Introducing CobKits.com - specializing in DIY and Citizen COBs
nfhiggs
Well-Known Member
I'm sorry but this is just pure nonsense. The current through the PN junction is purely a function of the voltage applied across the PN junction and the junction temperature - anything else in parallel with it is irrelevant if the voltage and temp remains constant. If I increase the voltage, the current increases in a non-linear curve. If I put another diode in parallel that has a lower Vf it will simply draw more current. The voltage only changes when the total load current exceeds the capacity of the power supply.
You're putting parallel non-linear, temp sensitive loads on a constant current supply. Only idiots do that. Or people that don't know what they are doing.
GrowLightResearch
Well-Known Member
Exactly. That is how this topic got started when @CobKits recommended to power the CoB in parallel with an HLG.
BTW the reason the parallel Vf increased is because the unbalanced parallel load increased the current in one LED from 600mA to 768mA raising the Vf.
DO NOT REPLY TO THIS TOPIC
I will create a new thread for this topic. I did not expect so many to think it is okay to connect CoBs in parallel when powered with an HLG.
CobKits
Well-Known Member
yes except youre citing examples of powering diodes i dont sell with drivers i dont sell or would ever recommend.
thats like me going to the buick forum and telling them how its dangerous to drive on the sidewalk
COBs and boards have more than enough diodes to soak up variations in voltage from die to die (unlike the small number of diodes your example)
cobs are perfectly safe to run in parallel when paired with an appropriate driver (unlike the bad driver selection in your example)
literally thousands of cobs being safely driven in parallel in gardens right now as we speak
go ahead and start (yet another) thread about driver selection and thermal runaway... but you shouldnt use cobs as your example because thats simply bad info
thats like me going to the buick forum and telling them how its dangerous to drive on the sidewalk
they do... because it is....
COBs and boards have more than enough diodes to soak up variations in voltage from die to die (unlike the small number of diodes your example)
cobs are perfectly safe to run in parallel when paired with an appropriate driver (unlike the bad driver selection in your example)
literally thousands of cobs being safely driven in parallel in gardens right now as we speak
go ahead and start (yet another) thread about driver selection and thermal runaway... but you shouldnt use cobs as your example because thats simply bad info
What's up guys I have a question I have 3-8 cob frames 2 frames have 8 1212 citizen 3500-4000k mix and one has 4-1212 and 4 cree Delta bravo I guess and all have 2-meanwell drivers the 200watt ones can't think of it but one has the 700mah and one frame has the reflectors well I am looking to sale them with or without the frames what you guys think I should ask price wise I think they have the 120mm pin heatsinks to and 4 cobs have smaller whatever timber sold me with a kit just wanted to see what u guys thought I could get for them need to sale.the asap thanks
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CobKits
Well-Known Member
Today's edition of "safe parallel wiring"
i just got the question:
How many Citizen CLU058-1825 80CRI can i put on a MeanWell HLG-240H-54B Driver?
my answer:
As many as you want. If you use 1 it will top out on voltage and run at ~150W
2 @~125W ea
3 @~85W each
.
.
.
.
10~@25W ea
etc.
In this case, with proper driver selection, and adequate cooling, it is impossible to run the cob into dangerous territory under any circumstances
i just got the question:
How many Citizen CLU058-1825 80CRI can i put on a MeanWell HLG-240H-54B Driver?
my answer:
As many as you want. If you use 1 it will top out on voltage and run at ~150W
2 @~125W ea
3 @~85W each
.
.
.
.
10~@25W ea
etc.
In this case, with proper driver selection, and adequate cooling, it is impossible to run the cob into dangerous territory under any circumstances
GrowLightResearch
Well-Known Member
One CLU058-1825C4 driven with an HLG-240H-54B with nothing connected to the dimmer wires will draw ~230 Watts. 52V x 4.45A
Top out on voltage? That's not a thing. 35 years in electrical engineering and I have never heard of anything like that. Voltage is a function of how many serial dice and has a range in this CoB of 48-56°C. No mater the voltage it is going to draw every mA it can get. With that HLG-250, it's 4.45 Amps 240 Watts. With substantial thermal management, it will easily survive.
Driving two, if balanced, they would each draw ~115W. Without any balancing circuitry, more likely, one would draw 140W and the other 90W. It could be better or much worse depending on Vf.
CobKits
Well-Known Member
No it wont. learn how to read a datasheet
sounds like you know nothing at all about the 54B driver. Maybe stick to commenting on things you know.
sounds like you dont understand LEDs at all for that matter
Again just please stop spreading misinformation, werent you going to start your own thread?
GrowLightResearch
Well-Known Member
.
A constant current driver means the current is constant. The datasheet says 4.45 Amps. That means the driver will supply 4.45 Amps without regard for the load The Vf of the CLU058 with a case temp of 25°C and 4.45 Amp is about 57V minus the temperature coefficient of 2.7V or a forward voltage of 54.5V typical.
The HLG is going to still push 4.45 Amps even if the LED voltage exceeds the 54V of the HLG. The HLG is a Buck step down regulator which senses the current and changes the duty cycle to modulate the current. A buck driver requires the input voltage headroom to be greater than the output typically by at least 4V at 1 Amp. More volts for higher currents. While the HLG is spec'd at 54V it is actually about 60V. So even if you cooled the LED with water chilled to 0°C and the Tj dropped to 25°C raising the Vf to 57V the HLG will still push 4.45 Amps.
