How safe are "no name" 18650 Lion cells? - Page 1
Forum section: electronics / general

author: alpher
author_rank: Frequent Contributor
timestamp: August 19, 2024, 03:14:46 pm
content: Yesterday I finally finished what is essentially a poor man Lithium powered UPS for my home internet/network backup. Place where I live has these annoying power interruptions that last for ~1 sec, they royally screw my cable modem connection as it takes a good couple of min. for it to reconnect. Not only that, there's also a VOIP adapter that has to be powered on after there's an active internet connection to it.When there's a power interruption and both the modem and VOIP are powered at the same time it finishes booting first before modem and more often than not I have to manually power cycle it for my phones to work. Long story short I'm feed up!Here's a picture of the whole setup:Firstly I wanted a high capacity lithium powered UPS, but they tend to be on rather expensive sideThen decided to biuld something from scratch, and it hit me, I don't really need an UPS, If I start with 12V battery I'm allready 70% there. Modem, and my NAS can both be powered from 12V battery directly, all I have to get is a couple of DC/DC converters, one 12 to 24V for my VOIP adapter and one 12 to 48V for my POE switch.So I bought these, they sit on that ugly contraption with the fan attached. Luckily I had a 10A 12V DIN psu sitting in my drawer, so after some wiring and a couple of fuses came up with what you see.For cell I went to amazon and bought these:https://a.co/d/7wnA8zaPlus a cheap chinese 50A 3S BMS and voilla!Now when all is done and working I had a second thought,What will hapen if any of these 18650 was to catch fire?As you see the whole cabinet is made of wood and the install is in my laundry room usually full of clothing or laundry.Should I just go back to plain lead acid battery ?I'm I overreacting?

author: tunk
author_rank: Super Contributor
timestamp: August 19, 2024, 04:02:49 pm
content: How do you charge them (or: a BMS plus a 12V PSU isn'ta charge curcuit)? I would test their capacity, if they'reclose to 3500mAh and all are roughly the same, the cellsmay be ok.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 19, 2024, 04:07:44 pm
content: Spend a little bit more time, and you might find a supplier who sells actual genuine brand name li-ion cells for same or lower price. I'm always astonished how expensive these "ultrafire" cells are. Maybe someone in Canada could chime in.

author: coppice
author_rank: Super Contributor
timestamp: August 19, 2024, 04:13:43 pm
content: Quote from: Siwastaja on August 19, 2024, 04:07:44 pmI'm always astonished how expensive any Li-ion cell from an easy to use source is. There doesn't seem be anywhere to buy them in small quantities at a moderate price.

author: wraper
author_rank: Unknown
timestamp: August 19, 2024, 04:13:50 pm
content: For this price you can buy genuine 3500mAh Samsung cells. Also do not forget you cannot safely solder these, so you'll need a spot welder. Buying LFP battery pack likely would be a better option.

author: wraper
author_rank: Unknown
timestamp: August 19, 2024, 04:17:51 pm
content: https://www.imrbatteries.com/sanyo-ncr18650ga-3450mah-10a-battery/

author: nctnico
author_rank: Super Contributor
timestamp: August 19, 2024, 04:19:17 pm
content: Quote from: wraper on August 19, 2024, 04:13:50 pmI agree. I'd start with a standard battery pack which has the BMS inside. Bonus points for a battery packs which is also certified for UN38.3 . I really don't get why people want to use Li-ion cells. These cells can push out a lot of energy. The contraption the OP has made looks like a incendiary bomb to me.

author: rteodor
author_rank: Frequent Contributor
timestamp: August 19, 2024, 04:25:13 pm
content: Quote from: alpher on August 19, 2024, 03:14:46 pmUnless you really,reallyhave trouble keeping 5 degC while charging, leave the lead-acid to the history and go for LiFePO.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 19, 2024, 04:26:13 pm
content: It is possible to construct a nice and safe battery pack from 18650 cells of high energy density chemistries but it requires quite some time in both sourcing the cells from a trusted source plus understanding in designing the packaging and BMS.One option for a pre-engineered battery pack is a power tool pack. They are not so expensive anymore. You can get 5s ("18V" or "20V") or 10s ("40V") packs this way with some sort of built-in BMS.

