Introducing - specializing in DIY and Citizen COBs

Discussion in 'LED and other Lighting' started by CobKits, Aug 2, 2016.


    verticalgrow Well-Known Member

    i would be happy too, looks like 60 happy & healthy plants.:weed:

    How many watts:confused:
    pop22 likes this.

    CobKits Well-Known Member Rollitup Advertiser

    thats 12 rigs of 8 luminus cxm22 on hlg-600h-54B drivers
    verticalgrow likes this.
    dabby duck

    dabby duck Well-Known Member

    Eh, Fudge amazon personally and Ebay eh....

    I was hoping maybe you had some downlow on a particular style or set....No prob though thanks for the reply, I will keep looking

    TD816 New Member

    @CobKits you are the man!! Order came in today, sooner then I expected. Thank you for hooking me up with the screws also (didnt expect that) and for refunding some of the shipping.

    Any idea when you might get in a Meanwell HLG-240H-C 1400ma driver in?

    Looking forward to doing more business with you.
    CobKits likes this.

    GrowLightResearch Well-Known Member

    I would have thought the same thing. I ran the test twice and confirmed the parallel Vf was higher. Current was supplied no voltage was applied as the voltage is a function of the LED's Vf. The max voltage was 54 from the HLG-60-54A.

    If I drove the parallel LEDs with 1200mA. How could it be possible for each LED to draw more than 600mA which would require more than 1200mA?

    Yes significantly. In the test I described the currents @ 1200 mA the individual currents were 764mA and 463mA. When I ran the same test on strips of 16 white Luxeon Rebel White, the results were similar
    Vf = 43.29 and 43.85.
    Two test currents = 375mA, and 770mA.
    Measured current @ 375ma = 240mA and 135mA. @ 770mA = 450ma and 320mA. Significantly different.

    When Vf is measured individually they voltages were 33.4V and 34.2V. When run in parallel the Vf parallel must be the same because the anodes and cathodes are connected together. The surprise was the parallel Vf was higher than the individual Vf.

    Test Circuit

    As shown the current measured through the shunt resistor is for both LEDs.
    When the switch is flipped, it measures only the current through LED1
    LED2 current = Iboth - ILED1

    Shunt voltage @ 600mA = 0.0045V
    Shunt voltage @ 1200mA = 0.009V


    0.015Ω Shunt Resistor


    Two Strips of 16 Luxeon Rebel White LEDs

    Last edited: Nov 17, 2017
    pop22 likes this.

    pop22 Well-Known Member

    can you measure the V and Ma for individual cpobs? See if it is a cob issue, wiring or cob holder connector resistance, etc, It would seem pointless to use Cv drivers if this is common.


    GrowLightResearch Well-Known Member

    See prior post with test circuit.
    When wired in parallel the anodes and cathode are wired to each other so the voltage must be the same.

    I measured the current to both then measured the current in one LED and calculated the other's current.

    A CC driver was used: HLG-60H-54A

    Only if wired in series, not when wired in parallel unless you include a shunt resistor to measure the current in each CoB.

    It is not an issue with the CoB or a wiring error. The issue is wiring in parallel two LEDs with different forward voltages forcing the voltage to something other than the LEDs actual forward voltage. Due to the dynamic nature of the Vf, the interaction between the two LEDs is complex.
    Last edited: Nov 17, 2017
    pop22 likes this.

    CobKits Well-Known Member Rollitup Advertiser

    can you start a new thread for your experiments?

    pop22 likes this.

    CobKits Well-Known Member Rollitup Advertiser

    just a heads up i have a procedure on monday so if you want stuff shipped by monday order it by mid-sunday. otherwise it will ship weds or fri (thurs is thanksgiving)
    pop22 likes this.

    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.

    blake9999 Well-Known Member

    pop22 likes this.

    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.


    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.
    BuddyColas likes this.

    CobKits Well-Known Member Rollitup Advertiser

    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
    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

    chuckie86 Well-Known Member

    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

    Attached Files:


    CobKits Well-Known Member Rollitup Advertiser

    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
    [email protected] ea


    In this case, with proper driver selection, and adequate cooling, it is impossible to run the cob into dangerous territory under any circumstances
    DrBlaze, blake9999 and nfhiggs like this.

    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 Rollitup Advertiser

    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?
    DrBlaze, key4, pop22 and 2 others like this.

    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

    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.

    From LED's Magazine: Avoiding thermal runaway when driving multiple LED strings


    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!

    Page with many articles regarding the issues associated with parallel LEDs
    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.​

    Attached Files:

    Last edited: Nov 20, 2017

    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.
    key4 and pop22 like this.

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