Problems wiring MC-E Ms in parallel?

[4thpage]

Has anyone experienced problems with wiring these guys in parallel (i.e. thermal runaway leading to the entire emitter going out)? After reading a particular section in the Welcome Mat post...

If driven by a CC source, one string can still undergo thermal runaway, but another string sharing the CC source will simply get less of the total current - the current was "hogged' by the other string. If your CC source in such a setup is set to drive LEDs near their limits, then having one string bear the load intended for two or more strings can be problematic. Remember that when LEDs pop, the circuit breaks, leaving the other strings in a parallel setup with a kind of surplus of current, which leads to even more rapid thermal runaway, which will eventually leave you in the dark. This is why it's generally recommended to wire LEDs in series, as well as using a CC source if possible.

...I'm getting a little nervous about my plan to do so. I was thinking of wiring two parallel-wired MC-E Ms in series with each other. With adequate heat sinking, this should be fine, right?

 

[DM51]

I've deleted the identical thread you posted in the Bicycle section.

Please note that cross-posting (duplication) of threads is not permitted (see Rule 9).

 

[bshanahan14rulz]

sounds fine to me, as I've heard MC-E chips are decently matched and the dice in parallel are all mounted very close on the same slug, so their temps won't be too different... But then again, I think I was corrected somewhere else by someone who said that it is never a good idea to run power LEDs paralleled.

Is this a critical application or just a hobby light?

 

[Nos]

the chips are Vf sorted. driving them parallel is no problem.

 

[4thpage]

Sorry about the cross posting. Won't make that mistake again

 

[4thpage]

sounds fine to me, as I've heard MC-E chips are decently matched and the dice in parallel are all mounted very close on the same slug, so their temps won't be too different... But then again, I think I was corrected somewhere else by someone who said that it is never a good idea to run power LEDs paralleled.

Is this a critical application or just a hobby light?

It's just a hobby light: for my commute and other night-riding fun!

 

[4thpage]

the chips are Vf sorted. driving them parallel is no problem.

That's what I was thinking. Thanks!

 

[yellow]

does not depend on heatsinking, it depends on the Vf of the individual die.

Electronically wise, driving led in parallel is really bad,
also (especially) me was one, who typed that P7s will "soon" die in numbers, when they were new ...
... but nothing of this happened, so it seems not to be this bad.


Whith one Quad-die led, You can securely hope that the four die are this much the same, that nothing happens.

 

[mikeveal]

does not depend on heatsinking, it depends on the Vf of the individual die.

Electronically wise, driving led in parallel is really bad,
also (especially) me was one, who typed that P7s will "soon" die in numbers, when they were new ...
... but nothing of this happened, so it seems not to be this bad.


Whith one Quad-die led, You can securely hope that the four die are this much the same, that nothing happens.

LED's have a negative temperature coefficient. As temperature increases, resistance decreases.

Thermal runaway happens because as resistance decreases, the current increases and power in that LED does too.

Multiple dies mounted in a single package are protected somewhat by the fact that the temperature of all dies must remain the same. So as one die tries to grab more current, it warms the others, which in turn try to get their share back. With a constant current driver and four well matched dies in parallel IN A SINGLE package (like a P&), there should be no problem.

It is however a very bad idea to put multiple packages in parallel.

Hope that helps.

 

[HarryN]

If you are really worried about it, you can always do some things to help balance it out. A small resistance in each string will overcome a lot of the imbalance.

 

[parnell]

I believe that most MC-E light are ran in parallel(please correct me if I am wrong.) I haven't read about any issues, i.e.when run correctly(amperage and voltage) in parallel. I'll stick with the industry standard.

I have a MC-E on a serial star that I will be making parallel. I have read that I just have to cut the serial connections and solder the tabs together. I will know in the next few weeks if it works, when the host is ready.