author: coppice
author_rank: Super Contributor
timestamp: August 19, 2024, 04:28:28 pm
content: Quote from: wraper on August 19, 2024, 04:17:51 pmTheir small volume prices look reasonable, and if the batteries they supply are genuine, that looks good for US customers. However, they don't export small quantities. All the suppliers I could find in Europe a few months ago were far more expensive, and some looked kinda dodgy.

author: alpher
author_rank: Frequent Contributor
timestamp: August 19, 2024, 04:56:21 pm
content: Quote from: wraper on August 19, 2024, 04:13:50 pmThanks for all the replies, here's more info, the cells are not soldered nor welded. They sit in battery holders and were sitting in a "balancing circuit" (basicly connected all in parallel through 1ohm resistors) for a couple of days before being inserted in the sockets. I also adjusted the psu voltage so it doesn't exceed 12.45V even with the battery dissconnected and very light load, so the cells cannot be overcharged.

author: wraper
author_rank: Unknown
timestamp: August 19, 2024, 05:39:01 pm
content: I have a huge doubt battery sockets can provide good enough contact resistance in long term. Especially considering 18650 was not designed to be fitted in socket.

author: shabaz
author_rank: Frequent Contributor
timestamp: August 19, 2024, 05:47:47 pm
content: QuoteHi,As another option (far less chance of problems occurring), you could just use non-rechargeable cells, or a burglar alarm type of rechargeable battery, no need to construct a battery. It shouldn't need a lot of capability to support your modem and router/WiFi for such short periods.When I was curious to monitor power outages, I just used 8 x AA cells, and a simple circuit that used either a MOSFET or relay (I can't recall) that automatically switched out the mains power brick within a fraction of a second of an outage, preventing equipment power-off or reset. I used this method to maintain the modem and router (not WiFi in my case, since it was non-essential to me, so I didn't have that issue).I didn't bother with recharging, because I could just swap out the cells when there's no outage, if they were depleting.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: August 20, 2024, 04:30:44 am
content: Quote from: alpher on August 19, 2024, 03:14:46 pmNot at all. If I didn't know the history of an 18650 cell I would treat it as though it will catch fire at some point in the future. Particularly "recovering" one from being over-discharged is a dangerous thing to do, they are at higher risk of internal short and if that happens while fully charged, the battery dissipates a lot of energy in a short time.LiFePO4 is a fair bit safer, but I'd still advise sourcing it from somewhere trustworthy.Lead-acid is very benign, especially the VRLA aka "sealed gel cell". But they all generate Hydrogen gas as part of the charging cycle (the VRLA just holds the gas inside, usually).Nothing is totally safe

author: thm_w
author_rank: Super Contributor
timestamp: August 20, 2024, 11:59:23 pm
content: Your amazon link doesn't work any more.But you bought 27 cells, lets say 10Wh per cell for I would guess $5 each. Total of 270Wh for $135.You could have got a premade 12V Lifepo4 with BMS, total of 380Wh for under $170.Would have been safer, easier, and will last longer.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: August 21, 2024, 12:09:19 am
content: your power woes remind me of this UPS using supercapacitorhttps://www.eevblog.com/forum/projects/ups-supercapacitor-conversion/Quote from: alpher on August 19, 2024, 03:14:46 pm

author: daisizhou
author_rank: Super Contributor
timestamp: August 21, 2024, 12:21:45 am
content: Quote from: alpher on August 19, 2024, 03:14:46 pmIn my opinion, any form of DC/AC or DC/DC will lose energy.My suggestion is to use lithium battery directly.For example: if you need DC12V, then assemble a 12V lithium battery pack,If you need DC24V, then assemble a 24V lithium battery pack.As for the lithium battery safety issue you mentioned,You just need to make sure your lithium battery capacity is large enough, there is no danger.Because danger often occurs during charging or discharging.When you charge or discharge with a small current, no heat will be generated, and there is no possibility of fire.

author: tunk
author_rank: Super Contributor
timestamp: August 21, 2024, 01:33:02 pm
content: How do you charge them?Not following the standard CC/CV/cut-off charging maybe a bigger safety problem than the cells themselves.Floating them at 12.45V may not be advisable.

author: wraper
author_rank: Unknown
timestamp: August 21, 2024, 02:06:40 pm
content: You should not charge them above 80%. Keeping them fully charged all the time greatly decreases their lifetime, complicates charging and compromises safety.

