Low Voltage Parallel vs High Voltage Series Drivers

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iScrtAznMan

Member
I hate to make a new thread about drivers, but I find conflicting or older information when searching about thermal runaway and I'm sure it could help a lot of new users too (or at least me).

Can you help me settle the advantages and disadvantages of low voltage (parallel) vs high voltage (series) drivers? I've been searching all over as to why @CobKits sells the MW hlg-***-48a for parallel wiring when most people run constant current drivers. The only good reasoning I could come up with are, safety (electrocution), cost and flexibility for people that can't afford to run their cobs soft or will add cobs later.

But isn't thermal/current runaway still an issue? The only cobs that could be okay are ones where the forward voltage is close to the driver limit since the increase in temperature will increase voltage requirements, turning the cob off and allowing the current to redistribute assuming the other cobs can handle the current. If you use a lower forward voltage cob, it won't be safe anymore. You also can't upgrade to higher voltage cobs so you're locked in at that specific voltage. In that case, wouldn't a dimmable constant current driver, like an hlg-***-c****b offer more flexibility for a specific wattage range, since you could just dim the driver if it's too strong? (I guess some drivers have pretty limited current ranges)

I guess you could employ techniques to distribute current evenly, but that would ruin any cost advantages that a high voltage driver wouldn't require. It also makes installation harder for low voltage cobs depending on the method used (I guess resistors aren't too bad but reduce efficiency. A current mirror could quickly get complicated if used in setups with a lot of cobs per driver. Resettable Fuses seem like the best option, but could result in all the lights shutting off for a bit if they don't reset quickly enough. Larger fuses (~50V 3A+) take 5+ seconds to trip too).

Edit: For the low voltage drivers that offer constant voltage, I thought I read somewhere on here that they only limit voltage until it gets up to temp or it hits max voltage. Just to clear up why I thought lower voltage cobs won't work with something like a hlg-185h-48a.
 
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Nenno44

Nenno44

Well-Known Member
I was un-aware that the MW hlg-***-48a drivers had to be wired in parallel....now I need to learn how to do that pretty quick.
 
Stephenj37826

Stephenj37826

Well-Known Member
The CV driver will provide the voltage up to its max that the cob requires. If you use A type Max voltage is adjustable. so if you are concerned with thermal runaway you have an option with A type driver. Put the setup together and let it warm up to operating temperature. Adjust max voltage down to what the system is using at that point. of a cob fails the vf of the other cobs would try to go up with the extra current but the driver will only provide the set max voltage. So it will limit the current to maintain the set voltage. Hope this helps.
 
S

Shugglet

Well-Known Member
Wire in series (as recommended) and avoid most problems.

For some setups it is impractical though. depends on your situation.
 
Ganjineer

Ganjineer

Member
Those HLG-***H-48A drivers still have constant current as well as constant voltage adjustment through the internal pot. They can be dimmed just like the HLG-***H-C****.

In my experience, the danger of thermal runaway is overstated. I've built numerous lights that utilized parallel LED strings and have never had any issues. You simply have to make sure that your strings incorporate matching LEDs. The choice between driving LEDs in parallel vs series should be dictated by your specific application and budget constraints.

That being said, there are a few protections against thermal runaway that you can utilize to protect your builds such as fuses, bimetallic thermal switches, and current mirrors. The most important action you can take is during the design of your light. You don't want to drive strings of LEDs in parallel in an application where you are approaching the maximal forward current of the LED and the heat sinks are just barely able to dissipate that heat. I recommend designing your setup in such a way that if one LED goes out in the string, the others can compensate for the extra shared current and heat dissipation. By following this approach, I've had actively cooled parallel strings that have lost a fan and the drop in heat dissipation was still not enough to take out the LED and induce thermal runaway.
 
Abiqua

Abiqua

Well-Known Member
Nenno44 said:
I was un-aware that the MW hlg-***-48a drivers had to be wired in parallel....now I need to learn how to do that pretty quick.
Click to expand...
Wiring in parallel is easy, instead of one big circuit like a series circuit, each diode gets a + and - from one common source. Add current for your sources.

In series. Add voltage together for your sources.Current remains the same.

Knowing these differences, it would be easy to see why you wouldn't parallel wire something like HLG -C line of Meanwell's.....usually with COB's....although the HLG boards are being used this way with a CC+CV? driver which is interesting to say the least.....:peace:
 
I

iScrtAznMan

Member
Ganjineer said:
Those HLG-***H-48A drivers still have constant current as well as constant voltage adjustment through the internal pot. They can be dimmed just like the HLG-***H-C****.

