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Battery selection for a new build - LG18650MJ1

bestkeptsecret

Bronze Contributor
Member For 3 Years
Hi guys.

I've just started designing my own mod and I am trying to make a decision on batteries. I really like the look of the LG MJ1 18650's. They are high capacity cells rated for 10A.

The reason I am looking at these is I want my mod to go one full day with heavy use with a 0.2ohm coil, and that I can stretch to 2 or 3 days with more moderate use before it needs to be charged.

My plan is to use 6 cells in parallel so the load will be shared, which is why I'm looking at lower current rating/ higher capacity options.

What do you think. Is this a good choice or does anyone have any better ideas?
 

Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
Without knowing the wattage you'll be vaping, it is impossible to say if this will be a good choice. The resistance of the coil is unimportant when determining the amp draw on each battery in a regulated mod.

The batteries that you mention are rated for 10A, but due to their high internal resistance they run very inefficiently if running them at 10A so above 5-7A the 3000mAh cells (Sony VTC6, Samsung 30Q, LG HG2) run longer before they need to be recharged.

At 5A the Panasonic/Sanyo NCR18650GA delivered 8.0Wh versus 7.7Wh for the LG MJ1.

There exist a few high capacity batteries that are bigger than an 18650 and that might be a better choice (depending on amp draw and depending on the size contraints) because they run more efficiently at 10A than the LG MJ1 does, e.g. the Shockli IMR26650 20A 5500mAh (black) and the Sanyo NCR20700B.
 

bestkeptsecret

Bronze Contributor
Member For 3 Years
Without knowing the wattage you'll be vaping, it is impossible to say if this will be a good choice. The resistance of the coil is unimportant when determining the amp draw on each battery in a regulated mod.

The batteries that you mention are rated for 10A, but due to their high internal resistance they run very inefficiently if running them at 10A so above 5-7A the 3000mAh cells (Sony VTC6, Samsung 30Q, LG HG2) run longer before they need to be recharged.

At 5A the Panasonic/Sanyo NCR18650GA delivered 8.0Wh versus 7.7Wh for the LG MJ1.

There exist a few high capacity batteries that are bigger than an 18650 and that might be a better choice (depending on amp draw and depending on the size contraints) because they run more efficiently at 10A than the LG MJ1 does, e.g. the Shockli IMR26650 20A 5500mAh (black) and the Sanyo NCR20700B.

Thanks for the info.

To clarify, I'm not 100% on what I'm going to do yet on controlling wattage.

I'm working on the basis I may ultimately build a PWM circuit to manipulate voltage, or I might just build a DC-DC stepdown. Sort of like the idea of doing both in the long term and having three modes - PWM mode to give variable, Low bypass to operate at a specific wattage and then high bypass which will just let the coil see the full battery voltage and draw accordingly. I think initially would just do the latter and look to make the mod more sophisticated over time.

With coils built to 0.2ohms even without taking into account the voltage drop on applying a load this configuration would only allow an Cmax of 21A (4.2/0.2=A) and following that through it gives you 88.2W (21x4.2). In reality you would see a voltage drop to 3.6 and you are going to be talking about 18A and 64.8W.

As we are talking about a load of around 18-21A split between 6 cells giving us a draw of 3-3.5A per cell im not sure that higher internal resistance would pose a problem for me?

Those Shokli batteries are certainly interesting though so thank you for that idea. 4 of those should give me essentially the same mAh. The immediate pro's/ cons that jump out is con - Adds 90g of weight, pro - only 4 cells to balance instead of 6. Dilemma's dilemma's.
 
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Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
The mAh number alone is useless because the run time is part determined by voltage. Run time = Wh = mAh / 1000 × V

If you compare the discharge graphs you'll see the Shockli runs at a much higher voltage throughout. I mean... even at 7A the Shockli's discharge curve is still entirely above the MJ1 at just 3A so you can expect 3× Shockli cells to outrun 6× MJ1 cells.
 

bestkeptsecret

Bronze Contributor
Member For 3 Years
The mAh number alone is useless because the run time is part determined by voltage. Run time = Wh = mAh / 1000 × V

If you compare the discharge graphs you'll see the Shockli runs at a much higher voltage throughout. I mean... even at 7A the Shockli's discharge curve is still entirely above the MJ1 at just 3A so you can expect 3× Shockli cells to outrun 6× MJ1 cells.