author: alpher
author_rank: Frequent Contributor
timestamp: August 21, 2024, 03:17:29 pm
content: Quote from: wraper on August 21, 2024, 02:06:40 pmSo if I keep the voltage at 12V even I'll be safe?

author: nctnico
author_rank: Super Contributor
timestamp: August 21, 2024, 03:27:13 pm
content: Quote from: daisizhou on August 21, 2024, 12:21:45 amNope. There are many more failure mechanisms involved with Li-ion batteries.

author: thm_w
author_rank: Super Contributor
timestamp: August 21, 2024, 08:52:45 pm
content: Quote from: tunk on August 21, 2024, 01:33:02 pmFloating is completely fine. As long as maximum charge rate isn't exceeded.Though 12V is safer/better than 12.45V as explained above.

author: jonpaul
author_rank: Super Contributor
timestamp: August 21, 2024, 11:36:12 pm
content: All Li batts are potential firebombsCheap Chi knockoffs ust more soj

author: alpher
author_rank: Frequent Contributor
timestamp: August 22, 2024, 11:36:20 pm
content: I've chickened out.

author: daisizhou
author_rank: Super Contributor
timestamp: August 23, 2024, 12:27:40 am
content: Quote from: alpher on August 22, 2024, 11:36:20 pmIf you use a lead-acid battery, the actual service life of this battery is about 2-3 years.I noticed that the manufacturer of this battery is a good one.But is it really the battery produced by this manufacturer?I noticed that you are not familiar with lithium batteries.Perhaps it’s because of the many rumors about lithium battery combustion in the news.People usually recommend using a welding machine to weld lithium batteries，But I have always used a soldering iron,And use solder to pack the battery pack.I once used a soldering iron to assemble a 120AH battery pack.This took me a long time, but I didn't want to buy a spot welder because I don't use it often.In principle, lithium batteries cannot be heated or welded.But it doesn't matter,As long as you understand it and prepare for the worst, I mean explosion or fireMy suggestion is that at any time, when charging and discharging with a small current, the charging limit voltage should not exceed the 4.2v limit value (single battery cell).All lithium batteries can be used normally,Anytime, Anywhere

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 12:36:01 am
content: Quote from: daisizhou on August 23, 2024, 12:27:40 amThe main problem with soldering is not that battery will immediately catch fire, most likely it won't if you do the job fast. It's that it may become wounded and pose danger down the road.

author: daisizhou
author_rank: Super Contributor
timestamp: August 23, 2024, 01:05:06 am
content: Quote from: wraper on August 23, 2024, 12:36:01 amThe fact proves that it will not.I have been doing this all the time and have not seen any abnormalitiesMaybe this is the same as the dangers of using lithium batteries.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 01:12:46 am
content: Quote from: daisizhou on August 23, 2024, 01:05:06 amSample size? If you've done it say 100 times and it didn't catch fire it does not disprove danger. Samsung recalled 2.5 millions of Galaxy Note 7 with only 35 reported cases of fire. If it's just 0.1% chance of catching fire, would you bet on it with chance of burning down your home. In other words, is it worth betting on a chance you might become 1 out of 1000 unlucky sucker.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 01:22:10 am
content: Quote from: daisizhou on August 23, 2024, 01:05:06 amIf you look on 18650 construction, you'd see no way you can solder negative electrode without somewhat frying battery internals.

author: alpher
author_rank: Frequent Contributor
timestamp: August 23, 2024, 02:38:14 am
content: Quote from: wraper on August 23, 2024, 01:22:10 amNow I'm curious, what is there in the costruction of lithium 18650 cell that cannot tolerate a couple of seconds of 350c at negative terminal but is fine with say 1/2sec at >1000c ? (spot welding temp). Please don't take me wrong, it's not a sarcasm of any sort, just genuine curiosity.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 04:02:03 am
content: Quote from: alpher on August 23, 2024, 02:38:14 amSpot welding releases heat in a very small area between welded surfaces for a very short time. Internals of the battery do not become hot as that small amount of heat quickly dissipates over larger area. To solder you need to heat a large area to the solder melting temperature for a few seconds. Inner side of the thin metal shell will become almost as hot as the outside.

