Led chip smoking

[Fred Trevvett]

Evening

I've bought a 100w led chip for a project (it's not much of a project to be honest, but I might stick a picture or two in the 3d printing section when it's done). Today I test wired it up to the battery that's powering it (36v hoverboard battery) and after maybe 5 seconds it starts to smoke. I'm guessing I need some sort of resistor set up but no idea what. I read on another forum (so this may be wrong):

'With a light bulb, you present it with the rated voltage, and then it takes a current related to the wattage.

With an LED, it's the other way around. You present it with an appropriate current, and then the LED 'drops' a voltage.

So if that's the case, what resistor do I need to get the supply down to 3A? (That figure's just taken from the eBay listing) Or do I need something else?

Link to led: https://www.ebay.co.uk/itm/33326274...xpB85XTmW&var=&widget_ver=artemis&media=EMAIL

And the battery: https://www.ebay.co.uk/itm/26521997...xpB85XTmW&var=&widget_ver=artemis&media=EMAIL

 

[Chippie]

Did mount it on a heatsink?

 

[Fred Trevvett]

No but I wondered if that would help...

I'm just surprised that it started smoking so fast, and I didn't expect heat sinks to be that effective. If you think that's all it needs then that's ideal, I'll just get one of them...

 

[Chippie]

My comment was based on reading the application data posted within the eBay advert.


Note:

Please add cooling before use

LED chip needs cooling to help

For the safety of the customers, also for the life of the product

 

[Fred Trevvett]

Aha...serves me right for not reading the small print...right let's get one of them on order and see if that does the trick

Cheers

 

[Kram]

LED's are quite effiecent, they dont radiate much heat at all, but they make plenty. You need a decent heatsink for 100W and a constant current supply.

You could under drive it with constant voltage around 30v but there is a very fine line between too little and too much - the curve is exponential.

Also 100w is stupidly bright, dont look directly at it as theres a good chance of eye injury at close range. 10w versions are bad enough!

 

[mike 109444]

And some heat sink paste

 

[skotl]

Single LEDs don't generate a lot of heat but COB lamps have dozens, sometimes hundreds, of surface mount LEDs in a high density cluster. This generates a huge amount of light but, as we all know, energy in means energy out so they also generate a huge amount of heat.

A 100W COB LED is a very small 100W heater: https://www.arrow.com/en/research-and-events/articles/understanding-the-basics-of-cob-led-cooling

Given the efficiencies of LEDs (reaching peak power within milliseconds) they will definitely start to smoke within seconds if they don't have sufficient cooling and likely won't last more than a few seconds without it.

That's why even a small 10W lamp has a decent sized heatsink:

 

[mike 109444]

If you look at some of the out door 100w or less lamps, they use the case as part of the heat sink and so are finned.
Note also if the battery you are using is a lipo type then they don't like being drained below a certain amount. In the "hoverboard" they maybe circuitry to protect the battery OR it may be in the battery, known as BM, as in battery management. Take care when experimenting with lipo's.

 

[m_c]

Those will need a heatsink, but the bigger issue is your 36V battery is probably putting out more than 36V.
36V is the nominal voltage. The actual voltage for a single Li-ion battery varies from 4.2V fully charged, down to 3.2V discharged, so your assumably 10 serial connected battery pack will be putting out 42V when fully charged.

Combine that with the ratings for the LED are probably on the very limit at 36V, that 42V is likely to burn out the LED very quickly.

What you really need is a constant current limit for the LED.
Current is far more important to LEDs than voltage. Both are obviously related, but if you control current, the voltage looks after itself.

 

[Fred Trevvett]

What you really need is a constant current limit for the LED.
Current is far more important to LEDs than voltage. Both are obviously related, but if you control current, the voltage looks after itself.

Very helpful, thanks - so what component do I need to add to regulate the current?

 

[skotl]

Those will need a heatsink, but the bigger issue is your 36V battery is probably putting out more than 36V.
36V is the nominal voltage. The actual voltage for a single Li-ion battery varies from 4.2V fully charged, down to 3.2V discharged, so your assumably 10 serial connected battery pack will be putting out 42V when fully charged.

Combine that with the ratings for the LED are probably on the very limit at 36V, that 42V is likely to burn out the LED very quickly.

What you really need is a constant current limit for the LED.
Current is far more important to LEDs than voltage. Both are obviously related, but if you control current, the voltage looks after itself.

Ummm... not really sure that's the case but I could be wrong.

COB modules have current regulators built in so the only requirement is an appropriate power supply and heat protection.

According to the spec on the ebay page, the 100W version wants 28-36V so I agree that 42V would be a problem (alongside the lack of a heatsink). But I don't think there's a requirement for an additional constant current regulator (aka resistor).

 

[m_c]

Ummm... not really sure that's the case but I could be wrong.

COB modules have current regulators built in so the only requirement is an appropriate power supply and heat protection.

According to the spec on the ebay page, the 100W version wants 28-36V so I agree that 42V would be a problem (alongside the lack of a heatsink). But I don't think there's a requirement for an additional constant current regulator (aka resistor).

You might be right, but I've never actually looked at these in any detail.
I'm sure there will be a datasheet available somewhere...

 

[m_c]

Out of curiosity I've just had a look at a couple datasheets for COB modules.
Both specify the module should be powered via a constant current supply, but the required voltage will vary with temperature, and that temperature should be monitored to ensure it remains below the maximum permitted level (or testing done to ensure it's well within the safety range, but that means you won't get as much light)

 

[Fred Trevvett]

Out of curiosity I've just had a look at a couple datasheets for COB modules.
Both specify the module should be powered via a constant current supply, but the required voltage will vary with temperature, and that temperature should be monitored to ensure it remains below the maximum permitted level (or testing done to ensure it's well within the safety range, but that means you won't get as much light)

Interesting, thanks

 

[Kram]

COB chips like these do not have current regulators built in and at the max rated voltage could be well over the spec. Theres a good bit of variation in LED's and more so with cheap cob chips. The constant current supply will cost more than the led.

Using a resistor is very inefficient and hot.

Search ebay/amazon for "Constant current boost buck".
Boost drivers raise voltage
Buck converters lower voltage.
The ones that have two adjustable potentiometers will allow constant current, more common on buck than boost. They are often in multi packs for a quid each.

@m_c The curve does change over temperature but generally its not enough to worry about. In terms of temperature, LED efficiency will also drop off greatly as they get hot, and the colours will shift.

Take care when experimenting with lipo's.

I cant agree more, lipo's will burn your house if you look at them wrong, store or charge incorrectly. There has been many experienced people loosing houses to lipo fires.
I have a few but quite careful how I use and store, never charged unattended.