how does dimming work in relation to efficiency and drive current?

Rahz

Rahz

Well-Known Member
banke1 said:
1. These setups pull approx the same wattage amount from the wall, correct?
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Pretty close. 2 of them at .7 amps will draw 3 watts less than 1 at 1.4 amps due to the fact that voltage input drops along with the current.

banke1 said:
2. Is Setup A just as efficient as Setup B? Same PPFD? Same heat emitted? Same Par W? obviously setup A has the potential to run a higher PPFD if run at more than 50%.
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Setup B is more efficient, more PPFD, less wattage and less heat.

SSGrower said:
How extreme can you go with the "dimming" by connecting additional leds to the same driver?
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The Meanwell drivers won't dim below 10%. Driver efficiency decreases when dimmed but the efficiency loss is reasonable down to about 20-25% of max at which point the driver will start heating up and the net efficiency increase is more modest due to diving driver efficiency. Above 20% the HLGs generally run high 80s which is not bad when you consider many drivers max out in the 80s.

But the most extreme dimming you can do would be to start with a low max current, either low current driver or running parallel strings on a higher current driver and max out the driver and maybe dim from there. OTOH, whether it makes sense to go below .7 amps will depend on local electrical costs. Putting more money in than you will eventually get out over a 4-5 year period isn't an increase in efficiency.
 
SSGrower

SSGrower

Well-Known Member
So since the driver I have is cc from 28-42v I could drive them to some lower current limit? If so where can I find that value the spec sheet for the led I have just has a blank for the minimum values. There is a typical of 38.5 and max of 42 for voltage and a 2.8 amp max current but again no minimum listed.
 
Rahz

Rahz

Well-Known Member
The typical voltage for a particular current is extrapolated from the Current -vs- Voltage chart in the datasheet.
 
SSGrower

SSGrower

Well-Known Member
Rahz said:
The Meanwell drivers won't dim below 10%. Driver efficiency decreases when dimmed but the efficiency loss is reasonable down to about 20-25% of max at which point the driver will start heating up and the net efficiency increase is more modest due to diving driver efficiency. Above 20% the HLGs generally run high 80s which is not bad when you consider many drivers max out in the 80s.

But the most extreme dimming you can do would be to start with a low max current, either low current driver or running parallel strings on a higher current driver and max out the driver and maybe dim from there. OTOH, whether it makes sense to go below .7 amps will depend on local electrical costs. Putting more money in than you will eventually get out over a 4-5 year period isn't an increase in efficiency.
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Rahz, I think you may have misunderstood my question the driver I have is not dimmable but if I have 1.5 amps to work with where is that lower current limit for the led (as the data sheet only posts a max and I have as yet to see a minimum value. I remember seeing some thing about driving at 200mA but wanted to get real bottom number.
 
Rahz

Rahz

Well-Known Member
SSGrower said:
Rahz, I think you may have misunderstood my question the driver I have is not dimmable but if I have 1.5 amps to work with where is that lower current limit for the led (as the data sheet only posts a max and I have as yet to see a minimum value. I remember seeing some thing about driving at 200mA but wanted to get real bottom number.
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If you run cobs in parallel they will split the voltage, 1.5 / # cobs in parallel = current. I don't think there is a real bottom number. The efficiency would probably level off at some point, but I'm not sure where that would be.
 
BOBBY_G

BOBBY_G

Well-Known Member
Rahz said:
If you run cobs in parallel they will split the voltage, 1.5 / # cobs in parallel = current. I don't think there is a real bottom number. The efficiency would probably level off at some point, but I'm not sure where that would be.
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efficiency has been measured to increase all the way down to 1W
 
alesh

alesh

Well-Known Member
VegasWinner said:
Setup A will perform less efficiently than setup B. Reasons. Setup B is designed to be 64% efficient, while setup A is designed to be 56% eficnet. Dimming setup A does not change the amount of current or amps, you draw, just discards half of them through the potentiometer, 100k, that is its job to waste current at a given resistance.

Setup B is more efficient and will perform more efficiently drawing the same amps for the duration of its existence, as 2was designed, while setup A will discard half of all of its amps decreasing the efficiency to maybe 28% through heat losses, called resistance. if you have to keep your fixture dimmed to 50% change the driver to the lower rated driver and be happier, and watch your power bill go down too. it is not watts we are seeking, it is lumens at the most efficient rate we are seeking. New ballgame, new rules. peace.
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Please don't post when you have *NO* idea what you're talking about. You're only making it more difficult for others.
 
alesh

alesh

Well-Known Member
BOBBY_G said:
doesnt work like that at all (or there would never be a reason to dim unless you were stressing your plants to death)

the driver reads the resistance value from the pot. all the current doesnt go thru the pot. think how hot that pot would be burning up 90% of the energy of a driver!!!!!

that said, dimming works by reducing current. cobs see what the cobs see, so the cobs in example A are identical efficiency to example B

difference is in driver efficiency.

