Charging a protected Li-Ion cell with a protected charger

[PinheadBE]

Hi,

I just wondered if it is ok to charge a protected 18650 cell with a charger that also has protections.
Something like this: https://www.aliexpress.com/item/12V-Charging-UPS-Uninterrupted-Protection-Integrated-Board-18650-Lithium-Battery-Boost-Module/32892470149.html

Aren't the two protection circuits going to pose problems ?

I suppose it will be ok, but, better be safe than sorry

Thanks

[spec]

Hi,

I just wondered if it is ok to charge a protected 18650 cell with a charger that also has protections.
Something like this: https://www.aliexpress.com/item/12V-Charging-UPS-Uninterrupted-Protection-Integrated-Board-18650-Lithium-Battery-Boost-Module/32892470149.html

Aren't the two protection circuits going to pose problems ?

I suppose it will be ok, but, better be safe than sorry

Thanks

Hi PinheadBE,

Never heard of any problems charging a protected LiIon battery with a normal charger.

From a theoretical point of view there will not be a fight between the two protection schemes because the scheme with the most stringent settings will function first and the other protection scheme will not be triggered.

The only area where the built-in protection could get triggered is if you had a fast charger with a very high charge current.

By the way, I understand that all first-tier manufacturer's large LiIon batteries have a built-in thermal fuse.

[PinheadBE]

Thank you for your reply

[Daixiwen]

By the way, I understand that all first-tier manufacturer's large LiIon batteries have a built-in thermal fuse.

No it's usually a circuit breaker triggered by an increase of the internal pressure. But you shouldn't consider this as a replacement for a safety mechanism. There are ways to provoke a fire without triggering the circuit breaker, by example by very slowly charging the battery slightly above the thermal runaway voltage with a very small current. Low temperatures make this easier too. So don't count on that safety as the only one against a defective charger.

By the way battery manufacturers don't like using the words "fire" or "explosion" so I should probably say "fast uncontrolled disassembly with high temperature degassing"

[PinheadBE]

By the way battery manufacturers don't like using the words "fire" or "explosion" so I should probably say "fast uncontrolled disassembly with high temperature degassing"

    Thank you: You just made my day ! 

[spec]

By the way, I understand that all first-tier manufacturer's large LiIon batteries have a built-in thermal fuse.

No it's usually a circuit breaker triggered by an increase of the internal pressure.

Hmm, interesting. My understanding was that there is a thermal fuse (and I may have got that wrong). In addition the battery has a strong case with blow off vents to release excessive pressure. 

But you shouldn't consider this as a replacement for a safety mechanism. There are ways to provoke a fire without triggering the circuit breaker, by example by very slowly charging the battery slightly above the thermal runaway voltage with a very small current. Low temperatures make this easier too. So don't count on that safety as the only one against a defective charger.

By the way battery manufacturers don't like using the words "fire" or "explosion" so I should probably say "fast uncontrolled disassembly with high temperature degassing"

I see we have the usual 'end of the world' stuff every time someone mentions LiIon batteries. It used to be lead acid at one time, then NiCad, and then NMH.

[Daixiwen]

The problem is that people that know a bit about the internal construction of batteries have often worked on safety too. I have done what we called "abusive tests" for 3 years on Lithium-Ion cells, finding all possible ways things could go badly, and this kind of work tends to make you paranoid

In addition the battery has a strong case with blow off vents to release excessive pressure.

Yes that's true. Often when there is excessive pressure there is also a thermal runaway going on and it's not just gas that comes out, it's a flame that can be 10 times longer than the cell itself.
I know that I sound "end of the world" but when you are working on something that can potentially burn your house down, take a few precautions. Protection circuits for Li-Ion are dead cheap, there is no reason for not using them, at least for charging. Please use them. Thermal runaway on a Li-Ion cell can start at a voltage as low as 4.35V, all it needs is a badly calibrated power supply.

[spec]

The problem is that people that know a bit about the internal construction of batteries have often worked on safety too. I have done what we called "abusive tests" for 3 years on Lithium-Ion cells, finding all possible ways things could go badly, and this kind of work tends to make you paranoid

In addition the battery has a strong case with blow off vents to release excessive pressure.

Yes that's true. Often when there is excessive pressure there is also a thermal runaway going on and it's not just gas that comes out, it's a flame that can be 10 times longer than the cell itself.
I know that I sound "end of the world" but when you are working on something that can potentially burn your house down, take a few precautions. Protection circuits for Li-Ion are dead cheap, there is no reason for not using them, at least for charging. Please use them. Thermal runaway on a Li-Ion cell can start at a voltage as low as 4.35V, all it needs is a badly calibrated power supply.

Yes, I know you mean well, but safety is not what the OP asked about.

But as we are on the safety track, you are right, the switch is operated by internal pressure. Here, AFAIK, are the safety measures that are on top tier batteries.

• Pressure switch
• PTC to limit current if overtemperature
• Strong case to contain pressure
• Blow-off vents to release pressure
• Inhibiting mat which melts on over temperature and prevents ion exchange
• Limit the amount of Lithium in a battery cell