18650 FFC charge protect circuit - Page 1
Forum section: electronics / projects

author: Zenkyle
author_rank: Newbie
timestamp: November 24, 2019, 01:58:55 am
content: Hello EEV Blog! This is my first post so please forgive me if it's not in the right place..I just finished building a flat flexible single cell 18650 charger! I'm pretty happy with the result but think I'm encountering a problem.. the battery is mostly charged (3.57v) but when charging cable is attached the charge complete LED is brightly lit and the charging LED is very dimly lit.. I've checked all connections and can't seem to find the reason. Battery voltage does not change while charging even after 30 min. I followed this tutorialhttps://www.instructables.com/id/DIY-LiPo-ChargeProtect5V-Boost-Circuit/Any ideas would be greatly appreciated.Attached is a photo of my circuit. The orange LED is hard to see but it's lit very dimly.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: November 24, 2019, 03:25:52 am
content: The datasheet for charger ic has window comparator for temperature on pin 1. It can not be grounded, or else there is undertemperature state, if you trust the datasheet. The pin 1 needs a voltage above 45% of vcc, not a grounded zero volts.

author: Zenkyle
author_rank: Newbie
timestamp: November 24, 2019, 03:38:33 am
content: Thank you for your response! I will try adding the voltage divider and see if it makes a difference.It's just odd to me since the tutorial I'm following grounds pin 1 and in the datasheet it says: "The temperature sense function can be disabled by grounding the TEMP pin."Any reason it may work for others but not in my specific application? Maybe because of the battery chemistry or capacity??

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2019, 04:45:13 am
content: You are correct grounding TEMP disables temperature detection with the TP4056.You have included both charge and protection^1, connect a load to the protected output and see if you can draw current, if you can not draw current then you can isolate the problem to the protection for sure, if you can draw current try forcing current through the protected output.See this thread, although you are using a different protection IC (according to the instructable link, without your schematic we can only guess you are using the same BOM) they can be common issues around startup, usually resolved by momentarily bypassing the protection mosfet or similar.https://www.eevblog.com/forum/projects/pain-and-suffering-getting-the-dw01-and-8205a-protection-circuit-work-right/---^1 at least I think you have, I see two chips there that look like they might be a protection IC and dual mosfet, and I guess that bit of flex running off in the air is the protected negative output

author: Zenkyle
author_rank: Newbie
timestamp: November 24, 2019, 05:58:00 am
content: This is fantastic! Thank you for your time!I am actually using the DW01+G in my circuit and not the FS312F-G so that link is prefect!The tutorial I'm following originally uses the DW01+g but changes it due to the lockout voltage being low. I would've also used the FS312f-G but I didn't catch the change until later. Everything else from his schematic is the same.I am getting current from the protected output (I've only tried powering a few LEDs so maybe like 60mA but no real demanding loads) should I try a higher load to confirm?That post seems to find the solution to his problem in the datasheet on page 8 that reads: "When a battery is connected to DW01-G for the first time, it may not enter the normal condition (dischargeable may not be enabled). In this case, short the CS and VSS pins or connect to a charger to restore to the normal condition."My problem is the battery won't charge so I don't think it's the same..I have tried changing the PROG pin resistors to change the charge current higher and lower but to no effect.

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2019, 07:09:09 am
content: Suggest you post your schematic.

author: Zenkyle
author_rank: Newbie
timestamp: November 24, 2019, 10:19:27 pm
content: Hopefully this is legible

author: Zenkyle
author_rank: Newbie
timestamp: November 24, 2019, 10:43:19 pm
content: Okay now I feel silly.. In writing down my schematic I realised the culprit. The 100ohm resistor on the battery pin.. I had put it in a slightly different place than the tutorial I was following and as a result the charge current was trying to pass through it I guess resulting in the "standby" state. I jumped the pads to test it and sure enough it started charging right away.Huge thanks for everyone's time! Such a simple goof I feel a little embarrassed posting it. Maybe it'll help someone down the line