Bulli Dual Core Experiment

[rawveg]

Over on UKV there's a nice long thread about the Bulli A2 Atomiser, and the question was posed by pancho (so this is his fault), if anyone had tried wiring a Bulli up with Dual Cores... well, I can't say that I have actually come across that, so this lunchtime, I decided to give it a go.

This isn't entirely scientific, and as I'm at work I haven't been able to do a video of the result, though I will do one and post it tonight if I can - though my daughter's birthday today may make it awkward, I'll still try....

Anyway... I was a little concerned about space in the A2, so for the purposes of this experiment I used the Bulli A1 Atomiser, which has a slightly larger footprint, and is therefore easier to wire with two atomiser coils.



Taking the A1 apart, I've already got one coil in there, which I only added yesterday.



I'm not daft, as that's a fairly new coil with only a little bit of use, I'm actually going to keep that coil and add a new one on the opposite side of the atomiser, like so:-



As you can see, there's the original coil, and the new coil which is, as yet, unprimed... the A1, I've found is a little more particular than the A2, in that once you've put the coil in place, you do need to tease it into an upward position. This is because I've found that the increased footprint of the A1 means that if you don't then a good part of your wick will remain at the opposite side of the atomiser chamber, and won't actually wick at all... however, if you tease it into an upright position, then the wick extends upwards, and picks up from the cartridge above. So before sealing the atomiser chamber, I primed the new wick and coil and teased both coils into an upright position. I reassembled, and then pushed the A1 into my Bulli Extreme...



The Bulli Extreme is not the nicest looking of mods, sadly, but this one has an RCA connector (Bulli refer to it as an A1 connector, but it's RCA) for use with the A1 Atomiser. I then took this outside (can't vape in the office), and gave it a try out.

First impressions are that I need to hold the button on for a couple of seconds to give both coils chance to heat up... I will try this later on with a pair of stacked CR123a's, but for now this is working on a single 18650, vaping Vapour World's RY4 24Mg strength VG.... once the coils had heated up, this thing hurt... I mean my tongue was literally stinging... it was almost like I'd started vaping on 50mg nic! You know that sensation you get when the Nic is too strong, it kind of tingles on the tongue and then hits you at the back of the throat? This is exactly what I get with this setup.

I can vape it, but after a few draws, I have to stop... my palette (and my head) can't take it.

Vapour production was about the same as single core if I'm brutally honest, I didn't notice an increase there at all, flavour was intense too! I need to try this with a lower nic content juice, which I don't have with me at the moment, and I also need to try this at 6v to see if there's much of a difference, but I think I will stay sat down for that one!

[Lee]

Looks like you may be onto something there. Can you change the resistance to see if that improves things?

[rawveg]

Jun 14, 2011 13:32:39 GMT Lee said:

Looks like you may be onto something there. Can you change the resistance to see if that improves things?

Absolutely... sadly I don't have a multimeter with me, which I need to use on the A1, so I've had to guesstimate... the original core was wound to 3 ohms, and the second core I wound in much the same way (same number of turns), but I do need to check this... all very unscientific of me I know, but well, when the opportunity arises carpe diem!

I'm thinking that I will need to wind to a lower resistance, which is in part why I'm going to try stacking some CR123's in there (which I'm about to do now as I'm heading off to the smoke shelter)....

[ian]

Nice one Tim,i love the way you get these ideas and follow them through so quickly.I saw Pancho mention it on UKV and you have done it already I also think you are on to a winner with this,great work as always.

[rawveg]

Thanks Ian!

Right, I've just been trying this out with stacked CR123a's... it definitely works... you hear the phrase "Like a Steam Train" alot... but let me put it this way, at 6v, this thing was generating so much vapour in the atomiser chamber (which on an A1 is fairly huge to begin with), that I actually couldn't hear anything going on.

Normally with a Bulli, you can hear that distinct hissing sound, like a snake under a blanket, but this was completely silent, and I was convinced I had burnt out the coils. I switched the stacked cells over for an 18650, and the hiss was back... OK, then, it's working...

So back in with the stacked cells, and I take my first draw and POW, right to the back of my throat, barely a draw needed... the coils hadn't needed time to warm up at all, it was there instantly... massive (I do not use the word lightly), massive amounts of vapour!

The only downside is that my juice isn't HV friendly, and sadly the taste had that distinct burnt flavour to it... check of the coil and they're still nice and moist, so it wasn't a problem with wicking, no dry spots, simply the juice...

So, the next part of this test will come later tonight. I'll wind two coils to 1.5 Ohms each, and then try those on a single 18650 cell and report back with the results!


Tim

[roachieuk (aka eciggery2011)]

Hi Tim,

Wow this would be brilliant if you can get it working this is totally amazing progress mate.By the sounds of things in progress this is something what i shall be following with eager tbh.For when i finally purchase my bulli it was something you know i was thinking of but just thought it would sound clap trap in all honesty but my idea was slightly diffrent and doubt if it would work.

But please keep it updated as i shall be watching this with great eagerness and hope.Thanks very much for sharing much appreciated.Well done for trying something that most wouldnt and hope you can get this working fully.

[rawveg]

Ok, no wonder this thing was blowing my head off... In parallel the coils are reading a resistance of 1 ohm... Will check each one on it's own but this definitely explains it...

I've tested the resistance of each coil individually, and the maths doesn't stack up...

Coil 1 reads 3.1 ohm
Coil 2 reads 2.7 ohm

Making 2.9 ohm on aggregate, however my reading was 1 ohm!

I'm going to see what effect higher resistance coils have when paired on the bulli, it would seem I can get a decent aggregate reading from the terminals with could in place..

Right, I think I've hit on something here....

At the moment I'm trying to wind higher resistance coils, based on the maths earlier not working out,i figured that if roughly doubled the resistance or number of turns per coil that the overall resistance would double. It does not.

