Charger power and PT from PC power supply?

[Whistle_Pig]

After reading various complaints about PT problems, I'm a bit dubious about buying one. And then I've read some folks mentioning possible issues with the USB port on their computer as well. I also am not pleased with the charger supplied with the 510 kit, because they supplied a very short cord, so AC power is inconvenient at my desk where I keep the charger.

So I came up with this brilliant idea. The 501 charger has a 12VDC in jack. A 5VDC supply can be regulated down to 3.7, or 3.1, or wherever I want to run my 510, if I ever decide to vape inside. The power supply in my PC has Molex 8981 connectors which suppy 12 and 5 VDC. I have extra Molex connectors laying around here someplace. I figure the PC power supply is nice fat regulated power source, with no danger of damaging my motherboard or the USB controller.

So I figure I wire up a molex plug to a keyed bulkhead connector on the front of my PC (keyed, so there's no way to get 12VDC where it'll cause damage). Connect a coaxial power connector on the 12V side, and make a little regulated supply on the 5V side. I'll have to get a hold of a 510 female connector (I see from searching that I can order those).

So, I did a quick sketch of the circuit, and here's where I could use a bit of advice. I know a little about electronics. But I don't know how to size the limiting resistor for ohms or wattage. (Actually, it's in my head somewhere, just too old to retrieve without some hinting.) I had originally thought I could put the zener in series with the atty, but most of the simple regulating circuits I see are of the form I drew.

So, assume I want to run my atty at 3.3VDC (I have no desire to overvolt it significantly; I'm happy with my 510 the way it is), that's 5.2 watts (given 2.1 ohms R).

Is this a bad idea? Should I just use a packaged regulator? If I do it this way, would a 1N5333BRLG be the correct zener? Did I draw the zener backwards?

TIA for any advice.

 

[Rocketman]

Mr. Pig ,
Your 5 volt to 3.3 volt idea is OK. The computer power supply could easily be used to vape from, and safer than using the USB. BUT,

I'll let you do the math on your circuit.
In order to get 3.3 volts at the 2.1 ohm atty 'while vaping' the extra 1.7 volts or so needs to be dropped by the resistor in your diagram. If it's over 1 ohm, what is the most you can get to your atty under load? (try 2 ohms and see what is going on in the circuit under load). If less than 1 ohm so the zener is conducting while you vape, what is going on while you stop vaping.

When you aren't vaping the zener (which IS drawn in the correct orientation) will be drawing how much current through the resistor? All the time?

How many watts will be dissipated by the 5 watt zener? and will it get hot? like really, really hot?
Maybe a couple of 6 amp (safety margin) diodes, each dropping about 0.6 to 0.7 volts under load (about 1.6 amps?) and dissipating about 1 watt each.

A regulator would be the best approach.

 

[Whistle_Pig]

Okay, I did some math. Whether it was the right math ...

I treated it as a simple resistor network, because I figured the zener has to provide a resistance equal to the atty resistance in order to drop the same voltage over a load in parallel. Could be I completely misunderstand something here, but since you're mentioning wattage as an issue, I figure I'm at least close. And yeah, the current draw while vaping is stupid -- I figured appx. 3.3A for the whole circuit.

So, I'll definitely look at a regulator. And read up on zeners too, for that matter.

Thanks for the input.

ETA: I decided to cheat and tried a few calculators such as this one, and I'm off by quite a bit, but the point remains. Also the gap in my recollection of this stuff. I know my copy of Grob's Basic Electronics won't be too difficult to dig up.