One COB thing bothers me

[ondercuver]

Hello fellow diy'ers

I'm researching COB's for some time now and it looks like every build is about the same ... cobs run in series with a few meanwell drivers .

My question is " is that necessary ? is there some science behind it? a paralel run would be less efficient?"

I'm not a sparky , but I would rather have a cob array all paralel wired , meanwell makes 36v @ 16.7A ..600w driver
HLG-600H-36A , that will drive as many 36v cobs I want and if one dies there's no drama .the others pick up the slack .

On the other hand , picking up the right CC driver is a PITA ... you're stuck with whatever array you built , can't add any more without adding drivers or if one cob burns the whole thing is stuck till you replace the cob .

Please illuminate me

 

[gbauto]

Re: one COB thing bothers me...

Driving the arrays in parallel exposes you to a much lower DC voltage so it's inherently safer to use but led's can experience what is known as thermal runaway. The array allows more drive current as its temp increases and without some current limiting it does a melt down. Not very common but it is a possibility. Series circuits ensure that each array sees the same drive current but the downside is the much higher drive voltage. I was trained as an electrician and have been bitten by AC before but DC is much more lethal to your body so extreme care should be taken.

 

[outdoormaster]

Re: one COB thing bothers me...

100% correct

 

[Grassmaster]

Re: one COB thing bothers me...

On my new 4 COB system I just installed yesterday. Only 2 Cobs are running on each driver. So it really doesn't make any difference.

So far I'm not disappointed at all. It will go as high as 420 watts if needed. I currently have it turned down to only 160 watts to veg 4 auto
flowers. Each plant has a fully adjustable COB directly above at recommended 1' away. 30,000 to 40,000 LUX! COB heat sinks are luke warm. With my LEC 315 it was always on full blast. The only control you had was distance from the light.

The only problem is I have to use a heater to keep the plants warm or they will wilt now that it's winter.

This is the only LED light that I could find which will cover a 3' by 3' as good or better than an LEC 315. So if the light quality and end results are as good I'm switching over.

 

[Scientific]

Re: one COB thing bothers me...

DC is much more lethal to your body

Really? That's the opposite of what I heard--that AC by it's alternating nature has greater potential to interfere with heart rhythm and so is more dangerous.

 

[Scientific]

Re: one COB thing bothers me...

My question is " is that necessary ? is there some science behind it? a paralel run would be less efficient?"

I don't have any practical experience with high power LEDs, but I can't think of a theoretical or scientific reason not to run them in parallel as long as you're not overdriving them, have the correct cooling, and are following all of the manufacturer's recommendations.

Maybe contact the manufacturer and/or read the spec sheets and application guides?

 

[Grassmaster]

Re: one COB thing bothers me...

Really? That's the opposite of what I heard--that AC by it's alternating nature has greater potential to interfere with heart rhythm and so is more dangerous.

One of the reason DC is so dangerous is that once it is flowing through your body it kind of grabs onto you. Because AC is constantly changing polarity makes it easy to open the circuit.

 

[Scientific]

Re: one COB thing bothers me...

One of the reason DC is so dangerous is that once it is flowing through your body it kind of grabs onto you. Because AC is constantly changing polarity makes it easy to open the circuit.

An 18" screwdriver I was holding carelessly once touched the exposed 400-volt DC B+ supply to a power tube. It was an extremely unpleasant experience.

 

[ondercuver]

Re: one COB thing bothers me...

Driving the arrays in parallel exposes you to a much lower DC voltage so it's inherently safer to use but led's can experience what is known as thermal runaway. The array allows more drive current as its temp increases and without some current limiting it does a melt down. Not very common but it is a possibility. Series circuits ensure that each array sees the same drive current but the downside is the much higher drive voltage. I was trained as an electrician and have been bitten by AC before but DC is much more lethal to your body so extreme care should be taken.

ok , didn't know about the possible meltdown , is that a meltdown of a cob or the source? ... I plan to drive 12 CLU048-1212 with a 600w @ 36volts c.v. power source ... so that's about 50% underdrive of the cobs on max setting of the source .

