DSH 384 Lithium Cell Protection
http://decisions.iecee.org/icons/ecblank.gif DSH 384
Lithium Cell Protection
4.3.21
60950(ed.2)
Standard: IEC60950, 2nd Clause: 4.3.21 Sheet n. P384
Page 1(1)
Subject: Lithium Cell Protection Key words:
-Lithium Cell
-Clearances
- failure mode
Provisional Decision taken by ETF2
and to be approved by CTL at its
38th meeting, in Toronto
Question:
Clause 4.3.21 requires that two levels of protection are required to prevent forced or reversed charge
or forced discharge if this would result in a hazard. Conventionally a combination of resistor, diode
or ic has been considered suitable and is for the series current path. However, a new consideration
has been raised in respect of adjacent tracks, separated by no more than operational insulation, which,
under s/c conditions will bypass the protective series components and provide charging current for
either chargeable or non-rechargeable batteries. Does this mean that there is therefore a requirement
for Reinforced separation?
If that is the case, then the controlling factor is the clearance of 0.8mm in Table 5 (circuits not subject
to transient over voltage). This is based on the fact that creepage cannot be less than clearance and
creepage can be calculated to be, for example at +5V, 0.4mm (based on rounding up 0.12mm to
0.2mm for Basic and doubling for reinforced.
Decision:
Operational insulation is suitable taking into account 5.4.4 because there is no risk of electric shock.
(see 1.2.9.1)
Care should be taken by determining clearance and creepage distances which column of the table has
to be used.(Transients have to be taken into account)
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