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Fluctuating resistance?
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Almost Jaded Offline
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Post: #1
Fluctuating resistance?
So it's no secret that I love my iStick 50/SubTank Mini combo.  I've been using them for weeks and loving it.  Today I made a new coil from the same spool I've been using, a 2mm with 5 wraps of 26 awg, .8 ohms, fresh OC.  When I first install it, it measures at 1.3 ohms for some reason?  After one fire it settles in at .8.  Cool.  Running at about 18 watts, it's hitting perfect for a few hours.  I'm running the iStick on wattage.

Couple hours into enjoying my new coil, I take a puff - holy SHIT it's hot and tastes horrible!  Look at the device - it's reading 2.1 ohms and has cranked the voltage way up to hit my 18 watt level.  But clearly, it's not really at 2 ohms, cause it's hitting HOT.  Fire it again, resistance settles back down.  For a minute.  Suddenly it's fluctuating all over the place.  Like, in real time as I'm looking at the display, it's flipping out, between .8 and 2.1 and everything in between, changing rapidly.  I switch to voltage mode, and that stops the hot hits as it settles aat 3.8 into whatever resistance it thinks it's seeing, but the hits become really irregular.

i take the tank apart and look at the coil/wick - all normal, all connected solidly.  Now I'm worried it's the iStick.  Throw in the old ProtTan3 - reads steady, hits fine.  Put an old OCC SubTank coil in - reads steady, hit's fine.  Put the RBA in - fluctuates.  So it's the RBA.  Take it apart again, futz with it a bit, put it back together, put it in - .9 ohms and steady.  For a while.  Starts fluctuating again.  Grr.

I have looked at the posts, the insulator...  Double checked for foreign objects...  Nothing is wrong.

Help..?    

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21-04-2015 12:30 AM
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Michael Offline
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Post: #2
RE: Fluctuating resistance?
I've had this same problem with RDAs on my SMY God Mod. Every now and then, one will start to read wrong, usually with catastrophic consequences to my lungs and taste buds. When this has happened to me, it has invariably been one coil shorting out or becoming disconnected, so it only reads the other coil. If I'm paying attention, I can tell when this has happened because the resistance doubles, if it's a .5 ohm dual coil build the short will make it read as anywhere from .9-1.1 ohms. 
That's on a dual coil RDA. That doesn't exactly work the same on a single coil RTA. Could be that the coil has a loose connection somewhere, something causing it to short, etc. 
21-04-2015 01:15 AM
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CL0UD_Z3R0 Offline
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Post: #3
RE: Fluctuating resistance?
In my experience, any kind of build up in the atty can catch small particles from coils and environmental debris and cause a coil to short. I had the issue, maybe, my first month into using an RDA and noticed that it would short once maybe twice, then my motion or my attempting to blow/clean it our would resolve the issue. This happened to me even more frequently when I was outside. May or not be your issue but, everything is worth looking into in these situations.
21-04-2015 02:26 AM
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Almost Jaded Offline
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Post: #4
RE: Fluctuating resistance?
What's killing me is I've disassembled it and checked all connections.  TWICE.  Everything seems to be all clear.  Problem seems to have rectified itself again, settled in at .9 ohms & hasn't been acting up.  We'll see.  

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21-04-2015 05:01 AM
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Michael Offline
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Post: #5
RE: Fluctuating resistance?
I had a similar issue with my iStick 20W, if I screwed it on just right it would work fine, but if I screwed it on just a hair farther it would start reading crazy resistance (anything from 3.0 ohms down to .1 ohms) and if I screwed it on all the way it wouldn't read the atty at all. Turned out my problem was that the o-ring insulator underneath the floating pin had gotten destroyed, so the pin (positive) was making contact with the threads (negative) and causing a short. 
I didn't mention it before since you said you've checked everything, but it could be worth taking a look at again just in case. 
21-04-2015 05:06 AM
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JohnnyMac Offline
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Post: #6
RE: Fluctuating resistance?
Every time I've had resistance issues its with the post screws holding down the coil wire., especially with the heavier gauge coils. Once they heat cycle the wire anneals and gives creating high resistance and poor connection. Tightening up the screws always fixes it.
21-04-2015 07:09 PM
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Almost Jaded Offline
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Post: #7
RE: Fluctuating resistance?
Well after disassembling it a 3rd time and having it stabilize a bit, but still fluctuating slightly, I said f$%& it and rebuilt it.  I completely disassembled the deck down to bare parts, made a new coil, cleaned and rebuilt the deck and put in the new coil, cleaned and reset the pin in the base of the SubTank, and put it all back together.  Now I have a nice, steady .7 ohm coil and everything's working fine.  I'll never know what the real culprit was, and as long as it works from here on, I don't care, LOL  

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21-04-2015 11:48 PM
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[-] The following 5 users Like Almost Jaded's post:
BOB (04-22-2015), CL0UD_Z3R0 (04-22-2015), Don (04-22-2015), JohnnyMac (04-22-2015), Michael (04-22-2015)
Breazy_Com Offline
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Post: #8
RE: Fluctuating resistance?
Well at least you got it fixed. Usually for me it ends up like Johnny said. The screws holding the wire have to be re tightened sometimes after using it for a little
24-04-2015 03:35 AM
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JohnnyMac (04-24-2015)
Don Offline
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Post: #9
RE: Fluctuating resistance?
Mods that measure resistance can be pretty inaccurate. I have a precision device I can compare the readings against. When a coil is firing its resistance will be way higher than when it is cold though. Just about every metal increases in resistance as it heats up. Which is why filament light bulbs almost always blow when you switch them on. The resistance is at its lowest and therefore the current at its highest when they are switched on.

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26-04-2015 09:09 PM
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Almost Jaded (04-26-2015)
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