Anton's build

[Anton]

You might want to put some sealant over those solder joints or they will corrode.

I smothered everything electrical that could possibly short somehow in hot glue before I fitted them. I'm going to take them off again soon though and put silicone sealant around the screw holes and around the backing plate where the light lenses contact it, because I realised if I don't seal these things up *really* well, they are going to fill up with mud the first time I offroad.

LEDs work on current, do they have series resistors fitted?

No, but these LED COB's were specifically designed to run on car electrics without them. I have a sneaking suspicion that they might have them, hidden away inside the board somewhere. Anything over 12v results in very little increase in light output.

These LED's were designed to be used in cars without any additional resistors, and I've given them a bit of a stress testing to see if anything will blow on a 6A 12-24V bench supply. They got hot (as you'd expect) but nothing blew even when I went past their rating for half an hour (I ran a bunch of them at 24V to see how reliable they were, and nothing blew, they just got hot, but not too hot to touch).

You think I should add some resistors, just in case? I thought about it, since what some Chinese reseller says is true and what is actually true don't always line up, but I didn't in the end because I didn't want them becoming noticeably dimmer - instead I ran a stress test to see if they'd hold up under extreme load.

I am a little worried that they don't represent enough of a load, and I could be creating a semi-"short", should I be worried about that do you think? I know very little about LED's.

[Rhinoman]

If you ran them at 24V for half an hour then that's a good enough test. Have you measured the current draw at 12V and 24V? it does sound like they have some internal current limiting.

[Anton]

No, I haven't - plus typo, that should've read that I ran them at 18v for half an hour...

I have a spare LED or two lying around and a multimeter doing not much, and I've been meaning to measure the current draw. I just keep forgetting as health issues and landlord issues are currently distracting me from zook related thingies.

I would rather like to know though, as since fitting them I have worried that they might not be healthy for my loom/battery if they don't represent a real load - they might be tantamount to a short circuit. That said, the SJ isn't being used at the moment, so they haven't actually been used since fitting them, so it's not a real problem, I have time to get my head on straight.

Edit - I just tried running them at 18v again, but I had to give the PSU back so I was running using a 16v 1A brick through a 3v-36v 3A regulator I got on ebay (which my multimeter has previously tole me puts out 3.6A but it got HOT - FAST). The lights light up at about 8v, get brighter until 13.8v, then don't get any brighter from there all the way to 24v (where I chickened out, I didn't think they'd last long as I was running without heatsinks, so they got hot enough that you can't touch them for more than a fraction of a second even just at 13.8v).

Wierdly, at about 13.8v, when they stop getting brighter, you see a kind of "click" in the light, where it dimms for just a second, as if they were switching modes somehow. I really can't see anyone bothering to put a regulator circuit inside these things that sell for a quid, at best there would be a resistor or two. So I can't tell you what's going on, all I can say is it's very weird. My guess is that the regulator is doing something weird at 13.8v. It is a small piece of £2 ebay Chinese rubbish, after all.

I'll have to stick one on a decent heatsink and then run it at various voltages. I'll also test the load properly, and work out what amps they're drawing per unit, so I know if I should be worried about them.

*Edit 2* - I've realised that the cheap Chinese regulator is doing weird things with the voltage. I've worked out that it will increase voltage to 13.8v but no more. Testing it with no load shows up to about 34v, but as soon as I apply a load, if it's set beyond 13.8v, the actual voltage across it's output poles reads at 13.0v. Lowering the no-load voltage to 13.8v or less results in a stable voltage that is the same with or without load.

So my testing procedure was invalid. Initially I monitored the voltage under load as I turned it up, and watched it climb. But this really needs 3 hands, so I switched to testing the output with no load, assuming loaded and no load voltages would be the same.



I think everything up to 13.8v is valid.

*Edit 3*

Seems to draw current like this:

11v - 0.02-0.03A (barely useful light emitted at this voltage, probably not enough for sidelights)
12v - 0.11-0.12A
12.5v - 0.17-0.18A
13v - 0.26-0.27A
13.5v - 0.3A

I'd have to plot a graph, but that looks fairly linear to me. Just to see, I put a set of LED's side by side, one at 13v and one set next to it I plugged into a 24v supply. The ones in the 24v supply briefly lit up and then gracefully went the way of the dinosoar. So obviously 24v is killing them.

I don't have anything between 13.8v and 24v to test with, so I've run out of test material.

[Rhinoman]

From those measurements I would think its just a resistor in there, if you can improve the heat-sinking then they will take a bit more power, the ones in the lights look to be mounted well.

[Anton]

Yes, I think you're right. I stress tested them with the backing plate on, 10 COB's running for half an hour, and they didn't get as hot as 2 COB's running for a minute or two without a heatsink.

Here's something worrying though...

These LED's came with little adapters to let you fit them into internal lighting on your car. Since they get so hot with no heatsink, that seems like a bad idea. However, not as bad as the adapter:



Doesn't look so bad, until you consider what I did to that thing with a nice and conductive spring in the middle and how easily I did this:



Yikes. Hope that's not indicative of the quality of the LED's I just fitted! Seriously, though, fire hazard. If you lot see something like this on ebay, don't. Please.

[donkeychomp]

Can I have that in English please

[Anton]

Whichwhatbit?

[ROBBIE]

Whichwhatbit?

All of it, starting from two of your posts back

[donkeychomp]

Seems an awful lot of bother when your lights were working before anyway...

[Martin86]

I bet your a Nightmere at Christmas with all your Lights Anton lol!!