EN 62368 (In an Annex - M.4.2.1) Secondary Lithium Battery Charging Safeguards

[Leroy105]

We have a system with a secondary lithium battery which needs to meet the charging safe guard requirements of EN 62368.

One of the requirements of EN 62368, tucked away in an annex, is M4.2.1, which states that your device must stop charging a battery at the highest operating temperature of the device.

(Image attached).

Our test lab wants to single fault the battery charging circuit and try to mess with the thermistor input.

Our reading of the requirement is that you single fault the system to ensure no over current / over current voltage occurs.

The second paragraph doesn't indicate you single fault the system for the temperature cut-off. It just says the battery charging circuit must stop charging and is ambiguous as in what states it must work.

Is this selective reading on our side? Do you think this section M.4.2.1 implies you apply faults for the temperature cut-off as well?

(Reason I ask is that, most of the temperature cut-offs are dependent on a thermistor and if you single fault some charging current to the thermistor input it seems like you will cause a malfunction on any modern battery charging IC).

 

[Benjamin Weber]

There are two SFC I can think of for a thermistor: open and short. Usually e thermistor is an NTC, so a short will present a very high temperature to the system, an open circuit will present a very low temperature. In the short-case, the charging should be stopped immediatley, independent from the ambient temperature. This should not be a problem. The open circuit on the other hand is more a problem, since the charging will not be stopped when the limit tmeperature is reached. This a SFC that would fit to cl. B.4.6 (short/open of passive components).

But there are some exemptions fro particalr components, maybe these are applicable for you?

 

[CharlieUK]

I think it depends

M.4.2.2 Compliance criteria
Compliance is checked by measuring the charging voltage, the charging current and the temperature of each individual cell of the secondary lithium battery under normal operating conditions, abnormal operating conditions and single fault conditions. The cell temperature shall be measured at the points specified by the battery manufacturer. Single fault conditions that may affect the charging voltage or charging current or the temperature shall be applied in accordance with Clause B.4.

B.4.2 Temperature controlling device
Except for temperature controlling safeguards, according G.3.1 to G.3.4, any single device or component of a circuit controlling the temperature during temperature measurement shall be open-circuited or short-circuited, whichever is more unfavourable.
Temperatures shall be measured according to B.1.6.

Is your thermistor a certified component (e.g. UL or TUV?) to IEC 60730-1 ?