First time SRK build tech help!

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Majoroverkill
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First time SRK build tech help!

OK, I have an older SRK with a single MCPCB in it. Here is whats on the way. I have 6 CREE XP-L2 V5 emitters from Digi and a SRK V2 FET + 7135 Driver from Mountain Electronics coming. I am fabricating a 3’8’‘ copper thermal pad to attach to the bottom of the MCPCB that fits inside the rim for added cooling. Thermal past will be added. I will cop out an area to clear the switch wires. Now I am going to use Panasonic NRC18650B cells with a max discharge current rate of 6,8 amps each, 27.2 amps total. Will the driver deliver what the batteries put out? if so I will be over charging each emitter by 1,533 amps each! The max current each emitter will handle is 3 amps each, I believe. I am into this build now for over 100.00 and would hate to blow it up. I need help understanding what this driver will do and if what I am doing is possible. Thanks all Big Smile

Doug S.

FmC
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Are you planning on using the stock mcpcb?

You really need to replace that with Direct Thermal Path boards, otherwise the emitters will overheat & probably burn out.

Plenty of great SRK builds on here if you search, to get a few tips. Here’s an example of a 5X I done a while back.

Majoroverkill
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I have the 6 emitter SRK, no room for 6 MCPCB’S

Doug S.

Rufusbduck
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It’s not like the batteries just dump out 6.8A each. The current depends on resistance in the circuit and the ratings on cells only specify the maximum safe current not the conditions under which it will be delivered. The 3A max for the LEDs also depends on certain conditions, fail to meet them and the LEDs will blow, meet them and they will be fine,exceed them and they can handle up to 5A each. To get the maximum from the cells you need heavy guage led wires and bypassed springs. To survive more than 3A each the LEDs should be mounted on direct thermal path copper stars(DTP). It can be difficult to fit the thicker wire between the reflector and solder pads. The added heat sink needs to fit well, as in slip fit to snug fit with minimal gaps for thermal compound to fill.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Rufusbduck
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Get some 10mm XM sinkpads, cut down some 16’s, use 16’s and a 4x reflector or a 3x reflector and 20mm hex copper stars. Basically, the first thing you do when planning a high current mod is plan for DTP copper and a high current driver. You’ve got half if it. Spring bypasses are icing on the cake.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Majoroverkill
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Thank you Rufusbduck, this helps a lot Big Smile I used my Dremel tool to carve out space’s in the reflector for the 12 gauge wire going to the MCPCB for clearance. The copper thermal pad added to he bottom of the MCPCB will be screwed to it so there is no movement and a tight fit. I did a spring by-pass using triple 18 gauge copper wire on all four springs and then on the back side added wire joining all four together to the chassis of the flashlight. Still very new to the game and your help means a lot to me. One other question for you. Is there somewhere I can get a custom copper MCPCB made? I know it would be expensive but would like to do it right even if the MCPCB cost me 40 to 50 bucks. Thank you again Rufusbduck.

Doug S.

Majoroverkill
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Looking at getting a 3 and 4 emitter SRK next week. I can order the 10mm pads and 16mm from Mountain Electronics. I prefer the 3 and 4 emitter SRK’S. The one I have now I got some 5+ years ago. Just got my ZENY 862D+ last week so I need to put it to work Big Smile I figure the more lights I mod the more I learn and besides I really enjoy it. I am a welder and have a couple welders and plasma cutter ect. I am looking at the Harbor Freight 7’‘ x 12’‘ lathe for 599.00. This would help a lot in my flashlight modding + great just to own. Now if I can convince the wife that I need the lathe Shocked http://www.harborfreight.com/7-inch-x-12-inch-precision-mini-lathe-93799...

Doug S.

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First off does your SRK even have XP LED footprint LED’s in it? I have only ever had 1 SRK with 3535 footprint. The rest are all XM-L 5050 footprint.

Second DO NOT install XP-L2’s or any other low Vf LED onto the SRK 3535 MCPCB, they will die instantly. I have now killed 3 separate sets of 7 emitters trying this, they WILL die. I finally got some XP-G2’s to live in it.

If it is using 5050 footprint LED’s then you are still stuck with the older XM-L2’s but I have had great luck running them on the stock mcpcb with an added shelf to keep them cool. Just adjust the wire length and thickness to limit max current to around ~3A or a tad more.

Majoroverkill
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Crap!! Just pulled the SRK apart and the emitters are measuring at 5mm. I just screwed the pooch didn’t I. Facepalm

Doug S.

Majoroverkill
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I’ll have to order new emitters next week! I’m into my flashlight hobby for over 900.00 this month alone! Crap crap crap. Facepalm I hate waiting on doing a project. I bought 8 of those XP-L2 V5’S.

Doug S.

Majoroverkill
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Thank you Texas_Ace, I did not even think of that Facepalm That would have been a costly experience.

Doug S.

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Oh well, you can use the L2’s in some other lights. I am really liking the L2’s in my other lights if you don’t do a lot of white wall hunting.