A coil made of 6 turns produces 3.1 ohms, the same result as 5 turns, the problem is that the same result is produced for 7 and 8 turns too.

This leads me to believe that there are limitations, imposed most probably by the distance between the electrodes, and the grade/size of the wire used.... I think here the problem is probably the distance between electrodes, as the more turns, the closer the turns need to be, if too many turns are in contact with each other, then the resistance offered by those turns is negated, by simple fact of the circuit is completed by the most efficient route.

This may go some way to explain why the math earlier didn't work. In the dual coil setup, the most efficient route to complete the circuit, the route of least resistance was the 1 ohm route.

Given this, and the effective distance between the electrodes, I can only conclude that a dual coil setup with a bulli, while possible, is not practical, as the effective resistance is too low.

If there are any ideas I would welcome them, but here endeth experiment 1... (experiment 2 cometh soon... watch out for it)....


Tim

[clockworks]

Try using some thinner (higher resistance) wire. There's a seller on eBay listing "Kanthal" resistance wire in various diameters. He quotes the resistance per metre of the different sizes.

As you've noticed, the resistance depends on the length of the wire. Forming a coil just allows you to pack more wire into a shorter effective length (distance between the connectors). If the coils touch, you are shortening the length of the wire.
Using thinner wire will allow you to wind a 5-turn coil with a higher resistance.

I think that the Bulli uses 0.20 wire. Try using 0.13 - it's approximately double the resistance of 0.20.

[Lee]

I thought when you made your coils you had to make sure they didn't touch. Otherwise there would be no point in adding more winds to change the resistance as like you say the circuit is completed by the most efficient route. I'd be interested to see you try clockworks suggestion of thinner wire to get a better result.

[rawveg]

Jun 15, 2011 7:36:54 GMT clockworks said:

Try using some thinner (higher resistance) wire. There's a seller on eBay listing "Kanthal" resistance wire in various diameters. He quotes the resistance per metre of the different sizes.

As you've noticed, the resistance depends on the length of the wire. Forming a coil just allows you to pack more wire into a shorter effective length (distance between the connectors). If the coils touch, you are shortening the length of the wire.
Using thinner wire will allow you to wind a 5-turn coil with a higher resistance.

I think that the Bulli uses 0.20 wire. Try using 0.13 - it's approximately double the resistance of 0.20.

I already use that trader (he has a site buymywire.com), and I've got .20, .16 and .13 Kanthal, I'll give the .13 a try if you you think that'll offer a greater resistance... to be honest though, it is moving slightly from what I wanted to achieve with this, but I'll give it ago.

What I mean by the above, is that I wanted to do this with the materials that a Bulli owner would naturally own... buying different grades of wire isn't too bad I suppose... but what the hey, I shall try it.

[rawveg]

Jun 15, 2011 8:29:48 GMT Lee said:

I thought when you made your coils you had to make sure they didn't touch. Otherwise there would be no point in adding more winds to change the resistance as like you say the circuit is completed by the most efficient route. I'd be interested to see you try clockworks suggestion of thinner wire to get a better result.

Yes, that's right, but that was kinda my point. The distance between the positive and negative terminals determines the maximum number of turns you can put on your coil before you're packing them in so tight that they will touch...but I will give this a try.

[Lee]

I get what your saying now. I've read that the wire comes in so many ohms per metre or whatever. So however many turns you make out of say an inch of wire, the resistance won't change. Is that right or am I confusing myself again?

[rawveg]

Jun 15, 2011 21:35:15 GMT Lee said:

I get what your saying now. I've read that the wire comes in so many ohms per metre or whatever. So however many turns you make out of say an inch of wire, the resistance won't change. Is that right or am I confusing myself again?

Not quite what I'm saying. You can vary the resistance with the number of turns, that part is right, but you're governed by the distance between the electrodes, so there is a point where no matter how many turns you make the resistance will remain a constant.

[Lee]

I'll have to get some wire and a multi meter, do some homework and try to figure it out myself. I really should have paid more attention in school.

[clockworks]

Just to clarify (or confuse further!):

The resistance is set by the effective length of the wire, and the cross-sectional area of the wire.
I say effective length, because tightly packed coils will short out. If two coils are touching, the effective length is reduced by one coil.

0.20 Kanthal wire has a resistance of 43.8ohms per metre. To get a 1.5ohm coil, you need to use a 34.25mm length of wire (1000/43.8 x 1.5). Note that this is the length of exposed wire between the terminals. The wire clamped inside the terminal is shorted by the terminal itself, and doesn't count.

How you wind the wire doesn't affect the resistance, as long as it doesn't short back to itself.
A straight piece of wire 34.25mm long will have the same resistance as a 34.25mm length with two big coils, or 3 medium coils, or 4 small coils, or five tiny coils.

The layout of the coils around the wick affects how the heat is transferred to the juice, and thus the amount and quality of vapour produced. This is where experimentation comes into play. I'd guess that a longer, looser, coiled section would work better than a short,tight, coiled section with longer ends. That's only a guess, mind.

Thinner wire has a higher resistance. In theory resistance is inversely proportional to the cross-sectional area, or the square of the radius of the cross-section. 0.13 wire has more than twice the resistance of 0.20 wire. I say in theory, because the figures don't work out exactly, but are pretty close. I guess maybe skin effect plays a part?
Whatever, the quoted ohms per metre lets you work out how much wire to use to get the required resistance - 1.5ohms needs:

34.25mm of 0.20 wire
22.5mm of 0.16 wire
15mm of .013 wire

So, 3 different ways of getting the same 1.5ohm resistance. I guess the 0.13 wire would be too short to turn into a coil, so your choice is between 0.16 and 0.20.