185H-C series @ 115V is 93% efficient all the way down to 50% load*
80H-C series @ 115V doesnt crack 91%

*there are people that say that 'total load' is determined by % of driver utilization at 100% (no dimming), and this efficiency is maintained dimming all the way down. others say if you dim an array using 100% of a driver down to 40%, you read the efficiency at 40%. moot point in this case as the excellent 185H-C driver is 93% efficient at 50% as well as 100%
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That's not exactly correct. Efficiency is closely related to driver's output voltage and more loosely related to the output current. https://www.rollitup.org/t/diy-led-cree-cxa3070.789575/page-97#post-11010292
 
SSGrower

SSGrower

Well-Known Member
Rahz said:
If you run cobs in parallel they will split the voltage, 1.5 / # cobs in parallel = current. I don't think there is a real bottom number. The efficiency would probably level off at some point, but I'm not sure where that would be.
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Got it and to clarify the 1.5 value is specific to my situation because of the drive current.

I feel like I crammed an entire semester of thermodynamics is digital functional eq into last night so forgive me if this is asinine but but I'm thinking about controlling efficiency with temperature, have you ane experience or thoughts on this? I'm doing some quasi-tative testing and seem to be finding the led array to be reaching a steady state of operation at 185F which just so happens to be the reported optimal operating temp?
 
Rahz

Rahz

Well-Known Member
Optimal is getting the chips as close to room temperature as possible. 185 is the max temperature suggested to keep the chips within operating limits, but efficiency goes up when they are ran cooler.
 
SSGrower

SSGrower

Well-Known Member
Optimal = Highest % of lumens vs. heat (and other losses) is obtained from the same power consumption or Optimal in the sense that the highest quantity of light is being produced from an equivalent power consumption?

But I think what I was asking is that if the current is controlled like in the power supplies used then as the LED goes above that max operating limit, given only sufficient cooling (nothing more nothing less), do these arrays enter a sort of endless loop where the excess heat causes the thing to operate less efficiently and thus cools down?
 
Rahz

Rahz

Well-Known Member
SSGrower said:
Optimal = Highest % of lumens vs. heat (and other losses) is obtained from the same power consumption or Optimal in the sense that the highest quantity of light is being produced from an equivalent power consumption?
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Both.

SSGrower said:
do these arrays enter a sort of endless loop where the excess heat causes the thing to operate less efficiently and thus cools down?
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No, they would continue to run hot.
 
BOBBY_G

BOBBY_G

Well-Known Member
alesh said:
That's not exactly correct. Efficiency is closely related to driver's output voltage and more loosely related to the output current. https://www.rollitup.org/t/diy-led-cree-cxa3070.789575/page-97#post-11010292
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great link, thanks!

well were sort of both right...

convert those to watts and then % load (based on 200W as 100%) and you'll see they just about fall right where you'd expect on the efficiency curve in the datasheet, but as supra observed low voltage does hit it harder (which kind of makes sense - high voltage is always more efficient, for transmission and line losses at least).

but its not a huge factor, for example even with 3 cobs at 63% efficient we get 91%, where we would anticipate 93% per the curve and the 5 cob case

also we see that for the intermediate 4 cob case while our efficiency is knocked down ever so slightly (less than 1%), it still remains fairly linear with dimming down to 48%

5 CXA3070s + 3 XML2
At full output 1155mA, 190.1Vf, 93.6% efficient (110% load)
Same string, dimmed to 525mA, 177Vf, 93% (46% load)

4 CXA3070s
At full output 1155mA 144Vf, 92.8% (83% load)
dimmed to 706mA, 137Vf, 92.3% (48% load)
dimmed to 479mA, 133Vf, 91.3% (32% load)

3 CXA3070s
1155mA, 108.5Vf, 90.9% (63% load)
480mA, 100.5Vf, 88.5% (24% load)
 
BOBBY_G

BOBBY_G

Well-Known Member
Rahz said:
That's what I meant when I said there's no bottom, but the gains for halving the current will start to level out.
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well yeah the law of diminishing returns starts as soon as you turn then down from 3.6A, due to the nature of the curve, the cost of equipment per unit of light goes up as by definition you need more cobs for same amount of light

that said, theres a reason why 700 ma-1400 ma is so popular. its a sweetspot
 
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