LiPo battery reading 0V after PCM but 3.2V at battery terminal - Page 1
Forum section: electronics / projects

author: freeflyer
author_rank: Contributor
timestamp: July 21, 2025, 08:05:26 pm
content: I bought the following LiPo battery from PiHut...https://thepihut.com/products/1200mah-3-7v-lipo-batteryBut the battery is now reading zero volts, so I thought it had been fully discharged and assumed it was because it had no PCM to protect against over discharge.Upon further investiation, I found the data sheet which shows it does have a PCM...https://www.batterypkcell.com/uploads/LP503562-1200mAh-3.7V-AD306055-20230615.pdfThe battery was only connected to a MIKROE-2757 (a boost SMPS with a 5V output)....https://www.mikroe.com/boost-4-clickThis board did not have the enable pin connected, so it would have only drawn a very small standby current.I tried charging the battery using this charger...https://thepihut.com/products/adafruit-micro-lipo-usb-liion-lipoly-charger-v1But after hours of charging the output was still 0V.So I opened up the battery and found the PCM...At the battery terminals the voltage is 3.2VDoes this mean the battery is still functional and was protected from over discharging from the PCM ?If so, why am I only seeing 0V on the output ?Is it possible to get it working again, bearing in mind the charger had no effect ?

author: tooki
author_rank: Super Contributor
timestamp: July 21, 2025, 08:30:29 pm
content: The protection IC in use (R5478N101CD,datasheet here) is apparently self-resetting ("auto release") if the voltages come back through the release thresholds. In this chip, the undervoltage detect threshold is 2.5V, and the undervoltage release voltage is 3.0V. So it should have reset automatically.Thus, presumably either the chip or one of the MOSFETs has failed. Look at the schematic for the PCM and probe out where the voltage disappears; that might give you a clue as to what has failed.

author: freeflyer
author_rank: Contributor
timestamp: July 21, 2025, 08:55:20 pm
content: Thanks tooki. What could have caused one of the components to fail ? Doesn’t give me much confidence if the protection circuit fails! Was I just unlucky and received a battery with a faulty PCM? If I buy a replacement is the same thing likely to happen again? I just want to make sure that there’s nothing I did to cause failure. It did work and I only enabled the smps when I used it, for the rest of the time the battery was left connected to the smps but disabledOnly thing I can think of is that the enable pin for the smps was floating which the datasheet says not to do.

author: thm_w
author_rank: Super Contributor
timestamp: July 21, 2025, 09:00:31 pm
content: What voltage do you measure on the output of that charger? Make sure its set to 4.2V and is outputting 4.2VAs tooki says follow the voltage through.

author: tooki
author_rank: Super Contributor
timestamp: July 21, 2025, 09:25:53 pm
content: Quote from: thm_w on July 21, 2025, 09:00:31 pmHuh? The voltage is not configurable. The switch on the charger sets the fast charge current.But moreover, the charger shouldn't output the full 4.2V yet anyway: it should do constant-current charging at the 100mA or 500mA fast charge current, with the voltage slowly rising until it hits 4.2V. Then it switches to the constant-voltage phase and terminates when the charging current has fallen to 7.5% of the fast charge current (so 7.5mA or 37.5mA, resp.).

author: thm_w
author_rank: Super Contributor
timestamp: July 21, 2025, 10:23:11 pm
content: Assumed it was a switch for 3.7/4.2 that was written beside it, but you're right its just Low/High setting.It should output the full 4.2V then.

author: Peabody
author_rank: Super Contributor
timestamp: July 22, 2025, 03:20:41 am
content: You might want to replace the protection module. I think those can be ordered online. Or you could get a TP4056 charger module with protection built in, and connect the battery to it.Looking through the datasheet, it mentions that one version is "latching" on over-discharge. But I can't tell how you would release the latch.By the way, the 8205A is dual N-channel mosfets. When both are turned on, they connect the battery's negative terminal to the circuit ground.

author: Kasper
author_rank: Frequent Contributor
timestamp: July 22, 2025, 05:33:35 am
content: Showing the other side of the PCM might help.Solder looks fine from this angle but just for an example, I once got a batch with 0402s on 0603 pads and 1 wasn't connected.I tested similar PCMs once and the only thing I remember them not recovering from was a bit too much current. Everything else, triggered the PCM's protection before too much damage was done.

author: freeflyer
author_rank: Contributor
timestamp: July 22, 2025, 12:40:15 pm
content: The other side of the PCM has no components...

