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> Normal vs. Fast Charging
Eldkatten
post Jun 2 2019, 09:56 AM
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Hello,

by chance I bought a charger that can handle fast charging (GOOBAY 45173), and in connection with this I collected some observations and have a few questions.

First about normal charging:
When I connect the Gemini to my normal charger, which can provide up to 2.0A @5V, the Gemini draws only slightly less than 0.5A. When I connect the Gemini to a 10000 mAh Powerbank, it draws about 1.5A @5V. Why is this?

Fast charging:
After a few seconds after connecting, the charger voltage jumps from 5V to 9V, and the Gemini draws about 1.6A @9V. So it is fastcharging. Does anybody do this regularly? Are there any observations as to whether fast charging influences battery life, in means of charging cycles?

I don't trust the fast charging process, and both the charger and the Gemini - i.e. the battery - get pretty hot during charging. I can't believe this isn't harmfull for the battery. Is it?

Kind regards
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Daniel W
post Jun 3 2019, 09:56 AM
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QUOTE(Eldkatten @ Jun 2 2019, 07:56 PM) *
First about normal charging: When I connect the Gemini to my normal charger, which can provide up to 2.0A @5V, the Gemini draws only slightly less than 0.5A. When I connect the Gemini to a 10000 mAh Powerbank, it draws about 1.5A @5V. Why is this?
Fast charging: After a few seconds after connecting, the charger voltage jumps from 5V to 9V, and the Gemini draws about 1.6A @9V. So it is fastcharging. Does anybody do this regularly?

The 0.5A is the basic USB current. Before the more advanced standards, a dedicated "charging port" could put a certain resistor between the D+ and D- lines to tell it can supply 1.5A, so I think that's what your battery bank does, but not your "normal" charger. For reference, my 2A@5V Samsung Galaxy Note 3 charger, happily provides 1.5A to my Gemini. So does my Note 8 charger, which supports Quick Charge, that is incompatible with Pump Express. I'd guess most people uses the charger included with the Gemini (supports up to 1.67A x 9V = 15W), so probably most users are "fast charging". To be picky, the charger also supports 1.25A x 12V = 15W, but the Gemini doesn't, so that mode won't be used.

As only near-empty batteries can take the full charge current (it should drop as the battery charges), fast charging devices should typically only get warm in the beginning and only when charged from a fairly depleted state, so the overall effect should be slight. That said, brands supporting 30W+ chargers for their phones, makes me think they're trading lifespan for speed. Since I have another main phone, my Gemini tends to have dropped to around 60% after a few days, at which point I tend to charge it. As the current at the level has dropped a bit, it tends not to get warm when I use the included charger. I tend to stop when the LED turn amber at 90%. There's little science behind those numbers, though, mostly convenience.

Things to avoid are prolonged exposure to heat and/or very high or low levels. Charging over night is probably mostly harmless, but doing so using a fast charger is pointless at best. Keeping a power bank plugged in to keep a device "topped up", will age the battery faster much than if charging when needed. For further reading, I think this is one on the better articles on the topic I've found: https://batteryuniversity.com/index.php/lea...based_batteries
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Eldkatten
post Jun 4 2019, 01:32 AM
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Hello Daniel W,

thanks a lot for the elaborated answer. It all makes perfect sense. The only question still open is why other devices draw 1.0A to 1.5A from my other charger, while the Gemini only takes 0.5A (0.47A to be precise)

Anyhow, I think I'll try fast charging again to see whether the temperature drops, and how the charging current develops over time.

Kind regards
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Daniel W
post Jun 4 2019, 06:09 AM
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QUOTE(Eldkatten @ Jun 4 2019, 11:32 AM) *
The only question still open is why other devices draw 1.0A to 1.5A from my other charger, while the Gemini only takes 0.5A (0.47A to be precise)

Given how twisty the history of USB is, and the variety of how different devices interprets (or not) the various standards, I'm not too surprised.
My Gemini, even at a 70% battery level, pulls around 2.2A at ~4.85V from my (non Pump Express) 2A rated Samsung chargers.
Maybe your other charger thinks that's a bit too much and limits the current to protect itself, while your battery bank doesn't.
Or maybe the Gemini, for some reason, fails to detect that your other charger has a dedicated charge port.
Or maybe it doesn't have a dedicated charge port per se, and the other devices just tries pulling 1-1.5A anyway, hoping for the best.
Or maybe the cable you are using, causes more of a voltage drop at higher currents than the Gemini is happy with.
Or maybe the Gemini doesn't like your USB power meter.
Or, or... or.... some questions just doesn't seem to have have clear-cut answers.

You could try your other charger with the Gemini, using the shortest, fattest USB cable you can find and see if that makes any difference.
Or maybe you could try a few other chargers, when, say, visiting friends, with the Gemini, to see which does and doesn't supply >0.5A.
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