You can use battery capacity against current drawn to give you a good steer. It is accepted practice in engineering circles. I completely agree W-h is liable to give a more accurate figure if done properly, but its no good us using the stated nominal voltages of batteries for that because they themselves are based on a current draw of 0.2C and it would give us a woefully inaccurate figure if we did. We would also need to calculate the nominal wattage of our device over the discharge cycle.

If you think about it a battery holding a higher voltage while it is discharging is going to be discharging at a faster rate in because I=V/R. With only three of those cells you are only going to have 16,500 mAh (More likely 16,200 in practice). With the 6 LG's you are going to have 21,000 mAh ( 20,400). If the Shockli's are maintaining a higher voltage at 7a throughout its discharge cycle than the LG's are at 3.5A the Shockli's are going to be waving goodbye to their mA's at a higher rate relative to the LG's. The double whammy is that the higher the current you draw from each cell against its C. the less of those little mA's you actually you get to use for what you wanted, because more and more of them start going off and doing things you didn't want them to
 

Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
I wasn't talking about using the stated nominal voltages of batteries. Instead, I was talking about the actual discharge graphs that were measured by people like Mooch... these graphs are constant-current, but the reality is that the current drawn from the batteries in a regulated mod each time when we press the fire button is dependent of the voltage we get from those same batteries, and this varies a lot between different batteries because different batteries have a different relationship between amp draw and voltage sag.

If you think about it correctly a battery holding a higher voltage while it is discharging is going to be discharging at a slower rate in a regulated mod because P = I × V where P is the power output in watts so in fact it is a regulated mod's job to make sure it is going to be discharging at a slower rate, i.e. the amp draw on each battery will be lower if the voltage each battery delivers will be higher, unlike with a mech mod (or in 'direct' mode). But that's not where the story ends. At 5A continuous down to 2.8V the LG MJ1 delivered a little over 3,150mAh so at 3-3.5A you can expect it to be about 3,200mAh maybe, but definitely not very much more than that. But 3-3.5A times 6 cells is 18-21A, whereas 64.8W divided by 18-21A is 3.6-3V, not 2.8V, so down to 3V cut-off in a regulated mod it will be much closer to 3,000mAh, which boils down to only about 18,000mAh with 6 of these cells. The Shockli at 10A continuous down to 2.8V delivered a whopping 5,471mAh. Now consider the fact that, due to the much higher voltage it runs at, with 3 cells you're going to be discharging it at much less than 6-7A per cell, i.e. not even remotely close to 10A continuous. So, down to 3V cut-off in a regulated mod, at those kinds of low wattages it will still deliver surprisingly very close to the advertised capacity of 5,500mAh per cell, or 16,500mAh with 3 of these cells. Turn the wattage up by even just a little bit above 64.8W, like, due to also factoring in the efficiency of the mod (if you hadn't already done that) as well as the added voltage drop you'll get from using 6 battery contacts instead of using only 3, and you'll see that 1,500mAh advantage starting to fade into the distant landscape pretty fast. It is like only a 10% advantage even if you don't bump the wattage up higher. (I'm bias, as I can't get a satisfying vape below 88W, and that is with a custom power curve the highest point of which is set to 128% so during the ramp up of the coil it reaches briefly up to 112.64W.)
 

Mattp169

Platinum Contributor
Vape Media
Member For 5 Years
if he builds a pwm its not regulated its basically a mech. but seriously just use some vtc6s there's no real price difference
and with pwm your going to be drawing 15-21 amps at all times. you might be surprised how long 2 vtc6s in parallel will run

also parallel is only going to give you 45-88 watts on a .2 build so make sure that is enough first
 

Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
if he builds a pwm its not regulated its basically a mech. but seriously just use some vtc6s there's no real price difference
and with pwm your going to be drawing 15-21 amps at all times. you might be surprised how long 2 vtc6s in parallel will run

also parallel is only going to give you 45-88 watts on a .2 build so make sure that is enough first
With a dual 18650 PWM and a .2 build I much prefer series (with a potentiometer dial) instead of parallel, but with VTC5A batteries it runs usually less than 3 hours for me. This is by setting the potentiometer to about 55% with the batteries fully charged, and then turning it up one small step each time in order to keep the vape from getting weaker, until finally it reaches 100% so that the batteries need to be changed out shortly after that... IMO dual 18650 mods don't give a whole lot of run time at all.
 

bestkeptsecret

Bronze Contributor
Member For 3 Years
if he builds a pwm its not regulated its basically a mech.
I'm still struggling with what qualifies as a mech. For some it seems putting a fuse in there just in case of a short is absolute heresy, let alone a low voltage cut off and a current bypass.

