Using MEAN WELL Inrush Current Limiters
Switch mode power supplies incorporate large capacitors in the input stage to keep the ripple voltage low.
However, upon start-up, these capacitors draw a large inrush current while charging up.
MEAN WELL’s ICL series inrush current limiters are the perfect solution for applications that demand a low inrush current.
MEAN WELL ICL-16 and ICL-28 Series Inrush Current Limiters
The MEAN WELL ICL-16 is a 16A inrush current limiter that can be used to reduce the temporary peak current caused by capacitive loads, such as switch mode power supplies and LED drivers. The ICL-28 is the 28A version of this device.
Installing the inrush current limiter between the AC circuit breaker and the load can effectively reduce the possibility of the AC circuit breaker falsely tripping, when AC loads are started up, increasing the overall reliability of the system.
The ICL-16 inrush current limiters consist of three parts:
- A cement resistor “R”, which compensates for the decreasing resistance within the NTC thermistor as the temperature increases, enabling the inrush current to be kept at the same level in a higher temperature environment as you would expect at normal room temperature.
- A bypass relay, which is used to short-circuit the cement resistor “R” once its suppression job has been done. This is triggered by the control circuit
- The control circuit, shown in the following diagram. This circuit combination significantly reduces the heat generated during operation and improves the suppression ability, thus differentiating the ICL-16 from other inrush current limiters that use NTC thermistors.
The MEAN WELL ICL-16 inrush current limiters are available in two different form factors:
How Many Power Supplies can be Connected to One ICL-16L Inrush Current Limiter?
MEAN WELL Australia has published a table, which sets out the suggested maximum number of power supplies that you can place on a miniature circuit breaker (MCB), both without an inrush current limiter and with an ICL-16 or ICL-28 inrush current limiter installed.
Click on the below link to download the table:
Selecting Circuit Breakers
A circuit breaker is an automatically operated electrical switch, which is used as an over-current protection device to protect electrical/electronic equipment from damage caused by overload or short circuit.
Circuit Breaker Types
One of the most common circuit breakers with a low current (not more than 125A) is the miniature circuit breaker (MCB).
When it comes to the instantaneous tripping current, MCBs can be split into 4 types according to their tripping characteristics: A, B, C or D.
- Type A is for the protection of very sensitive circuits such as semiconductors. Its instantaneous tripping current is 2In to 3In (In is the rated current of an MCB).
- Type B is suitable for computers, electronic equipment and residential circuit protection. Its instantaneous tripping current is 3In to 5In.
- Type C is for general device protection in control circuits, protection of lighting circuits with high inrush current and all other supplementary circuit protection systems. Its instantaneous tripping current is from 5In to 10In.
- Type D is for the protection of high inrush loads like transformers, solenoid valves, etc. Its instantaneous tripping current is 10In to 20In.
To operate with MEAN WELL power supplies or LED drivers, type “C” or “D” MCBs are recommended.
Type C Circuit Breakers
You will usually find the following specifications in the data sheet for an MCB.
This is the input voltage the breaker is designed to operate at under normal condition. For example: AC 240V or 120V.
Number of Poles:
The number of circuitries the breaker can operate on at one time.
For example, a 2-pole, or 2P, circuit breaker can let-through or disconnect two circuitries. There are 1-pole (1P), 2-pole (2P), 3-pole (3P) and 4-pole (4P) circuit breakers; 3P and 4P breakers are often used in a 3-phase circuitry network.
Rated Current (AT or In):
The highest amount of current a breaker can carry indefinitely at a certain ambient temperature.
Frame-size rating (AF):
The range of the highest current-level-setting tripping unit that can fit the breaker.
Rated Ultimate Short-circuit Breaking Capacity (Icu):
The maximum short-circuit current under a specified range that the breaker can break, such as 380V-30kA; the circuit breaker is not required to carry the rated current after the operation or test for Icu. In other words, the breaker can break this fault current, but it may not be usable afterwards.
Rated Service Short-circuit Breaking Capacity (Ics):
The capability of the breaker to provide normal operation after breaking the short-circuit current under specified range, such as 380V-15kA. In other words, the breaker can break this fault current and will still be usable afterwards. Ics is a percentage of Icu.
A circuit breaker is considered violating the regulation if any one of the above items is not listed in the data sheet.
Things to Consider when Selecting a Circuit Breaker
When choosing an MCB for your power supply, or LED driver, you should follow these 2 rules:
The rated current (In) of the MCB must always be greater than the total input current of your power supply, or LED driver. In general, the rated current (In) should not be less than the total input current multiplied by a coefficient of 1.25.
The rated service short circuit breaking capacity (Ics) of the MCB must always be greater than the total inrush current of your power supply, or LED driver.
An inrush current occurs during the initial start-up. Typically, the duration of this inrush current is very short, lasting only a few microseconds. As long as the total inrush current does not exceed the rated service short circuit breaking capacity (Ics), the MCB will operate properly without being damaged.
A BHA32C16 MCB by SHIHLIN ELECTRIC is chosen for a lighting system powered by the MEAN WELL HLG-80H LED drivers.
The BHA32C16 is a Type “C” breaker (5 times In)
Rated voltage: 380Vac
Rated current: 16A
Rated service short circuit breaking capacity (Ics): 6KA/380Vac.
Inrush current: 70A/230VaC
Input current: 0.425A/230Vac.
How many MEAN WELL HLG-80H LED drivers can be used with the BHA32C16 MCB withstand without tripping?
16A/1.25 = 12.8A; 12.8A/0.425A = 30 (units)
70*30 = 2100A<6kA
According to the calculation above, 30 units of the HLG-80H can be installed in the system.
The data mentioned above is based on a 25°C ambient temperature.
If your system is used in a higher ambient temperature location, please refer to the ambient temperature correction curve of your MCB to de-rate the rated current (In) of the MCB.
It should be noted that the LED power supply data sheet will specify a much lower number of LED drivers per breaker. This is because a much more conservative approach is taken in the calculations, as it is not known what brand breaker would be used.
A suitable miniature circuit breaker (MCB) should be used when MEAN WELL power supplies or LED drivers are connected to a system. This is because an MCB can prevent systems from immediately tripping at start up.
If it is difficult to select one single MCB for a system with a high input current, it is suggested that you divide the system into several smaller systems with a lower input current and then choose a readily available MCB for these smaller systems.
The above calculation is based on a general method, which does not involve inrush current.
Calculating inrush current requires T50 - the time duration of the inrush current pulse at 50% of Ipeak - and proof factor (K) - the pulse duration against surge current. Not all circuit breaker manufacturers publish the K factor data. Therefore, this article does not mention that calculation for inrush current.
Inrush current is an inevitable phenomenon while the start-up of switch mode power supplies. If the circuit breaker is being falsely tripped, it is a good idea to install an ICL-16 inrush current limiter between the breaker and the load to limit the inrush current.
For further information contact MEAN WELL Australia.