author: freeflyer
author_rank: Contributor
timestamp: July 22, 2025, 04:21:55 pm
content: I measured the current when a battery is connected to the smps with it disabled and the current was ~4uASo I’m trying to understand why leaving the original battery connected has rendered it a write off.Am I correct in saying this should not have happened ?If the battery did become discharged then the PCM should have protected it from being over discharged and I should have been able to recharge it, correct ?

author: Kasper
author_rank: Frequent Contributor
timestamp: July 22, 2025, 04:37:13 pm
content: Quote from: freeflyer on July 22, 2025, 04:21:55 pmDid the battery ever work?

author: tszaboo
author_rank: Super Contributor
timestamp: July 22, 2025, 04:44:38 pm
content: 3.2V is OK for such battery. So you can charge the cell itself.Some protection circuits need to "initialize" after it's put together. So they don't turn on the output if the cell is replaced or soldered first. What you do is, you short out the FETs, so connect the cell negative terminal to the output negative terminal. If you don't feel comfortable with a direct short you can us like a 20 Ohm resistor to do this. Probably the pack will come alive. If it doesn't return the battery under warranty I guess.

author: freeflyer
author_rank: Contributor
timestamp: July 22, 2025, 05:10:41 pm
content: Quote from: Kasper on July 22, 2025, 04:37:13 pmYes ive been using it for about a month. I charged it when I first received it

author: tooki
author_rank: Super Contributor
timestamp: July 22, 2025, 05:10:49 pm
content: Quote from: thm_w on July 21, 2025, 10:23:11 pm3.7V and 4.2V refer to the same battery type:nominalvoltage 3.7V,peakvoltage around 4.2V.Quote from: thm_w on July 21, 2025, 10:23:11 pmOnly once the constant-current charging phase finishes. (It probably outputs that if no battery is connected.)

author: freeflyer
author_rank: Contributor
timestamp: July 22, 2025, 05:13:53 pm
content: Quote from: tszaboo on July 22, 2025, 04:44:38 pmI have been using the battery for about a month and charged it when I received it.I am confident with shorting the FETS, but I shouldnt need to do this everytime the battery needs charging.I have access to a bench PSU with current limit at work so could try charging directly at the battery terminal.But this wont be a solution for production, you dont have to short the FETS for other battery systems ! Once the battery is discharged you simply plug it into a charger

author: Kasper
author_rank: Frequent Contributor
timestamp: July 22, 2025, 05:25:15 pm
content: Sounds like something damaged or tripped your PCM. I'd try tszaboo's reset procedure. If that doesnt work, manual charge with current limit (1mA should be plenty) for 1 second on the battery wires not the tabs. I've reset PCMs before by doing that.Since you mention production, you should get familiar with the PCM: what is it supposed to protect against? How do you safely test each of those protections? After protection is triggered can you reset it?Many chargers wont charge if they see 0V on battery wires. Bypassing PCM and charging battery directly won't solve the PCM problem unless the PCM has an oddly high cutoff voltage. That's something you should probably test anyways, if you are considering going to production.Did ESD trigger the PCM? Do you follow ESD precautions? Have carpet in your lab? Wear sweaters? Do you have pets that have access to it?

author: tszaboo
author_rank: Super Contributor
timestamp: July 22, 2025, 08:19:10 pm
content: Quote from: freeflyer on July 22, 2025, 05:13:53 pmI don't recommend using a bench power supply to charge a battery. I've seen the batteries blowing up, and the power supplies blowing up when this is attempted. I myself blew up the output triac of a very nice Agilent U8001 power supply when I switched off the current while the battery was still connected. Good thing I could take it apart learn from it and repair it.

author: freeflyer
author_rank: Contributor
timestamp: July 23, 2025, 07:37:38 pm
content: Quote from: Kasper on July 22, 2025, 05:25:15 pmNo I dont take ESD precautions when handling tempoary development board setups unless they are expensive.I will take ESD precautions when my custom PCB arrives though and I do so when handling expensive or sensitive boards.But are you refering to taking ESD precautions when handling the battery ?I'm sure most people handling LiPo batteries don't take ESD precautions and I've never seen warnings or comments to take ESD precautions for batteries

author: Kasper
author_rank: Frequent Contributor
timestamp: July 28, 2025, 07:16:22 pm
content: Quote from: freeflyer on July 23, 2025, 07:37:38 pmI think it is unlikely for a PCM to get damaged or trip by ESD or anything else, with the gentle use that you describe. ESD seems unlikely but is anything else more likely? Maybe a failed solder joint? Maybe your circuit is sourcing or supplying more power than you think it is?If you try reseting the ECM, we will atleast have an idea whether it was tripped or damaged.