So my plan is to charge a powerbank with a bicycle dynamo. I have got it to work with a full bridge rectifier and a linear regulator, it just isn't very effective. I used the following circuit:

schematic diagram

(The hatched box is the circuit that comes with the powerbank).

After some research I found that using a buck-boost converter is way more effective. So I ordered the following from AliExpress: https://www.aliexpress.com/item/Boost-Buck-DC-DC-adjustable-step-up-down-Converter-XL6009-Module-Solar-Voltage/32661520979.html?spm=a2g0s.9042311.0.0.36774c4dvUq5VL

I connected it to my DC voltage generator to set the voltage to approximately 4.5 V, since that's what the power bank would need. Until here it all worked fine.

Then I connected it to my circuit instead of the linear regulator. When I started spinning the dynamo, the output-voltage of the buck-boost converter would rise quickly to 20 or 25 V (probably even more, didn't want to try that though, in fear of breaking it) with only 3 to 4 V input. I also tried it without the capacitor (1500 μF), hoping that would solve the issue, which it unfortunately didn't.

I know there are different types of buck-boost converters and I might have picked the wrong kind... Could someone please help me to get this working?

Any help is appreciated.


Edit: The linear regulator I used is a L7805CV, which has an output voltage of 5V.

Here the schematics of the circuit I used with the buck-boost converter: enter image description here

The Capacitor should be big enough. I measured it with an old oscilloscope and it looked fine as far as I can tell (by that I mean it was a more or less smooth line).

  • \$\begingroup\$ Did you measure the output of the linear regulator? \$\endgroup\$
    – pnatk
    Nov 13, 2018 at 16:30
  • 1
    \$\begingroup\$ When testing the buck boost, did you do it under load? Add a load resistor or some leds with resistor you wouldn't worry about blowing. \$\endgroup\$
    – Passerby
    Nov 13, 2018 at 16:48
  • \$\begingroup\$ I think you're basically screwed. The XL6009 controller on that module is fundamentally a boost converter. The only way to get it to buck is in a SEPIC configuration, and I don't see how the components on the module would achieve that. \$\endgroup\$
    – Dave Tweed
    Nov 13, 2018 at 18:42
  • \$\begingroup\$ @DaveTweed So what do you suggest I should do? Get another buck-boost converter? Which one would you recommend? \$\endgroup\$
    – D. Tschan
    Nov 13, 2018 at 19:07
  • 2
    \$\begingroup\$ @winny nothing about this is related to usb handshakes. Nothing. \$\endgroup\$
    – Passerby
    Nov 13, 2018 at 20:43

1 Answer 1


The bicycle "dynamo" you have shown in the schematic is an alternator. (A dynamo is an electrical generator that creates direct current using a commutator.) This means that the voltage on the input to your buck-boost converter will be seeing half-wave rectified AC unless the capacitor is big enough to maintain voltage during the valleys. (Why is there no C value shown on the schematic?)

If you edit your question to show an accurate schematic of your setup we may be able to help further.

  • \$\begingroup\$ The Dynamo is a AC generator then. That's why I used the full bridge rectifier \$\endgroup\$
    – D. Tschan
    Nov 13, 2018 at 19:09
  • \$\begingroup\$ OP includes the capacitor value in the question text. \$\endgroup\$
    – Passerby
    Nov 13, 2018 at 20:45
  • \$\begingroup\$ Sorry, if it was there I missed it. \$\endgroup\$
    – Transistor
    Nov 13, 2018 at 22:14

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