Defeating battery charging circuit on small radio - Page 1
Forum section: electronics / beginners

author: taste_tester
author_rank: Regular Contributor
timestamp: July 22, 2022, 07:25:27 am
content: There is this radio I have two of because I typically use it all day as long as I'm awake... I don't trust the no-name battery to be safe to charge every day, and besides one I have in the kitchen I want to leave plugged in and always there.Anyway, typical very old phone / digital camera style Li-ion 3.7v battery, also known as "BL5C" is usedIt does not have any kind of DC power input, only micro USB for charging the battery.Even with a battery removed, if the unit is switched off, the battery charging animation appears.I'm not sure if it's simply what is displayed in that mode, or if the charging circuit is activeI could measure some voltage at the battery charge pin, but of course i'm putting some kind of a load on it, what's more the Battery Size Indicator pin is around 82 kOhm so I was wondering if the resistance of the DMM is close enough that the charge circuit starts outputting power.In other words, i'm not certain that the battery charge circuit is active when i'm not measuring it.Should i cut some traces related to charging the circuit and call it a day? Could anything bad even happen if left in the "standby/charging" state for an extended period of time?

author: SeanB
author_rank: Super Contributor
timestamp: July 22, 2022, 10:53:20 am
content: Just leave the battery out, and see if it still operates. If not, try first adding in a capacitor across those charge pins, using probably 4700uF 10V, and see if that provides enough power to turn on the radio, as often they use the battery to provide peak power for operation, and simply float charge otherwise.

author: kjr18
author_rank: Regular Contributor
timestamp: July 23, 2022, 06:31:36 am
content: I think it might be not possible. You mentioned charging animation - does this radio has a display? Or the charging animation is achieved by flashing some led's?There are few ways to charge a battery, from cheapest (one diode from usb to battery and relaying on internal protection circuit to terminate charge on overvoltage) to dedicated charging chip (something like TP4056) and finally using whatever is built-in in main chip. I think it might be first, or second one, as anything that uses SoC, would not use anything like BL5C type battery.

author: taste_tester
author_rank: Regular Contributor
timestamp: July 24, 2022, 07:54:47 pm
content: Quote from: kjr18 on July 23, 2022, 06:31:36 amThanks for the reply and I apologize for getting back here slowly.Yes it has a display, so it has a graphic when it's powered off, but charging:[Not my photo]It's the first one, no dedicated charging chip.I'm sure i'm overthinking it (why not just unplug the usb when not in use for extended periods of time!)I have left the unit plugged into USB power and no battery with no obvious or discernible adverse affects for the last 2 days,My main concern is really power being wasted.Hmm, maybe i just need to make an 18650 backpack for the radio.I also wanted to ask what is this component by the battery connector? I don't really recognize it. That's not the battery connector, is it? (Highlighted with pink)

author: taste_tester
author_rank: Regular Contributor
timestamp: July 24, 2022, 08:18:34 pm
content: I think the capacitor idea is great, thanks. I have tons of 1000uf of 10-16v so that is great.

author: wraper
author_rank: Unknown
timestamp: July 24, 2022, 08:21:11 pm
content: Ah, already deleted comment soon after posting since it appeared you have no issue of it working and my comment was about getting it working without a battery. Though if charging animation disappears when battery is fully charged, capacitor hack probably may help.

author: Infraviolet
author_rank: Super Contributor
timestamp: July 30, 2022, 12:34:33 am
content: My thoughts would be to 3d print a replica of the battery form factor and find a way to attach metal contacts in the appropriate spots, then power these from an external source (could print a holder which clips on nicely to the radio's back) with a voltage close to what you'd expect from the old battery when fully charged. This could perhaps be powered from a wall wart of a regulated voltage fed in to an adjustable DC-DC switching converter to give the voltage you'd want to replicate the battery voltage with.

author: MathWizard
author_rank: Super Contributor
timestamp: July 30, 2022, 03:40:11 am
content: There's might just be some enable pin for the charging chip, find Vcc, gnd, and even just mapping the other parts attached to it, and it might be there. Or it's some auto run chip, and the MCU has some sensing circuit to the battery, that might just have to be pulled up to get the MCU to turn of the charging animation....The next time I try and "hack" a basic MCU, I'll want to find it's memory address map, and that sort of thing, and see if I can't find some instruction value, that might tell me what it was doing.Or I should just start using ardinuo when I get the time.

author: kjr18
author_rank: Regular Contributor
timestamp: August 02, 2022, 08:09:30 am
content: Yes, that component highlighted in pink is indeed battery connector. Also this device charges battery via single diode, M1 with forward drop around 1.1V @ 1A, thus regulating charge current that way (end of charge is via DW01 protection ic integrated in battery itself).I found on YT some repair video that focused on replacing usb connector, and there I saw traces better than on photo you posted. As you can see on attached screenshot, I think that R7 might be responsible for detecting USB voltage, as on one side it's on USB and other side goes somewhere, too bad I can't see where, probably to main micro.