Although unbalanced strings and CoB often will lead to thermal runaway it's not about thermal runaway, it's about unbalanced strings and CoBs where thermal issues are a major contributing factor.
RE: Current Balance
Where do you get the idea that it's okay to power LEDs strings or CoBs in parallel.
Show me documentation from any manufacturer or an accredited source that says it's okay to power LEDs in parallel. You cannot, becasue no such thing exists.
From EDN A respected and authoritative Electrical Engineering source.
A paper titled Overcome the challenges of driving parallel LED strings
https://www.edn.com/design/led/4424539/2/Overcome-the-challenges-of-driving-parallel-LED-strings
An LED is similar to a standard diode by virtue of being a current-driven device. It has an I-V curve in which the current and voltage are non-linear and a small change in its forward voltage can translate into a large current change.
A typical white LED can have a forward voltage of 3.3V with as much as a 20% variation at its rated current. If 10 LEDs are used in series, it’s possible that one string may require 33V to adequately drive it, while a second string requires 39.6V at the same current. If these two strings are wired in parallel, the lower voltage string pulls significantly more current than intended..
The voltage across one sense resistor can be regulated by an external control circuit to adjust the output voltage higher or lower to accurately control the LED current. While this regulates the LED current in one string, it does not necessarily do a good job for the second. It can actually make the current in the second worse, as in the case where the control loop increases the output voltage for the regulated string, but the second string has the lower voltage drop of the two.
Another problem is when the first string’s required voltage is less than the second’s. The feedback sets the output voltage to get proper regulation in the first string, but the second doesn’t have enough voltage headroom and the current in that string is reduced.
http://www.ledsmagazine.com/articles/print/volume-6/issue-2/features/led-design-forum-avoiding-thermal-runaway-when-driving-multiple-led-strings-magazine.html
The basic assumption made with this circuit suggestion is that the 700mA regulated current from the LED driver will be shared approximately evenly across both strings of LEDs, i.e. each string of LEDs will see 350mA of current. However, this is rarely the case.
In a test using identical SMD LEDs from a single production batch and using 1 Ohm resistors to help balance out the forward voltages, the currents flowing in each string were measured to be 306mA and 394mA. The LED driver was still doing its job of correctly limiting the current to 700mA, but the over‐current flowing through the second string was seriously overdriving the LEDs.
Worse, as the LEDs started to get warm, the combined forward voltage of the higher current string started to decrease. This increased the imbalance and more current started to flow through the already over‐driven string. The current through the other string of LEDs reduced as the constant current driver compensated, so they started to cool down and their forward voltage increased.
The net result was thermal runaway with the majority of current flowing through one string only, even though the LEDs were mounted on a large metal heat sink. The test was stopped when the current imbalance was 600mA to 100mA. Obviously, if this situation was allowed to continue, the over‐driven string would eventually fail and then the entire 700mA would flow through the remaining intact string and destroy that as well.
And this circuit is often given as a recommended application example!
https://ledsinparallel.wordpress.com/
I have attached 3 PDFs regarding parallel strings.
I understand you you do not have the cognitive capacity to dazzle with brilliance, but please discontinue trying to baffle people with your BS. You are doing everyone that believes you BS a disservice.
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BuddyColas
Well-Known Member
Listen to the Force, "Start your own thread, Luke!"
nfhiggs
Well-Known Member
Still haven't figured out how constant voltage works eh? Perhaps you should actually look up the specs on the HLG-240H-54B....
Funny how Samsung LED strips manage to function with as many as 16 parallel strings. Perhaps you should stop relying on outdated info.
CobKits
Well-Known Member
False. please start your own thread with your thermal runaway scenarios (or look back at the threads where all this was covered 2 years ago)
CobKits
Well-Known Member
if you DIY it wont cost you that much to replce them 2 x 400W @ about $800-900 total, or you can put 600W in each 4x4 and yield more (~$1100 total)
GrowLightResearch
Well-Known Member
Key phrase being "manage to function". The question is how well do they function and could you do better by driving them properly. 35 years ago I was using Sylvania GrowLux bulbs and they did fairly well. Could I do better than GrowLux? Yes. Do GrowLux function? Yes. Your anecdotal evidence is of no value.
I really like what you have done with the Samsung strips. So much better than your former DIY CoB fixture.
Samsung has an advantage becasue they can use Vf binned LEDs where the Vf is tightly matched. The best binning Samsung offer the general public for LM561is 300mV.
I do not use outdated info. I ran more tests a couple of weeks ago with CoBs and with strips back in March. There are no paper written say it is okay to drive CoBs or strips in parallel. There are plenty of papers from reliable sources saying NOT to drive them in parallel.
Just because they light up does not mean they are not unbalanced. Measure the forward voltage and current in the individual strips.
I typically design strips to operate at 48V and use 54V HLGs and HEPs. In my lab I have just about every 54V HLG Mean Well makes. So when I said they run up to 60V that's because I have measured it many times. I manufacture my own inexpensive buck drivers which can be powered with CC or CV power supplies. I also use Texas Instruments LM3466 to balance the current in multiple strips.
No one here has offered anything supporting parallel wiring.
Idiotic remark,save them for someone that might give a shit..
Hey buddy I have 3-8 cob kits listed on eBay for sale I got all the parts for 2 of them from cobkits but yea saling mine and the work awesome and I run 8 citizen 1212 in my one 4x4 and work great well good luck on finding lights cobkits will get ya going at decent price is