LED Driver Calculation Check PLEASE!!!

[ToTaLCHaoS13]

So I'm finally getting around to building my lights and would appreciate some feedback/verification of my calculations. The system will be over a 72X24X24 SPS setup. Here is the plan:

Run three strings of lights
- (48) Cree XPGWHT-L1 Cool Whites w/ 40' optix
- (48) Cree XPEBLU-L1 Blues w/ 40' optix
- (48) Cree XTEARY-00 Royal Blues w/ 40' optix

Each string of 48 LED's will need ~168V max and will be run at 700mA current. Knowing this I am looking at using an Inventronics EUC-120S070DT, 120 watt, 700mA dimmable constant current driver on each string. Sound correct?

I'm comfortable with the high voltage and everything else since I plan to fully insulate the fixture and pot all LED's. My only concern is whether I should go with a higher voltage driver so I don't run any risk of running out of voltage if additional LED's are necessary. On the other hand I want to get the most life, least heat possible on the drivers so loading closer to the max voltage is better, right? The next size up driver jumps to 200W which would mean my 48 led strings would be pulling very close to the low end voltage for them.

Please let me know if my calculations are off anywhere or if I am missing any key points in my plan.

[kcress]

So I'm finally getting around to building my lights and would appreciate some feedback/verification of my calculations. The system will be over a 72X24X24 SPS setup. Here is the plan:



Run three strings of lights
- (48) Cree XPGWHT-L1 Cool Whites w/ 40' optix
- (48) Cree XPEBLU-L1 Blues w/ 40' optix
- (48) Cree XTEARY-00 Royal Blues w/ 40' optix

The numbers show you need about 108 LEDs. You're a bit bright here.
You will simply HATE that many Blues. Most people regret having more than a few and generally few people use any when they have lots of royal blue. If you like blue, and you're sure shaping up here to look like you do, then you want 1/3 Neutral Whites and 2/3s RB. You can swap out a few RB for B if you feel you must.

Each string of 48 LED's will need ~168V max and will be run at 700mA current. Knowing this I am looking at using an Inventronics EUC-120S070DT, 120 watt, 700mA dimmable constant current driver on each string. Sound correct?
Correct? Absolutely not! Any solution that includes a voltage higher than 50V is unacceptable. We're talking about life safety here. A reach for simplicity at the expense of safety is a bad plan. This has been covered about 2 dozen times in these fora. The risk of 50V+ in our DIY fixtures that hang over bodies of water and are touched by unprotected humans is excessive. You should redesign for 48V max drivers.


I'm comfortable with the high voltage and everything else since I plan to fully insulate the fixture and pot all LED's.
I'm sorry but you have no idea how ludicrous this type design is. The cost and hassle of a "fully insulated fixture and potted LEDs" vastly exceeds just doing the job correctly in first place. LEDs fail - believe it or not - how do you figure out which one has failed when they're all "safely potted"?!? That's just the beginning of the folly. Heat removal, optics adjustment, service, and upgrading are all lost with the gross burden imposed by potting. Not to mention the additional costs.

I suggest you try building a modest safe system for your sump or something else so you can get some hands on experience. You'll soon see why 99% of us build safe and sane and inexpensive 48V systems.


Please let me know if my calculations are off anywhere or if I am missing any key points in my plan.
There you have it. :D

[ToTaLCHaoS13]

Thanks Kcress. I appreciate the feedback. What formula did you use to determine how many LED's I should use? Also, with the lower voltage drivers, do most people not even cover up the wiring connections at all? That seems kinda scary to me...

[mcgyvr]

Thanks Kcress. I appreciate the feedback. What formula did you use to determine how many LED's I should use? Also, with the lower voltage drivers, do most people not even cover up the wiring connections at all? That seems kinda scary to me...
In general..The resistance of the human body does not allow one to be shocked under 60VDC. I work in the telecom industry where 48VDC is king and routinely touch live bus bars,etc... Now drop a wrench across those bus bars and you will watch it vaporize before your eyes.. But in general, under 60VDC is considered an SELV circuit (safety extra low voltage) and poses MUCH less risk than anything over that.

