7.4v rba?

[sentinefour]

Anyone got pics of 7.4v rba setups?

Just curious how many coil wraps would be needed to safely use two 18350 batteries in series (3.7+3.7) for 7.4 volts going to an IGO-W. Would one longer coil be better/ safer? I think I'll need 4+ ohms... not sure dual coil ran parallel would better or worse. Also curious if a heavier ~24-26 AWG wire would be better. Also curious if microcoils would be best.

 

[Butters78]

To be honest I think you're too new to the game to be stacking batteries and what not. Slow down a little.

 

[sawlight]

You really need to have an understanding of Ohms law and batteries to be able to do this safely. What batteries are you using? What is there "C" rating? You "think" you need around 4 ohms, you need to KNOW!
So, with this set up,
7.4v at 4 ohms, 13.69 watts at 1.85 amps, not terribly unsafe in itself, BUT! Are the batteries matched? Have they had the same number of cycles on them? Are the labeled in pairs and kept that way so one doesn't have a higher internal resistance than the other?
We have really done what we can to get away from stacking batteries as it can be inherently dangerous if the batteries aren't cared for and fed properly.
Please, do some more research, learn Ohms law and the forces at work before trying this.

 

[sentinefour]

To be honest I think you're too new to the game to be stacking batteries and what not. Slow down a little.

I've done the research, just wondering if anyone else does this, and has pics. I know what I'm doing, sorry for not having 6,765 posts racked up in nearly 2 years

 

[sentinefour]

You really need to have an understanding of Ohms law and batteries to be able to do this safely. What batteries are you using? What is there "C" rating? You "think" you need around 4 ohms, you need to KNOW!
So, with this set up,
7.4v at 4 ohms, 13.69 watts at 1.85 amps, not terribly unsafe in itself, BUT! Are the batteries matched? Have they had the same number of cycles on them? Are the labeled in pairs and kept that way so one doesn't have a higher internal resistance than the other?
We have really done what we can to get away from stacking batteries as it can be inherently dangerous if the batteries aren't cared for and fed properly.
Please, do some more research, learn Ohms law and the forces at work before trying this.

True! My current batteries are cheap chinese knock offs, no idea the C rating, but yeah I see how important it is to make sure the batteries are of the highest quality. A nice mod + tank with cheap batteries is like putting the cheapest tires on a luxury car... it's silly. I did a little math and came up with 4 ohms to stay within ~6 watts per coil, which is playing on the safe side.

 

[Butters78]

I've done the research, just wondering if anyone else does this, and has pics. I know what I'm doing, sorry for not having 6,765 posts racked up in nearly 2 years

Most of my posts are about my discotheque antics.

 

[sentinefour]

Most of my posts are about my discotheque antics.

This is a great forum, I didn't mean to bash. Just wish you were more helpful. Have you done a 7.4V build?

 

[sawlight]

A 6-7 wrap with 32 gauge should be around 2 ohms, I normally do a 5-6 and get 1.5-1.7 ohm coils. This will net you around 4 ohms, but you will need to check with an ohm meter! The heavier gauge wire will take less wraps, but you will need to check this to know where you are for sure!
Back in the day, we did around 3 ohms on a 5-6v device, by stacking and using a buck circuit to drop the voltage, but like I said, we are trying to get away from this for obvious reasons.
Yes, don't even think about it with the cheap batteries you have! At the minimum get the AW IMR batteries. If you want to run four, two in, two charging, make sure you label them in pairs and keep them that way!

 

[Butters78]

This is a great forum, I didn't mean to bash. Just wish you were more helpful. Have you done a 7.4V build?

Sawlight covered it. I just think it's not wise to stack batteries without protection unless you're using it in something protected like a buzz pro for example.

 

[sentinefour]

A 6-7 wrap with 32 gauge should be around 2 ohms, I normally do a 5-6 and get 1.5-1.7 ohm coils. This will net you around 4 ohms, but you will need to check with an ohm meter! The heavier gauge wire will take less wraps, but you will need to check this to know where you are for sure!
Back in the day, we did around 3 ohms on a 5-6v device, by stacking and using a buck circuit to drop the voltage, but like I said, we are trying to get away from this for obvious reasons.
Yes, don't even think about it with the cheap batteries you have! At the minimum get the AW IMR batteries. If you want to run four, two in, two charging, make sure you label them in pairs and keep them that way!

Thanks a bunch. Just curious. Yeah I didn't think 3.7v batts were around that long. I'm not trying this, just was curious, because I haven't heard of it being done. I just like the idea of having more than twice the surface area of a heated coil on a wick. I think it would make an insane amount of vapor. But yeah, I don't have the equipment to safely do this. Thanks again.

