Question about CHOETECH 10400, voltage and power banks in general?

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manta
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Question about CHOETECH 10400, voltage and power banks in general?

Hello,

I recently acquired the following power bank from Choetech:

CHOETECH Power Bank with Quick Charge 3.0

I specifically picked this power bank for the LiPo cells. The power bank is functioning fine and I have no complains but I have noticed one little quirk.

When the power bank is off, the blue port has no power at all, meaning that if you plug in a USB power meter it doesn’t measure anything. But in contrast the other port on the power bank, labeled as USB2, measures a voltage of 3.67V.

In short with the power bank off, the secondary port has voltage when the primary port (blue) does not. When you turn the power bank on, both ports switch to 5.25V.

My question is, if this is normal or not? Can anyone else confirm this is happening on their power bank and if so what’s the benefit of such a design.

For the record, the store I purchased the power bank from has confirmed that this is happening with all of the samples they have. So it’s not a problem specifically tied with the one I purchased.

Many thanks!

Edited by: manta on 12/11/2017 - 02:13
Ricez
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They usually have 2 different controller ICs, 1 for each port when dealing with QC vs regular USB. I assume one just disables the boost circuit and leaves the output connected direct to the internal battery.

e.g. https://www.youtube.com/watch?v=TyY-aO1G-CY

It’s just a quirk. The only thing to worry about is if the cells are still protected when the unit is turned off or you could end up over discharging the cells e.g. by using a dumb load like an LED

manta
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Ricez, thank you for that video. It was very informative.

If what I am measuring with the powerbak off is the internal battery, can I use that reading to monitor the cells?

Fully charged I am measuring 3,67V and at roughly 75% battery remaining I am measuring 3,10V.

What’s the lowest safe voltage I should be keeping these cells at?

I realise all this is probably handled by the onboard circuit but… food for thought!

According to the manufacturer these are LG 2600mA cells.

Ricez
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I’m not sure the low cutoff, you could probably find an LG 18650 datasheet to find it

And yes you should see the battery voltage on the usb port

manta
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gauss163 wrote:
manta wrote:
[…] If what I am measuring with the powerbak off is the internal battery, can I use that reading to monitor the cells? Fully charged I am measuring 3,67V and at roughly 75% battery remaining I am measuring 3,10V […]

It can’t be (Li-ion) battery voltage (even with a diode drop) since that 0.57V drop from full corresponds to a 55% or 95% capacity drop, not 25%

Well, the measuring system is just 4 leds on the power bank. I am not sure if estimation is based on voltage but the power bank is brand new and probably needs a cycle or two.* The cells are advertised as LiPo if that makes any difference.

It would be interesting though if by just plugging in a USB meter you can check the voltage on the cells which would make it much more reliable than a rough estimate every 25% for each led on the power bank.

—-

  • First discharge to 25% reads 2.93V.