I want to go this way because of ergonomics ... 1x600w for a 12 cob array , ps will stay outside of the tent , and this will cover 4x4 ... wil have 2 of them in a 4x8 tent.
This setup will be easily scalable for me as I expand the grow, I have about 1200ft of space waiting to go green but first want to grasp the whole thing before diving in.

I gave it a lot of thought , cobs are the only way to go , it will be actually cheaper than HID

 

[gbauto]

Re: one COB thing bothers me...

Really? That's the opposite of what I heard--that AC by it's alternating nature has greater potential to interfere with heart rhythm and so is more dangerous.

Another of my past professions was as a mechanic(hence-AUTO). When hybrids and EV came onto the scene I had quite a few training sessions on servicing the battery packs-these are up to 200VDC and are LETHAL. Ask Thomas Edison how safe DC power can be...(I suppose you could have a seance to channel all of the animals he fried)

 

[ondercuver]

defibrillators are DC ... I'm not saying AC is good for you , but high voltage dc can be just as bad

 

[Scientific]

Re: one COB thing bothers me...

Ask Thomas Edison how safe DC power can be...(I suppose you could have a seance to channel all of the animals he fried)

Actually, Edison was a proponent of DC power and killed animals with AC in attempts to persuade the public that AC was dangerous. Tesla was the AC advocate.

Edison's least favorite of Tesla's "impractical" ideas was the concept of using alternating current (AC) technology to bring electricity to the people. Edison insisted that his own direct current (DC) system was superior, in that it maintained a lower voltage from power station to consumer, and was, therefore, safer.​

In my training, we learned that about 80 volts is the threshold of lethality under normal circumstances, and anything under 40 volts didn't present very much of a shock hazard (not talking about high current situations there, but EMF high enough to overcome the skin's normal resistance).

Of course we need to be safe with any electric power (and to get back on topic too I suppose...)

 

[Scientific]

Re: one COB thing bothers me...

Maybe contact the manufacturer and/or read the spec sheets and application guides?

Electronic manufacturers publish an enormous amount of engineering data that is available at the cost of a few moments of looking (which is a huge and welcome change from the pre-Internet days in which I used to maintain an engineering department's technical library, begging manufacturer's to please mail us the latest manuals and yelling at the people who kept walking off with them.)

Digi-Key is always a great place to look. Awesome company.

Anyway, following my own advice, a minute's Googling for CLU048-1212 led to a search string of "Driving", "Instruction Manual(COB LED Package)"), which got this from the manufacturer of the CLU048-1212:

When connecting multiple identical LED package
products, the series connection makes current flowing
through LED packages uniform. Citizen Electronics
recommends series connection to ensure stable light emitting
output and reliability. On the other hand, a
parallel connection should be considered for Vf variation
between LED packages. Some measures, such as the
appropriate current regulation resistor being connected to
each LED package in series based on the temperature
conditions in actual use, are required to apply even current
to each LED package with different Vf characteristics.​

So it looks like either method is acceptable to the manufacturer, but they recommend series connection.

Merry Christmas!

 

[Scientific]

Re: one COB thing bothers me...

led's can experience what is known as thermal runaway. The array allows more drive current as its temp increases and without some current limiting it does a melt down. Not very common but it is a possibility.

Looks like the manufacturer warns about that when using a constant voltage drive system:

3. Constant voltage drive system
Cautions for constant voltage driving

...an LED has a tendency for Vf, which applies a certain current to an LED, to decrease as the
temperature increases...

From another perspective, when an LED is operated with a certain voltage, the more the temperature increases, the
larger the current that flows through the LED.

In cases of driving with a constant voltage... temperature changes lead to changes in Vf and current as the temperature of an LED is unstable due to variance in environmental temperature or other factors.

Accordingly, the brightness of an LED can be unstable as it depends on current. Thus, when driving with a constant
voltage is employed, an appropriate measure such as the connection of current control resistance needs to be
implemented based on an assumption of the temperature in actual use.

Instability due to driving with constant current
Temperature change of LED --> Vf change --> Current change --> Brightness change

 

[ondercuver]

Good thing I didn't order the meanwells .

Thank both of you for the input.

It's pretty clear CV could work but due to vf changing with the temp will make choosing a resistor kind of a chore , don't have the nerves to tackel that , I want to build something easily repairable and with repeated results.