author: daisizhou
author_rank: Super Contributor
timestamp: August 23, 2024, 05:19:57 am
content: Quote from: wraper on August 23, 2024, 04:02:03 amIt doesn't matter.I even used fire to roast the bottom of the 18650 negative electrode.When welding, you need to stay focused at all times and take fire prevention and fire extinguishing measures.I'm just telling you my real experience.If many people don’t believe it, they can choose not to use lithium batteries.Many are just alarmistDifferent people have different opinions.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 23, 2024, 11:27:40 am
content: Quote from: alpher on August 23, 2024, 02:38:14 amSpot welding, depending on process, takes something from mere milliseconds to maybe max 100ms. Heat simply doesn't conduct far in the case material during that time, even if localized temperature is 1000degC. The lower the temperature, the longer you need to deliver the same amount of energy to the joint, and during that longer time, the more heat escapes to the surroundings, so you need even more energy to compensate.It is marginally possible to solder a cell, but it requires a very high temperature large iron tip and the soldering needs to happen very quickly, with small amount of solder. There is very little room for error.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 23, 2024, 11:31:53 am
content: Quote from: daisizhou on August 23, 2024, 05:19:57 amObviously you need to use a specific spot welder designed to weld battery terminals. It controls the weld time and energy exactly. Spot welding happens in a time frame which is impossible for a human to control.But sure, when dealing with li-ion battery manufacturing you do need to have fire prevention and extinguishing plan. For example, maybe a cell is faulty, or maybe the welding machine develops a rare fault where its control/limiting system fails and it keeps welding when it should stop after 50 milliseconds.QuoteThere are opinions (like, do you prefer strawberry or vanilla ice cream?); then there are facts. Fact is that li-ion battery packs are always manufactured with spot welding processes, and any soldering is pretty risky business.

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 12:43:19 pm
content: Quote from: alpher on August 22, 2024, 11:36:20 pmFTFY

author: Rick Law
author_rank: Super Contributor
timestamp: August 24, 2024, 08:32:27 pm
content: Quote from: alpher on August 22, 2024, 11:36:20 pmAs you question stated, they areno-names, no one want to slap a brand on it so no one want to put their reputation to it's reliability or quality.With no-name, it is entirely possible that grab any 10, you may have 5 different source for these 10 batteries. Some may be re-wraps, only the re-wrapper may know how the battery is before the re-wrapping. Worst yet, it may be second generation re-wrapping. I've re-wrap dozens of batteries from laptop power packs. Based on the laptop pack's info, some (math) work out to have 3.6V nominal, some have 3.75V; some charge to 4.2V, some charge to 4.25V. In my case, since I did the re-wrap, I know which is which.Not entirely a bad idea to use SLA.If you do want to do want to use Lithium, you should alsoconsider using one of those better quality/brand "car starter booster" lithium jumper pack. At least they would be engineered with proper BMS. and perhaps comes with re-charger as well. You would have the brand name of the jumper pack assome assurance - to the degree of that better quality/brand.I alsodon't entirely trust those battery holder's contacts. The springs in particular. Years ago I was using 3x18650 on battery holder and I was doing some test on the devices powered by this 3P 18650 pack. So the batteries were removed and I use alligator clips to use an external power source to one of the battery-holder slot to power the devices under test, at about 3A to 4A. After a while of testing, that damn battery spring became a heat coil and started to melted the holder... I suppose 3A to 4A while it is fine spread over 3 slots in holder, it exceeded the rating for a slot for a single cell. One can imagine what if one cell is bad, the other two will be supplying more current via their springs. Worst if one is shorted, the other two will be dumping current into that cell. Even if the cell can withstand it, now I have another point of danger - the battery holder spring heat coil...A few things I learned (which you may already know):1. Device for power outage (UPS) needs better reliability and better robustness. You really don't want to resolve even minor issues when you have neither light nor soldering-iron to fix problem.2. Build-in indicator (with on/off) is a good thing to add. For example, those simple 3 or 4 digit LED volt meter that show the voltage just by turning it on You don't want to dig out your DMM and try to touch some point in your circuit while holding a flash-light in the dark. So for two bucks, you can have a volt meter with a 3-throw switch showing your battery voltage, your (post dc-dc conversion) output voltage, or off to conserve power.3. While your in-house equipment is working fine via your UPS, when it come tointernet, there may be other dependencies. The ISP's equipment needs power too and they may be supplies by the same grid that powers your area. In my case, if the next block south of me is down, even if I have power to my equipment, my ISP's equipment don't... The incoming cable has no signal... (So when I did my last router/cable-modem update, I no longer have standby UPS power on it.)