Why'd it cook?

[lazaah]

Hardware:

MW HLG-185H-1400B
4x 5 Vero 10 4k
1x 4 Vero 10 4k

Due to space constraints I had to shorten one of my strings from five emitters to four. This resulted in the emitter closest to ground blowing [after 30 seconds], with the heatsinks becoming too hot to touch.

My understanding was having unbalanced strings in [terms of a cc/vv driver] resulted in uneven light dissipation between strings, not immediate thermal runaway and detonation. I expected the strings of five to draw ~133v and the string of four ~108v, at 280mA.

Could someone enlighten me as to why my theory was incorrect and/or how I may achieve what I was trying to?

 

[AquariusPanta]

Hardware:

MW HLG-185H-1400B
4x 5 Vero 10 4k
1x 4 Vero 10 4k

Due to space constraints I had to shorten one of my strings from five emitters to four. This resulted in the emitter closest to ground blowing [after 30 seconds], with the heatsinks becoming too hot to touch.

My understanding was having unbalanced strings in [terms of a cc/vv driver] resulted in uneven light dissipation between strings, not immediate thermal runaway and detonation. I expected the strings of five to draw ~133v and the string of four ~108v, at 280mA.

Could someone enlighten me as to why my theory was incorrect and/or how I may achieve what I was trying to?

I like picture books.

 

[lazaah]

I like picture books.

Just for you dude,

 

[alesh]

In order to run a few strings in parallel on the same driver, the strings should have the exact same forward voltage. In your case, one had a lower Vf and almost all current was passing through the short string. It's better to avoid parallel strings on one driver even if they have the same number of LEDs.

 

[guod]

Btw.
the other 3 cobs in that String are as good as dead.

 

[lazaah]

Btw.
the other 3 cobs in that String are as good as dead.

As in they will now be damaged and have reduced output? The all light up fine individually tested on a 30v 350mA driver...

 

[SnapsProvolone]

The string with less resistance will have a higher wattage than the other strings.

 

[churchhaze]

The voltage across all 5 strings is same because they are in parallel.

This means the diodes in the string of 4 must each have a significantly higher voltage drop than the diodes in the strings of 5. All the strings must add up to the same total voltage drop.

Since the voltage vs current characteristics of diodes are exponential instead of linear, that increased voltage translates to exponentially more current flowing through that string than vs the ones with 5 cobs in series.

 

[mc130p]

That's the problem with parallel setups. You need current limiting resistors on each branch and fuses to protect in case of a short or something like what happened to OP(imbalance of R on each line)....sorry about your luck, man! Thanks for sharing though

 

[lazaah]

garh!

Oh well, lesson learn't the hard way, but it could of been worse!

Maybe in time ill turn that string into moon lighting. hah.

For some reason I had it in my head that that string would only "pull" the required voltage. It's painfully obvious now that isn't the case... Cheers for being nice about it.

 

[Abiqua]

Cheer up I did this last night:

didn't have my sunglasses on and left this on the diode a little too long...both seem to work ok too....but now I am trying to clean the diode. Almost wiped it with IPA, but gonna wait and ask

 

[alesh]

Use IPA.

From Bridgelux AN's

 

[Abiqua]

Use IPA.

From Bridgelux AN's
View attachment 3305095

Thank you so much @alesh .....I wanted to wait to confirm and was reading in the datasheet as well and hadn't found it!

 

[Abiqua]

holy sheeeeit....it worked and worked well!
there is a tiny spot in the top coating that isn't "shiny anymore, so probably replace it sooner than later, but it works for now....

 

[alesh]

How did it happen btw? At the first look it seemed like you missed ashtray

 

[Abiqua]

How did it happen btw? At the first look it seemed like you missed ashtray

hee hee no smoking around the equipment!

i melted the probe to my cheap little thermometer. The light was hanging at a weird angle and i was blinded and thought I was touching the bare sink....oops...lesson learned.

@salmonetin
Many thanks! Many lessons I should learn after blinding navigating this 1st build and reading all this info!

 

[JavaCo]