Limiting Inrush Current on LED driver

[andycsmith]

Hi,

I have purchased one of these https://www.tagra-lighting.co.uk/product/24v-premium-tagra-professional-ip67-encased-led-driver-100w-4-16a/ LED drivers for a friend to drive some LED Strips and have just recently discovered that the inrush current could be at least 70A, I'm looking to wiring this into the existing lighting circuit, which in the UK would have a 6A fuse so I need to limit the Inrush Current to this to avoid fuses tripping,.

Is it as simple as putting a NTC in line, if so can someone recommend one that would do the job or would it be better to use an active current limiter. Any advice would be appreciated.

Thanks,

Andy

[TimNJ]

I would not expect a single 70A inrush peak will blow any fuses, unless you have fast acting type installed in your fusebox. 70A is not uncommon for modern switchmode converters in my experience.

[ledtester]

I would just get in touch with the manufacturer:

https://www.tagra-lighting.co.uk/contact/

They should be able to tell you if the inrush current will be a problem and how to mitigate it -- after all, it's in their interest to help customers install and use their product.

[Ice-Tea]

Not as uncommon as you might think

Residential fuses are curve C I think:



So, even a 10A breaker should easily support that inrush.

[Jwillis]

If your still concerned about inrush current you can put a soft start module between the source and LED driver.  A proper soft start doesn't limit the voltage but slows the current until the capacitors charge then a relay closes the circuit for direct power from the source . Much more efficient than tossing in a bunch of NTC's and hoping  for the best.Single phase soft starts are fairly inexpensive and can relieve the extra stress on rectifiers from excessive inrush current.

[Zero999]

When I had a problem with LED drivers blowing the plug-top fuse, I used a simple series resistor to limit the current surge. The voltage drop was low enough, that it didn't heat up much.

[BrokenYugo]

Nasty inrush current is nothing new in lighting (go measure a cold 100 watt light bulb sometime), I'd try it before assuming things will need modification.

[ocset]

I need to limit the Inrush Current to this to avoid fuses tripping,.

..you ask an excellent question. But you cannot select a fuse which will avoid nuisance tripping from inrush pulses......because eventually, after so many inrush current pulses, your poor fuse will die. Its just a matter of how many inrush pulses you want to withstand before it dies...and you select the fuse on that basis. But yes, inrush kills fuses...eventually...its just a matter of how long it holds out.

Pages 6 and 7 show you how to select a fuse for this...based on the inrush current pulse shape etc
https://www.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_fuseology_selection_guide.pdf.pdf

What you usually do is calculate the "pulse I^2.t". (using the chart shown in the littelfuse link.)
Then, for example, to survive 100000 inrush pulses, you would need a fuse with an I^2.t" value of (100/22) * "pulse I^2.t".
Might as well take the worst case pulse at "on at mains peak".

And yes, their are piles upon piles of scrapped electronics products , all over the world, which have been scrapped for no other reason than the fuse died after so many inrush pulses......and all because the nice manufacturer (or rather the millionaire middle man who used the manufacturer)  didnt want the added cost of an inrush limiter....which could have been as cheap and simple as an "on at zero cross"  circuit.

In truth,  to be kind to the environment, all offline power supplies should start up through a massive inrush resistor, which allows through just enough current to power a  mains zero crossing detector". Then, a little micro should  switch on a relay or back-to-back fet etc which shorts out the big inrush resistor....and this being done at the zero cross.
............____________------------

So from the inrush pulse example, (LTspice sim attached, LTspice is free)  the I^2.t = 0.5 * 284^2 * 241us = 9.72
(as per the littelfuse fuseology example)
So, to get a fuse that can withstand 100000 of these pulses, it must have a melting i^2.t of (100/22) * 9.72 = 44.2    A^2.s

…So as you can see, the 3.15A version of this (0034.3122) is good for 100000 pulses of inrush at mains peak, at high mains of 265VAC.
https://us.schurter.com/bundles/snceschurter/epim/_ProdPool_/newDS/en/typ_FST_5x20.pdf

[andycsmith]

Thanks for the responses, I contacted the manufacturer and they advised that if there was only one drive on a circuit then there will not be a problem.

[MathWizard]

Not as uncommon as you might think

Residential fuses are curve C I think:



So, even a 10A breaker should easily support that inrush.

People/scientists label graphs/etc lots of ways? I'm just wondering if in Germany, or other countires, which axis do they normally have time on (when not doing Cosmology or GR lol) ?

[ve7xen]

Not as uncommon as you might think

Residential fuses are curve C I think:



So, even a 10A breaker should easily support that inrush.

People/scientists label graphs/etc lots of ways? I'm just wondering if in Germany, or other countires, which axis do they normally have time on (when not doing Cosmology or GR lol) ?

Independent variable on x, dependent variable(s) on y. In this case, the time is the dependent variable, so it goes on y axis. This is the same everywhere.

[hsn93]

When I had a problem with LED drivers blowing the plug-top fuse, I used a simple series resistor to limit the current surge. The voltage drop was low enough, that it didn't heat up much.

a question .. why you didnt use NTC for the inrush .. is there practical reason .. or you just didnt have it on hand ..

[Zero999]

When I had a problem with LED drivers blowing the plug-top fuse, I used a simple series resistor to limit the current surge. The voltage drop was low enough, that it didn't heat up much.

a question .. why you didnt use NTC for the inrush .. is there practical reason .. or you just didnt have it on hand ..

The running current was so low, NTC wouldn't have made much difference, since it didn't heat up enough.