TalentCell LF120A1 LiFePo4 behavior - Page 1
Forum section: electronics / general

author: rgray107918
author_rank: Contributor
timestamp: March 25, 2021, 02:23:21 pm
content: Hi all,I searched the forums but didn't find something on what I'm asking. Sorry in advance for being a novice, and not able to better describe what I'm asking....I bought 2, 12Ah LF120A1 batteries on amazon. One of them seems to be DOA. I contacted TalentCell and they are replacing it free of charge.Here is my question.Using a bench power supply and two bench meters I have the voltage set to 14.6V and limited the current to 4amps. When I turn the power supply off, the voltage meter reads 14.6V. At this point I can connect a 12V, 12 LED array bulb and the battery hums along just fine. I can also connect a parallel resistor load of 4 resistors totaling 4.16 ohms, and the battery will hum along outputting 2.9A no problem.Things get weird when I try to connect an amateur radio transciever.... At that point the battery voltage starts around 5V and quickly bleeds down to a few mV. The radio (Icom IC-706MkIIg) has a relay that engages when connected to a power source, and the relay coil draws ~80mA as measured. The battery dies as soon as I connect the radio, and the relay never clicks (I haven't measured this, but I don't hear the lovely "click" of the relay and the power switch of the radio doesn't work). I inadvertently discovered that the battery behaves the same when I disconnect the power supply and reconnect it...at disconnect, the battery reads a happy 14.6V on the meter, but when I plug the banana jack back into the power supply the voltage bleeds off to nothing.Any ideas why it would behave this way, powering some loads just fine but not others?Thanks for any help!!

author: Siwastaja
author_rank: Super Contributor
timestamp: March 25, 2021, 02:33:48 pm
content: Sounds like the battery might have an internal overcurrent protection switch which is overly sensitive to inrush when connecting the radio which might have some capacitors taking initial inrush. Just a guess.Can't find a specsheet with a quick search. Do check the maximum peak current rating.

author: rgray107918
author_rank: Contributor
timestamp: March 25, 2021, 02:48:57 pm
content: For informational purposes, TalentCell customer support has been very good for me. I took a shot in the dark and asked them for a BMS schematic, and they sent me a full datasheet! Sweet.Let's call the weird battery, battery #2. Battery #1 will power the radio fine, no issues. I forgot to mention that I added some components to battery #2, but even after removing them batt #2 still behaves the same. Additionally when I installed the components on batt #1, it performs normally. I added a battery monitor display, kill switch, and LED. The switch and LED are from my junk box, but here is the monitor.https://www.amazon.com/gp/product/B07T8GN61Z/ref=ppx_yo_dt_b_asin_image_o09_s00?ie=UTF8&psc=1I am also attaching the datasheet from TalentCell. I am by no means good with schematics. I can glean the basics, and pick out components, but I am not able to determine how a circuit works.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 25, 2021, 03:32:47 pm
content: Specsheet says 35A for 10ms is enough to trip the protection in worst-case unit.Now all that's left is to power the radio through a current probe (or shunt resistor with low enough burden voltage at 35A) and use a scope to measure the inrush current waveform. Failing that, you can just skip the measurement and try if limiting inrush current solves the problem; precharge the radio through a series power resistor, say a few to few dozen ohms for a second, then bypass (short) this resistor.

author: rgray107918
author_rank: Contributor
timestamp: March 25, 2021, 03:37:53 pm
content: As I said, I am a compete novice to this stuff, but my radio spec says it only draws 20A max, and that is at full power transmit. Is it really possible that when just connecting a power source the radio actually draws 35A? I ask because I honestly don't know.Edit:I used Google. I'm still reading about in rush, but I guess it really could draw that much.

author: rgray107918
author_rank: Contributor
timestamp: March 25, 2021, 04:08:20 pm
content: Ok, I'm not 100% positive I understand, but is this the idea?Would I connect the radio first, then short the resistor so it is in parallel *edit -with the jumper wire*?If that's not right, can you walk me through it?

author: f4eru
author_rank: Super Contributor
timestamp: March 25, 2021, 05:33:55 pm
content: I would use a NO relay delay based circuit to limit the inrush current, together with a pre-charge resistor.A huge mega coil in paralell with a 2 ohm resistor may do also.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 26, 2021, 10:58:09 am
content: If the radio has large electrolytic capacitors, it can easily pull say 100A for some milliseconds.If maximum peak inrush current is not specified in the radio datasheet, the only way is to measure.Large capacitive loads require precharge, i.e., inrush current limitation techniques, but the radio likely isn'tthatlarge of capacitive load.If 20A is specified as maximum normal operational current, 40A of inrush current would be just double that, so nothing special, probably not even worth mentioning.When connected, many DC loads take like 5-10 times the normal operating current without blinking an eye.

author: rgray107918
author_rank: Contributor
timestamp: March 26, 2021, 11:08:50 am
content: I am in the process of uploading some pictures. I took the battery apart, and C6 is removed from the board. I am 99.9% certain I did not knock it off the board when I took the battery apart. I feel pretty confident I didn;t knock if off, because I was aware there was a PCB beneath the cover, and was extremely careful not let any hand tools contact anything under the cover.I scored around the seam with a scalpel, Then slipped the scalpel under the top lip, and then I used a non-metallic solder tool to pry the top off, but I never let the tip of the solder tool to extend beyond the lip of the cover, if that makes sense.Could C6 being off the board cause the issues I am seeing?

author: rgray107918
author_rank: Contributor
timestamp: March 26, 2021, 11:32:30 am
content: I found C6! It was stuck to the bottom of the sticky contact paper. Even if it may not be causing the issues I am seeing, it still needs to be soldered back on.Luckily, I am SMT certified for soldering. I am a technician, and definitely not an engineer. I am much more comfortable soldering or assembling and testing than I am reading my way through a schematic or doing any electronics design. Gimme a box of parts, and a build-to and I can build or repair anything.....ask me to design it, or troubleshoot it, and I'm totally lost.It is not letting me attach all the pictures, so here are links.https://drive.google.com/file/d/1S-FmUds00LTmjBMwMWYAgBySBgeAtegY/view?usp=sharinghttps://drive.google.com/file/d/1RiD67k3AA7q7OkHVxNgxGf3H5fCgyFHc/view?usp=sharinghttps://drive.google.com/file/d/1RiaxUqa8JWwsu3RJf1IoXAolmcn03itM/view?usp=sharinghttps://drive.google.com/file/d/1RusvG1i7xAp8W4W5K-a5MWNxKRRxP_WK/view?usp=sharing

author: rgray107918
author_rank: Contributor
timestamp: March 26, 2021, 12:11:20 pm
content: Replacing C6 fixed it. It works!!

author: Siwastaja
author_rank: Super Contributor
timestamp: March 26, 2021, 02:53:31 pm
content: This tells a sad story about the quality control of such battery management modules. And this is in a finished product. The same boards can be bought off Ebay/Aliexpress and I'm sure they are even worse / completely untested.

author: rgray107918
author_rank: Contributor
timestamp: March 26, 2021, 03:41:33 pm
content: I agree. You get what you pay for. I bought these, knowing they were the cheapest batteries I could find. I also have some of the skills required to perform minor troubleshooting and repair, but some customers may not.TalentCell replaced the battery, which is good customer service, but good manufacturing would have prevented me needing the customer service. This does seem like something that should have been caught before the battery left the factory.There was a small perforation in the paper, likely caused by something during manufacturing that caused the damage, which would have had to happen prior to the lid being attached. The battery should have been tested, after final assembly.I'm glad it worked out for me - now I'll have 3 batteries.