White LED, crazy idea... or not?

[Dan Euritt]

<<<-- Originally posted by Mike Rehmus : So I'll go with the 12 V LiON pack for $90 (with charger and cables) as the power supply. IT has 4,000 milliamps of capacity -->>>

i use the rayovac nimh 15 minute rechargeable aa batteries to power the in-car camera rig... i believe that they are at least 2,000 mah each, ~1.26 volts, ~$3.50 per battery at walmart.

that's a lot more power, for a lot less money, than you'll ever get with lithium ion... and lithium ion is rated as "Moderate discharge current - not suitable for heavy loads" : http://www.batteryuniversity.com/partone-5.htm

lithium ion may have a slightly better charge density, but it comes at a steep price.

another ~$5(?) in radio shack battery holders, and you can mount those aa's anywhere you want.

using an ampmeter and a voltmeter, i tested several of those nimh in series at a .632 amp drain... they lasted somewhere around an hour before the voltage started dropping significantly, and upwards of two hours before the voltage dropped enuf to threaten shutting down the recorder.

[John Gaspain]

what do you think of these, 100 loose leds?

http://cgi.ebay.com/ws/eBayISAPI.dll...835189145&rd=1

or the semi-truck backup lights. I know these are BRIGHT!

http://cgi.ebay.com/ws/eBayISAPI.dll...488334437&rd=1

im thinking the backup lights are the way to go, you get 2 light modules for a total of 80 lights for 80 bucks! already in a waterproof housing!!!


or a smaller 27x2 led lights
http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW


http://or use these as hair lights<b...category=33713

[Mike Rehmus]

<<<-- i use the rayovac nimh 15 minute rechargeable aa batteries to power the in-car camera rig... i believe that they are at least 2,000 mah each, ~1.26 volts, ~$3.50 per battery at walmart.

that's a lot more power, for a lot less money, than you'll ever get with lithium ion... and lithium ion is rated as "Moderate discharge current - not suitable for heavy loads" : -->>>

Since the 42 LED lamp draws a measured 79 ma, I don't think I'll have a power discharge issue with the LiON. 4,000 mah (this particular battery) will always beat 2,000 mah, I think.

You will need 10 of the nimh to get to the minimum 12 volts this lamp requires . . . that's $35 and to equal the power density of the LiON, you will need two sets to get as long a run time.

So that's $70 plus you have to purchase the battery holders, make up a cable, and buy a charger which is another $15.00 or so. Except I've not found a charger that will handle 10 batteries at once so you require 2 chargers to keep the batteries up in sets. (assuming you want an equivalent run-time from the lamp)

This LiON comes in an enclosure that is visually nice, not a group of battery holders that themselves need a housing. Charger was included as is a very nice detachable coiled cable to carry the power from the battery to the lamp. I can easily velcro the battery to the handle of my PD150 camera or to the back of the battery, alongside the wireless receiver, on my DSR-300.

Since this rig will be seen by my customers, it is, I think, the best way to go right now.

What I'd like to have is something that is light and contains the lamp and the batteries without adding lots of pounds to the top of the camera. Hence the desire for pancake batteries because they stack so easily.

I'm not against nimh and use them in quite a few applications. They just offered no advantage in this application and they have to be packaged, a significant time consideration.

When you say your in-car rig, what are you powering?

[Mike Rehmus]

<<<-- Originally posted by John Gaspain : what do you think of these, 100 loose leds?

http://cgi.ebay.com/ws/eBayISAPI.dll...835189145&rd=1

or the semi-truck backup lights. I know these are BRIGHT!

http://cgi.ebay.com/ws/eBayISAPI.dll...488334437&rd=1

im thinking the backup lights are the way to go, you get 2 light modules for a total of 80 lights for 80 bucks! already in a waterproof housing!!! -->>>

The way they get very bright white LEDs is by making the phosphor coating very thin. That does two things:

It drives the color temperature way up because more of the blue LED light 'sneaks' through the phosphor.

The phosphor 'wears out' more quickly since there isn't as much of it.

If a LED is rated at 100,000 hours, the light output at EOL is less than 1/2 the starting output. Unfortunately, the drop off starts fairly early in the life of the LED. The good news is that none of us will probably even get to the start of the drop off curve.

There is a distinct lack of important information about the two items you cite.

- No spectral info other than 'white'
- No disbursion information, e.g., how wide a beam do they create (although the picture of the individual LEDs shows a strong lens which suggests they may have a very narrow beam).

Especially without spectral information, you don't know what you are getting. Can you afford $80 for an experiment? If so, please let us know how they work out.

[John Gaspain]

ya...if I do get em, how can I measure color temperature?

[Giroud Francois]

an easy way to drop down voltage is to insert a diode into the line. Usually you loose about 0.7V per diode.
You can find diodes supporting several amps very easily and it cost almost nothing. The only issue is the voltage drop is permanent so when the battery goes low you still loose power when it is unneeded.
The top of the regulation is to use a low-drop regulator.
this is a one chip module that can regulate anything with a 0.5v loss. you just need a resistor to set the voltage you want.
They are usually pretty expensive (about 10-15$ ) and must be mounted on an aluminum cooler, but it is still a cheap solution.
I use some of them to get 12V from my li-ion 14.4 cells.

