from a power source.

Now let’s get back to bike dynamos. According to a test I conducted later on, it took around 3.17 hours to fully charge my iPhone 11 Pro via a 1A power source.This is equivalent to 15.85Wh of energy. With its 12W generator, the F12W Pro can churn out 1A of current as soon as the bike reaches the speed of 15km/h. But if a power bank is used, like for those low-power dynamos, more energy will be needed to make up for the energy loss incurred in the process of charging, storing, and retrieving. The estimated total energy needed to fill up the iPhone and compensate for the loss will be: 15.85Wh / (100% – 30%) = 22.65Wh. 

A lot of low-power dynamos are not able to charge an iPhone directly because: firstly, they need an additional circuit to regulate the alternating current and stabilize the voltage; secondly, the efficiency of those circuits may put the net output power below the useful level. Therefore, those low-power dynamos need to rely on power banks to store up the energy first. So, to fully charge the same iPhone, it will take 22.65Wh of energy, as in our estimation above. Assuming those additional circuits have 100% efficiency and the dynamo is operating at its full capacity, it will still need 22.65Wh / 3W = 7.55 hours of cycling.

3.17 hours v.s. 7.55 hours!

Mr. Yang and his team have substantial reasons to believe their F12W-PRO is so far the best.

There is a speed limit of 70km per hour set upon the use of SPIN UP F12W-Pro though. If your speed exceeds the limit, excessive high voltage will build up at the generator’s mother board and eventually break down its components permanently. And such limit is set for bikes with 700C wheels, for which 70km per hour is about 550 turns per minute. That means if you are mounting your F12W-PRO to a smaller wheel, the speed limit for you is lower.

It was a very enriching morning. Soon it would be lunch time. Before heading out for lunch together and me bringing a SPIN UP F12W-PRO home for more thorough trial, my conversation with Mr. Yang strayed to Nikola Tesla, the inventor of AC induction motor and the square root of three for the three phase electrical systems…

Would I Pay USD499 for the SPIN UP F12W-PRO

At the time of writing this post, I have been using the dynamo for more than 3 months. I will share my experience with it in more posts to come. All in all, it has been working very well. I have no intention of returning it to Mr. Yang. I will pay the hefty yet worthy USD499.

Part 3 Charging Performance Report

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