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I want to make an ultimate powerbank for my biking trips. This involves accepting a dynamo input and slow charging the battery pack with its ~3W and also cramming as much energy as possible as fast as possible in case when wall power is available.

Is there an easy way to make the USB input be a well behaved device that supports QuickCharge? I'm hoping for something along the lines of TPS2514 (that's what I'm planning to use for output) where I would somehow choose maximal allowed voltage and then ask the chip to give me everything the source has. No data transfer is necessary for my device.

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  • \$\begingroup\$ The TPS2514 only puts signals on the data lines to make devices think your USB is a charger. That is nowhere near any proper QuickCharge implementation. There are several QuickCharge standards, what version are you aiming for? Implementing QuickCharge with higher voltages 9 V, 12 V etc will not be trivial. I would just buy a ready made power bank with the right functionality. \$\endgroup\$ – Bimpelrekkie Apr 30 at 12:23
  • \$\begingroup\$ I'm not aiming for any version in particular, I just want fast charging :-) (That probably means 2.0 or 3.0). I'm still considering opening a store bought power bank and hacking in the dynamo input, but I'm not sure that it would be the best solution. \$\endgroup\$ – cube Apr 30 at 12:45
  • \$\begingroup\$ I'm not aiming for any version in particular, I just want fast charging :-) Consider that it is often the device (phone, tablet) you're charging which determines the charging speed. No use implementing QC 3.0 if your phone doesn't work properly with that. \$\endgroup\$ – Bimpelrekkie Apr 30 at 12:50
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    \$\begingroup\$ The question is too broad to answer. "not not aiming for any version in particular, I just want fast charging", "I would somehow choose maximal allowed voltage"... You need to define all your parameters yourself, define what kind of capabilities you can handle. Unfortunately the device end of QC is undisclosed, and usually is implemented within Qualcomm processors. \$\endgroup\$ – Ale..chenski Apr 30 at 15:29
  • \$\begingroup\$ Thank you, the fact that device end of QC is undisclosed is new for me and is very useful to know. It means I can stop searching for any ready made ICs. I found this arduino library: github.com/septillion-git/QC2Control which is going to be a nice place to start experimenting. \$\endgroup\$ – cube May 1 at 6:52
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slow charging the battery pack with its ~3W and also cramming as much energy as possible as fast as possible in case when wall power is available

Some/many powerbanks will do just that. I.e., they take as much power as they can up to their designed maximum. Well-behaved devices take care not to overload the USB port, others (cheaper ones) don't care. And because they don't expect to get all the current they could handle anyway, most will work at basically arbitrarily low power/current if more is not available.

The system self-regulates/-stabilizes when the power bank tries to draw more current than the USB port/charger will provide, in which case the voltage from the port will drop, which reduces the current the power bank draws for charging and thus stabilizes at the minimum of the power the power bank wants/needs and the power/current the port can supply.

You may well find that a not-well-behaved powerbank violates the USB standard by charging from a USB port at, e.g., 700mA and 4.3V. I.e., it draws more current than the standard permits (500mA), which results in a voltage drop to below USB standard voltage and hopefully won't damage the USB port.

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