Lithoum batteries with internal protection PCB...always safe?

[treez]

Hello,

The following lithium polymer battery comes with an internal protection PCB, which stops its terminal voltage rising above 8.5V, and stops it being discharged below 5V.

https://www.all-battery.com/74volt-5500mahli-polymerpackwithpcb.aspx


...so does that mean that it can never be made to catch fire, like normal lithium batteries, and can we say that with this protection PCB, its just as safe as a NiMH or NiCd battery?

 

[Tahmid]

In the page linked to, this is mentioned:

Features and Benefits

2 cell Li-Polymer 5500mAh ultra high capacity battery pack.
Internal PCB for protection: over-charging cut-off; 8.5V; over-discharging cut-off; 5V
Maximum dis-charging current: 18A
Maximum charging current: 7A
Dimensions: 152.5mm x 58mm x 14.5mm
Weight: 10 Oz
Recommended charger: Universal Li-ion / Li-polymer Smart Charger to charge this battery pack.

which stops its terminal voltage rising above 8.5V, and stops it being discharged below 5V.

I have shown this in bold above. This is what you've read from the Features and Benefits.

However, just below "Features and Benefits", you can see this:

Caution:

Improper use like overcharging and over discharging can cause explosion and/or fire. User of the battery is required to have the sufficient Li-polymer charging experience and technical knowledge. Tenergy or All-Battery.com are not responsible for any damage or injury caused by misuse, misunderstanding or abuse of this product.

...so does that mean that it can never be made to catch fire, like normal lithium batteries, and can we say that with this protection PCB, its just as safe as a NiMH or NiCd battery?

Not according to the caution they've provided.

 

[treez]

Thanks Tahmid, i think you are probably thinking the same as me....that is..."what is the point of putting a protection PCB in the lithium battery if its not going to stop fires?

 

[FvM]

what is the point of putting a protection PCB in the lithium battery if its not going to stop fires?

It's handling the risks it's designed for, but necessarily all risks. There are e.g. non-electrical safety risks like mechanical shock.

 

[treez]

i see, but mech shock can affect all batteries, and most chemistries such as Nicd and Nimh dont have protection pcb's in them.

I am wondering why they bother to put a protection pcb in the lithium ones....it clearly does not stop fires........a 2 series cell lithium battery with 8.45V on its terminals would start a fire, and the pcb would not detect this. ...because its trip point is 8.5V.?

 

[FvM]

I'm not sure what's your point. I guess, the actual problem is to decide LiPO is safe enough for your application. Without knowing the details, I imagine that some aspects of LiPO batteries, e.g. shipment restrictions can be a problem. Features like the said protection PCB will most likely allow a less restrictive battery handling, both in production and at user site, so it's reasonable although it doesn't solve all problems.

 

[treez]

our application is emergency light, battery salesmen tell us not to use lithium because it can cause fires, but my laptop has lithium and it doesnt cause fires, i suppose the laptop has protection features, but so too could the emergency light.

 

[Tahmid]

but my laptop has lithium and it doesnt cause fires, i suppose the laptop has protection features, but so too could the emergency light.

Yes of course. Your laptop has lithium battery and your cellphone does too. If all protection can be properly implemented there shouldn't be a problem. After all the only instances of fires I've heard from lithium batteries in cellphones are due to overcharge (even though I would assume that protection against this should be implemented). Maybe that's the thing. I've heard of phones exploding due to overcharge whereas they supposedly all have protection circuitry.

So, the PCB could protect against overvoltage and undervoltage, but this could maybe not be enough. Say if the terminals of the battery were shorted. Could the protection circuit react quickly enough to make sure no harm is done? The PCB will protect against overvoltage, but will it protect against too high charging current surges?