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 :smiley:

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.

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

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.

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.

Thank you Rufusbduck, this helps a lot :smiley: 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.

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 :smiley: 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 :open_mouth:

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.

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

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. :person_facepalming: I hate waiting on doing a project. I bought 8 of those XP-L2 V5’S.

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

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 8x 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.

Thank you Texas_Ace. I think I pooched all my orders :person_facepalming: 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.

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.

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.

Can you explain why this happens?

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.

Here is a chart from CREE on the emitter sizes.

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.

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