12V wired box mod > atomizer gives shock

[yo han]

OK so "shock" may be exaggerated but it doesn't feel nice.
Let me show you what I've built and hopefully someone can come up with a solution to my problem.

I was looking to build a very cheap wired box mod for use behind the computer and in my car.
I had a couple of these XL4015 buck converters lying around and thought I might as well use one of those since I didn't need room for batteries inside anyway. They have a wide working range and deliver up to 5A continues draw so I can use my Subtank mini with a 1.2 Ohm coil and vape up to 30W.
I've put a fixed 2.61K metal film resistor + 10K potentiometer in place of the multi-turn potentiometer so now the output voltage range is 3 to 10V.

Here's a list of the parts I've used including prices I've paid (most from eBay).

Case: $1.50
XL4015: $1.75
IRLB3034: $1
Potentiometer: $1.50
2x resistor: $0.20
Push button switch: $0.50
510 connector: $1.65
DC socket: $0.25
Volt/Amp meter: $3.80
Wire: $0.50

Total: $12.65

The XL4015 has overload protection so you may just as well use a simple (and much cheaper) Volt meter to lower the cost even more but I like seeing the amps I'm drawing and it also gives me the option to calculate wattage.

Here's how I wired it up (I"m not an experienced circuit builder so the drawing probably sucks but you get the idea).
The thick lines are high current while the thin lines are low current.

It works great except every time my lips touch the metal of the tank I get this stinging feeling of electricity.
Using a metal drip tip is a no-go this way and I've temporaily solved it by putting a piece of rubber at the top of the tank I'm using. However, I don't want to have to put a condom on my tank every time I'm using the mod so hopefully someone can come up with a suggestion to solve it.

Here are some pics of the finished mod. I wasn't after creating something pretty but purely funcional at the lowest possible price. Hope you like it.

 

[Cool-breeze]

If you've got current going through the outside of your tank sounds to me like your 510 connection isn't propperly insulated. I'd suggest trying that tank on a dif mod and a dif tank on the problem mod. I say that because it seems fainltly possible the tank/ atomizer got damaged and is completing a circuit. Again it's unlikely but the easiest to test. Otherwise my money is on needing a new 510 piece. You could also check for any exposed wire inside the mod and see if a loose connection is the culrprit.

 

[yo han]

Just measured the 510 connector, no shorts of any kind. Tried several tanks: all the same.

I forgot to mention that I also have one of those factory made wired eGo-looking adapters with a USB plug and was running that on a 5V/6A DC adapter giving the same stinging feeling albeit less noticeable than this one (probably because it was 5V instead of 12V?)

 

[SupplyDaddy]

If anything, I would say your problem is that you have the mosfet Before the board with the In-going voltage, instead of After the board on the out-going voltage. Your mosfet is dealing with with 1 set of specs (voltage/amps) while the board/510 is dealing with a totally different set of specs. Could be causing arching on the board.

And while I some what agree you could have an issue with the 510, being on an ABS box kind of helps insulate it. But you didn't include the inside pics which would help id that problem. Old style 510? That would make the issue more plausible.

Have you ensured that is no solder splash over on the various connections and on the bottom of the board?

I also wouldn't trust a $1 IRLB3034......

 

[SupplyDaddy]

Is your meter wiring shown correctly on the diagram? Hard to tell if it's showing a dual wiring from the Input And the Output, or just from the Input.

 

[yo han]

Thanks for the response (again )
It's kinda crammed inside the box but I can assure you everything's clean as a whistle, well soldered and absolutely no chance of bare wires touching eachother.
The 510 I'm using has a spring loaded center pin.

 

[SupplyDaddy]

Are you sure you don't have grounding issues with your household wiring?

Just measured the 510 connector, no shorts of any kind. Tried several tanks: all the same.

I forgot to mention that I also have one of those factory made wired eGo-looking adapters with a USB plug and was running that on a 5V/6A DC adapter giving the same stinging feeling albeit less noticeable than this one (probably because it was 5V instead of 12V?)

 

[yo han]

The meter is wired as follows:
thin wires are for powering the meter and are connected as shown in the diagram.
Then there are 3 terminals: red (positive), black (gnd) and blue (shunt).
The red is connected to the positive wire coming from the XL4015 and running to the center pin of the 510.
The black is connected to the negative wire coming from the XL4015
The blue wire is connected to the outer part of the 510

No issues with household wiring. Been checked last year.

 

[SupplyDaddy]

Well, after all that, I can only fall back onto my original statement with the mosfet wiring. Try it with the mosfet connected to the output of the board (just like that was the battery connections on most boxes) instead of the input. You can unplug the device when not being used so that shouldn't strain the board.

Only other options would be bad mosfet, bad board or the resistor is too high (15k is normally the one suggested).

