But is it a strange quirk of this charger to, without knowing reverse it's polarity as in post #4? This is something that I wasn't expecting and I've never known before.
I do not quite understand what this IC does and how it works.

 

First, its not a "strange quirk" or phenomenon, its operating as designed to detect battery polarity and charge accordingly.
That said, if the battery is very depleted, then the IC is unable to detect a voltage/polarity.
In your case, by reversing the battery, it was then able to detect a voltage and charge accordingly.
Why?, well we would have to see schematic for the IC itself, or possible determine why from detailed IC data sheet.
There is most likely some "point" at which the IC is unable to decide, which is what you encountered on you first battery insertion.

These are the IC Features
1. Built-in reference source, no-load voltage output, no external components to adjust the load voltage
2. Support Normal mode and two lights three light mode, colorful lights mode
3. The maximum charge current: 400mA
4. Support for 0V battery charge (the battery is connected), and pre-trickle charge mode, the battery better protection
5. Battery full of fast switching to constant voltage charging mode, the battery can be charged more full
6. Automatic Identification battery polarity
7. The short circuit protection
8. Overtemperature protection
9. Precharge function
10. Highly integrated, very few external components

#4 "Support for 0V battery charge" seems to imply it handles depleted battery (but who knows)
and then there's
#6 Automatic Identification battery polarity
but we don't really know how it works or it's "algorithm" for detection, we can only guess.

What we do know with some certainty is why experienced the battery charge when inserted in the opposite direction.
We aren't sure why it failed to detect/charge on your initial battery insertion.

 

Thanks to @vu2nan, post #58, we now have an explanation of the mystery (or at least the most important part).

 

Ok, thanks. But at the end of the day it will be always wise to check the polarities at each end before inserting a battery.

 

The charger feature of being able to handle reversed polarity safely is particularly useful for some versions of the 18650 cell, e.g. a tagged terminal version, where cell polarity is not blindingly obvious.

 

No it seems you can't put the battery either way because as I mentioned above, I originally put the battery in the charger the 'correct' way (negative end of the battery towards the spring) and the green light remained on and the battery did not charge up.

Some sort of chip level failure, temporary or permanent is yet to be seen.

it will be always wise to check the polarities at each end before inserting a battery.

Even wiser, buy new. Non-Chinese type. There ARE better ones out there.

 

You're right, Bob.

Here's a 'traced from PCB' or 'Reverse engineered' schematic.

https://danyk.cz/reverz30_en.html


View attachment 277398

And the accompanying text.

Schematic of a Chinese 3.7V Li-Ion / Li-Pol mains charger for 18650 (and also AA) rechargeable cells. Very simple switching power supply with just a single transistor 13001 and a single half-wave rectifier. No fuse, no inrush resistor, no EMI filter, no snubber network on primary winding. Very poor isolation in the transformer and on the PCB board. Totally non-compliant in EU, US, UK, etc. Contains HT3582DM Li-Ion charging controller chip with red/green LED indicator and automatic polarity detection. The cell can be inserted both ways around.

Nandu.

vu2nan/Nandu, excellent job on reverse engineering the schematic. Very interesting that, by far, the bulk of the circuit (i.e. everything left of the IC, is simply 110-220VAC/5V AC-DC converter to supply 5V to smart charger IC. Wonder if this would be considered "typical design" for a global input AC-DC conversion? Also surprising that the half-wave rectification with 100u filter supplying a rather dirty/variable supply to IC and it still works reliably.

 

vu2nan/Nandu, excellent job on reverse engineering the schematic. Very interesting that, by far, the bulk of the circuit (i.e. everything left of the IC, is simply 110-220VAC/5V AC-DC converter to supply 5V to smart charger IC. Wonder if this would be considered "typical design" for a global input AC-DC conversion? Also surprising that the half-wave rectification with 100u filter supplying a rather dirty/variable supply to IC and it still works reliably.

Hi wraujr,

I have not reverse engineered the schematic!

The credit is due to Danyk of Czechoslovakia (https://danyk.cz/index.html).

Yes, it's a simple SMPS-based, Li-ion battery charger that employs the HT3582DM, a universal charger control IC.

Nandu.

 

At last. the mystery is solved.
That's indeed, a nice chip.

 

At last. the mystery is solved.
That's indeed, a nice chip.

Hi,
I have a similar charger, that went 'wonky', so I disconnected all of the circuit, and now connect to a model battery charger directly using crocodile clips. (Which beeps if I've connected in reverse)
Camerart.