LED Inrush Current

Thread Starter

fordo

Joined Aug 20, 2015
19
About a year ago I purchased several high quality outdoor motion detector/spotlights. I had a minor issue with one and called the mfg.’s tech support. After resolving the issue somehow I had mentioned that I was using LED bulbs. The tech support guy advised me the warranty may be voided if I continued using LEDs because the internal switching circuit for the light bulbs (of the motion detector) could not handle the repeated high inrush currents from LED bulbs. He suggested I use halogen or incandescent bulbs. They were expensive motion detectors and had five year warranties so without much further thought I just went out and bought a six pack of Gx halogen bulbs (I’ll leave it up to you to figure out the brand!).

Fast forward to just recently. Of the original halogen bulbs, one burned out after about eight months, its replacement burned out one day after I installed it, and one was dead on arrival (I ohmed it out first).

Disgusted with halogens, I decided to go down the path of seeing what I could do to limit the inrush current to the motion detectors so I could use LEDs. I ended up at Ametherm’s website and started to go through some of their preliminary calculations for selecting an NTC (thermistor) as a possible solution. Then a light came on in my head (no inrush current here!).

The OEM specs for the motion detector says they are rated at 1000 watts. From reliable sources on the internet (Fluke and others) an incandescent light bulb has an inrush current of about 15x its steady state current. So, two 500 watt bulbs have a steady state current of 1000 watts/ 120 volts = 8.3 amps with an inrush of 15 x 8.3 amps = 125 amps. I didn’t have a 500 watt incandescent bulb but I did have a100 watt bulb that read about 10 Ω (cold), so this all sounded reasonable.

Ametherm’s website indicates typical LED light drivers have an inrush of about 100x steady state current. The biggest PAR38 LED lamps I could find for my motion detectors were 250 watt equivalents that actually only consumed 32 watts. Each motion detector has two sockets so 2 x 32 watts = 64 watts ⇒ 120 volts/64 watts = 0.53 amps steady state ⇒ 0.53 amps x 100 = 53 amps inrush.

53 amps of inrush for LED’s is much less than 125 amps for a 1000 watt incandescent load inrush. So I should be ok using two 32 watt LEDs, right? I didn’t call the OEM back after doing these calculations but thought I’d first reach out to see if anyone could find if I was missing something or I made some other error. Opinions, thoughts?
 

Yaakov

Joined Jan 27, 2019
3,930
The assertion by the CSR that in-rush current with LED drivers is a problem is absurd. The in-rush current for tungsten filament lamps is enormous, as you have worked out for yourself.

If there is a problem (and I don’t know what it would be) using LED lamps with their product, it’s not in-rush current.
 

Tonyr1084

Joined Sep 24, 2015
6,583
I've had motion detector lights all around my house. The porch has a motion detector that is wired to turn three LED lights on. The side porch has a single LED light, and the back yard sensor has two PAR-38 LED lamps. I've been running them for over five years without problems. The side porch light is most exposed to weather and the suns daytime heat and it is a little finicky about switching on. But that may be due to dust or bugs getting inside the sensor. Otherwise, they all still work just fine.

Last week I was talking to tech support about a TV issue. I just bought a TV that was "Apple AirPlay" compatible. Bought it for just that reason. Got it home and set it up. Worked great. For one day. Then the next and subsequent days it wouldn't work. So I did a factory reset and went through all the setup again. And for one day the AirPlay worked, then after that it didn't. So I called tech support and the guy told me it wouldn't work because my computer and TV were not on the same network. Well, they ARE. Only, the router has one Mac Address and the TV has a different address. He said it wouldn't work. So then why did it work the first day and then stop? He - well, we lost connection. I think he hung up.

Tech support isn't always staffed with people who KNOW what they're doing, but rather are staffed with people who have a script to follow. If this doesn't work then do this. If that doesn't work then restart everything. Which I already did. Today the TV goes back because I can no longer access the factory reset program. There's a button for doing a full factory rest but it only puts the TV into safe mode. I can not remove my router nor can I remove the saved password. I'm upset. The TV isn't worth the money for the hassles. If I have to, I'll just run a 10 foot HDMI cable. The point is that you may have talked to someone who doesn't know what they're talking about. I've NEVER heard of LED Inrush Current. And after years of running six LED's on PIR motion sensor lights with no problem I'd tend to say you spoke with someone who didn't know what they were talking about.
 

dl324

Joined Mar 30, 2015
13,815
Opinions, thoughts?
My experience has been that most technical support people don't know what they're talking about. I used to go to CompUSA, Office Depot, and the like and ask technical questions from "technical" people. They didn't know I worked for a microprocessor manufacturer and had been building my own computers for years and tried BSing me. However, one guy did give me a steep discount on an extended warranty and recommended that I get a replacement battery for the laptop just before it was out of warranty.
 

MisterBill2

Joined Jan 23, 2018
10,465
There is certainly one possible problem if the motion sensor uses a solid state device to control the mains output. If that is the case it MUST be used with a dimable device. I have destroyed a CFL switching it on with a motion sensor, the failure was rather spectacular, a bright flash followed by nasty smoke. So there may be a compatability problem, but it is not inrush current. The problem is waveform distortion by the motion sensor device switching element. So use dimmable LEDs and there will be no problem. Been there and doing that, it works.
 