It's a nice looking box! But not much good until you solve the shock issue.

 

[yo han]

Thanks for liking the box but your reasoning makes no sense to me. The mosfet is no more than a simple switch. It couldn't, ever, make this happen since there's no positive 12V signal with enough current involved that could cause the thing I'm experiencing. The resistor you mention couldn't make this happen either. All it does is lower the current that gives the mosfet a trigger to switch. Whatever the resistance, if it works, it works. I really appreciate your input but I just haven't read anything that can help solving the problem. I suspect he XL4015 being the thing that causes it but what exactly it is, I have no clue.

 

[rhelton]

I have only ever had this happen when mocking up a couple mods I was building. I got a pretty good shock and it was because I did not have a proper return ground in the system. Once everything was in its place and securely soldered it went away. Im gonna read back thru and see if I can help locate it for you.

 

[asdaq]

I would suggest trying a different atty. The shock you are getting is that your body is more efficient at completing the circuit than the atty itself. If you insulate yourself from circuit in the ways you describe with a different drip tip or a the synthetic ring then it does not happen. If switching out the atty helps, then have a look at the one giving the shock and see if taking it all apart and cleaning threads, screws and other points of contact that are building up resistance. You can also use a multimeter checking various points to measure resistance and spot culprit areas.

 

[Mooch]

Thanks for liking the box but your reasoning makes no sense to me. The mosfet is no more than a simple switch. It couldn't, ever, make this happen since there's no positive 12V signal with enough current involved that could cause the thing I'm experiencing. The resistor you mention couldn't make this happen either. All it does is lower the current that gives the mosfet a trigger to switch. Whatever the resistance, if it works, it works. I really appreciate your input but I just haven't read anything that can help solving the problem. I suspect he XL4015 being the thing that causes it but what exactly it is, I have no clue.

You could be right...when the MOSFET opens you are removing the converter's ground and they hate that.
It's still poweed by the 12V line, and still leaks a few microamps through the MOSFET to derive a lousy ground with, so the converter can really freak out. It's lost its solid reference point and can vary its output voltage considerably or lose stability and oscillate.
It would be much better to switch to a P-FET on the high side, just after the battery 12V connection. That way everything is powered down completely when the MOSFET is off and you retain a solid ground reference at all timex. You have 12V to work with so even with drained batteries you should be able to turn most P-FETs on hard enough.

Also, when you lift the ground (MOSFET turns off) the entire 510 jumps to 12V. There's no longer a grounded connection to the 510 so the 12V goes through the coil and just sits there on the now ungrounded outside of the 510 and the case, just daring you to take a draw.

 

[Mooch]

Does the XL4015 have an Enable input? You could skip using the MOSFET altogether and switch that to fire. Though a series resistor and then a small capacitor to ground at the Enable input would slow things down and help prevent glitching.

 

[yo han]

Thanks for the detailed explanation!
My knowledge about electronics isn't enough to fully understand everything but I think I know what you're saying.
I was wondering; can't the mosfet be used to switch the +12V instead of the ground signal? Perhaps it's a stupid suggestion but that's because I don't know enough about how it works.

 

[Mooch]

Definitely not a stupid question.
You can use a mosfet to switch the 12V line but not the IRLB3034 you have. It"s a "N" mosfet and it must be between the load (your XL4015, the atty, etc.) and ground in order to work. You need a "P" mosfet if you want to switch the 12V line. I don't have a link handy but somebody must have posted a circuit with a recommendation for a P mosfet. Just be sure it can handle the current you're pulling.

Or...

Check out figure 9 in the CL4015 datasheet: http://www.xlsemi.com/datasheet/XL4015 datasheet.pdf
It shows how you you can use a diode and resistor to the feedback pin (FB) to turn it on/off without a MOSFET.

 

[yo han]

Thanks for everything Mooch!
However, before I go tearing it apart, can you explain how I can get a tiny shock as long as the fire button is pressed? I understand that when the mosfet is open the whole 510 gets 12V but not when closed right? So where's it coming from? There are many people using this same setup with battery operated box mods and I've never heard of anyone having this problem.
I like the idea of using the FB on the 4015 but the mosfet also switches the Volt/Amp meter in my setup and requires 4.5V minimum so I can't use the output of the 4015 to power it when it's set below that voltage.

 

[Mooch]

Ahhh...good point! I didn't realize that it still shocked you even after pressing the fire button.
Do you have a DMM? We should take a couple of voltage readings when off and when on.

 

[yo han]

Sure, I have a Fluke DMM and already confirmed the 12V on the gnd side of the 510 so if you tell me what to measure I'm happy to post the results.

 

[Mooch]

Sure, I have a Fluke DMM and already confirmed the 12V on the gnd side of the 510 so if you tell me what to measure I'm happy to post the results.

Replied to your PM.