I also struggle to understand what qualifies as a regulated mod. When you are talking power supplies a regulated supply is one that provides a constant voltage, but no mod does that. The only things that so called regulated mods seem to have in common is PWM and safety features like low resistance protection, low voltage cut off, and firing timing limit.

Based on the features of a so called regulated mod, my plan would fit into that category, as it will have low voltage protection and low resistance protection as well as a PWM circuit albeit with a bypass.

but seriously just use some vtc6s there's no real price difference
and with pwm your going to be drawing 15-21 amps at all times. you might be surprised how long 2 vtc6s in parallel will run
Not long enough sadly, that's why I'm looking at putting 6 cells in parallel if I go with 18650's. I also like the idea of considerably reducing the load on each cell because that brings a lot of benefit too.

also parallel is only going to give you 45-88 watts on a .2 build so make sure that is enough first
I'm counting on it. Its one of the reasons I would be happy bypasing my PCM function and running the mod in full power mode without any Voltage restriction. I've been happy running 0.15 coils on 55W so I think that this setup will be powerful enough for me.
 

Mattp169

Platinum Contributor
Vape Media
Member For 5 Years
You are right, what qualifies as mech vs regulated vs whatever?

To me It has nothing to do with safety features.

There are
  • Variable Wattage
  • EVERYTHING ELSE

In a Variable Wattage we use watts/voltage/efficiency to determine battery amp draw. That is how most devices that are called regulated nowadays work. I think it has to do with the fact and I may be wrong, the battery powers the board, then the board manipulates the power and outputs to the atty how it sees fit based on its programming. So the atty is not drawing power directly from the battery

Everything else such as pwm and variable voltage the atty receives power directly from the battery with just something that limits or alters the voltage the atty receives so you use Ohm's law here

Then of course mech mods do not alter the power outputted from the battery in anyway and you still you Ohm's law here

You could technically add reverse polarity, 10 second cutoff etc to a mech, that doesn't make it regulated nor does it alter how you calculate amp draw on the batteries, but that also increases voltage sag which is the problem because I believe most mech users and mech enthusiasts are about getting as much pure power from battery to the atty with as little interference as possible.

But carambrda has a point, every cell was designed with specific purposes in mind, so they all act differently under different loads. mooch has many nice discharge graphs to view to see which one may work best for your needs. I like your thinking, that you cold go with a lower CDR since you will be in parallel, but that doesn't mean the runtime will be better
looking at the charts
mj1 - https://www.e-cigarette-forum.com/attachments/image-jpeg.613573/
vtc6 https://www.e-cigarette-forum.com/attachments/19da4692-7db1-4f48-88f2-061ff73aa5b8-png.712749/

The vtc6 at 10 amps runs about the same as mj1 at 5 amps but the mj1 does last longer slightly. However there is no data for the vtc6 at 5 amps or even at the 2.4-3.5 amp draw you will actually have in your proposed setup. SO it may be possible that the VTC6 at such low amp draws outperforms the mj1 or vice versa.
The question in my mind is how low of a voltage will be acceptable for a satisfying vape for you. In my PWMs I set my potentiometer are 50% and once the batteries are at about 3.1 volts each, the vape becomes unsatisfying to me. At 3V you may get at most 200 mah difference between the mj1 and the vtc6. but since every battery is slightly different you may see none. now if you find below 3.0 V still satisfying then you will get some additional runtime ALso since you will be doing 6 batteries in parallel that may add to the runtime difference as well.

To me this is a fascinating question, testing versus real world application
ALso the question of how hard do you want it to hit is a factor as well
 

bestkeptsecret

Bronze Contributor
Member For 3 Years
You are right, what qualifies as mech vs regulated vs whatever?

To me It has nothing to do with safety features.

There are
  • Variable Wattage
  • EVERYTHING ELSE

In a Variable Wattage we use watts/voltage/efficiency to determine battery amp draw. That is how most devices that are called regulated nowadays work. I think it has to do with the fact and I may be wrong, the battery powers the board, then the board manipulates the power and outputs to the atty how it sees fit based on its programming. So the atty is not drawing power directly from the battery

Everything else such as pwm and variable voltage the atty receives power directly from the battery with just something that limits or alters the voltage the atty receives so you use Ohm's law here

I think you are right to a point, its more you can take the analysis further. While some devices may let us adjust a wattage figure the electronics aren't doing that directly. You recognise that in what you say above. All the electronics are doing when you fire the device is making and breaking the atomiser circuit very very quickly and by varying the time of the on against the off it gives you a different average voltage across your coils over time. That affects the average current drawn over time and so by virtue of P=IV, it affects average wattage over time. That's all PWM is in a nutshell. Voltage is always the thing being manipulated as you have identified.

