Which P7 emitter for 3 D M#G mod?

[4D223]

Hi all, I am hoping somebody can help me with some advice on what emitter to use in my mod. I am struggling to make sense of all the "Bin" codes etc. I want to use D NiMh batts and DD for simplicity. I have been useing the search function and looking at DSXOJ/emitter/Heatsink combo's at Britelumens and CSXOI at KD. What does it all MEAN. I know how to solder/trim the M#g switch tower down etc but I am NO EE. Just hoping sombody can point me in the right direction.
Thanks in advance.

 

[Justin Case]

The first letter is the luminous flux bin. The middle 3 letters are the tint. The last letter is the forward voltage bin. Thus, DSXOJ is D flux bin (800-900 lumens when driven at 700mA per die), SXO tint, and J voltage bin (3.50V-3.75V). CSXOI is C flux bin (700-800 lumens when driven at 700mA per die), SXO tint, and I voltage bin (3.25V-3.50V).

Normally, you would prefer the I voltage bin. Lower forward voltage means a more efficient LED. However, in direct drive, your goal also is to match the LED's forward voltage with the battery voltage you will deliver to the LED.

3xNiMH hot off the charger can be ~1.45V per cell, so you could deliver 4.35V initially to the LED. Of course, the battery voltage will sag quickly under load, but good D NiMH cells can probably hold close to 1.25V per cell, or 3.75V total.

Thus, a J voltage bin P7 might be a better match for DD using 3xNiMH.

There are no hard and fast rules. It depends on the luck of the draw. You might get an I voltage bin P7 that measures 3.50V at 700mA per die, or you might get one closer to 3.25V. Similarly, you might get a J voltage bin P7 with Vf closer to 3.75V or closer to 3.50V.

Also note that as the LED heats up, its Vf actually decreases, further complicating the issue.

For a few dollars more and not much extra complexity, you could make a 2-board sandwich using two of the simple single mode, 4xAMC7135 linear regulator drivers. Search CPF for "stefanfs", who has a guide on such mods. Then, your LED choice is easy. Get a DxxxI-bin P7.

For tint, SXO is a little blue for my tastes. I prefer SWO, SVO, SVN, and the like. PhotonFanatic in the Dealer's Corner on CPF Marketplace sells DSVNI-bin P7s.

 

[Al Combs]

+1 to Justin Case's advise about using a J bin for direct drive. Even then it's possible to exceed the LED's Vf with 3 D-cells. Do you have a DMM with a 10 amp scale? The 10 bucks it would cost to buy a cheap one is good insurance. I just completed a 2C-Mag using PhotonFanatic's DSVNI P7. I used a pair of DX's 1,400 ma AMC7135 regulators in parallel to get 2.8 amps output. Here is the StefanFS MagLite P7 thread. When I put my DMM probes directly on the LED while running it read 3.28 volts. If you tried to direct drive this LED from 3*D NiMH's it would definitely blow.

If you want to have a look at the bin specs for yourself, you can download a copy of the P7 series binning & labeling pdf from SSC's website. The Emitter Spec's are on the same page and give a better general description of the P7. The B&L pdf lists a graph of the tint code, but being in black and white is kind of useless. Here is a good reference link for the tint of various Bin Codes. Scroll down the page and click on the thumbnail for "SSC Z-Power (All) (Pure White)."

 

[Justin Case]

You could use a current limiting resistor if the LED is being overdriven. However, if you go that route, I think that you may as well go with an 8xAMC7135 driver instead.

If you had a bench power supply so that you could characterize the P7 in terms of its V vs I behavior, then identifying the specific resistor value would be easy. You'd pick off the the desired Vf that gives you 2.8A input to the LED. Let's say that voltage is 3.55V. You'd put your DMM across the P7's terminals while running your 3D Mag and measure the actual Vf that you are getting for your overdrive condition. Let's say that value is 4.00V (which corresponds to some tail current draw measurement greater than 2.8A). To drop the voltage to the desired 3.65V, which would give you 2.8A delivered to the LED, you need

R = (4.00V - 3.65V)/2.8A = 1/8 ohm

The power dissipated in the resistor is I^2 * R = 2.8^2 * 0.125 = 1W

So you need at a 1/8 ohm, 1W (min) resistor.

If you don't have a bench power supply, then just assume a conservative case: [email protected] = 3.50V for your J-bin P7 and do the calculation.

 

[4D223]

Thanks guys, appreciate the feedback, I looked at the SSC website and it is starting to make a bit more sense. I will continue to read up and try to broaden my knowledge base. Thanks once again.
Pete