[Mike Rehmus]

And they are fairly efficient (although I haven't measured one and don't remember the real numbers.

Color temperature is difficult as a spectraphotometer isn't something we normally have hanging around. They are made but the are expensive.

My DSR-300 gives me the color temperature when I white balance it so that's what I use.

[Dan Euritt]

<<<-- Originally posted by Mike Rehmus : 4,000 mah (this particular battery) will always beat 2,000 mah, I think.

You will need 10 of the nimh to get to the minimum 12 volts this lamp requires . . . that's $35 and to equal the power density of the LiON, you will need two sets to get as long a run time.
-->>>

one of us has the math wrong... 10 nimh aa batteries @2,000 mah each = 20,000 mah total; but then again, it's been years since i looked at my dc power formulas!

the power density actually refers to how many mah are in equal-sized physical containers... nimh aa vs. lithium ion aa, for instance... i think that's a win for lithium ion, assuming you can get that technology in aa's.

you are right about the current drain, tho... it's not going to be a problem for lithium ion!

i can get 4 nimh aa's + charger for $28 at walmart... so for $90, i can re-charge my entire 20,000 mah power supply in 15 minutes... you'll never be able to do that with lithium ion! there are also covered aa battery boxes available that will clean up the way things look, but yeah, it all has to be custom-assembled.

i've been looking at doing led lighting for the in-car camera rig... i need to match the interior illumination to the outside... i'm running a sony xc-999 lipstick camera mounted to an i/o port rollbar mount, recording to a full-on 6 mb/s solid state mpeg2 recorder, no videotape at all... i built a stereo pre-amp as well, mounted all that stuff to a custom aluminum rig that zip-ties to the rollbar... i think that it'll stand up to just about any vibration.

[Giroud Francois]

actually, if you speak about AA cell, it is only 1.2V, so you need to chain 10 of them to get 12V.
when chaining cells, voltage adds up but current (mA) stay the same. to add current, you need to mount all celes in parallel.
you better need to try 3.6v li-ion elements who offers the best capacity versus weigth/size ration.
unfortunately they requires special chargers.
They are easy to find as you can get them for free from defective Laptop battery packs. Most of these packs have one dead element thar renders them useless for the pc, but once dismantled have still enough value to justify the spending into a li-ion charger.

[John Gaspain]

Alright im gonna take the plunge on some "Backup lights" $80 bucks no biggie. If it doesnt work I'll have some big flashlights. Im gonna go to a truck stop and try to get just one. Im gonna follow smoe truckers around and see what they look like. LOL

on second thought, I may just go buy a Britek...

[Dan Euritt]

you guys are right about the batteries in series... i'd have to have 20 of 'em to equal that lithion ion pack... ouch!

i have read that lithium ion has an optimal weight/size ratio, so that 3.6v thing makes sense.

is there a dimmable function to any of this? would the color temp change? maybe you could just turn on or off additional rows of lights instead.

[Mike Rehmus]

Between their rated 14 and 12 VDV operating voltage, the light does change. But there isn't an output control mechanism that really works other than switching LEDs in and out of the circuit.

The problem with that is that unless the LEDs are set up for diffuse light in the first place, you might notice a 'hole' in the light cast by the fixture. the output from a LED is, depending on the lens (which mainly controls dispersion) molded into the top of the LED, very columnated.

[Ignacio Rodriguez]

Would not the brightest thing to do (pun not intended) be set up the LEDs in arrays that need a low voltage (i.e., no serializing or only in pairs) and use a voltage regulator circuit?

[Mike Rehmus]

Ultimately, perhaps. But you cannot get too low as the forward voltage requirements of an LED is 3.5-4 volts. So you could chose to put two of them in series and match the 7.2 volts of a camera LiON battery. Maybe. Not very much voltage margin

But the quickest way to get underway with very limited time is to purchase an array of LEDs already in a lamp housing. Without asking for a special product, the lowest voltage range they offer is 12-14 VDC. Makes sense since so much of the world has 12 volts available.

Furthermore, I have not yet found a reliable source of warm white LEDs and don't want cool white for this application.

Beyond that, you have to decide what style of lens you want on the LEDs otherwise they all seem to come with a very narrow beam disbursion which doesn't work too well for videography.

Finally, this lamp came with all the correct LEDs, matched, tested mounted in a standard fixture and, BTW, bi-polar.

A lot of features for a relatively low cost.

[Mike Rehmus]

Update - The LiON battery has been powering the LED lamp for over 8 hours now and looks like it would run another 8 to 16 hours before the battery reaches depletion.

Good enough for a town this size.

BTW, the battery weighs just over 12 OZ, is about 6" long by about 1.5 by 1.75 inches in cross section with a 4 LED charge indicator. Its output is switchable in several steps between 3 and 12 volts.

Also came with a very nice leather pouch with a belt clip and D-rings for hanging it from a strap. The pouch also has a pocket for the output power cord. Power cord is a coil-cord and will stretch to about 4 feet or so. Charger appears to be intelligent and is a wall-wart. A cigarette lighter charger was included so one can charge it while in the car.

Now all I have to do is complete the enclosure.