Inrush Current describes the max instantaneous input of current, which is drawn by an electrical device when it is first powered on. A power supply will often draw a greater current than its steady-state current during the initial start-up phase. This "Inrush" is caused by a PSU's capacitors being charged, or because magnetic flux has not been fully built up. Usually, Inrush doesn't last much longer than a few milliseconds, but even in such a short amount of time it can result in circuit breakers tripping.
The inrush current is much higher than the nominal operating current. In most cases, inrush current can be as much 70 to 100 times higher for a short period of time, usually being worst during the first half-cycle. At the input side of the LED driver, there will be (1/2 ~1 cycle, ex. 1/100 ~ 1/50 seconds for 50 Hz AC source) at the moment of powering on before settling down again.
To compound this, most circuit breakers have different inrush trip curves. To find the trip curve of a particular breaker, it is best to find the datasheet of the breaker in question.
We do suggest erring on the side of caution when powering on your devices; while it's unlikely that Inrush Current will damage your PSU, powering on and off too quickly (repeated flicking of switch) may cause electrical trips, especially if you have multiple devices set up (because of the huge inrush current). In such as instance and only if powering a big quantity of LED strip drivers, in order to avoid protection mode being activated or MCB tripping, it is suggested that you power on the LED drivers sequentially using any method, automated or manual. Note that with heavy inrush currents, D type MCB's may be used. There are special MCBs on the market which are designed to handle In-rush current and generally speaking you must have at least a 6A Lighting MCB, along with making sure that you design your installation in the event you are using multiple drivers.
Calculating for Inrush current (example):
The following calculation is meant to serve as a practical example of how to work out an approximation of inrush current required for a circuit breaker with 3 power supplies of 200W each.
If using 3 x 200W LED strip Drivers:
200W ÷ 240V (primary input) = 0.83 (Amps) x 100 (worst-case scenario for inrush current) = 83A
So, if we calculate 3 x 83, we reach 249A - this is the inrush current that circuit breaker "trip curve" should be able to stand for powering 3 x 200W LED drivers in parallel.
Please note: Some manufacturers may list lower amperage for the same wattage drivers. This can be done for marketing reasons and are not necessarily calculating for a full cycle. Hi-Line does not try to sell based on lowest values, which is why the above is based on absolute worst-case scenario.
For further reading on how to go about selecting the right MCB for you, in addition to other safety advice, please visit Beama's page below and download their PDF guide on circuit breaker selection:
BEAMA Circuit Breaker Selection Guide
RCD issues are another thing to consider, in which case please see the very informative IET Guide HERE.
Hi-Line Lighting provides a wide range of LED Drivers. Please refer to our full Driver catalogue for more information.
Comments
0 comments
Article is closed for comments.