LED lighting on a budget!

[fishoutawater]

Would it be feasible to shape/make a heat sink like a reflector is made? Allowing you to aim the LEDs? I was thinking that if you could keep most of the light off of the glass it would drastically cut down on the algae scraping. I think it would also minimize the "tank" look, like LFP did on his xenon lighting fixture.

 

[der_wille_zur_macht]

Would it be feasible to shape/make a heat sink like a reflector is made? Allowing you to aim the LEDs? I was thinking that if you could keep most of the light off of the glass it would drastically cut down on the algae scraping. I think it would also minimize the "tank" look, like LFP did on his xenon lighting fixture.

Yes, that's a reasonable idea - but don't forget about optics. They can play a HUGE role in controlling where the light goes.

 

[Toppy]

Hello from Spain:

Has anyone considered this?

http://www.dealextreme.com/details.dx/sku.3146

There are also available at 1050mA

Thanks!

 

[der_wille_zur_macht]

That would be a very bad choice for large lighting arrays for several reasons. Mainly, you're taking an "overhead" hit to efficiency for each LED instead of for a large string of LEDs. Also, the IC that design uses for current regulation has (IMHO) fairly unsuitable tolerances, and since there's TWO of them to get the 700mA target, the tolerances are even wider.

Lastly, by the time you find a suitable power supply, it's likely not going to be much cheaper than an off the shelf driver, much less a "cheapness optimized" DIY effort.

 

[Toppy]

Thanks!

Is this variable resistor similar as the one on the original post?

http://cgi.ebay.es/10-ohm-Precision...tem&pt=LH_DefaultDomain_0&hash=item3a58d74acb


PD: Sorry about my english, it is not my mother language.

 

[der_wille_zur_macht]

Those are tiny little trimmer pots. You want big meaty power resistors. See this comment:

There is one other thing we must not forget. That's the power rating of the resistor. It tosses away power to drop that needed 1.5 Volts. We need to make sure it is physically big enough to handle the needed power.

We calculate the power that will be dissipated. 1.5V X 0.7A = 1.05W or 1 watt. Now the rule for sizing resistors is to always double its power rating. This means we want at least a 2W resistor. This keeps the resistor cooler. It could still be too hot to touch but that's OK.

You can't ignore the power rating on the resistor or it'll burn up. I don't see a power rating on those trimmers you posted, but I would guess it's a tiny fraction of a watt.

 

[Toppy]

I can´t easily find 10 ohm variable resistor with decent power rate. May it be 25-50 ohm ? Will it be precise?

Thanks

 

[kcress]

I think I provided a link to the resistors above.

 

[Toppy]

I think I provided a link to the resistors above.

It´s true, but I´m in Spain, and I don´t locate a reseller in Europe, so I am looking for a similar resistor.

 

[Toppy]

Please don´t let this thread die!

 

[kcress]

I can´t easily find 10 ohm variable resistor with decent power rate. May it be 25-50 ohm ? Will it be precise?

Thanks

It needs to be an adjustable power resistor like the one I suggested. If Digikey is not a solution for you you would need to hunt around for whatever stands in for Digikey in your area.

If you are just building one or two strings you might be able to find some equivalent resistor at a surplus electronics site.

Most component manufacturers have world-wide distribution networks. You could look at the Digikey part, find the manufacturer. Go to the manufacturer's site and find who distributes for them in your location.

 

[stancfii]

I'm trying to figure this all out and put plans together, so let me know if this would work.

1.) A 24V 2.65A power supply could potentially run 7 strings of 8 LEDs that are 3Vf and 350mA (i.e. the Cree XP-G cool white).

2.) If 8 of the 3Vf LEDs are on one string, no resistor is needed, just a CB.

3.) Instead of 8 XP-G, I could run 6 XP-E on a string (they are 3.2Vf), with a resistor.

4.) Can 3.2Vf and 3Vf bulbs be mixed on a string as long as total Vf<24 and a resistor is used?

5.) Since I will not be using 7 strings (maybe 4), do I need to have something do dissipate the remaining amperage?

Thanks

 

[kcress]

I'm trying to figure this all out and put plans together, so let me know if this would work.

1.) A 24V 2.65A power supply could potentially run 7 strings of 8 LEDs that are 3Vf and 350mA (i.e. the Cree XP-G cool white).

Yes except you are pushing the limits of 8 of those LEDs against 24VDC since the values they give you for LEDs are averages only. Bank on 7.

2.) If 8 of the 3Vf LEDs are on one string, no resistor is needed, just a CB.

CB? If you mean fuse I would still use one because if your LEDs ever fail shorted the current just climbs and climbs. A fuse halts this and either the loss of all LEDs or the loss of your house. You always need a resistor! It's what's controlling the current.

3.) Instead of 8 XP-G, I could run 6 XP-E on a string (they are 3.2Vf), with a resistor.

Yes. Maybe even 7.

4.) Can 3.2Vf and 3Vf bulbs be mixed on a string as long as total Vf<24 and a resistor is used?

Yes.

5.) Since I will not be using 7 strings (maybe 4), do I need to have something do dissipate the remaining amperage?

Certainly not. That supply's amperage number is that supply's POTENTIAL not what it absolutely always puts out. Like your car with a 100hp engine, but you only get what you need/use.

 

[stancfii]

Thanks! I feel like I just passed a physics test Yes, I meant fuse... CB (circuit breaker) was what my fingers typed instead since that is what I see all day in the airplane.

 

[stancfii]

One more question:

I realized that I was looking at a Vf of 3.3 @ 350mA for the XR-E. I see that it is capable of being "driven" up to 1000mA @ 3.7Vf. On a 6 LED string, can I turn down the resistor so that there is more volts per LED (3.7 instead of 3.3) to increase the brightness? I take it this would be the exact same as using a 1000ma buckpuck instead of a 350ma, and I would be forced to have far fewer strings?

 

[kcress]

Certainly! As long as the string voltage remains below the supply voltage and you leave a bit of overhead for the resistor adjustment.

 

[fowlr2reef?]

very informative thread. have finally waded to the end of it. i kinda dont even wanna post on this thread as my brain pan is hurtin now. must assimilate data. syntax error...

 

[fowlr2reef?]

Thanks! I feel like I just passed a physics test Yes, I meant fuse... CB (circuit breaker) was what my fingers typed instead since that is what I see all day in the airplane.

awsome analogy. this thread will make one use their brain. unused muscles are hurting. :thumbsup:

 

[Jandrews]

has anyone ever looked into using 5mm LED's. what is the down fall of using them over the cred

 

[TheFishMan65]

Usually it is efficiency. You need X amount of lumen. I am guessing the 5mm don't put out much so you needs hundred or thousands. Also if look at lumens per watt they are probably very low - so you have big electric bill. Those are the usual answers. If you point to a data sheet I can try and be more specific.