Now.. is there anything wrong with LED drivers above the SELV limit?.. No.. Are there additional dangers,etc.. that make them not suitable for inexperienced users?.. YES
Can fixtures with higher voltage LED drivers be made fairly safe?.. Sure.
Its just frowned upon here because of the level of experience/skill of most DIY'ers here.

[ToTaLCHaoS13]

Mcgyvr, that was by far the most useful explanation I have ever recieved regarding voltage. Thank you.

On another note, I've now spent 6 hours reading threads arguing whether LED or MH is better. Would like to say it's been helpful but frankly am more confused about what direction to go than I was before... I now remember why I lost the desire to pursue this a year ago...

[kcress]

Thanks Kcress. I appreciate the feedback. What formula did you use to determine how many LED's I should use? Also, with the lower voltage drivers, do most people not even cover up the wiring connections at all? That seems kinda scary to me...

Hi hi hi.

The rewlofthumb for Cree style LEDs when lighting tanks of 24" depth or less is all about area. Length x Width
Your tank 72" x 24" = 1728 sqin.

Now for:
FO tanks. (Fish Only)

Area/20 = number of LEDs

Soft Coral tanks

Area/18 = number of LEDs

For SPS tanks
Area/16 = number of LEDs.

Your case 1728/16 = 108 LEDs

Now this RofThumb also expects:
No optics
LEDs within about 4 inches of the surface
XPG whites
XTE RB
All LEDs driven at around 700mA.

Given these facts most people will enjoy and the tanks will thrive with about 36 NW and 72 RB.

Choosing to live buy using 48V drivers means your strings can be at most: 48V/ 3.3V = 14LEDs

I'd probably run three strings of 13 for the white. Perhaps I'd include 2 WW and 2 CW in with the other 8 NW of each white string.

For the blue side I'd run 5 strings of 14 LEDs. You could add in maybe 1B to the other 13RB if you're after a "20k" look.

Of course you need to follow the parallel string build rules.

I suggest you read thru this very complete build thread. Please note the very detailed description of how you pre-flight a build BEFORE you ever power it up. Done correctly there are is NO drama associated with your first power up. (Unless you fry your retinas. LOL)

http://www.reefcentral.com/forums/showthread.php?t=1973462


As for drivers use whatever sub-50V drivers you want. Keep in mind that you really don't want more than about 6 drivers that don't have power factor correction (PFC) inputs running in your house.

Your build could be done with 2 ELN60-48 Meanwells running the whites. That would be two strings on one and one on the other. The parallel strings would need the fuses and resistors. The parallel strings would run at 650mA each instead of 700mA. This would be just fine.

Then on the blue side you'd run 3 ELN60-48. Two of them would have parallel strings. The third wouldn't.

The above layup has an added benefit. Since drivers down ever fully dim you still have a snap off and on to 10%. You can mediate that by letting your paralleled groups shut off first. This dumps off 6/8s of your LEDs leaving only two strings 1W and 1B to dim down to snap-off. This, of course, requires you spread around your last two strings to cover your tank.

Other points.
If you use optics around 4 inches above the water make sure they're W I D E or you can get disco - an undesired result.

If your fixture is going to be higher than 6" you need to use optics. Widmer in here did a spectacular build that he mounted directly against the ceiling and projected the light down in to his tank using optics. That's really nice because it gets the fixture entirely out of the field of view - the tank just appears to glow.

Other points. You should only have one cord going to your build. It's the law (for good reason) and it looks cleaner too.

Under 14" from the water you MUST include a shield in front of your fixture or it will degrade swiftly from spritz contamination.

Do your best to keep the LED domes cool.

