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Cheap Lighting ideas?

Mikster said:
Certainly is confusing

This chap looks like its setup in series DIY High Power LED Aquarium Lighting – Part V at Ken's Aquariums & Pond
Click to expand...

What you need for your driver mate is something like this:
LED Driver Power Transformer 30w-54w (10-18)x3w waterproof AC85~265V 680mA | eBay

It would run 3-5 10w leds, and would run them at 680ma that is about 70% brightness

Or here is one that would run them at 100% brightness

AC 85-265V DC 20-38V 900mA 30W Waterproof Transformer LED Power Supply Driver | eBay
 
Mikster said:
Thanks for that, they both look top dollar!

Going to give LED Driver Power Transformer 30w-54w (10-18)x3w waterproof AC85~265V 680mA | eBay a go, best to under power

but I am still confused, why this is unsuitable 12V 5A 60W Switch Switching Power Supply Driver For LED Light Strip 200-240V NEW | eBay for running a one/two/etc 12v LED's in parallel? volts are the force behind the current so why will this burn out?

think i might get an electronics book off amazon, doubt they do one on LEDS :)
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Yeah me too, from my understanding your current driver should work fine, I have a feeling that ian_m just jumped in to the conversation without properly reviewing the information, I can't see why you would have a problem with 6x 12v 900ma leds in parallel with a 12v 5a driver, giving you a 820ma drive current for each led, the only issue that I can see is that you won't be able to dim them. Someone please feel free to correct me if i'm wrong:)
 
The power supply above is a constant voltage power supply (12 Volts) in this case designed for connection to an LED driver not directly to LED's.

Below is a circuit I used in my circuit simulator with 3 high power LEDs (900mA in this case) being driven directly from a power source ramping from 0V to 12V.
ledcircuit.png

Below is the results.
ledtransfer.png

X axis is applied voltage and Y axis is current through diode chain.
As you can see the current, as not being limited, very quickly rises to quite a large value (nearly 5A in this case), which would destroy the LED's. This is why you employ constant current (or a current limiting resistor) or else the LED's will be destroyed.

Adding an 8.2Ohm current limiting resistor in series with the LED's produces this, current 800mA at 12V, so OK for 900mA LED's.
ledtransfer2.png

The problem with this is the power dissipation of the resistor is 5Watts which means big'ish resistor, issues with getting rid of the heat and only about 40% of power is going into the LED's.
 
ian_m said:
The power supply above is a constant voltage power supply (12 Volts) in this case designed for connection to an LED driver not directly to LED's.

Below is a circuit I used in my circuit simulator with 3 high power LEDs (900mA in this case) being driven directly from a power source ramping from 0V .
Click to expand...

But he is talking about running the led's in parallel, not series like in your diagram??
 
Can Anyone on this forum say they are qualified to correct this discussion? I think there are a few people including me that would like to know the correct information. Obviously 2 very strong arguments here that can be confusing for an LED beginner such as my self! :)

Sent from my GT-I9100 using Tapatalk 2
 
rolexbene said:
But he is talking about running the led's in parallel, not series like in your diagram??
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You never run LED's is parallel, as previously explained, as slight variations in LED manufacturing parameters means that one of the LED's (the one with the lowest threshold voltage) will hog all the current and potentially burn out.

Below is the current through 2 LED's in parallel but with one having 5% difference in its threshold voltage, as can been seen one takes more current than the other.
2ledstransfer.png
 
rolexbene said:
You may find this article useful from Reeflights.com a specialist in led lighting describing how to run very similar led's using a 3.2A driver in parallel.
Wiring Diagrams | Reef LED LightsReef LED Lights
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Observe the balancing 1Ohm resistor not shown on the diagrams.

And repeating my simulation of parallel LED's but with limiting resistor in each string, no current hogging occurs and both LED's take roughly the same current.
balancedleds.png
 
I completely understand running lower voltage LED's in series from a higher Voltage low amp driver works, its documented on loads of sites blogs etc.
But, how comes running 1 12v LED from a 12v Power supply doesn't work?
if i was to have a 12v 900ma power supply it would work?
its the fact this power supply runs 5a (even though its 0-5a) will blow the one LED?
if i split the amps over 5 or 6 12v LED's then is safe?

Its just me but Rolexbene's link above makes complete sense to me, this doesn't. Not that i mind binning the power supply its only a few quid. My inner geek is now curious.
 
Mikster said:
But, how comes running 1 12v LED from a 12v Power supply doesn't work?
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Its because there is no such thing as a 12V LED. LED's run on current eg 900mA etc.

When you push a current through an LED it generates a voltage across the LED, this voltage, for white LED's for instance, is in the range 3 to 4 volts, depending on LED, temperature, current, manufacturer, manufacturers batch, age etc. So there is really no fixed voltage rating for an LED.

The LED voltage is quoted so you don't attempt to drive say 20 LED's from an LED driver that can only generate 40V maximum output. To drive 20 white LED's with each being about 3.5V you would need a power supply that generates at least 70V output to stand any chance of getting current through them.
 
Mikster said:
I completely understand running lower voltage LED's in series from a higher Voltage low....
Click to expand...


If i was to have a 12v 900ma power supply it would work?
Yes any DC power supply running at 12v 900ma or less will work

its the fact this power supply runs 5a (even though its 0-5a) will blow the one LED?
Yes I believe it will blow 1 led but am not 100%, maybe try asking the sales person.

if i split the amps over 5 or 6 12v LED's then is safe?
I beleive it is safe, Ian_m does not for some reason. Guess your just have to risk blowing an led and try it. If it doesn't work just sell the driver on and buy a variable voltage fixed amp driver like the ones I suggested above. I am no expert, just share a similar interest to you and am filling you in from my research and basic understanding of electronics.
 
rolexbene said:
If i was to have a 12v 900ma power supply it would work?
Yes any DC power supply running at 12v 900ma or less will work

its the fact this power supply runs 5a (even though its 0-5a) will blow the one LED?
Yes I believe it will blow 1 led but am not 100%, maybe try asking the sales person.

if i split the amps over 5 or 6 12v LED's then is safe?
I beleive it is safe, Ian_m does not for some reason. Guess your just have to risk blowing an led and try it. If it doesn't work just sell the driver on and buy a variable voltage fixed amp driver like the ones I suggested above. I am no expert, just share a similar interest to you and am filling you in from my research and basic understanding of electronics.
Click to expand...

Its ok, i dont mind blowing stuff up, least we will know for sure. :)
 
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