Mascot Power Blog

Test for Discharge across mains plugs

Input voltage of a mains powered charger or PSU is high voltage, which is dangerous to touch. 230VAC 50Hz voltage fluctuates sinusoidally between -325V and maximum 325V fifty times every second. Usually the charger or PSU is having one or more X capacitors at the input to prevent excessive conducted and radiated emissions. This capacitor is carrying the same high voltage waveform.

When the user disconnects the battery charger from the mains, the user has access to the pins on the AC plug, which is carrying the instantaneous voltage across the EMC input capacitor. Nowadays energy saving is very important. The charger should ideally consume no power from 230VAC mains when not charging a battery. This means the voltage of the input capacitor may remain at the instantaneous voltage level upon disconnection from mains socket. This voltage may be as high as 325V and even more.

If the input capacitance is relatively low, e.g. less than 100nF (nano Farad), the energy stored in capacitor may be considered low enough to be considered safe. However, the requirements in various safety standards for different applications vary a lot.

Mascot wants to design their product to comply with all kind of possible use. Hence, the charger or PSU must comply with the requirements listed below.

NOTE: the following tests are for qualified technicians only.

 

Pass/Fail voltage levels defined per standard:

Input at test: Max. Rated Voltage

Cx = rated nominal capacitance of capacitors in input circuit

Cxt = rated nominal capacitance + specified tolerance from datasheet of capacitors in input circuit

 

IEC 61010-1 "Electrical equipment for measurement, control, and laboratory use":

test at any Cx

On pins on plug: < 60V after 5 seconds.

On Terminals for fixed installation: < 60V after 10 seconds.

 

IEC 60065 " Audio, video and similar electronic apparatus" (Expire 20.12.2020, use IEC 62368-1):

test only if Cx > 0.1 µF

< 60V after 2 seconds

 

IEC 60950-1 "Information technology equipment" (Expire 20.12.2020, use IEC 62368-1):

test only if Cx > 0.1 µF

Pluggable Type A = ordinary mains plugs: < 37% of mains voltage after 1 second

Pluggable Type B = industrial plugs: < 37% of mains voltage after 10 seconds

 

IEC 60335-1 "Household and similar electrical appliances":

test only if Cx ≥ 0.1 µF

≤ 34V after 1 second

 

IEC 60601-1 "Medical electrical equipment":

test only if Cx > 0.1 µF

< 60V after 1 second

 

IEC 62368-1 " Audio/video, information and communication technology equipment":

test at any Cxt

For Ordinary persons:  

< 60V after 2 seconds at Cxt ≥ 300 nF, higher voltage limits for Cxt < 300 nF

For Instructed persons and in Single Fault Conditions (SFC):        

< 120V after 2 seconds at Cxt ≥ 300 nF, higher voltage limits for Cxt < 300 nF

 

Notes to Discharge Test to IEC 60950-1 & IEC 62368-1:

Discharge resistors situated before a fuse are required to be in compliance with (tested or certified to) IEC 60065 Cl. 14 a) or b) or to IEC 62368-1 Annex G.10.1, G.10.2. After a fuse Single Fault Condition (SFC) testing is done, unless as above.

For a resistor SFC is both open and short for resistors not complying with IEC 60065 Cl. 14 a) or b) or IEC 62368-1 Annex G.10.1, G.10.2. Opening a discharge resistor will disable the discharge circuit and often make the product non-compliant with the discharge requirements. Shorting a resistor in a group of discharge resistors will improve the discharge but consideration of creepage/clearance distance must be done. The test of  IEC 62368-1 Annex G. 10.2 is a 1.2/50 µs impulse test done after a 21 day Damp Heat Test (IEC 60068-2-78). Resistor value shall not deviate more than ± 10% after the test. Compliant resistors may have separate certifications or the test house may do the 21 days impulse test in the project.

 

 

 

Author:

Editor Dag P