On a device with no variable wattage / Joules/ Voltage option all it is doing is not giving you that PWM circuit or control over its timings. Neither is truly regulated in the sense that they take the battery and before doing anything else, look to ensure a constant voltage is fed to the circuitry or to the atomiser no matter what state the battery is in.

From what I can tell from actual device performance every single one works basically the same. They accept a batteries characteristics, live with it, and just work with the voltage as it dips from 4.2 to 2.5 as it discharges. Based on real world performance I don't think the devices do anything to manage/ account for the voltage drop across the battery over its discharge cycle. It seems to me that with a variable wattage device all they do is take a read of the resistance of your atomiser when you attach it and then they divide that resistance by 3.6 to calculate A. The length of the on/off ratio applied to Vin to give a Vaverage is then based on the calculated A multiplied by 3.6 to give you your selected W.

I recon the closest the actual wattage gets to what is displayed on a device is at the battery discharge midpoint. On full charge I reckon it is actually higher, and under the midpoint it is lower. I'm convinced this is how they work because I notice a gradual reduction in performance over the discharge cycle unless I start low and gradually ramp up the selected wattage as the battery discharges. I'd really love to get my hands on an actual circuit diagrams for a couple of regulated mods and then work through them to confirm this is the case.

Then of course mech mods do not alter the power outputted from the battery in anyway and you still you Ohm's law here
Very true and thinking all this through as above. I think we have an answer. The only fixed difference between a regulated and a non regulated mod is PWM.

You could technically add reverse polarity, 10 second cutoff etc to a mech, that doesn't make it regulated nor does it alter how you calculate amp draw on the batteries, but that also increases voltage sag which is the problem because I believe most mech users and mech enthusiasts are about getting as much pure power from battery to the atty with as little interference as possible.
I don't think the protection side of things has that much impact to be honest because ultimately the protection electronics is all very low current circuitry. which is then interacting with the high power circuit to the atomiser by way of transistors. You can see that at a basic level simply by looking at things like the evolve boards and the wire gauges they recommend in their wiring diagrams.

But carambrda has a point, every cell was designed with specific purposes in mind, so they all act differently under different loads. mooch has many nice discharge graphs to view to see which one may work best for your needs.
I've looked through many of them as well as some from electronic engineering sites/ resources. There is a lot to be said for Mooch's efforts. Its great that he takes the time to do so much testing at different A's. Its how you interpret and apply that information is what counts though.

I like your thinking, that you cold go with a lower CDR since you will be in parallel, but that doesn't mean the runtime will be better
looking at the charts
mj1 - https://www.e-cigarette-forum.com/attachments/image-jpeg.613573/
vtc6 https://www.e-cigarette-forum.com/attachments/19da4692-7db1-4f48-88f2-061ff73aa5b8-png.712749/

The vtc6 at 10 amps runs about the same as mj1 at 5 amps but the mj1 does last longer slightly. However there is no data for the vtc6 at 5 amps or even at the 2.4-3.5 amp draw you will actually have in your proposed setup. SO it may be possible that the VTC6 at such low amp draws outperforms the mj1 or vice versa..
Ye cannae change the laws of physics, Cap'n as Mr Scott might say. While there is no test result at the exact amperage that would apply to my design, I can say with certainty that the lower the current drawn from the battery the longer it will last and the more efficiently you will make use of the battery capacity.

This is where I do wonder about Mooch's methodology a little. Personally I would like to see him plotting V against time, rather than Amp-hours. Also he seems to completely ignore how batteries are rated in terms of their mAh. If you want to know if a battery does what it says on the tin you have to understand and respect how the calculations are made. The mAh rating of a Li-ion battery is determined by discharge at 0.2 of its continuous A rating. To see if the quoted mAh of the MJ1 is overstated you would need to test at 2A and he doesn't do that. For the VTC6 it needs to be tested at 3A.

On the MJ1 he's started at 5A and on the VTC he's started at 10A so he hasn't actually tested whether the mAh printed on the batteries is accurate. Which is one of the things he seeks to do with his tests.

