Dangerous 12v LED lamps. (Well, maybe not?)

[SantaClaw]

Hello, I'm new here. To make a long story short, I've got a cabin in the woods with solar power, and I'm in the process of upgrading it.

So, I started out by changing the dead 12V batteries out with an AGM battery, basically, I went from two 110AH deep cycle batteries, to one 208 AH AGM battery.
Anyhow, I started counting light points and found I had 7 halogen spots/9w and a florescent light over the sink, and that was about it.

So the search for warm white LED lamps/bulbs that would fit into the BA15s sockets started. I was after cheap low energy LED lamps, and I came across these:

http://www.dx.com/p/1156-ba15s-p21w-3w-200lm-22-smd-1206-led-warm-white-car-tail-light-steering-lamp-12v-308013#.Vn23WllUUkg

Well, 3w = a bit much but what the heck, I've got enough power to run those for days, even with no sunlight, a condition we have for a couple of months a year where I live (Northern Norway) so I ordered a set of 7.

I got the first 6 on the 24'th, Christmas eve, exited about the prospect of proper lighting for my cabin, I hooked one of them up to my Korad KA3305P psu, and jumped to 12v with a 500mA current limit.
First thing I noticed was the smell. Basically, the instant It got power it started smelling a combination of burned plastic and burned pcb. Horrible smell.
Oh, and it does work, don't get me wrong, it lights up, and it's most definitively Warm White. No doubt.

The first thing I noticed was that it only drew about 125mA at 12v, so no where near the rated 3W as this equates to 1.5W.
The second thing I noticed was that the current draw was increasing steadily, and seemed to peak at 142mA or 1.7W

The third thing I noticed was the Heat it put out.
My K-Type probe hit 45c on the metal case, and over 50c on the LED emitters/pcb itself (22c ambient)...

So I thought, what would happen if I hooked them up to a more realistic 12.85V, the resting voltage of my AGM ?

So I did.

Smell = worse. Current draw hit 162mA, or 2.081W
Same amount of light, no extra output, just more heat.
Diode temp = 60c Metal casing temp: 50c

This is now to hot to handle, it's hanging free air by a couple of wires soldered on, so the max cooling it will ever get.

So, what would happen if I put this in, lets say my car's rear lights?
My car will happily output up to 15V on a cold day (-40c is not uncommon here, 270A alternator, 200A on idle), so that's what I fed this.. lol

Now, It got a lot brighter. For sure, maybe even close to the rated 200 lumen...

Current draw hit 214mA, at 15V = 3.21W
Metal case temp, hit 75c(K-type), the LED emitters hit 90c

But then, it started dropping off, I mean, after 20 minutes, the current drawn is down to 184mA, that's a drop of 30mA. or .485w ... hm... Half an hour after they where switched on, it's at 177mA

Anyone know why they are drawing less current after being turned on for a longer period of time? Burning out?

Imagine putting that inside a rear light casing? On a hot summers day?  I think we're talking fire...
So, yeah... I'm not going to use these, ever.


*Camera battery= dead, charging, so photos to  come.

[Seekonk]

I have a 12V camp.  Now really, wasn't that pretty cheap to get such an education in LED operation?  I have a half dozen GU5 or something and half of them twinkle now after very little use.

[SantaClaw]

I have a 12V camp.  Now really, wasn't that pretty cheap to get such an education in LED operation?  I have a half dozen GU5 or something and half of them twinkle now after very little use.

Lol, I guess so...

Down to 156mA draw now, after 1.5 hours @ 15v. Metal socket temp is down to 50c, LED/PCB temp is down to 65c  2.34W

If I point the LED emitters directly into my Infrared thermometer, I read 121c, but I think that's just the LED's giving off IR.

The current draw seems to be dropping steadily.



Edit: I added the photo as well, down to 153 mA:

[Whales]

LEDs become less efficient as they heat up and their impedence drops, so they start drawing more current. 

Lots of LED lights are dodgy for their given specs (instead running fine at much more lenient specs).  It does not look like these lights have much heatsinking at all, pending what the socket you put them into looks like.  Bigger ones/ones with nice aluminium blocks would perform much better.  The temperature is probably fine, but the smells are not.

[mikerj]

Many of these cheap Chinese LED automotive lamps tend to have short lives because of the complete lack of thermal management in the the design, poor cuurent regulation (often just a low value series resistor) and also because they have no protection against moisture.

That said, my father replaced the G4 halogen lamps inside his motorhome with some eBay specials (like these) and they have so far lasted 18 months or so and work very well in terms of light output and current consumption compared to the halogen lamps.

[SantaClaw]

LEDs become less efficient as they heat up and their impedance drops, so they start drawing more current. 

That part I figured.  That it would increase as it heats up I mean, but why is it now dropping? Down to 152mA after about 2 hours of operating, down from 214mA That's a 62mA drop over just 2 hours of use. Almost 1 watt... lol

I think It will be interesting to see what remains after a few more hours of use, do a little investigative teardown after it dies completely... lol

Edit: Attached a photo of the front of the thing, with the LED's light up, see small black spots on some of them. Down to 149mA now.

[amyk]

Imagine putting that inside a rear light casing? On a hot summers day?  I think we're talking fire...

Incandescent bulbs get much hotter in normal operation... 100C is quite cool by incandescent standards.

it's hanging free air by a couple of wires soldered on, so the max cooling it will ever get.

That's also not the environment of its intended automotive application - the socket acts as a pretty substantial heatsink, not to mention the metal chassis of the car to which it's grounded will be nearby.

[Seekonk]

A while back I bought  18W flush mount replacement 120V LED fixtures for my camp.  Utility gave a big in store discount making them cheap.  The LED normally operated at 42VDC.  I tore out their inverter and used a cheap boost inverter to get 34V constant voltage.  That ran the lamp at about 6W which was plenty of light.  Made one adjustable that went down to 1/2W still quite a bit of light for getting around at night.  No need to worry about thermal runaway.   The boost inverters crap out at about 10W.

[SeanB]

You probably would be much better off buying some cheap LED strip which operates off 12V, and using some aluminium square tube to stick it to to act as a heatsink, then putting it into your existing fittings as a replacement.  That way you get a better light source, and they do run quite cool with the 19mm square extrusion as a heatsink under them.

[SantaClaw]

So, down to 125 mA today, that's just 1.875 watts.

[Seekonk]

I commented on another thread that LED are more efficient at lower current.  Of course immediately someone had to say that wasn't true and at some low current it would drop.   They provided some calculations and a link.  Never could figure out where he got his values.   From data sheet this data was provided,  lm/W = 155@175mA, 137@350mA, 120@500mA, 112@700mA.  38% more efficient at low power or 13% more loss each time the current is increased about 200mA. 

[SantaClaw]

So, after a very long time with continuous use, I'm down to 88mA @ 15V....
1.32W

Still very bright though....

I still don't get why this is?