Busting the "top hot spot" myth

[pdib]

Really, this AGA top hot spot business really has my knickers in a knot! It has nothing to do with the distance between the wick and the positive post. Its about the tension, man! Some of my vertical ss mesh setups have had this "hot leg" issue, but it always proves to be that my top wrap is too tight; right before the wire leaves the wick. (In fact, every hot spot i've ever had is immediately above a tight area on my wrap, or is a coil that is way too loose.) Relieve some tension by turning both trapping nuts on the positive post in the appropriate direction and then redistribute/equalize tension between coils by picking/brushing. The last thing you want to do is to try and bring the wick closer to the post by dragging it over there with the top coil! . . . . Really! (I say all this with tough LOVE )

 

[sling00]

I _can't_ get my coil right! If I use 32 awg Kanthal, i get the top hotspot every time, If i use the 28 gauge, I can't get enough wraps to get the ohms high enough to not fry the juice. My best attempt at a coil just crapped out a couple hours ago (It was working SO GOOD TOO!)

How many wraps and what gauge are you using on your AGA?

 

[Rule62]

Really, this AGA top hot spot business really has my knickers in a knot! It has nothing to do with the distance between the wick and the positive post. Its about the tension, man! Some of my vertical ss mesh setups have had this "hot leg" issue, but it always proves to be that my top wrap is too tight; right before the wire leaves the wick. (In fact, every hot spot i've ever had is immediately above a tight area on my wrap, or is a coil that is way too loose.) Relieve some tension by turning both trapping nuts on the positive post in the appropriate direction and then redistribute/equalize tension between coils by picking/brushing. The last thing you want to do is to try and bring the wick closer to the post by dragging it over there with the top coil! . . . . Really! (I say all this with tough LOVE )

Yep. Totally agree.

 

[pdib]

I've used 28 Nichrome 5/6, 28 Kanthal 3/4, 30 Nichrome 3/4 for .8Ω to 1Ω (solid wicks from 4" of 400 and 5" of 500). I prefer the drill bit method, with adjustments after the wick is in. I once did a 7/8 wrap of 30g inside a phoenix. That was tight.

 

[WinchellNomNom]

Really, this AGA top hot spot business really has my knickers in a knot! It has nothing to do with the distance between the wick and the positive post. Its about the tension, man! Some of my vertical ss mesh setups have had this "hot leg" issue, but it always proves to be that my top wrap is too tight; right before the wire leaves the wick. (In fact, every hot spot i've ever had is immediately above a tight area on my wrap, or is a coil that is way too loose.) Relieve some tension by turning both trapping nuts on the positive post in the appropriate direction and then redistribute/equalize tension between coils by picking/brushing. The last thing you want to do is to try and bring the wick closer to the post by dragging it over there with the top coil! . . . . Really! (I say all this with tough LOVE )

Well said. I just leave enough slack at the top coil and then tighten to perfection

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[vapdivrr]

I _can't_ get my coil right! If I use 32 awg Kanthal, i get the top hotspot every time, If i use the 28 gauge, I can't get enough wraps to get the ohms high enough to not fry the juice. My best attempt at a coil just crapped out a couple hours ago (It was working SO GOOD TOO!)

How many wraps and what gauge are you using on your AGA?

sounds like 30g is in your cards.

 

[Starik]

Why wouldn't the top spot get hot? There's no juice cooling it. The whole wire heats up, the only reason it doesn't glow red when loaded is the juice absorbing the heat. But if you have a big open space where the wire is just suspended in the air, it's going to glow, right?

 

[StaircaseWit]

Why wouldn't the top spot get hot? There's no juice cooling it. The whole wire heats up, the only reason it doesn't glow red when loaded is the juice absorbing the heat. But if you have a big open space where the wire is just suspended in the air, it's going to glow, right?

If you roll a coil on a drill bit and attach it to an RBA without a wick, it will glow from the middle of the coil out and never glow the legs that reach to the negative and positive connections. It should glow the same way on any wick, without hotspots if it is setup correctly. You're correct that juice cooling is what keeps the middle loops of the coil from glowing when wicking properly, but top- or bottom-leg hotspots are symptoms of an improperly set up coil/wick combination.

 

[WinchellNomNom]

Why wouldn't the top spot get hot? There's no juice cooling it. The whole wire heats up, the only reason it doesn't glow red when loaded is the juice absorbing the heat. But if you have a big open space where the wire is just suspended in the air, it's going to glow, right?

Electricity takes the path of least resistance. So remove the wick and juice from the equation and a proper coil should glow red evenly and not just at the top. The electricity is flowing unimpeded from point a to point b minus the even resistance from the resistance wire.

