Lost with ohms!

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Nede

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Jan 21, 2015
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2
Finland
Hi all! I just started to build my first RBA (itaste dual coil). My problem is that when I put the first coil the resistance is as expected but when I attach the second one (identical to the first one) the ohms of the first coil drastically drop. I don't understand the reason. Shouldn't the resistance of the first coil remain same no matter what is the second coil? I understand the total resistance changes but why the individual resistances change?

I try to get around 2 ohms total with two coils. This should come by having two coils of around 4 ohms.

I put a figure to make this clear. First one shows the resistance of a single coil, the second one shows the resistance of the same coil when a second coil is attached. The last figure shows the total resistance with the two coils. What am I missing here :ohmy:

ohms.jpg
 

Bunnykiller

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when running resistances ( coils) in parallel, the resistance drops... when run in series the resistance increases

heres the math... Parallel resistances 1/((1/R1) + (1/R2) + ....)) = R total. Series resistances R1+ R2+... = R total

series set up is like train cars on a track parallel set up is when all the coils share the same positive and negative connection
 

Lord Cardigan

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May 7, 2014
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The resistance of the combined coils is what counts. You build a 2ohm coil, stick it in - 2 ohms. If you put a second identical coil (2ohm) and install them on the same unit, you get 1ohm total. This is the combined resistance, not that of each coil. Only the combined counts.

Possibly you are not sufficiently installing both coils. Make sure the connection for both is perfect, then check. If they aren't both screwed in correctly you can get weird resistances and therefore drastically different performance.
 

Lord Cardigan

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May 7, 2014
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I don't want to be rude or insinuate anything but I feel I have to say this; try much more simple builds. You are only learning so I don't think it's a good idea to be using dual coil let alone dual parallel coils. Get good at either singles or duals, then start to play with parallel, you'll make life a lot easier for yourself.

All those youtube videos where people whip up a somewhat tricky coil then bang on about the flavor being superior gets ridiculous. Just start with a either a single or a dual, make it perfectly neat and install it. You definitely should not be having these issues and I feel going for parallel is just going to complicate matters.

If you insist, pay attention to the legs on the positive post. You may have a stray leg of one coil touching the other side, causing resistance change when you have two coils installed.
 

BlkWolfMidnight

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Oh my word,

Ok, so yes anytime that you add an additional coil it will half the resistance, two 1.0 ohm coils will read .5 collectively (see formula's posted for figuring out ohm per 2 coils). As to why it works is because each "Coil" is treated as an independent resistor and not a single unit, if you soldered 2 resistors on a single circuit board you would get the same result. Yay for wonky science at work, but yes this is the way it is.

Ok, so back to your build, you need to hit up the tube of you (youtube) and watch some video's on how to build a proper coil or heck I'll be happy to Skype with you if that will help but please don't use that build. I'm counting at least 10 wrap parallel coil per side build. There is the right way to jump in to RBA's and the wrong way, currently your more towards the wrong then the right. Thanks for posting before trying that build out on your own, safety first as I like to say.
 

diablo2713

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Jan 20, 2015
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Dissonance

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The reason your readings are so messed up is because your coil has a short. This will cause erratic readings in resistance & hot spot(s) that will produce an extremely unpleasant vape.

I'm going to agree single coils are better to learn with, for the simple reason of there's less to mess up. With dual coils, not only do you have to wrap 2 identical coils, mount them identically, make sure none of the leads are shorting out the other coil, and (for contact coils) make sure they're both squeezed equally... But you have to try to wick them both exactly the same so you can learn proper wicking. Overall there are more possible problems and troubleshooting is a little harder with dual coils. With a single coil, you just worry about doing it once. If something goes wrong, it's easier to figure out exactly what, why, and how to fix it. Coils glowing on the edge? You either have a messed up wrap, hot legs, or a hot spot (or all 3 :p ). Coils glowing in the center? Probably a wicking problem, but your coil could be too small diameter wise as well. A hotspot is also possible, but much less likely and it would be obvious from how it looks when fired.

Also, parallel coils are hard. I don't mean hard like practice a week and you got it, I mean even people that have perfected their skills still mess up coils occasionally. Since two wires are running parallel, having a contact coil is pretty much required, which means those two wires have to run EXACTLY parallel to eachother while maintaining perfect contact with the wire on either side... And those are just the problems you have while wrapping it, which is by far the easy part. Save those for after you've perfected your single coils, perfected your dual coils, and played with a few harder builds (Diamond coil, vertical coils, claptons, etc.).