Tonyr1084

Joined Sep 24, 2015
6,583
To point - I have LED's in the laundry room and a PIR Motion Detector Switch. You don't have to put a basket of clothes down to switch on the light. The very first issue I ran into was the LED's would never extinguish. They always had a good amount of light when they should have been off. Somewhere in my history I've discovered that you CAN dim an LED that isn't designed for dimming operation by including a single incandescent bulb in the same circuit. So down stairs there are four LED Pot Lights and a single globe incandescent light. When no motion is detected the lights time out and shut completely off. When motion is detected they come on instantaneously.

How does that apply to your situation? Not 100% sure. But you don't have to replace ALL LED's, you CAN use one incandescent in circuit.

One interesting note about the PIR on the back porch - when it detects motion and switches on the lights flash bright, but then calm down to normal operation. And this has been going on for several years. I don't have a date when I started with LED's back there, but I'd guess and say around 2014.
 

k1ng 1337

Joined Sep 11, 2020
219
To point - I have LED's in the laundry room and a PIR Motion Detector Switch. You don't have to put a basket of clothes down to switch on the light. The very first issue I ran into was the LED's would never extinguish. They always had a good amount of light when they should have been off. Somewhere in my history I've discovered that you CAN dim an LED that isn't designed for dimming operation by including a single incandescent bulb in the same circuit. So down stairs there are four LED Pot Lights and a single globe incandescent light. When no motion is detected the lights time out and shut completely off. When motion is detected they come on instantaneously.

How does that apply to your situation? Not 100% sure. But you don't have to replace ALL LED's, you CAN use one incandescent in circuit.

One interesting note about the PIR on the back porch - when it detects motion and switches on the lights flash bright, but then calm down to normal operation. And this has been going on for several years. I don't have a date when I started with LED's back there, but I'd guess and say around 2014.
The idea being the incandescent bulb introduces ohmic resistance into the circuit? Why did your LEDs stay lit without the bulb?
 

Tonyr1084

Joined Sep 24, 2015
6,583
Why did your LEDs stay lit without the bulb?
That I don't know. Apparently something in the PIR needs a load to be able to fully switch off. The LED's don't represent enough of a load to do that. Nevertheless, this is why I find it hard to believe LED's have a high inrush of current. Though I've never tested for that, perhaps that would be a good experiment. I HAVE a clamp meter and some LED bulbs laying around. Maybe I'll patch together a lamp socket and power cord. Plug it into a switched outlet and observe the clamp meter's reading - PROVIDED I can get it to hold the high reading long enough to read its draw. However, I suspect that's not going to happen without some sort of logger and an analog meter.
 

Lo_volt

Joined Apr 3, 2014
240
To point - I have LED's in the laundry room and a PIR Motion Detector Switch. You don't have to put a basket of clothes down to switch on the light. The very first issue I ran into was the LED's would never extinguish.
Tonyr1084, I have a LED security motion flood light that has two modes. In one mode it acts like the traditional motion sensor lights. When it detects motion, it turns on. After a delay it turns completely off. In the other mode, it stays on constantly, however when it detects no motion, it only dims. On detecting motion it switches to full brightness. Perhaps your motion sensor in your laundry room works in a similar manner?
 

k1ng 1337

Joined Sep 11, 2020
219
That I don't know. Apparently something in the PIR needs a load to be able to fully switch off. The LED's don't represent enough of a load to do that. Nevertheless, this is why I find it hard to believe LED's have a high inrush of current. Though I've never tested for that, perhaps that would be a good experiment. I HAVE a clamp meter and some LED bulbs laying around. Maybe I'll patch together a lamp socket and power cord. Plug it into a switched outlet and observe the clamp meter's reading - PROVIDED I can get it to hold the high reading long enough to read its draw. However, I suspect that's not going to happen without some sort of logger and an analog meter.
No comment how the incandescent bulb alters the circuit?
 

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MisterBill2

Joined Jan 23, 2018
10,465
No comment how the incandescent bulb alters the circuit?
If there is an RC snubber protecting the switching device, that may pass enough AC to light the LED bulbs a bit. That is one possibility. But the discussion was about the claimed LED inrush, which the original statement came from some customer service person who obviously did not know more than to repeat phrases they had seen someplace.
The dimmer problem is caused by harmonics present in a circuit that uses capacitive reactance to drop voltage, because the harmonics push more current through and so the voltage rises and something breaks down and fails.
Shunting the LED devices with a resistor will lower the leakage voltage by draining the charge passing through the snubber. It is a lot like completing a voltage divider string instead of having just a series resistor that does not drop any voltage until current flows.
 
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MikeA

Joined Jan 20, 2013
287
The driver might, it has caps. But it cant compete with tungsten.
But how does a tungsten inrush look like on a scope? I bet different than caps.

I had exactly the same problem as the poster. Motion light had a tiny 10A relay that is used in pretty much every IoT device out there. It was getting fused "on" by inrush current to the caps on the LED driver. Not always. Sometimes. Knocking on the relay with a screwdriver fixed it after a fusing. An NTC between that relay and LED driver fixed it permanently. Never an issue in many years since.
 

MisterBill2

Joined Jan 23, 2018
10,465
I never thought about an NTC resistor. Brilliant idea! Thanks!! What size rating and what brand? I have been lucky with motion sensors so far, but that may change. Some have relays, some do not.
 

MikeA

Joined Jan 20, 2013
287
I never thought about an NTC resistor. Brilliant idea! Thanks!! What size rating and what brand? I have been lucky with motion sensors so far, but that may change. Some have relays, some do not.
This is the power supply that was causing me trouble. Very cheap, but has worked for many years.

16W, 20uF on the input, and I had 3 of them in parallel on the relay, so 60uF total.

led-power-supply.JPG

And the NTC I had laying around that worked was SCK-108.

ntc.png
 
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