LED Work lights still glowing after turning off

Submitted: Monday, Oct 30, 2017 at 10:31

ThreadID: 135807 Views:3101 Replies:7 FollowUps:6

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Top End Az

All
I have recently wired up and installed a pair of 30w LED work lights on my roofrack for camping, and for reversing on occasions down boat ramps due to my deteriorating eyesight these days.
I have previously wired up other sets and have been fine. However, when I turn the switch off they still "glow" for want of a better word for about 20-30 seconds after I have killed the power. They don't glow at full brightness, but probably only at 10-20% brightness. I don't want to be driving around with them glowing obviously.
I have used a Narva switch on the dash, with the cabling running through the firewall and along the chassis rails and up on to the roof rack. I have used a relay, and although probably unnecessary, I plan on possibly adding others.
Is it just a case that the lights are using any residual power in the cabling until they extinguish?
Any suggestions would be great. I'm not an electrical guru, so any advice would be great.

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Reply By: Member - peter_mcc - Monday, Oct 30, 2017 at 10:44

Monday, Oct 30, 2017 at 10:44

LED lights have a power supply inside them to convert the 12V from the car into something more appropriate for the LED (usually a current limited supply rather than a constant voltage). I suspect what you are seeing is the capacitors in the power supply discharging slowly.

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Reply By: HKB Electronics - Monday, Oct 30, 2017 at 11:54

Monday, Oct 30, 2017 at 11:54

Personally haven't seen a led light that does not go out once the power is removed, try disconnecting them at the light and see if this gets rid of the affect, if so it is the way you have wired them, possibly a resistive positive feeding back through a light in the switch or relay coil/spike suppression, sure you have the relay wired correctly?

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Follow Up By: Frank P (NSW) - Monday, Oct 30, 2017 at 12:12

Monday, Oct 30, 2017 at 12:12

I've never seen or heard of LED lights doing what the OP has described.

But following on from HKB's "possibly a resistive positive feeding back through a light in the switch or relay coil/spike suppression", it might be worth checking for parasitic current after they've shut down. A parasitic current may be insufficient to operate the LEDs, but if present will flatten the supply battery if left unattended or uncharged for long enough.

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Follow Up By: Top End Az - Monday, Oct 30, 2017 at 12:14

Monday, Oct 30, 2017 at 12:14

Ok, I'll have a look at it later tonight thanks. I've done a few relays in my time and followed the same as another set of LED's I have on the side of the roofrack which don't do this. I will double check this though whilst at it. Otherwise it may be the wiring up of the switch which is a 4 pin Narva 63026BL rocker of which I only used 3 pins.
I'm not too familiar with some of the terms such as spike suprression or parasitic current. I've wired up spotlights, light bars, UHF before so have a bit of an idea about this, but this one has me stumped.

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Follow Up By: Frank P (NSW) - Monday, Oct 30, 2017 at 13:18

Monday, Oct 30, 2017 at 13:18

Parasitic current is just current that shouldn't be there when the circuit is "off".

If it is there it will be small - milliamps.

If it is not, then I lean toward the discharging capacitor theory.

You know how to use a multimeter?

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Follow Up By: Top End Az - Monday, Oct 30, 2017 at 13:45

Monday, Oct 30, 2017 at 13:45

Thanks for the clarification. I'll whip the multimeter out and check tonight. Many thanks.

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Reply By: Malcom M - Monday, Oct 30, 2017 at 12:40

Monday, Oct 30, 2017 at 12:40

Do you have a fuse box installed?
Some of these have a 'blown fuse' indicator LED in them and if the fuse has blown, the LED will pass a small amount of current on to the circuit.
That current can be enough to dimly operate the light strip. Have had this happen to me a couple times.

Otherwise I agree with the 1st reply about discharging capacitors.
Some lights have extra electronics in them for dimming etc so do not always turn off instantly.

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Follow Up By:- Monday, Oct 30, 2017 at 13:00

Monday, Oct 30, 2017 at 13:00

I'm using a fused relay and I checked it earlier, it's all good. Starting to think along the discharging capacitors theory myself, although checking switch and relay wiring is still my first priority.

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Reply By: 9900Eagle - Monday, Oct 30, 2017 at 15:32

Monday, Oct 30, 2017 at 15:32

Sure way to check, is disconnect one light and power it straight from a battery, if it glows when you take a wire off the battery it as said a capacitor discharging.

I have a series of led down lights in my house on different switches and when they are turned off they glow for around 15 seconds and gradually fade out.

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Reply By: RMD - Monday, Oct 30, 2017 at 16:15

Monday, Oct 30, 2017 at 16:15

If the LED lamps you are using are the COB type, (Chip on Board), they have a material around them which emits light and enhance the COB chip output. That surrounding material does retain/produce some glow after switch off.

If it was stray current flowfrom a parallel connected circuit ,(which it isn't) they would continue to glow until the source current is removed. So it won't be that as it is switched off by a relay. Unless the relay contacts have a carbon/dirt across the contacts the glow won't be caused by a relay.

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Follow Up By: Top End Az - Monday, Oct 30, 2017 at 16:28

Monday, Oct 30, 2017 at 16:28

30w LED work light

Hi RMD
That sounds like it makes sense. Yeah its a brand new relay out of the packet so should be clean. The lights are the same as the ones above.

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Reply By: Batt's - Sunday, Nov 05, 2017 at 11:13

Sunday, Nov 05, 2017 at 11:13

Some led's will slowly dim when turned off like the ones in my canopy but their very low power draw my 18w reverse light turns off straight away.
I would attach it directly to the battery bypassing your wiring set up and see if it happens that will help to find the problem a lot faster. If it doesn't happen the it will be in your wiring set up it maybe a dodgy relay you get that sometimes. I would expect a 30w to burn up residual power after being turned of in the blink of an eye.

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