What you want are some basic XM-L2’s in the tint of your choice. I have an 8× 3D U2 version that works great and has around 10k lumens with a TA driver (was around 8k with the FET+1 V2). The tint is nice and they work just fine.

Majoroverkill
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Thank you Texas_Ace. I think I pooched all my orders Facepalm I have a couple BLF 16mm Copper MCPCB XPL XPE XPG Direct Thermal Path Circuit Board coming that I don’t even think the emitters I ordered will work with.

Doug S.

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Yeah, the xp-L2 is the same footprint as the XP-G series. They use the 3535 footprint. So they will work fine on those mcpcb’s, Although I am not aware of a BLF brand of mcpcb’s. I have been using the ones from simon (convoy) for all my lights.

Majoroverkill
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Thanks again, all just learning stages and I appreciate the heads up big time. I’m looking now on Digi for the right Emitters. That site can be difficult to navigate but I’ll find them eventually.

Doug S.

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Texas_Ace wrote:

Second DO NOT install XP-L2’s or any other low Vf LED onto the SRK 3535 MCPCB, they will die instantly. I have now killed 3 separate sets of 7 emitters trying this, they WILL die. I finally got some XP-G2’s to live in it.

Can you explain why this happens?

Majoroverkill
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The 5mm and the 3.45mm foot prints. If you install a 3.45mm emitter on the 5mm board the neg and pos will touch causing it to ground out and boom, no more flashlight.

Doug S.

Majoroverkill
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Here is a chart from CREE on the emitter sizes. http://www.cree.com/led-components-and-modules/products/xlamp

Doug S.

Texas_Ace
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k-wong wrote:
Texas_Ace wrote:

Second DO NOT install XP-L2’s or any other low Vf LED onto the SRK 3535 MCPCB, they will die instantly. I have now killed 3 separate sets of 7 emitters trying this, they WILL die. I finally got some XP-G2’s to live in it.

Can you explain why this happens?

The 3535 footprint has a very small thermal pad and this greatly limits the amount of heat it can get rid of. This leads to overheating when you put a high current LED on it without DTP.

The 5050 footprint would do the same thing with a low Vf LED, but at this point there are not any out that I am aware of.

Majoroverkill
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Not seeing any of the XM-L 3D U2 emitters available on Digi right now.

Doug S.

Texas_Ace
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MTN sells XM-L2’s along with lots of others.

Majoroverkill
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Looks like Mountain Electronics has the XM-L2 U4 A1 available. Might go with these for now. 4.49 each at 6 emitters. don’t you hate making mistakes Facepalm

Doug S.

Texas_Ace
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I like the more neutral tints myself but everyone has their own opinions.

Majoroverkill
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Does anyone make custom MCPCB’S that you know of?

Doug S.

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There are some places that do but why would you need them? They are also pricey of course.

Majoroverkill
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Those where the only ones I saw available right now.

Doug S.

Majoroverkill
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Just a possibility for the SRK, would be nice to have a single copper MCPCB that fit the SRK. Wouldn’t mind spending 40 or so on it.

Doug S.

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Many people have wanted this, the issue is getting it made. The buy in cost would be close to $1000 if I had to guess.

Then you have to figure out which SRK model you want to target, the 4x? 8X? more?

Majoroverkill
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WOW! fare cry from what I was thinking lol. I see exactly what your saying though.

Doug S.

Majoroverkill
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OK, just purchases the XM-L2 U4 A1’s from Mountain. Really not crazy about that temperature, a little to blue for my liking. But if I don’t like it I’ll order another set of emitters later lol

Doug S.

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There was a company that posted a few months ago about custom mcpcb’s. I think Jos(Djozz) worked with them on a Nichia 119 copper star. If you do consider going ahead with that post an interest thread and I’m sure you’ll get takers, many of the early group buys were on parts as opposed to whole torches. Maybe RMM would be interested in stocking some along with his SRK drivers. 3/4 LED mcpcb’s will probably be the most popular as beyond that number the light turns into a flooder. It might even be possible to design one that fits either 3 or 4 LEDs.

To understand why LEDs overheat you have to understand the heat path. The led die that makes the light gets very hot and sits on a small square fiberglass substrate with thermal conduits from the die to the heat pad. This is soldered to the metal core pcb on +/- and heat pads which conduct the heat to the metal below. Most have a layer of copper, then an insulating layer, then the metal core. That insulating layer slows the transfer out of the die and into the core and when sharing the same core the back up can become critical and the LEDs poof. DTP has no insulating layer under the heat pad to slow the transfer and copper conducts heat much faster than aluminum so the back up won’t occur there, instead one must look to the next stage in the heat path which is from the mcpcb’s to the host, that is where your slug comes into play. It creates a buffer that also has more surface are in contact with the host. What you’re looking to do is create or maximize the ability for heat to move from the die(s) into the host and/or your hand. To do that you can try to maximize the surface area across each break in the thermal chain while minimizing the thermal resistance at these breaks.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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