Designing with LED driver inrush currents

[01laverickd]

Hi,

I am just trying to get my head around designing circuits with high bays, in particular the inrush current from these lights.

So say I've got 10 (for ease) 150watt high bays (6.5Amp load @ 230v) with an inrush current of 40amp fitting (400amp) . The instaneous trip current for a 10 B type is 50A, and a type C 100A.

Both the above would trip surely, 400A>100A I know practically they don't, why?

Is it because the inrush current duration is so short?

Also, how would you switch the high bays with such a high inrush current? Surely relay and contactors would weld at them currents?

Any advice welcome as always, ive fitted the high bay led drivers but on someone else's design but I was just curious to how you would design with these types of inrush currents.

Thanks.

 

[bill01803]

The C10 can do 100A for 7 seconds so should be fine

 

[01laverickd]

Hi Bill, thanks for the reply.

The current wouldn't be there long, probably talking milliseconds, if that. Would I have to see the manufacturers data on the mcb? To see what current they can take for the time the inrush current is present with tripping?

 

[bill01803]

Fig 3A5

 

[pc1966]

LED driver inrush is usually very short, fractions of a millisecond which makes the electromechanical "instant" trip see less effect as it is a short time for any such mechanical system to react.

Here they give some examples with the current peak around 0.24ms and actually have the trip currents for a Schneider breaker on that sort of a time-scale:
https://www.eldoled.com/support/learning-center/how-to-choose-the-right-circuit-breaker/

 

[01laverickd]

LED driver inrush is usually very short, fractions of a millisecond which makes the electromechanical "instant" trip see less effect as it is a short time for any such mechanical system to react.

Here they give some examples with the current peak around 0.24ms and actually have the trip currents for a Schneider breaker on that sort of a time-scale:
https://www.eldoled.com/support/learning-center/how-to-choose-the-right-circuit-breaker/

I actually found that sheet and have downloaded it for future use, very helpful thank you pc!

It still could give people big headaches if they go in just thinking they can retrofit to LEDs if they are not wary of this. I think the manufacturers of in the above page you mention say that their drivers under 100watt don't have to have the inrush calculated as its minimal but over 100w you must take it into account.

Thanks again.

 

[pc1966]

Yes, the LED calculation is not easy as both the inrush profile and MCB's reactions to very short pulses are rarely documented.

But the x5 factor on steady-state they found is probably a reasonable starting point for a B-curve MCB, probably around 2.5 for C-curve.

 

[pc1966]

As in 6A B-curve should be good for 1.2A = 280W LED simultaneously switch. That sort of rule-of-thumb.