In my experience, the danger of thermal runaway is overstated. I've built numerous lights that utilized parallel LED strings and have never had any issues. You simply have to make sure that your strings incorporate matching LEDs. The choice between driving LEDs in parallel vs series should be dictated by your specific application and budget constraints.

That being said, there are a few protections against thermal runaway that you can utilize to protect your builds such as fuses, bimetallic thermal switches, and current mirrors. The most important action you can take is during the design of your light. You don't want to drive strings of LEDs in parallel in an application where you are approaching the maximal forward current of the LED and the heat sinks are just barely able to dissipate that heat. I recommend designing your setup in such a way that if one LED goes out in the string, the others can compensate for the extra shared current and heat dissipation. By following this approach, I've had actively cooled parallel strings that have lost a fan and the drop in heat dissipation was still not enough to take out the LED and induce thermal runaway.
Click to expand...
What type of application constraints or budgets changes the choice between parallel or series? I didn't think there was a huge price difference, or do you mean because of scaling issues.
 
CobKits

CobKits

Well-Known Member
Stephenj37826 said:
The CV driver will provide the voltage up to its max that the cob requires. If you use A type Max voltage is adjustable. so if you are concerned with thermal runaway you have an option with A type driver. Put the setup together and let it warm up to operating temperature. Adjust max voltage down to what the system is using at that point. of a cob fails the vf of the other cobs would try to go up with the extra current but the driver will only provide the set max voltage. So it will limit the current to maintain the set voltage. Hope this helps.
Click to expand...
^this.

i need to make a youtube video for these drivers
 
Ganjineer

Ganjineer

Member
iScrtAznMan said:
What type of application constraints or budgets changes the choice between parallel or series? I didn't think there was a huge price difference, or do you mean because of scaling issues.
Click to expand...
Pretty much. It used to be that the high voltage drivers for series applications were more expensive and harder to obtain, that really isn't the case anymore. Series drivers are a little more flexible with using unmatched LEDs (as long as you aren't exceeding the maximal safe forward current of the LEDs) and so that gives you a little extra flexibility in terms of the upgrade path in the future. Given this, if price difference or availability isn't an issue, then I would choose a high voltage series driver. However, that may or may not be right for everyone's application, for example if you already have the drivers on hand or you don't want the electrocution risk of working with high voltage DC.
 
Abiqua

Abiqua

Well-Known Member
iScrtAznMan said:
What are HLG boards? I'm a noob and baked noodles sound good to me.
Click to expand...
They are robinCnn's Quantum Boards....made by Horticulture Lighting Group and most of us, are using Meanwell HLG-C drivers for said boards as well.......what a a cluster F

didn't realize that until you pointed it out Cobby @CobKits
 
Stephenj37826

Stephenj37826

Well-Known Member
OK I'm going to explain this the best I can.

These board's are no different than cobs in how they function. There are strings of diodes in cobs run in series. Those strings are then run in parallel. So the VF of any given cob is the vf of any given string in that cob. The quantum boards(better name to avoid confusion) are strings of 38 diodes equaling the ~100-110 VF. We could easily run them in strings of 10 and run a constant voltage driver"our second choice" . We choose to have a constant current driver so that's why it seems confusing. Just look at them just like a cob that is 100 volts. The molex connectors are rated to 300 volts (higher than most cob holders) so if the driver will provide the voltage you can run up too 3 boards in series( I have done 2 with hlg320 C-1400. So 2 boards in series and another set of board in series these two "strings" in parallel on that driver is roughly 80 watts a board.
 
Abiqua

Abiqua

Well-Known Member
See, I was picturing the 2nd idea where you were just halving the current 2 boards and running a CC in "parallel"........because a 100v 1400 amp driver is easy to find......

but then the part about the 320 -1400 makes no sense in terms of running three in series when vF is 105 avg...and the voltage is less than 300v from that driver at that current?

:peace:
 
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goofy81

Well-Known Member
I was about to purchase the meanwell 600w drivers to run my cobs .
I ended up with drivers suited for series because I could use the existing (and thinner) wires I already had.
 
Forrestfirebuds

Forrestfirebuds

Member
Hey guys so ive built a few lights and have done both constant current and constant voltage. My question is about my constant voltage drivers. They are the meanwell hlg 240 36b and i can hook up as many cobs in parallel as i want but the current on each cob goes down. Currently i have 4 running on each driver so im running my cobs a 1675ma. Is is possible to hook up 2 or 3 strings of cobs that are in series and run those strings parallel to my driver? Or can i run 2 or 3 strings of cobs that are in parallel and run those strings parallel to my driver? And what are the pros and cons of each set up? Thanks
 
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