What's wrong with this circuit?

[FoundYourVapes]

Thread reposted to the "Modding Forum" section.

 

[Coastal Cowboy]

You may not have the seniority yet to post in it, but there's a whole sub-forum for what you're attempting to do.

Modding Forum

 

[suprtrkr]

Hi and welcome to the board. I am not an electronics tech to absorb your schematic at a glance. I could probably figure it out after a while, and I once designed a similar (possibly identical, it's been years) layout to do exactly what you're trying to do with it. As @Coastal Cowboy recommends, take it over to the Modding Forum. When I did the same with my circuit I was told the only thing wrong with was is it's overly complex. If you want the voltage indicator LEDs as a coolness gimmick, fine, build it; and you'll find advice on resistance values etc over in the aforesaid Modding Forum. But you don't need them. With a mech mod, the vape gets weak long before the battery is anywhere near discharged. You'll know, trust me. I routinely coil my mechs in the .5Ω range and I swap batteries for fresh at about half charge (~3.7V) because there's no vapor any more. You also don't need SW1. Just take the battery out. And if you put SW1 in anyway, it's going to be a large and expensive piece of gear because it's going to have to out-rate the max battery discharge current. If you really want to do it, it'll be easier-- and fit inside something the size of a mod-- to replace SW1 with another MOSFET of the opposite channel to your firing MOSFET and use a tiny switch to open and close the gate. I may be wrong (I said I'm not an electronics tech), but it looks like you're high-side switching Q1, so you probably intend a P-Chan MOSFET for it. If so, then replace SW with an N-Chan and wire it "upside down," using a maintained contact switch to open the gate rather than a momentary. But again, the easy way is to just take out the battery. (If you're concerned about it firing in your pocket or something, rather than a means of turning the machine off and on, then just series a maintained contact slider with the fire button where it will carry a few milliamps, rather than in the battery negative bus where it must carry tens of Amps. Another option would be to use a tamper proof switch, which is rather hard to accidentally depress.)

Good luck with it. Excellent advice, far better than mine, is available with the modders forum. Let us know how you get on and do post pics when you get it rolling.

Edit: I forgot-- another problem you're going to have is the Zener probably-- almost certainly-- has a breakdown voltage high enough to trigger the gate at least some in either Q1 or Q2 or both, so you might get some backfeed, resulting in a "constant on" of the low batt light or even worse an autofire of the firing circuit.

 

[FoundYourVapes]

@suprtrkr I already moved this thread, thanks. I'm worried about this since at 0.3 ohms even at 3V it would give 30W, and that is still plenty watts. While I'm positively sure I would notice it, giving it to someone might be quite risky. The idea of not having any sign of battery charge is kinda

Since I am building this on a cheap flashlight body, as that is what I figured I would have the most freedom with, the SW1 would be the tail cap switch, so space is not an issue. The rest of the circuitry is in the top portion, and I will have think through adding a switch there. The mosfet idea is what I will consider, although a simpler solution would be to have a screw that would touch and secure the battery only when screwed in, otherwise separated by a plastic bushing. Taking out the battery will be more elegant and clean though, soo.. I don't know yet.

Anyway, you mentioned the zener's breakdown voltage, I made a mistake there thinking that the resistors would bring the value down to below 0V, which would keep the gates closed, which is impossible of course.

Thanks a lot for the reply

 

[suprtrkr]

@suprtrkr I already moved this thread, thanks. I'm worried about this since at 0.3 ohms even at 3V it would give 30W, and that is still plenty watts. While I'm positively sure I would notice it, giving it to someone might be quite risky. The idea of not having any sign of battery charge is kinda

Since I am building this on a cheap flashlight body, as that is what I figured I would have the most freedom with, the SW1 would be the tail cap switch, so space is not an issue. The rest of the circuitry is in the top portion, and I will have think through adding a switch there. The mosfet idea is what I will consider, although a simpler solution would be to have a screw that would touch and secure the battery only when screwed in, otherwise separated by a plastic bushing. Taking out the battery will be more elegant and clean though, soo.. I don't know yet.

Anyway, you mentioned the zener's breakdown voltage, I made a mistake there thinking that the resistors would bring the value down to below 0V, which would keep the gates closed, which is impossible of course.

Thanks a lot for the reply

Any time. Good luck with it. There are some real experts over there.

 

[BrotherBob]

I made a mistake there thinking that the resistors would bring the value down to below 0V, which would keep the gates closed, which is impossible of course.

Welcome and glad you joined.
Never taken elect circ. 101 but whatever you do, please be careful.