led's and resistors

[funkyfish77]

alrite folks I'm in need of a little help with resistors .i have http://www.ebay.com/itm/220947560986?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 this driver.
specs
Description:

Input Voltage: 85-265VAC
Output Voltage: 46-55VDC
Frequency range: 50-60Hz
Current: 700mA - 1.95A
Power Factor Optimization: >99%(220V), 99.3%(110V)
Efficiency: >88%
Operating Temperature: 0~50°C
Storage Temperature: -20~95°C
Size: 120 x 56mm
Net weight: 236g
Application: 5 x 20W 45mil LED panel in series

and 3 of http://www.ebay.com/itm/220990452654?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

specs
Description:

Color temperature/Wavelength: 3 chips 20500K + 6 chips 453nm Royal blue
Led chips: EPSTAR EDI-EA1143 45mil
Download Manufacturer Data Sheet
PAR reading(Instrument: Apogee MQ-200): 308
DC forward Voltage: 10-11V
DC forward current: 2000mA max
Rated power: 22W max
Viewing Angle: 120 Degree
Intensity Luminous (Iv): 490LM
Life span 50000 hours guarantee

now i have 2 50ohm 10 watt resistors and 1 10ohm 10 watt resistor soldered parallel to give me 8.12ohms on multimeter. ok here's my question if i wired the resistors in series with the leds on the above driver would my leds be ok?

from the calculators I've used online the leds should run at 1.7 A . am i correct in my assumption? any and all opinions welcome

thanks
funky

 

[kcress]

This is a little difficult since like most epay cr@p the specs they give you are lack important details. For instance is that even a current driver? We've seen lots of Chinese "LED drivers" that aren't since they are only voltage sources..

If it is a current driver its minimum drive voltage is 46V. Your LED engines are 11 volts max times three = 33V.

This means you need to totally waste a bunch of power to make up the voltage difference across some resistor(s).
46V - 33V = 13V.

If you run at the maximum current of 1.95A then the resistor needs to be:
13V / 1.95A = 6.6 ohms.

The power dumped here by the resistor is:
1.95A x 1.95A x 6.6 ohms = 25W
That means you need about a 50W resistor to keep it from glowing red hot.

However if you want to turn the current down to 700mA the resistance would need to be:
13V / 700mA = 18.5 ohms.

If you use your proposed resistor stack you will have to run around:
13V / 8.12 ohms = 1.6A or higher.

The stack will need to dissipate:
1.7A x 1.7A x 8.12 ohms = 23.4W
Which means they will toast because you really need a minimum of 2x the power dissipation.

Keep in mind that your "cheap" driver will be absolutely deadly to touch in several places. It will be the most electrically dangerous thing in your house.

Opinion? I think this route is an attempt to save some money while, (not really), by exchanging robustness for control limitations and fewer bits and pieces for a great deal of waste heat and inefficiency. This ultimately puts you into an experimental position with regards to your aquarium inhabitants.



All the numbers depend on the actual LED running voltages at the current you select.

 

[funkyfish77]

kool thanks man . it's not a money thing it's more for me to play with till everything else comes in . i dont know much about this kind of stuff so why not . i'm learning something new i did not know yesterday . thanks agian

funky

 

[mcgyvr]

just buy 2 more leds and be done with it..
or a better driver..
Just do not use a resistor.. That driver is specific for 5 x 20W leds only.


and good on ya kcress for "reminding" him about the unsafe/deadly conditions of non-enclosed drivers. IMO they are NOT for hobbiest DIY projects like these and should not be used or recommended here ever. Even a recommendation to "enclose" them should not be attempted without a decent level/understanding of thermal management. Better to be safe than sorry here...

 

[kcress]

just buy 2 more leds and be done with it..

My sentiments exactly. Then turn them down a bit more.

 

[funkyfish77]

i have 10 more coming soon i was just bored looking to experiment with what i have .i'm not to wild about the open driver ether thats why i ordered meanwell drivers the other day . thanks for the tips .

funky

ps these are not going over a tank just screwing around

 

[kcress]

Man.. That's a relief. Thanks for mentioning that. Onward and upward.