Do old Luxeons have a positive slug?

[Fallingwater]

Or, in other words, when swapping in a SSC, do I have to worry about insulating the slug or do I just put the conductive spacer in its place and I'm done?
Thanks.

 

[Morelite]

SSC LEDs have a positive slug, so you do need to electrically isolate it from the heatsink.

 

[Fallingwater]

That was not the question. I know SSCs do, I want to know if Luxeons do as well.

 

[Lynx_Arc]

Just tested an emitter I am sure is either a lux 1 or 3 and the slug seems to be electrically isolated from the LED neither + or - would light it up through the slug.

 

[Fallingwater]

Thanks a lot, this is exactly what I needed to know. Whatever possessed SSC when they decided to make the slug positive?

Little related question: I've seen spacers for Luxeon-SSC swaps on sale. Are they conductive?

Thanks.

 

[Oznog]

Just tested an emitter I am sure is either a lux 1 or 3 and the slug seems to be electrically isolated from the LED neither + or - would light it up through the slug.

NO. As per Luxeon spec sheet, the emitter is NOT electrically neutral NOR is it positive nor negative. This is not necessarily measurable. Unless they've changed something.

As per spec sheet it must be electrically neutral. Which sucks. Also, IIRC it cannot be soldered (aluminum I think). Also IIRC the "Star" boards don't actually isolate the emitter it's just a heat spreader, so you'd need like a big insulating thermal pad for them or isolate the whole heatsink and let it float.

 

[Lynx_Arc]

by my simple test it appears to be unable to be used as either + or - to complete the circuit so I would guess that means it doesn't conduct which means you could heatsink it to a surface of either polarity as long as the other polarity is insulated.

 

[Oznog]

by my simple test it appears to be unable to be used as either + or - to complete the circuit so I would guess that means it doesn't conduct which means you could heatsink it to a surface of either polarity as long as the other polarity is insulated.

Right there in the spec sheet: thermal pad is not electrically neutral nor common with anode or cathode in the I/III/V/K2 devices. Must be isolated from the electrical path.

So don't do that.

Luxeon Rebel is different, it WAS designed with an electrically neutral thermal path. The thermal pad can be connected to anode, cathode, a potential outside anode or cathode, or ground. I'm sure there's some kind of limit to the potential voltage between thermal pad and anode/cathode before the insulation breaks down, but it is not specified.

 

[Lynx_Arc]

The only thing I could think of that woulc require electrical isolation is if the resistance of the LED change or shorts out to the slug when the LED is either heated up or fried. If the slug doesn't have an electrical path ever to connect to the anode and cathode I am wondering why it hasn't been used without isolation. I seem to remember a few modders that found replacing a lux with an SSC P4 required adhesive where thermal grease had been previously.

 

[Lynx_Arc]

I had one other thought.... it is quite possible in the specifications they allowed for future possibility of having the anode or cathode electrically connected to the slug like the SSC P4 does. Convincing people to electrically isolate the slug would make future manufacturing designs and replacement less of an issue.

 

[tebore]

The thing with the Lux slugs were the heat path was connected to the ESD diode. Yes it's not neutral. However depending on the amount of power in your system you should be ok to not isolate them.

There's a bunch of lights that didn't isolate them. If you want to be using them up to spec then they should be isolated. It probably has something to do with the function of the ESD diode.

 

[Fallingwater]

I had one other thought.... it is quite possible in the specifications they allowed for future possibility of having the anode or cathode electrically connected to the slug like the SSC P4 does. Convincing people to electrically isolate the slug would make future manufacturing designs and replacement less of an issue.

I've no problem if the slug conducts negative - actually you could use conductive thermal paste and do away with the negative wire altogether. But a positively conductive slug is just dumb.

 

[Lynx_Arc]

I've no problem if the slug conducts negative - actually you could use conductive thermal paste and do away with the negative wire altogether. But a positively conductive slug is just dumb.

I wonder if having it conduct helps the heat transfer better or not?

 

[HarryN]

I routinely use Lux IIIs and Lux Vs (InGaN colors) with the slug connected to (-). I know that you are not supposed to, but it is ok as long as you don't run multiple LEDs this way. Perhaps I should be more clear about this - this assumes you are using a resistor to manage the current flow.

If you are using a more sophisticated driver, where the (+) and (-) of the battery pack are electrically isolated from the (+) and (-) of the driver leads, then this might not be such a good idea.

It has been proven by many that if you attempt to run multiple of these LEDs in series, and the slugs are electrically common, they will fail.

There is very little current involved in the slug, so only a very thin layer of electrically isolating material is required - just a paint on layer. Still, I agree - kind of a pain.

 

[IsaacHayes]

The only luxeons with postive tied to the slug are the warm colored ones. amber, red, red orange. If you connect the slug to negative you will short out and fry the bond wire instantly as the power from the positive lead will short to the slug. However if that happens, the LED is not lost, you can still power it with positive to the slug... LOL (the die is connected right to the slug)

When using a SSC, it's best to isolate the slug no matter what light usually since it's connected positivly as well.

 

[yellow]

old Luxeons slug is not neutral, but one, maybe 2 can go,
as soon as there are 3 mounted onto the same sink, they short themselves out

means: P4 has to be isolated


PS: if the mounting place is anodized, that is isolation and You dont have to take any care for the led