I’ve been out of modding for a few years and am finally getting around to building a few lights using Convoy M1 hosts. I had to order 20mm Luminus SST-40 N5 6500K LEDs on Copper DTP MCPCB since I only had 16mm from the P60 modding days. I’m wondering if the bottom of the MCPCB is conductive. A simple continuity test on the 16mm makes me believe the bottom is conductive, but I’m no expert.
If the bottom of the MCPCB is conductive, what would be the proper way to insulate that from the host since the inside of the M1 head is bare aluminum?
If everything goes correctly, these will be rifle lights. I’ve successfully modded and loaned out a few Surefire x300 lights with better LEDs that stood up to a few years of high-round count classes. It should be interesting to see if these can hold up to rifle use. I’m researching beforehand, but might not be searching for the correct terms here, so I decided to ask in a post.
If the bottom of the MCPCB is insulated from the Positive and Negative of the LED, why does a simple continuity test between the bottom of the MCPCB and different points on the LED produce a sound from the multi-meter? That’s what confused me.
Outside of a light there should be no continuity between Positive and the MCPCB or Negative and the MCPCB.
However
Once the MCPCB is mounted and soldered into a light, the MCPCB and driver will be grounded to the body and you will have continuity between Negative and MCPCB.
This isn’t anything to worry about unless 2 or more of the pads on the MCPCB are bridged.
If Negative and DTP are bridged, when you click on the light, you’ll get DD(Direct Drive) Turbo because the electrical connections will be bypassing the driver.
If Positive and DTP are bridged, when you click on the light, there will be a short.
If you’re testing around the outside of the LED itself (rather than the postive and negative pads you would solder the leads to), and the different points on the LED that show continuity to the MCPCB base are the exposed middle pad (exposed because it’s slightly wider than the LED), then you would expect continuity.
Testing on the LED only for now. I don’t have the 20mm LEDs in hand to assemble and test yet. Just a quick point check on the 16mm I do have and no continuity between positive or negative but certain points on the LED and the bottom of the MCPCB did have continuity.
If that’s normal, nothing to worry about then. Its been a few years and I’m having to learn all this over again. Thank you for your help. This time I’m taking notes and saving them to the cloud for future reference.
Yea. The center pad of the LED (thermal pad) and the bottom of the MCPCB will have continuity. “Direct thermal path” means there is no electrical insulator there. The center pad of most LEDs is electrically isolated from the anode and cathode of the LED so it does not need any special consideration.
I don’t think that is necessary, or would make much of a difference besides possibly making a mess.
The most important area is under the MCPCB to transfer the heat to the shelf and then out to the head. The MCPCB and the shelf should be as flat as possible to maximize the surface area to transfer the heat and the thermal paste helps to make up any imperfections.
With the M1 the bezel screws the reflector down onto the MCBCB then onto the shelf. So any excess thermal paste will be squeezed out.
