New 3 cell lipo reading zero on cell? - Page 1
Forum section: electronics / beginners

author: Beamin
author_rank: Super Contributor
timestamp: August 19, 2017, 01:08:32 am
content: I just bought this today. I got a descent battery charger with all the good stuff. I charged this pack up twice (1Amp: battery is rated at 3C which should handle 1.5amps but I erred on the side of caution.) and on the third charge I get the charger saying "Low voltage on one or more cells"So I measure the black of the dual power lead and test the colors:Brown 0.0vYellow 3.7blue 3.7Red 7.4vIs one cell down to ZERO? I didn't think it could do that? The battery was used in a high speed quad copter that drains this battery in 3 minutes. Worked fine until just now. I would expect it to read some thing but not exactly zero. Could the wire be messed up?

author: Inverted18650
author_rank: Frequent Contributor
timestamp: August 19, 2017, 01:22:22 am
content: I don't see a brown in the pic. But it should be 3.0-4.2 on one line, 6-8.4 on the next, 9-12.6 on the 3rd, and one is common ground. If it's new and you can, send it back, if you keep it, peel the plastic back and have a look at the small PCB at the top of the pack. See if the connectors have come off or melted the solder. If the connectors are solid, then your cell is likely bad. You can test it separately once the pack is apart.Edit:Typing on phone with cracked screen and its auto inputting words..sorry I'll switch to PC. This pic is a 4S so it has one extra tab on PCB.Edit two:I read this incorrectly my apologies:you have measured correctly if you used the black as the common and moved the probe along the others, my bad, dumb moment...it's a 450mAh pack with a 50C rating.. kinda nuts that means your getting 12V @ 22 A's out of this pack @ 50C which is likely to kill it within a few cycles unless it is a very high quality pack.

author: Rerouter
author_rank: Super Contributor
timestamp: August 19, 2017, 02:56:54 am
content: As your measuring 7.4V across the outer 2, its a dead / shorted cell, the battery is gone, and its time to source a new one.

author: amyk
author_rank: Super Contributor
timestamp: August 19, 2017, 03:47:00 am
content: Quote from: Rerouter on August 19, 2017, 02:56:54 amIt's essentially turned into a 2S pack --- the middle cell of the 3 has gone to 0V, i.e. dead.

author: Beamin
author_rank: Super Contributor
timestamp: August 23, 2017, 11:02:28 pm
content: The pack is going to be returned but I wanted to see why it failed. It cost almost $30uSD (supposed to be high quality) and was being used in a drone where the pack was being discharged in less then three minutes.So those wires are supposed to be sequential? If so how can two read the same? Wouldn't that mean that just one cell is working?

author: Rerouter
author_rank: Super Contributor
timestamp: August 24, 2017, 02:07:17 am
content: If a cell is over discharged it can fail shorted, this is why 2 wires measure the same voltage,Was the pack balance charged before use? if not then 1 cell could have been marginal while the other 2 where over charged.If it was, and you discharged the pack to the point it fell out of the air, that cell was likely the weakest in the pack and collapsed from ~2.7V to 0 in a few seconds (there is almost no capacity at this end) Its not uncommon for the cells to be slightly mismatched, but in general if one cell is out by 20% from the others i get a little suss,A easy way to spot this is how long it takes to balance charge a pack, if they all come out of the box at a similar charge, ideally it should be seconds to balance in, If its 10 minutes, it likely means you have either 1 strong or 1 weak cell confusing things.

author: Beamin
author_rank: Super Contributor
timestamp: August 25, 2017, 01:03:40 am
content: The drone cuts off at a certain level and the radio has a timer. What I suspect happened was I turned on the props for about one second after I had landed it and normally it won't let you run it if its dead so I figured it was OK but looking back I suspect these motors draw so much crazy power it was enough to kill the pack in about 1 second. I'm bringing the drone back to the store because it was the total opposite of what I wanted which was to look at things from high up."I want something long range with long battery life that flys slow and easy to fly.""This one will be perfect for you. And it goes quite fast if you want it to.""OK"The drone is for racing ONLY. The battery lasts 2.5 minutes the range is very short (indoors really) and is extremely difficult to fly since it really only goes fast and is really heavy with small high speed props. Hovering is extremely difficult since any change in tilt and it flys away. It climbs as fast as it flies which is probably 20-30 MPH which is crazy for something so small. It looks like a really expensive toy. The FPV is useless as you get disoriented so quickly and you can't go any distance with it. I almost never trust the sales people and the one time I do I get burned.