# Power Supply for Testing and DIY projects

I recently got sucked in to the world of high output L.E.D. lights and I would like to use my adjustable power supply to test led and laser modules. My question is how many mA should I set my power supply at ? I would like to simulate various battery set-ups ranging from a single 3.0V CR123 to double 4.2v rechargeable 16340s and 18650s. Do I need to double the mA for each additional module I have connected? I know some of my P60 modules can draw up to 1.4mA so how many mA should I feed them. Thank you in advance this site is great.

Hi K&L! Welcome to BLF! The answer probably depends on whatever batteries your are simulating, but also not enough to fry the driver or LED. I've never tried to use a power supply, but I think it could be a good way of doing some tests.

I just did some tests on a single AA light that was drawing 2 amps from a NiMH battery. But 2 amps from a lithium-ion battery could cause some serious problems. With LED's the more voltage supplied to the LED, the more current they will draw.

Seems like the best route would be to test the draw on batteries first and then apply that via the the power supply. Be aware that there is a significant voltage sag with most batteries, so if possible you should measure their voltage and current under load (rather than the voltage at rest which will be a little higher). Some of the reviews of lights here show voltage and current readings, so that might be some help too.

If you have a variable power supply, you can set voltage starting at about 1.5V or 3V depending on what kind of battery it's assumed to use. If the light lights up brightly, it means it's got a boost circuit. If not (ie buck driver), start at about 3V and move up until the led goes bright. Rechargeable lithiums are assumed to be using about a 3.5-4v source.

The other number you're going to be looking at is the current display next door. This will tell you when to stop. Power to the circuit or led is current times voltage. So 3V * 1A = 3W. These high flux led's are all about 3.5W or so (actually 1A to the emitter, but you won't know at this point unless you stick the supply right onto the emitter/star, so we assume a conservative Vf of about 3.5v at 1A), or 5W for cree xp-g's. You have about 20-30% or so extra on top if going through a driver, so don't go too far over 4.5W into the circuit. So assuming a typical led, if you're applying 4.2V into a driver, don't go too far over 1.1-1.2A. You probably won't kill anything though unless it's way overkill and for a long time, and the led will warn you by turning blue-ish, so no need to be to skittish. If a module is regulated to high voltages, what'll happen is as you apply more voltage, the current will drop correspondingly, so the product (I * V) will keep under the max power up to when it stops regulating.

When you have more than one led in parallel, used same methodology but you can assume about twice the current. In series, use double the Vf assume above and same current.

Ok, that makes perfect sense. Most of my current light are P60 hosts with XP-Gs.Now I can test before I decide which batteries and how many I will use. I think my next project will be lighting my salt water aquarium with XP-Gs so this info really helps. I will use the power supply for now but I hope to find a transformer that can do the job. Thanks again.

I don't think using LEDs to light an aquarium is the best idea - you need UV for a salt water aquarium if memory serves. For general illumination it'll be fine but for living rock and the like you do want UV.

My previous coral reef set up was successful using a halide with a kelvin rating ranging from 5000K-8000K in combination with a power compact flourescent actinic 50000K bulb. My main goal is to utilize XP-Gs to replace the power hungry heat making halide. If I can find leds to replace the PCF actinic that would be nice too.

I'd take a look at the LED grow lamps, they might serve well in conjunction with a more actinic light source. And would have to be cheaper to run and buy than metal halide bulbs. If you can see how one is put together it might give you ideas to suit what you want.

I don't think anyone makes LEDs with a very short wavelength/very high colour temperature that can output any real power which a marine tank is going to need.

My local aqaurium store is bragging about how great their new Cree light set ups are but they start at \$150 for a 5 emitter light. They are called Aqua Rays and I found some info about them at americanaquariumproducts.com. The company who makes the claim they are the only ones who have access to the correct bins but it looks to me like many of the color temps are the same as on Cree's datasheets. I plan on testing on a small 25 gallon that is only about 18" deep and I'm hoping to make a equil or more powerfull light for less \$. Cool White XP-Gs are listed at 5000k-8300k on the Cree datasheet so I'm thinking I can replace the halide with them. Please correct me if I am wrong or missing some factors. Thanks again and sorry this went down the aquarium path but I do plan on using budget light parts. I have been testing my flashlights with my power supply thanks to everyones help.

Take note that the spectral output of led's are not the same as other sources, and I would think that may be important for your application (I assume this needs to approximate sunlight). Temp is a derivative number. They're all blue led's + phosphor, so they have a peak at blue plus a lower magnitude spread at a lower frequency. Google for white led spectrum images.

Ps. 5000K-8000K above generally means a shifting spectral output. I don't have time to explore this now, but this is not the same as a range for different cree bins).

So I took a quick look at aquarium lighting requirements, and it does seem led's are a good way to go. The peak at blue matches actinic req's (I presume because of the way water filters light), and you get a daylight spectrum from the phosphor. Cree's cool or outdoor white bins seem about right depending on how much plants you have.

To get the right bins, buy at cutter.com.au. But to be fair, \$150 for 5 led's is not really overpriced for an engineered prefab solution. You'll need drivers, transformer for them, enclosure, and your time to make it.

The cheapest ways to to go:

Custom solution is to either get 5 or so led's and a serial driver on dx. This makes the equivalent of this http://www.dealextreme.com/details.dx/sku.35242, but you can pick the bin. You'll also need a heatsink because the are about 3-4W each max and you'll be runnnig them constantly.

or

You can consider MR16 type bulbs

http://www.dealextreme.com/details.dx/sku.30208

These are often 12V input but you can probably find AC ones.

The problem with buying these cheapies is that bin is a bit of a crapshoot. But on the plus side, it might be cheap enough to get some mr16 enclose and a couple samples of them off ebay or dx to try out to see how they work out.

Thanks for taking the time to check out the subject. I feel much better about my DIY project now that I have some advise from an knowledgeable person like you. I just happen to have some of those MR16 leds that I bought to replace some standard MR16 but they didn't fit the fixtures I wanted to put them in so I will start by giving those a try. Thanks again.

Thanks for taking the time to check out the subject. I feel much better about my DIY project now that I have some advise from an knowledgeable person like you. I just happen to have some of those MR16 leds that I bought to replace some standard MR16 but they didn't fit the fixtures I wanted to put them in so I will start by giving those a try. Thanks again.