Technical > Lighting and Electronics

Some general information on hub dynamos and USB charging.

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Pavel:

--- Quote from: in4 on April 03, 2016, 09:01:23 pm ---Thanks for posting, its a great resource for those of us looking a little more closely at the subject. I'm thinking about the best way to run a frontlight and charge a gps, android phone, android tablet (perhaps!) and one of those water sterilising pens. I'd like to keep things as simple as is practical but there are a lot of options out there...which is a good thing.

--- End quote ---

I guess we have left the carefree cycling of the 1970's far behind. :)

igarocom:
[Edited to remove commercial promotion, since unauthorized advertising is prohibited by Forum member guidelines. -- Dan, Thorn Forum Administrator]

Hello,

[The] reason you can't get more power from Sinewave, e-Werk, USB-Werk etc is because these devices uses chipsets which have a current limit (i.e Sinewave 1A/5W, and E-Werk has a 2.8W limitation at 5V). This is the reason many of the devices level off in the chart.

The "free power" technique is just two electrolytics capacitors back to back and assists to ride out the low frequency generated by the dynamo. What matters is that there is sufficient capacitance on the input side of the circuitry, meaning it can be in two places; 1. across the dynamo (this technique) or 2. after rectification.

So here's the thing, if you're going reasonably quick and have a load attached then the AC across the dynamo might be 6V. A typical Shimano hub resistance is 4.3ohm which gives a backflow of 1.4A when the hub's AC is at 0V. If the load (i.e USB device) is high enough then part of this will go through the circuit.

Consider when you don't have a load attached and you're going downhill at speed. The AC is now 50V and amperage being put back into the dynamo is 11.6A at peak. The capacitors can't sustain that discharge rate cycle and will fail either through wearout or heat, but while they are operational that power is being reversed into the dynamo.

I made an argument on another German website that efficiency at low speed is more important in real-life conditions. I'll now explain:

Riders will rarely see more than 5w from the dynamo (certainly not consistently) and most USB devices that accept high current input will park the current at a determined level. They do this by increasing load and testing the voltage drop on power on to determine what power level can be drawn (i.e USBv1 is 100mA, USBv2 usually 500mA-1A, power adapter 1.5-2A). If I take the Sony M4 Aqua for example (using an Igaro D1) the input current is 0.74A. It doesn't matter if I go 60mph, it will remain 0.74A. If I plug the same phone into a wall charger it'll take 1.5A. Why? because it "asked" for 1.5A and the voltage drop was too low, so it switched to 0.74A and stuck at that level. Most phones and USB powerbanks will do this - it's a requirement of being able to charge from USB sources of different current levels.

This is exactly why the Sinewave Revolution takes 10 seconds to turn on. [Another brand, t]he Igaro D1 also has a similar approach but monitors the dynamo frequency (I don't know if the Revolution does this). Also worth mentioning, if the charger has no voltage cutoff then the device may not charge at all (hence E-Werk doesn't work with iPhone).

In summary I recommend you take [published charger efficiency and output] charts with pinch of salt as you'll probably never be able to charge the internal "cache" battery and a smartphone at the same time, and if you go down the USB Werk route you'll have such low efficiency by way of cache battery losses that you'll not be able to keep your phone charged at all. This is the difference between sticking a dynamo on a motor for a graph and actually getting out there and riding. I'd impress upon you that when I did that (I'm a RTW tourer) and analysed the best means of keeping devices powered I concluded a powerbank works best for convenience (might as well charge something if not the phone/gps), but otherwise get the juice directly into the device. The best means of doing that is through efficient USB circuitry, because 3W of power in real world riding means efficiency is a deal breaker. There is no "free power".

Cheers,

Andrew

E-wan:
interesting

does anyone know of a USB battery that allows charging pass through and fast USB charging using a higher current

planning on powering a Samsung galaxy S5 and Lezyne Macro Drive 600XL front light Both of which support fast USB charging

Thanks

John Saxby:
E-wan, a note that my Anker 2600 does not allow pass-through charging. Not a problem for me, as I don't need the latter.  If I need to charge a device at the same time as my battery, I just use the Y-splitter cable.  Recharging then takes longer, of course.

DAntrim:
I use the power monkey extreme battery to charge my Galaxy S5 which allows pass through charging, which also gives the option of charging the battery from mains, dynamo or solar.

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