• Here is a link to the full explanation: https://rollitup.org/t/welcome-back-did-you-try-turning-it-off-and-on-again.1104810/

Why'd it cook?

lazaah

lazaah

Well-Known Member
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

AquariusPanta

Well-Known Member
lazaah said:
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?
Click to expand...
I like picture books.
 
alesh

alesh

Well-Known Member
Untitled.png
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.
 
C

churchhaze

Well-Known Member
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.
 
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mc130p

mc130p

Well-Known Member
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

lazaah

Well-Known Member
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

Abiqua

Well-Known Member
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 :peace:

burnt to shit.jpg burnt to shit2.jpg
 
Abiqua

Abiqua

Well-Known Member
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....
burnt to shit3.jpg
 
Abiqua

Abiqua

Well-Known Member
alesh said:
How did it happen btw? At the first look it seemed like you missed ashtray :-D
Click to expand...
hee hee :joint: 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!
 
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