Safe method to test my crees?

[boxy]

As a new member, i'd like to request a safe method of testing my 10 new crees, from DX. ive heard all crees are different and i have a multimeter... how do i measure the current draw from for example my large collection of nimh AA's. If i fully charge a 3 of my 2000mah cells, without a constant current device how do i test them?

Boxy

 

[Lynx_Arc]

test them as in what?
you can run them at the same current levels but the voltages may vary (Vf) you can test them at the same voltage but the current draw may vary too. You can use a light meter and get them to put out the same amount of lumens and check the voltage and current levels. you can compare tints on a white surface.
Not sure what you want to accomplish and why you mention a large collection of nimh cells.

 

[boxy]

I think i may need to add a little detail here, my multimeter has a 10Ah range, i know i need some kind of resistor, what i want to know is what wattage-ohms it should be and how i can measure the relevant details of each led?

boxy

 

[boxy]

i think ive just realised i asked the wrong question. i want to know the Vf of my leds as well as figuring out the lowest current i can run them without needing loads of cooling. i want to make a long running lamp.

I should have said that from the start.

boxy

 

[Lynx_Arc]

Not sure what current you want to run and/or test them at. I am not totally up on crees that much..... but without a clue to what current you want to run them at I cannot (using ohms law) guess what resistor you would need to do this. You can put the meter in series when you get your resistor value based upon what current drive level you want. Make sure if you are driving them hard to use proper heatsinking or you will fry them. I am not sure if you have emitters or stars either.

 

[Lynx_Arc]

i think ive just realised i asked the wrong question. i want to know the Vf of my leds as well as figuring out the lowest current i can run them without needing loads of cooling. i want to make a long running lamp.

I should have said that from the start.

boxy

to know the Vf.... you need to know the bin of them first.
long running lamp means ?
be more specific... I cannot guess if it is a nightlight, a reading lamp, area light 3 lumens 15 lumens... 35 lumens... you could run it from 5ma current to 200ma.
how long is long? 8 hours? 3 days?

 

[boxy]

ok, regardless, i would in a perfect world like to power these leds with ten 2000mah nimh's for ten hours. with the option of an emergency setting which should run for 5 hours if held. Also 10 crees is a max boundary for this lamp, not a minimum. My reasoning for this lamp, if it makes more sense this way, is that leds are more efficient, cooler and long living the less you power them with.

Boxy

 

[boxy]

damn it, i still never said the bin. they are xre q5

 

[boxy]

damn it again.

I didnt say what i want this for.

I live in a basement with a lot of computers, and few windows.

The computers have half a day of ups power, but i cant see in the dark.

Boxy

 

[boxy]

actually, if my specifications will give too much light-current draw for indoor use, then please feel free to advise me. (i have a suspicion)

Boxy

 

[Doh!Nut]

OK we are getting there :wave:

You want a light that will allow you to work with your computers after you have lost power and the PC are working on UPS.

If you just need to see a keyboard then you need very little light.
You could use a pair of used AA alkaline batteries to give 50-100 ma to the LED to heatsink this you dont need much, gluing the LED to pretty much any bit of metal would work, I am sure you could get some perforated metal from a drive cage or some other bit of PC hardware to dangle the LED from the top of the screen.

If you are talking about lighting the whole room then I would be mounting 3 LED on an old CPU heatsink wiring them up in series and running them off 8AA NiMh, this should give 3.2v across each LED. You can then place these around the room.

Depends how often you are thinking of using these lights if it is a weekly occourance then you will want a lot of light and NiMh are fine. if it is once every 6 months the batts will have discharged too much so I would use AA alkaline.

Nick

Also if you look at a camping store you can get a "Leisure battery" looks like a big car battery but designed for deep discharge- you can relatively cheaply increase your UPS capacity this way.

 

[Lynx_Arc]

what do you NEED to do with these computers and how much light as DN suggests... do you actually need? If you only need to get around you don't need 10 crees to light things unless you have a rather large place and need to see it all at once. You could get by putting 1 cree over a 10x10 area at 50-200ma if you only need to get around there. Now if you were working on things you may want more but IMO wiring up 10 LEDS for backup lighting may be overkill when you could get a nice headlamp and strategically place batteries/cree setups in a few spots like some lanterns.

 

[boxy]

excellent ideas doh!nut except for a few minor details. I do get frequent power cuts, but i need to live here too. I can boil water from gas for a drink, but my favorite lady wouldnt like torch mode for long. What she needs is a 3 room batterybacked system, possibly charged from the ups 12v (i just thought of that) which can be turned off one room at a time.

Boxy

 

[Lynx_Arc]

I think what you really need to do is experiment with the crees. Get a variable resistor and heat sink one of them, get a flashlight on and turn the lights off.... adjust the cree up some with your hand on the knob and an eye on the ammeter and crank it up looking at the current and walk around seeing how much light you got.

 

[boxy]

lynx, no these leds will almost never all be on at the same time i think.
one in the bathroom
bedroom,
lounge,
kitchen,
one end of the hallway
the other end
the porch,
the cupboard at the end of the hallway.
maybe an alternate one in the kitchen and in the hallway.
never all at the same time.
maybe 4 at the same time for short periods.

Boxy

 

[boxy]

HAHaha. that was exactly why i made the original post.

any suggestions of resistors (high power enough) to run a cree q5 at various currents( i have a box of variable resistors)without making magic smoke?

Boxy

 

[boxy]

what i DONT have is any high power resistors

 

[Lynx_Arc]

I would need to do research to give you numbers and instead I need to get some sleep I have been up all night. If someone that knows everything about crees doesn't fix you up I will see what I can figure out in the afternoon. Try two nimh AAs on them (if they are stars for fun..... should be ok for a minute or so if the stars don't get hot and you can get a clue how much light you would get at lower currents as I am guessing you will get between 40-120ma to the LEDs which will be brighter than you expect. 3 AAs will drive the crees hard perhaps 1.5A or more not recommended without serious heatsinking as I have read people have driven crees at 2A with serious heatsinking but that would be a lot brighter and less than an hour runtime for you lol.

 

[boxy]

let me think about this, if i start the variable resistor at max ohms, the led should be dim right? assuming i run it at 3.6v 3x aa nimh. zero ohms, (turning the other way) should be near the direct drive voltage?
as long as i keep the resistance high the brightness will be dim?

how can i drive this system at a low say 100ma per led? i'll do testing, but i need to know.

Boxy

 

[boxy]

sorry lynx, i keep posting after you reply to me.