[TropTrea]

In general..The resistance of the human body does not allow one to be shocked under 60VDC. I work in the telecom industry where 48VDC is king and routinely touch live bus bars,etc... Now drop a wrench across those bus bars and you will watch it vaporize before your eyes.. But in general, under 60VDC is considered an SELV circuit (safety extra low voltage) and poses MUCH less risk than anything over that.

Now.. is there anything wrong with LED drivers above the SELV limit?.. No.. Are there additional dangers,etc.. that make them not suitable for inexperienced users?.. YES
Can fixtures with higher voltage LED drivers be made fairly safe?.. Sure.
Its just frowned upon here because of the level of experience/skill of most DIY'ers here.

There is only one big probl;em. I personaly have gotten some serios electrical burns from 48 Volts DC. There are other factors that must be considered than simple body resistance. With a salt watrer enviroment the electricity takes a path over the surface through the salty water that can be on your skin.

[TropTrea]

Hi hi hi.

The rewlofthumb for Cree style LEDs when lighting tanks of 24" depth or less is all about area. Length x Width
Your tank 72" x 24" = 1728 sqin.

Now for:
FO tanks. (Fish Only)

Area/20 = number of LEDs

Soft Coral tanks

Area/18 = number of LEDs

For SPS tanks
Area/16 = number of LEDs.

Your case 1728/16 = 108 LEDs

Now this RofThumb also expects:
No optics
LEDs within about 4 inches of the surface
XPG whites
XTE RB
All LEDs driven at around 700mA. .


Again there are no hard rules here. I have a 40 Breeder tank which is 36" X 18" and per your formula should be using 40 LED's for SPS corals. I'm running only 24 and have great color growth and color. My combination is also 8 Blues, 12 Royal Blues and 4 Neutral Whites. Yes the tank is bluer than moany people like but the coral colors floresce fantasticly including the red. Also color has a lot to do with personal choice. Remember your adding the Royal Blues and Blues for the coral then suplementing with white to appeal to your eye.

[TropTrea]

Some other thoughts you may want to consider. Running the LED's at 700ma like Cree mentioned would be roughly 2 Watts for each LED. The XPG's can be run safely up to 5 watts reducing the number of LED's you need in almost half. There are also newer more effecient XM-L LED's that will run safely at 10 Watts. Using either of these on your Whites would allow you run all your whites off of one driver like an HLN 90 series from Meanwell. For your blues you can ruinn them all off of one HLG 185 driver if you how to work parrellel and series strings together.

[gbru316]

In general..The resistance of the human body does not allow one to be shocked under 60VDC. I work in the telecom industry where 48VDC is king and routinely touch live bus bars,etc... Now drop a wrench across those bus bars and you will watch it vaporize before your eyes.. But in general, under 60VDC is considered an SELV circuit (safety extra low voltage) and poses MUCH less risk than anything over that.

Now.. is there anything wrong with LED drivers above the SELV limit?.. No.. Are there additional dangers,etc.. that make them not suitable for inexperienced users?.. YES
Can fixtures with higher voltage LED drivers be made fairly safe?.. Sure.
Its just frowned upon here because of the level of experience/skill of most DIY'ers here.


100 mA is enough to stop the heart. External skin resistance is as low as 100 ohms when wet with saltwater internal resistance is as low as 85 ohms. With resistance in that range, a 9v battery could potentially kill.

Have fun playing with your bus bars bare handed (I hope you use the back of your hand as opposed to grabbing them). It only takes one accident to end your life.

Per OSHA:
5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.

6-30 mA Painful shock, muscular control is lost. This is called the freezing current or "let-go" range.

50-150 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.

1000-4300 mA Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.

10,000 mA Cardiac arrest, severe burns and probable death.

OSHA electricity dangers (http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html)

But, I'm sure you knew all that, and your statements were made out of complacency and "It hasn't hurt me yet" mentality, versus proper techniques and training.