 

[sawlight]

Well, think about how long laptops have been around? 3.7v batteries were out before them because that's what they use to power them! Remember the old "bag phones"? Packs of 18650's to power them. I can go on, but I think you get the idea, they've been around a lot longer than people think.

 

[Visus]

It can only make as much vapor as it can be fed

A slr micro coil @26 gauge 3.7v will choke you, theres so much vapor..

 

[Thrasher]

I dont think people are stacking batteries in a mech as this is inherently unsafe and too many variables.
the only stacked battery regulated/vv mods are just using them to make sure the current is there then stepping down the voltage.

 

[dr g]

4 ohms is likely too high. At that wattage there's no reason to stack.

I would strongly suggest not stacking with 18350s. There's just no real reason to and some significant safety concerns.

 

[UncleChuck]

I can't think of any reasons why you would need to stack batteries with a mech and RBA, but if you must, remember that a battery off the charger is around 4.2v. So stacked fresh batteries will be over 8v starting out. Just something to take into account with power calculation. Make sure you have good batteries as well, for 18350s AFAIK there's nothing better than the AWs. Anyone know if MNKE makes any high current 350s?

Personally I feel the dangers of stacking batteries are greatly overblown. As long as you don't draw more current than the battery can handle you aren't stressing the batteries, and if you aren't stressing the batteries I can't see any reason to worry.

The resistance you need to aim for depends on the thickness of the wire. Thicker wire, you'll need a lower resistance to get a given level of performance. Thinner wire, you'll need a much higher resistance level to avoid burning your juice. 3ohms with 28 gauge wire could work well, although that's going to be a HUGE coil. I have trouble fitting 1.5ohm with 28ga in some of my smaller RDAs. You could try a split coil, where the coil is basically bent in half and has two wicks. It looks like a dual coil setup, but it's actually just a single coil, so you can fit more wraps in a given area.

 

[Oomee]

I've done the research, just wondering if anyone else does this, and has pics. I know what I'm doing, sorry for not having 6,765 posts racked up in nearly 2 years

True! My current batteries are cheap chinese knock offs, no idea the C rating, but yeah I see how important it is to make sure the batteries are of the highest quality. A nice mod + tank with cheap batteries is like putting the cheapest tires on a luxury car... it's silly. I did a little math and came up with 4 ohms to stay within ~6 watts per coil, which is playing on the safe side.

Hehehe .
Need I say more ?

 

[AttyPops]

The problem is, sorry to say this, you need more research. You basically shouldn't have to ask if you understand it. That's not to say asking is bad, but you can't claim full understanding and need to ask at the same time.

Firstly, you'd want around 2 or 2.3 ohms for a "normal" 3.7 volt source. Some go lower, like 1.8. This is for standard ga wire. With heavier ga you need more watts so even lower ohms.

Now, if you double the volts, you're going to have to double the ohms OR MORE due to the fact that the voltage is squared in the calculations (Watts = Voltage²/ohms).

You need to figure out the wattage you need for the ga wire you're using. Then use the watts and the voltages to figure out the ohms you need to get those watts PER COIL.

So if you're stacking batteries and doing calculations you'll see that 7.4 volts and, say, 8 watts is 6.8 ohms and about 1 amp.
So a dual coil would come in at 3.4 ohms (two 6.8 ohm coils) at 7.4 volts with 8 watts per coil and use a little over 2 amps.

Make sense?

The real issue is stacking batteries. Those smaller batteries have lower C ratings. And the max-amps for batteries DO NOT STACK like voltage does. So your amp limits on the device are the amp limit of ONE battery. And you have double the "oomph" of the doubled voltage pushing current when there's a problem. It's easy (at least twice as easy) to overheat a cell when they are stacked due to that extra voltage in the circuit. So if there's a short, you not only exceed a single cell's amp rating, but you push the excess current twice as hard through that cell.

So at least use the safest batteries (highest amp rating) you can find. Good ones. And check for shorts.

A couple of other things:
1) Make sure the mod is well vented.
2) consider a vape fuse if it's within the amp rages you are working with and fits in the mod and doesn't block the vents.
3) You may wish to do the calculations both ways...with single and stacked cells. You'll find that a single cell with higher C rating can do what you want in a safer manner. Just swap it out sooner for another one.

 

[dr g]

Well the double-voltage, double-resistance thing doesn't really hold up. In my experience larger coils eat wattage at an increasingly greater rate, it's not a linear relationship. IMO if you increase resistance that much you are going too far.