Parallel setup

[qwerkus]

Hello,

I'd like more informations about parallel setup of high power cobs. Could someone help me out ? From what I read, the main drawback is thermal runaway, which, if I understand it correctly, means as the cob heats up, its vf lowered, which means it hogs more juice, heats more... and so on. That's why constant current drivers and serial setups seems the obvious choice. Or is it ?

When dealing with high powered cobs, serial setups easily mean 200+Volts, which can be quite hazardous. Than come situations where parallel setups seems more interesting - like a variable number of LEDs, or just cheaper drivers.

My question is: how to stabilize parallel setups ? How about constant current & constant voltage drivers ? If the max. allow voltage can be fixed, would it stop the thermal runaway ? I guess this question has already been asked, but I could not find a clear guide on the topic. Feel free to post links/comments. It would be nice if this becomes a "101" on parallel setups.

many thanks,

qwerkus

 

[CobKits]

My question is: how to stabilize parallel setups

use a sufficient number of cobs that can handle dropping a good percentage of them

or fuse them

or build a current mirror

or use an adjustable voltage driver to limit voltage and thus current

lots of ways to skin a cat

 

[qwerkus]

use a sufficient number of cobs that can handle dropping a good percentage of them

or fuse them

or build a current mirror

or use an adjustable voltage driver to limit voltage and thus current

lots of ways to skin a cat

Not sure the cat would appreciate it , but thank you for your fast reply.
Simplest option (for me) seems to be the constant voltage driver. Would it work with something like this one: http://www.meanwell.com/webapp/product/search.aspx?prod=hlg-150h
Anyone succeeded in doing so ?

 

[CobKits]

sure same principle as the 120s and 185s i carry

 

[alesh]

I'm wondering how much current in each string varies in actual use. It would also be interesting to compare actively and passively cooled setups in this regard.

 

[nevergoodenuf]

I had checked forward voltage on some China made Bridgelux COB and the voltage between a batch of them was within, if I remember correctly, .01 volts of each other. I have just made a bunch of Y's for adding more COBs. Even the lights I bought from China were wired in parallel with different color temps. When this community started building lights, we aimed for an extra cool 60*c or less as a target Tc. I think as we get away from over cooling our COBs, and just aim for the minimum cooling per COB, thermal runaway is more possible. I have had most of my builds running in parallel with no problems, but for instance, I have enough cooling to run one COB at full power and still aim for below 60*c, but can add multiple COB to get the wattage per COB I am looking for.
I run Luna 300's on a 320 watt heat sink, but seldom run them at 320 watts. Add a Y, now 2 COB's at 160 watts, add another Y, now 3 COB's at 110 watts and so on.

 

[qwerkus]

I had checked forward voltage on some China made Bridgelux COB and the voltage between a batch of them was within, if I remember correctly, .01 volts of each other. I have just made a bunch of Y's for adding more COBs. Even the lights I bought from China were wired in parallel with different color temps. When this community started building lights, we aimed for an extra cool 60*c or less as a target Tc. I think as we get away from over cooling our COBs, and just aim for the minimum cooling per COB, thermal runaway is more possible. I have had most of my builds running in parallel with no problems, but for instance, I have enough cooling to run one COB at full power and still aim for below 60*c, but can add multiple COB to get the wattage per COB I am looking for.
I run Luna 300's on a 320 watt heat sink, but seldom run them at 320 watts. Add a Y, now 2 COB's at 160 watts, add another Y, now 3 COB's at 110 watts and so on.

Interesting feedback. Do you use any balancing circuits (like mirror current or simple resistors) ? Only constant voltage driver ?

 

[nevergoodenuf]

The HLG line is both CC + CV and nothing extra.

 

[CobKits]

I'm wondering how much current in each string varies in actual use. It would also be interesting to compare actively and passively cooled setups in this regard.

ive got a few rolling right now but without unwiring active setups i have doubts as to the accuracy of the multiple cheap mA displays id need to measure in real-time

if somebody has a rec on a digital panel meter with decent precision thats $10 or less ill grab a bunch and do some testing

 

[Trippyness]

Using higher voltage driver than needed or voltage mirror will fix it as there will be more than enough voltage.
I run parallel 9 COBS running a 40V 10a Driver. Have not had a single issues and light is evenly distributed.
Each COB is running just under 34V, a few are running 35v but thats the reason for the 40v Driver to overcompensate.
In my moms tent I run 10 x 10WCOBS at 12v 10a and they all run 11V. No issues.

 

[qwerkus]

I'm thinking of running 3x cxa3070 in parallel with HLG-150H-42 driver; should have enough headroom. Anything I should think about before actually building it ?

 

[qwerkus]

Alright, the problem with the simple-meanwell-parallel driving seems to be double for me: on one side, there is still the possibility of a (small) thermal runaway, and on the other side, the setup does not give enough flexibility. I don't know about you, but over time, I accumulated various COBs from various manufacturers, each with its own Vf and ideal driving current. A simple setup where one could easily drive and replace COBs would indeed be helpful, so here is what I came up with:

2 psu system:
- the railtrack holding the lamps is plugged onto a high power high efficiency switching power supply. Something in the 200-300W range, 24V. The nice thing here: ebay is litterally overflowing with good 12-24V meanwell power supplies, for very good prices.
- each lamp (cob + heatsink + reflector + cover) is plugged into the railtrack, and fitted with a small boost converter, like this one:
https://www.aliexpress.com/item/XL6009-Boost-Converter-Step-Up-Adjustable-15W-5-32V-to-5-50V-DC-DC-Power-Supply/32625458625.html?spm=2114.10010108.1000014.6.xVMCHI&scm=1007.13338.51110.0&pvid=3b3f157a-950c-4def-8d5b-cb1dbabfecb0&tpp=1
This one seems a bit better and offers a CC potentiometer - albight 4x more expensive:
https://www.aliexpress.com/item/DC-DC-boost-converter-Constant-Current-Mobile-Power-supply-10A-250W-LED-Driver/32642489577.html?spm=2114.10010108.1000014.10.VT9VTl&scm=1007.13338.49930.0&pvid=6c9986cd-69ce-499a-b518-868354d56f3e&tpp=1

Seems to me the losses would be negligeable, and the overall setup allow for maximum flexibility. Now the ideal dc-dc driver would be a constant current only boost converter, but I could not find suitable ones yet (only cv-cc). Those sold by meanwell are outside my Vf or CC range.


What do you guys think about this ?

 

[CobKits]

Seems to me the losses would be negligeable

well between the two power supplies youre under 90% driver efficiency, so that might be a stretch

 

[Abiqua]

fyi a current mirror is essentially just a current regulator using two identical NPN transitors. good insurance no matter what ideally.

 

[qwerkus]

fyi a current mirror is essentially just a current regulator using two identical NPN transitors. good insurance no matter what ideally.

Doesn't this only work with symetrical current ? My setup has different currents. This would mean different transistors + resitors - I'd rather go with a ready to use module.

 

[mx5spd]

So in parallel a COB burns out and Current goes up to the rest? For example want to run a group at 1 amp fuse each one at 2 amps?