Lithium 12v tool battery charger... no negative connection?

[budwich]

I have a drill and battery but no charger so I bought a "universal charger" 120ac in ... 12vdc out (not really universal in lithium world). Anyway it has three contacts, positive, negative and "T" (temperature sensor). I connected those contacts to the contacts on the battery. No charging happened and only the status light is on (green solid) which the label indicates "100% charged".... but the battery isn't near that at around 9v and dying. There doesn't appear to be any difference whether the battery is connected or not. I got suspicious and pulled the thing apart. Started looking for basic stuff like broken contacts, loose components and checking some voltages in (120vac), 165v"DC" after the basic rectifier stage at the input (unfiltered). Then I looked at the output contacts. I could see how the positive and "T" contacts were connected, but for the life of me can't see how the negative contact does anything as there is no connection path on the board to any part of the circuit. Is this some new way of charging lithium batteries... charging thru the temperature sensor (sensor measured ~13Kohms... room temp ) ???

I can't see how the charger could ever work. Having said that, is there some sort of connection / component that I could add to make it work? Attached is picture of the back side of the board (circuit side) and the component side.

Anyway help with understanding what the heck is happening with this "design" and how can I "fix" it would be greatly appreciated... and maybe save my tool and battery from the recycle bin.

[Sam Scarbo]

That unconnected contact is not the -ve terminal. The top contact is, which is connected to the -ve lead of the electrolytic cap C3.

[stj]

that looks very incomplete.
can you read the part number on the chip? i think it's just a cheap psu

[stj]

btw, for vague stuff charging, look into a clone B6 charger.
those are good.

[budwich]

That unconnected contact is not the -ve terminal. The top contact is, which is connected to the -ve lead of the electrolytic cap C3.

My bad... I should have done more labelling on the picture. There might be confusion on the "flip" between the two pictures. . I am also going by the labelling on the shell which has the negative going to the contact highlighted. I think the "T" contact is the one that you are alluding to. Sorry for the confusion.

[budwich]

that looks very incomplete.
can you read the part number on the chip? i think it's just a cheap psu

My guess (very small numbering) is GG1052 and the second number on this small chip is maybe BO7L2435.

As for "incomplete", what area are you looking at particularly?

[stj]

http://en.cokintech.com/product-item-18.html
that schematic is probably close

[budwich]

http://en.cokintech.com/product-item-18.html
that schematic is probably close

Thanks... I will see if I can follow the "hint". I don't see how the "T sensor" feeds into this. The "RJ0!" looks somewhat suspiciously missing.... but it only connects some traces together but not to the Negative lug / contact. Looking at the RH02, that appears to be some sort of "zero ohm fuse".... maybe?

ADDED: I think I see how the RJ's are. They are placed for changing which contact is + and -.... basically moving it from RJ02 to RJ01 reverses the polarity.

[budwich]

That unconnected contact is not the -ve terminal. The top contact is, which is connected to the -ve lead of the electrolytic cap C3.

After looking the schematic that was linked by Great Sage, now I think I see what you are saying. The charger does not actaully use the "T sensor" connection AND the case is MISLABELLED. The "Tsensor" contact on the charger is actually the negative contact. Hopefully, I have that right. Thanks.

[budwich]

I just did a quick test using the "new found epiphany" and the charge light is now in "charge mode". Hopefully, the GG1052 has enough smarts in its internals to keep the thing from over charging. Assuming the charging current is less than ~1amp and voltage is contained (open circuit was 13.4v DC), the battery should be ok?

[budwich]

I did one charge cycle. The unit switches to "100% - green led" when done. Not sure if it accomplished the full charge... have to see how long the drill lasts.
thanks again for the guidance on this that got my drill back in service.