Hi all: I have decided I want to try to build an unregulated mod in the size and shape of a tobacco pipe, meaning there's not a lot of room to get fancy. I had hoped for native IMR battery voltage, nominally 3.7V, and to power an atty down to .5 Ohms. Using the handy-dandy Ohm's law calculator-- may the Almighty bless the author and whoever linked it here; long may they live and may their tribes increase-- I figured a half-Ohm atty at 4.2V on a fresh charge would be busting nearly 8.5 amps of current to deliver 35+W to the atty for however long you had the button pressed. And the size of the contemplated mod is such an 18650 or 18500 battery is too long. Frankly, 8+ Amps is a skosh more than I'd care to draw from an 18350. However, an estate-sized, apple-shape pipe bowl is over 2" in diameter, some push three. Thus my thinking is I can fit a pair of 18350's vertically, side by side, and connect them in parallel. Then I will be back in safe Amp loading territory, so long as nobody get's stoopid and runs an atty down in the 1/4 Ohm range, and it will boost the available battery capacity for free.
I'm hardly a EE, but for my sins I was an electrician in my youth, so the idea of circuits and Ohm's law is not utterly beyond me. However, electronics is not my thing. So I've been reading here, and elsewhere on the net, to try and learn something about it. Not building a metallic tube mod, I don't really have the option of hand-carving a 20A pushbutton switch out of copper bar stock, and I'd be worried about deterioration of the contacts on the switch and the battery anyway, albeit ~3.7V is low for arcing. An electromechanical relay is too big, so I thought about a transistor for switching. It turns out they don't make them in the required current ranges in a convenient size, but power MOSFET's are available in the right current range, and can be had in TO-220 packaging, which is small enough to fit in the mod. I got to looking around and thought Fairchild's FQP30N06L just might do the job. My first stab at laying out a circuit for the mod looked like this (feel free to laugh, I've already figured out it won't work):
View attachment 351308
Edit: The attachment didn't come through. I'll try it again.
I had hoped to use the zener to provide both low battery protection and a comparator signal (voltage before and after the zener) for a low battery LED indicator. The transistor and LED (center of the diagram) is sort of like the bottom half of a NAND logic gate except, since I didn't want to energize the collector of the transistor array unless the button was pushed, and that would also be the signal applied to the base of the top transistor, thus the top one was not needed; a simple piece of wire would work just as well as it would not be possible for the emitter of the top transistor to be high unless the button was pushed, and then it always would be. But when I got to trying to calculate resistor values I figured out I didn't know much about zeners. I wasn't sure if the zener would clip voltage to the value of the part, or if it would pass any voltage higher than the cutoff point. So, I took myself down to the local Radio Shack to purchase any zener I could get having a breakdown voltage within the range of something I could easily maze up on my desk with batteries. I wound up with a Fairchild 5.1V IN4733, applied 6V across it and discovered a zener clips to it's nominal voltage less its forward voltage. That wasn't a handicap as 4.2ishV was plenty to tickle the gate of the MOSFET. But when I tried it across 3V to make sure it would shut down the MOSFET below the minimum voltage, that's when I discovered what leakage was all about. I read about the leakage in the datasheet, but I didn't understand what it meant until my trusty Fluke 87 indicated about 1.2V still coming through the zener from a 3.24V supply. (I know, I know, they call them semiconductors for a reason, sigh.) That blew my circuit design out of the water because, unfortunately, 1V is also enough to tickle the gate on the MOSFET and it would not shut down. It also would never light the low batt LED because it would do the same for the base of the transistor.
So, it's back to the drawing board on some kind of low battery shutdown and LED indication. I haven't even begun to figure it out, but it looks like I might be able to use a 7485 comparator or a 741 op amp chip(s) to provide the signal I need, assuming I can figure some dodge to provide a stable reference voltage from a variable voltage battery supply (sigh). But then, I'm not sure I can fit all that plus a MOSFET and two batteries in a pipe bowl. We'll have to work on that some. If I get a circuit that works, I can then figure out how to physically configure it in the smallest possible space. I figure enough parts to build the circuit 8 or 10 times will let me screw up enough to get something that might work and be small enough
Even so, for the EE's out there, I do have some questions:
1) Is the FQP30N06L a good MOSFET for what I want to do? If not, why not? What might be better?
2) I think I need the diode on the mod side of the 510 connector to protect the MOSFET from the reverse voltage spike generated by the collapsing magnetic field from taking the power off the atty coil. Is that right? If so, can somebody either spec that part for me, or explain how to calculate the voltage and wattage capacity I need?
3) I was taught as an electrician the switch always goes between the source and the load, rather than between the load and the ground return for safety's sake. Series is series, of course, and it will work to interrupt the load anywhere in the circuit, but placing it after the load leaves the load energized at all times when the circuit is powered, regardless of switch position. I caught a post on controlling a MOSFET with an Arundino that says to do it the way I drew it, so that's how I drew it. But it makes me shake my head because I don't understand it. Comment?
4) The same post says to wire the MOSFET backwards to what I would normally do, that is run V+ through the load and then to the Drain of the MOSFET, taking the V- off the Source of the MOSFET. So, that's how I drew it as well. But that doesn't make any sense either.
