Safety of protected and unprotected Li batteries - Page 1
Forum section: electronics / projects

author: Zinger
author_rank: Contributor
timestamp: April 09, 2017, 11:03:35 pm
content: Are Li batteries equipped with protection circuit boards (e.g. this Tenergy 11.1 V, 5200 mAh packhttp://www.tenergy.com/31099) as safe as the batteries in consumer devices?I'm working on a project that requires two 10 ft LED strips. The device is portable, so I'd like to use LiPo batteries for their power capacity, size and weight. I started researching LiPo batteries on several RC forums and was frankly terrified by the videos of LiPos exploding and the warnings about proper charging, discharging and storage procedures.I was about to resign myself to using NiMHs when I realized that the battery pack I'm using for prototyping is Li as are my laptop and phone batteries. I began researching protection circuits and batteries with built-in PCB. It seems like they provide the safety and convenience of consumer grade Li devices. I won't need a fire proof ammo can just to charge them and they won't explode in the middle of a hotel.Is that accurate?The LEDs I'm using are 12V and draw 5A per 10 ft strip. The batteries will be enclosed in a ventilated, hard case so they are unlikely to be punctured or physically damaged.I'm pretty new at this kind of stuff. I'd appreciate any advice.

author: nctnico
author_rank: Super Contributor
timestamp: April 09, 2017, 11:26:00 pm
content: Look for UN38.3 certificied battery packs. The UN38.3 certification involves testing various safety aspects of a Li-ion battery pack.Just do yourself a favour and don't mess with unprotected cells.

author: Zinger
author_rank: Contributor
timestamp: April 10, 2017, 12:12:49 am
content: Thanks,That's exactly what I needed to know.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 10, 2017, 01:14:07 am
content: You might consider using LiFePO4 (Lithium Iron Phosphate) batteries instead of regular Lithium Ion or Lithium Polymer batteries. They don't have the energy capacity of their cousins, but they're much more stable.Basically, Lithium Phosphate batteries are no more dangerous than any other rechargeable battery (e.g. Nimh). If you search youtube for LiFePO4, you'll find various videos of people doing horrible things to the batteries without any explosions ("Let's hacksaw this charged battery open to see what's inside.").They really have to work hard to get the batteries to do anything bad. Like any high-power battery they should be treated with respect, but you don't have to be afraid of them. You still need a Battery Management System (BMS) to ensure long life.Ed

author: edpalmer42
author_rank: Super Contributor
timestamp: April 10, 2017, 04:05:43 am
content: Quote from: blueskull on April 10, 2017, 01:24:40 amI don't know if that's necessarily true or not. When I looked on ebay, I found 18650 LiFePO4 protected cells that were limited to 4 or 5 amps just like Li-ion. I also found cells that were rated for 40 - 50 - 60 amp discharge rates! Maybe it's just safer to build cells like that using LiFePO4 technology.But in the case of external shorts, isn't that what fuses are for?Ed

author: edpalmer42
author_rank: Super Contributor
timestamp: April 10, 2017, 05:18:23 am
content: Quote from: blueskull on April 10, 2017, 04:13:30 amOkay, then don't buy the high-rate cells. They're specially made for high-rate applications. Any rechargeable cell can bite you if things go wrong. That's why I said to treat it with respect. You can pull over 20 amps out of a AA ni-cad cell if you short it. Does that make ni-cad cells dangerous? No. Does it mean you should treat them with respect? Yes!I recently bought a bunch of unprotected 18650 LiFePO4 cells to use for battery backup purposes. They were intended for use in solar garden lights and just have flat contacts. I very much doubt that they're capable of really high short-circuit currents and I have no intention of finding out. When I design my circuit, I'll include appropriate protection.I have a battery charger which can measure the internal impedance of a battery. It rates these cells as 100 - 200 milliohms. By comparison, I've got some Eveready AA Nimh, only 1300 mah cells that are ~50 milliohms. I don't know if these numbers are accurate, but they suggest that the LiFePO4 cells could put out 32 amps while the Nimh cells could put out 24 amps unless an internal fuse blows. Either one could ruin your day under the wrong circumstances.Alwaysrespect a battery, no matter how big or small it is!Ed

author: danmcb
author_rank: Regular Contributor
timestamp: April 10, 2017, 08:20:14 am
content: it's not just shorting you have to worry about. There is also over-voltage while charging. This is as likely to cause bad stuff to happen (during charging or after, as the cell has been damaged but perhaps will not become unstable until being used later). It could happen because of a defective or badly designed charger.Just don't use unprotected cells.