I have a Convoy S2+ pill and emitter that works if the MCPCB is free to dangle on the power leads, but not when I push it down onto the pill. What beginner’s mistake am I making? There’s a trace of thermal compound on the bottom, but the edges of the MCPCB are bare metal and I didn’t imagine it was necessary to have it electrically isolated from the pill.
Background: I bought two S2+s. One has a Cree emitter with an OP reflector that I like, but the old firmware. The other has a Luminus SST20 with a smooth reflector that I don’t like so much, but Biscotti firmware which I prefer. so I swapped the LED boards. The SST20 is working fine, but the Cree isn’t.
Because the LED lights up as long as it’s loose, it isn’t a problem of wrong polarity or the new driver somehow not liking this emitter. I haven’t damaged the power leads as far as I can see. When the MCPCB contacts the pill and the LED doesn’t light, the driver doesn’t pull any current, so I assume it has short-circuit protection.
I don’t think these drivers can have short circuit protection. If the LED positive shorts with the pill it bypasses the driver. So I don’t know what your problem is. Verify that the driver ground is making good contact with the pill. And that the wires have a good solder connection with the MCPCB. I’m imagining a possibility where the solder connection is not solid, and you pushing the MCPCB down actually opens the connection momentarily.
Many thanks both. There’s 380 ohms between the negative terminal of the LED (the blue wire) and the body of the pill. That doesn’t sound right? Should it be zero ohms?
On the other side, the driver board looks OK and the soldered joints to the pill body are sound.
I’d previously re-made the joints to the MCPCB, just in case, and they look OK. The leads are silicone-sheathed, so there’s no scorching. Obviously something is damaged or not connecting properly, but I can’t think where. I’ll take the LED off and try again.
The positive LED lead is connected directly to the battery, the torch body is connected to battery negative and the driver sits between the body(battery negative) and the negative lead.
So, if LED positive shorts with the pill you will be directly shorting the battery - no light, lots of heat, molten springs and potentially very dangerous, definitely something to avoid.
This also means you would expect resistance between LED negative and battery negative, i couldn’t tell you how much though.
I’m sorry i can’t help with the actual problem though, i don’t know what’s causing it.
Thanks for clarifying. I get 0.3 Ω from the LED positive lead to the positive battery terminal. I also get the same resistance from the LED positive lead to the exposed metal of the MCPCB, which explains why the light goes out when the MCPCB touches the pill.
Yerssss… So why on earth no fireworks when I first tried it? Clever protection circuit on my LG MJ1 cell? For testing I’m using a PSU with short-circuit protection.
I wondered if I’d blown up the driver, but no, I can still program different modes. And it can’t be a polarity error because the Cree board is clearly marked, and besides it works when I feed power directly to the LED terminals.
Whatever the reason, no fireworks=yaaaaaaay!
If it was a polarity error then the LED wouldn’t light up when off the pill but even then the board shouldn’t be negative when wired correctly, but then i only have a basic understanding of how MCPCBs are structured so may be missing something.
Only things i can think are that either there is a bit of solder or a loose strand of cable shorting the positive pad to the side of the MCPCB, or if it’s a DTP board maybe a short under the LED itself connecting the positive pad to the centre pad. That would make it less likely to work in the original S2+ though, though i suppose not impossible if there was enough non-conductive paste.
Have you tried to put the original MCPCB back on to see if the same thing happens? That could help determine if it’s an MCPCB issue or perhaps a wire issue.
You nailed it. Thank you! I am normally good at soldering, but those pads are smaller than I thought, and rather close to the edge of the board. All fine now.
So, surely a protection circuit somewhere – either the driver board or the battery – must have saved me from the China Syndrome (the nuclear kind, not the one drifting through my open window right now). Unexpected, but comforting.