Just a small tip for you as well: Try to adjust your coil as little as possible once you mount it. To minimize adjusting, try bending the leads so all you have to do is hold your mandrel in the coil and pull the leads taught through the post holes to mount it. Small adjustments like pre-bending your positive lead to the bottom center of your coil for a center post build (like what looks attempted in your parallel build) and the negative lead out so it'll slide right into the post can make things a whole lot easier, ESPECIALLY when it comes to the harder builds (like parallels). Needle nose and those small curved pliers are amazing for this :D

also since you have an rda with only 3 post's check out this video on sleeper builds


https://www.youtube.com/watch?v=xcKwOQzGLEU&index=1&list=PL2AOaPvyEcx16ei0CPvQ76XLa2rBILmmP

He's not quite ready for sleeper builds :p Let him learn how to wrap a proper coil normally first :D Also, I think you meant continuous builds... Sleeper builds implies a specific wire, gauge, coil, and wicking method. Rip trippers was an idiot when he made the video that confused everyone :p E: Wow, didn't click the video to see it was rip trippers til after I wrote this comment... Didn't mean for that to come off as aggressive, I was just making the comment in general not knowing that's what you linked xD
 
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diablo2713

Full Member
Jan 20, 2015
8
0
FL, USA
The reason your readings are so messed up is because your coil has a short. This will cause erratic readings in resistance & hot spot(s) that will produce an extremely unpleasant vape.

I'm going to agree single coils are better to learn with, for the simple reason of there's less to mess up. With dual coils, not only do you have to wrap 2 identical coils, mount them identically, make sure none of the leads are shorting out the other coil, and (for contact coils) make sure they're both squeezed equally... But you have to try to wick them both exactly the same so you can learn proper wicking. Overall there are more possible problems and troubleshooting is a little harder with dual coils. With a single coil, you just worry about doing it once. If something goes wrong, it's easier to figure out exactly what, why, and how to fix it. Coils glowing on the edge? You either have a messed up wrap, hot legs, or a hot spot (or all 3 :p ). Coils glowing in the center? Probably a wicking problem, but your coil could be too small diameter wise as well. A hotspot is also possible, but much less likely and it would be obvious from how it looks when fired.

Also, parallel coils are hard. I don't mean hard like practice a week and you got it, I mean even people that have perfected their skills still mess up coils occasionally. Since two wires are running parallel, having a contact coil is pretty much required, which means those two wires have to run EXACTLY parallel to eachother while maintaining perfect contact with the wire on either side... And those are just the problems you have while wrapping it, which is by far the easy part. Save those for after you've perfected your single coils, perfected your dual coils, and played with a few harder builds (Diamond coil, vertical coils, claptons, etc.).

Just a small tip for you as well: Try to adjust your coil as little as possible once you mount it. To minimize adjusting, try bending the leads so all you have to do is hold your mandrel in the coil and pull the leads taught through the post holes to mount it. Small adjustments like pre-bending your positive lead to the bottom center of your coil for a center post build (like what looks attempted in your parallel build) and the negative lead out so it'll slide right into the post can make things a whole lot easier, ESPECIALLY when it comes to the harder builds (like parallels). Needle nose and those small curved pliers are amazing for this :D



He's not quite ready for sleeper builds :p Let him learn how to wrap a proper coil normally first :D Also, I think you meant continuous builds... Sleeper builds implies a specific wire, gauge, coil, and wicking method. Rip trippers was an idiot when he made the video that confused everyone :p E: Wow, didn't click the video to see it was rip trippers til after I wrote this comment... Didn't mean for that to come off as aggressive, I was just making the comment in general not knowing that's what you linked xD

yea i probably should have said that build is for when you get good at the basics and i did not know that was the incorrect name for that coil thanks for the info
 

DaveP

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May 22, 2010
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It's hard to judge from your picture, but it looks like one of those coils has 20 something wraps. With 28ga kanthal, you only need 8 wraps around a 3mm rod to get 2 ohms. You also can't let coils wrap over each other or let the end lead wrap over the coils to get to the termination point.

As others have said, you'd be better off the wind one coil and vape it for a while, get a feel for how the process works, and then try adding a second coil. Check your coil resistance before you mount it. Check it after mounting. There should be no change. If there's a change in resistance you probably have some turns contacting the base and shorting out the coil. The coil should have some air space between the turns and the base. Yours looks like the coil is laying flat down on the base and at least shorting some turns to ground.

With two coils you will get approximately half the resistance of one coil when you have two in parallel. With two coils you can get away with the calculation: coil1 + coil2 divided by 2. It's close enough for ecig work.
 
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