Add the wick. When the electricity flows from the center post through your wire where it first touches the wick or beyond and there is less resistance at that point than the resistance wire, it will take that path. So this contact point is now point b. Point a to b will be the hot spot

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[45root]

i found it to be because of shorts. i have been doing unoxidized wicks lately and when first firing them up, that is the first thing you see. with short steady pulses, you can work it out. the further down you get, the longer the pulse duration. this process has taught me a lot.

 

[Starik]

Electricity takes the path of least resistance. So remove the wick and juice from the equation and a proper coil should glow red evenly and not just at the top. The electricity is flowing unimpeded from point a to point b minus the even resistance from the resistance wire.

Add the wick. When the electricity flows from the center post through your wire where it first touches the wick or beyond and there is less resistance at that point than the resistance wire, it will take that path. So this contact point is now point b. Point a to b will be the hot spot

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I get that.

But let's say you wrap a wick properly and the path of least resistance follows the wire all the way from where the coil touches the negative post to where it touches the positive post. Then you fill your atty with juice. Your wick is wicking as a wick should.

You fire.

Electricity is flowing through the wire, making it hot. It WANTS TO GLOW its so hot. But it can't do that! There's all this damned e liquid in the way soaking up the heat! But at the top, OH at the delicious TOP, there's this arid wasteland... no moisture may set foot here. And it is here that the coil shall GLOW!!!!

Or am I imagining it wrong?

 

[pdib]

you may be imagining it right; but you are imagining. So, yes, you're wrong.

 

[pdib]

That being said. Why, in your imagination, does everyone's top leg not glow?

 

[Starik]

That being said. Why, in your imagination, does everyone's top leg not glow?

Explain it to me. Why doesn't it glow if it has electricity flowing through it and nothing cooling it down?

 

[Starik]

This isn't magic, people. The hotter your coil is, the closer is has to be to a source of liquid, or else it will glow red hot.

The shorter that top connection is, the closer all the wire is to the juicy wick. Washers can help with that.

 

[UncleChuck]

Explain it to me. Why doesn't it glow if it has electricity flowing through it and nothing cooling it down?

At least 2 reasons I can think of:

The metal post acts as a heat sink. The closer to the post you get, the easier heat from the wire is wicked into the metal post.

When wire is straight, with air all around it, there is a greater ability for the wire to cool down. When it's bent into a coil, it is surrounded by other hot coils, so it holds onto its heat longer.

 

[45root]

This isn't magic, people. The hotter your coil is, the closer is has to be to a source of liquid, or else it will glow red hot.

The shorter that top connection is, the closer all the wire is to the juicy wick. Washers can help with that.

its science. unfortunately, im not smart enough to explain it. if your wick is wicking properly, the entire wick will be wet. if you have a hotspot at the top, its a short. it doesnt take much.

 

[WinchellNomNom]

This isn't magic, people. The hotter your coil is, the closer is has to be to a source of liquid, or else it will glow red hot.

The shorter that top connection is, the closer all the wire is to the juicy wick. Washers can help with that.

Look up heat sink and besides that, when you start vaping and your coil gets broken in, your resistance rises even if its only slightly from juice build up and other factors. The coils that touch the juice more frequently builds up more resistance and thats why on a proper set up that top wire between the wick and the center post and the lead extending from the wick to the negative screw doesnt get as hot as the rest of the wire. You can verify this with a meter if you like on a well broken in coil.

Im not saying that washers or a closer center post isnt better. Just saying it isnt a must.

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[octa]

A top coil hot spot is most likely a product of wick shorting out in wick hole is what I've heard & find to be the case a lot. Move wick slightly up or down and if that doesn't remedy it then oxidize the area where wick contacts wick hole watching out for frays also.

 

[dam718]

i found it to be because of shorts. i have been doing unoxidized wicks lately and when first firing them up, that is the first thing you see. with short steady pulses, you can work it out. the further down you get, the longer the pulse duration. this process has taught me a lot.

It's absolutely because of shorts, and having the tension too tight on the top wrap just exacerbates that problem. It causes the resistance wire to kind of dig in to the wick, which will cause a short every time... The only RBA I know of where this effect is minimized is a ZAP that has a silicon gromet in the wick hole. As long as the wick isn't touching the bottom cap of the tank, the wick is isolated from any metal part of the RBA, therefore not shorted to ground. If your wick touches the sides of the wick hole or the bottom plate of the tank, you are almost surely shorted to ground. The wick itself is high enough resistance that this shouldn't be an issue, but it can be if your coil is diggint into the wick anywhere...