5) Not on the circuit diagram-- I have to start over on that one, I fear; but not to worry, I'm sure I'll have more questions later-- but I recently caught a post here on the board saying the Efest purple 35A batteries I recently wasted my money on were, in fact, actually 20A batteries repackaged with a lie on the label. So I just ordered some Sony VTC5 2600mAh 30A's to replace them and will relegate the Efest's to my regulated mods as soon as they arrive. My question is, anybody have an opinion as to whether I can trust the labeling on the Sony's?
Thanks for the help, everybody, and my deep appreciation for you pro's out there wasting you time on those of us who don't know anything. Happy vaping...
I'm hardly a EE, but for my sins I was an electrician in my youth, so the idea of circuits and Ohm's law is not utterly beyond me. However, electronics is not my thing. So I've been reading here, and elsewhere on the net, to try and learn something about it. Not building a metallic tube mod, I don't really have the option of hand-carving a 20A pushbutton switch out of copper bar stock, and I'd be worried about deterioration of the contacts on the switch and the battery anyway, albeit ~3.7V is low for arcing. An electromechanical relay is too big, so I thought about a transistor for switching. It turns out they don't make them in the required current ranges in a convenient size, but power MOSFET's are available in the right current range, and can be had in TO-220 packaging, which is small enough to fit in the mod. I got to looking around and thought Fairchild's FQP30N06L just might do the job. My first stab at laying out a circuit for the mod looked like this (feel free to laugh, I've already figured out it won't work):
View attachment 351308
Edit: The attachment didn't come through. I'll try it again.
I had hoped to use the zener to provide both low battery protection and a comparator signal (voltage before and after the zener) for a low battery LED indicator. The transistor and LED (center of the diagram) is sort of like the bottom half of a NAND logic gate except, since I didn't want to energize the collector of the transistor array unless the button was pushed, and that would also be the signal applied to the base of the top transistor, thus the top one was not needed; a simple piece of wire would work just as well as it would not be possible for the emitter of the top transistor to be high unless the button was pushed, and then it always would be. But when I got to trying to calculate resistor values I figured out I didn't know much about zeners. I wasn't sure if the zener would clip voltage to the value of the part, or if it would pass any voltage higher than the cutoff point. So, I took myself down to the local Radio Shack to purchase any zener I could get having a breakdown voltage within the range of something I could easily maze up on my desk with batteries. I wound up with a Fairchild 5.1V IN4733, applied 6V across it and discovered a zener clips to it's nominal voltage less its forward voltage. That wasn't a handicap as 4.2ishV was plenty to tickle the gate of the MOSFET. But when I tried it across 3V to make sure it would shut down the MOSFET below the minimum voltage, that's when I discovered what leakage was all about. I read about the leakage in the datasheet, but I didn't understand what it meant until my trusty Fluke 87 indicated about 1.2V still coming through the zener from a 3.24V supply. (I know, I know, they call them semiconductors for a reason, sigh.) That blew my circuit design out of the water because, unfortunately, 1V is also enough to tickle the gate on the MOSFET and it would not shut down. It also would never light the low batt LED because it would do the same for the base of the transistor.
So, it's back to the drawing board on some kind of low battery shutdown and LED indication. I haven't even begun to figure it out, but it looks like I might be able to use a 7485 comparator or a 741 op amp chip(s) to provide the signal I need, assuming I can figure some dodge to provide a stable reference voltage from a variable voltage battery supply (sigh). But then, I'm not sure I can fit all that plus a MOSFET and two batteries in a pipe bowl. We'll have to work on that some. If I get a circuit that works, I can then figure out how to physically configure it in the smallest possible space. I figure enough parts to build the circuit 8 or 10 times will let me screw up enough to get something that might work and be small enough
Even so, for the EE's out there, I do have some questions:
1) Is the FQP30N06L a good MOSFET for what I want to do? If not, why not? What might be better?
2) I think I need the diode on the mod side of the 510 connector to protect the MOSFET from the reverse voltage spike generated by the collapsing magnetic field from taking the power off the atty coil. Is that right? If so, can somebody either spec that part for me, or explain how to calculate the voltage and wattage capacity I need?
3) I was taught as an electrician the switch always goes between the source and the load, rather than between the load and the ground return for safety's sake. Series is series, of course, and it will work to interrupt the load anywhere in the circuit, but placing it after the load leaves the load energized at all times when the circuit is powered, regardless of switch position. I caught a post on controlling a MOSFET with an Arundino that says to do it the way I drew it, so that's how I drew it. But it makes me shake my head because I don't understand it. Comment?
4) The same post says to wire the MOSFET backwards to what I would normally do, that is run V+ through the load and then to the Drain of the MOSFET, taking the V- off the Source of the MOSFET. So, that's how I drew it as well. But that doesn't make any sense either.
5) Not on the circuit diagram-- I have to start over on that one, I fear; but not to worry, I'm sure I'll have more questions later-- but I recently caught a post here on the board saying the Efest purple 35A batteries I recently wasted my money on were, in fact, actually 20A batteries repackaged with a lie on the label. So I just ordered some Sony VTC5 2600mAh 30A's to replace them and will relegate the Efest's to my regulated mods as soon as they arrive. My question is, anybody have an opinion as to whether I can trust the labeling on the Sony's?
Thanks for the help, everybody, and my deep appreciation for you pro's out there wasting you time on those of us who don't know anything. Happy vaping...
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