Report on 18650 UPS module

Other Hardware General Electronics
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On some recent thread, there was a mention of this new 18650 charger/boost converter module.

https://www.ebay.com/itm/315307599233?var=613780278579

I try to keep up on these as new versions appear, so I ordered one, and wanted to report on what I found.

The good side is that the module does not have the minimum current auto-off found on most powerbanks. So you don't have to sink current to keep it alive. And you can charge the battery and power the load at the same time. So the claim that it's a "UPS" appears valid. It has a USB-C power input port and a USB-A output port. Charging current is set to 420mA.

The module uses the ETA9640 chip, which is a combination linear charger and 5V boost converter, all on the same chip. One would think that this should handle everything, including the load sharing circuit that allows charging and load powering at the same time. But there must be something that doesn't perform correctly, because also found on this module is a second 5V boost converter. The second converter is always running when power is coming in on USB. At the same time, the output of the ETA9640 is channeled through a P-channel mosfet which is turned off when USB power is present. So when USB power is present, the second boost converter always powers the load, which leaves the ETA9640 to charge the battery. When there's no USB input, the battery powers the ETA9640's boost converter which powers the load. It's not clear why this second boost circuit is needed, but it may have something to do with termination charging current when load current is present.

The big problem with this module is that since the battery's connection to the boost converter is inside the ETA9640, the battery will be powering the boost converter all the time - unless you remove the battery, which is not something you want to do with an 18650. Moreover, when I actually measure battery current when nothing is plugged into the module, I get 650uA. That's way too much for a battery-powered system. If this is to be used as battery backup UPS that's rarely invoked, it probably doesn't matter much, but for a project that will be mostly battery powered, battery life will suffer with this amount of idle current, and the battery will continually cycle between 4.2V and 4.1V.

An alternative which specifically provides for installing an on/off switch ahead of the boost converter, which would eliminate any idle current as well as permit charging the battery when the device is switched off, there's this module:

https://www.aliexpress.us/item/3256805528302478.html

However, it needs a capacitor added to the USB input to work properly, and doesn't have a USB-A output. Nothing is perfect, I guess. Well, the Adafruit power modules may be. I just haven't looked at them.

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There are a couple threads on this forum where the proper designs are revealed. There is some new chips now that work properly with less components both in Solar and non-soar configurations.
These circuits were available a while ago, I had a medium solar system that worked perfectly for 5 years until I sold the RV last summer. Of course it cost over $10,000 but now hobbyists can get very similar tech for true UPS operation.

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Solar complicates things, but Adafruit has a bq24074 module that I think works on any input. However, it doesn't include the boost converter, and is not budget-friendly. And I haven't seen any cheap clones from the Far East.

Anyway, I just found the circuit design on this one to be quite strange. The boost converter part of the ETA9640 is not needed. So they could have used a TP4056 chip, and saved an inductor. Just seems odd.

4

Thanks for the review.

Does it protect the battery from over-discharge, over-current etc?

5

Yes, it uses the XB7608 for protection. It appears to work like a DW01, except it has the mosfets inside the chip. So it only has three terminals - B-, ground, and Vcc, plus one resistor and one capacitor.

Also, it has some complicated mosfet stuff surrounding the battery terminals that I haven't figured out, but suspect are reverse polarity protection.

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