He also cuts off the tests at 2.8 which is no good for testing the quoted rating. I get why he does it, but ultimately if you want to see if whats printed on the batteries stacks up you have to Test at 0.2 x Acont and end the test at 2.5V. Its because he doesn't do this that on those graphs you highlighted, that none of the discharge lines come close to 3.000 / 3.500Ah

As far as the VTC test is concerned, something went wrong and a retest was needed. There is absolutely no way a cell can discharge more slowly at 20A than at 15A. Its impossible. If you are testing a cell with a certain capacity, and you draw current more quickly it has to deplete faster - That much is simple common sense. The other thing to remember is that the harder you work a battery the less of its capacity is usable because the energy stored starts getting used in other ways. Look at the temp difference between the 15A and 20A test. That heat is coming from the stored energy.

The question in my mind is how low of a voltage will be acceptable for a satisfying vape for you.
I'm enclined to think that 3V is probably my cut off. That's going to give me 45W at 0.2R and I 45-55 seems to work OK for me.

In my PWMs I set my potentiometer are 50% and once the batteries are at about 3.1 volts each, the vape becomes unsatisfying to me. At 3V you may get at most 200 mah difference between the mj1 and the vtc6. but since every battery is slightly different you may see none. now if you find below 3.0 V still satisfying then you will get some additional runtime ALso since you will be doing 6 batteries in parallel that may add to the runtime difference as well.
Without knowing exactly what your setup is, where you are measuring V to come up with 3.1 and what your pot is actually doing at 50% its hard to draw a comparison. I suppose it doesn't really matter. the big advantage I will get from keeping the load on each cell down is that I will get a higher V for longer. I will certainly get far more run time. With 6 batteries in parallel i'm not taxing the batteries as hard, not losing anywhere near as many of my mAh's to heat. and I will have a huge amount of capacity compared to a 2 cell setup. My batteries should last longer before they need replacing too. The compromise I'm making (there has to be a trade off somewhere) is size and weight.

To me this is a fascinating question, testing versus real world application
If it makes you feel better you are not alone, as you can probably tell by now ;)

Also the question of how hard do you want it to hit is a factor as well
That just comes to coil size and voltage really. By keeping my current draw on each battery low, I would be minimising voltage sag, making the most of what you can realistically achieve in terms of voltage across the coil in a non-series setup. I've been alright with what I can get out of a 0.4 ohm setup so 0.2 will work for me. I reckon.
 
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Mattp169

Platinum Contributor
Vape Media
Member For 5 Years
well you seem to know more than 90% of the vapers out there.
Love the star trek reference extra points for that
mooch's tests are more centered towards pushing batteries to their max potential, because its about what is safe usually. He doesn't focus on the minimums

When you say PWM...i understand that most mods are pulsing regardless of how they are designed. However in the vaping world PWM is a specific style of mod used MAINLy but not always with a potentiometer. there is no wattage adjustment. I get that VW mods are still pulsing but PWM mods and VW are different animals in the vaping world and the calculations I was taught to determine amp draw on the battery is different P=IV vs W/V/Efficiency
I'll be the first to admit I do not understand exactly what is going on in the chips. I just research and do my best

In terms of my own setups I use 2x18650s PWM mods in series that at 50% on the potentiometer simulate more like 50 watts on my .8ohm coils
I know the V of the batteries because my charger tells me that when I put them in so I know it's around 3.1 per cell where my PWMs start lacking even if I start turning the potentiometer up

Based on what you have said I would suspect you might get the same or better run time on the vtc6 at the 2.4-3.5 amp draw you are proposing

I think Mooch cuts off at 2.9ish V on his charts because I BELIEVE and I may be wrong he has stated running them down to 2.5 puts more strain on the battery and shortens their life. But I do get what you are saying about why the charts should go that low. PLUS MOST mods that have low battery cutoff stop at 3.0ish volts per cell. I think this is done to limit amp draw on the battery in a VW device

Mooch is more interested in safety then what a cell can do or was designed to do. He approaches it as what will vapers do with this battery and people will push the limits of safety and do stupid stuff. So I think he presents his data is a way to show you what's the most or worst you should do to a battery and still be safe-ish since most things concerning safety on a cell revolve around amp draw and temperature

Your concept is A Typical I feel. I am still not sure the advantage of carrying around a big ass mod that is 6x 18650s vs a 2x18650 and carrying extra batteries. But everyone has their own unique situations. SO you should do what works best for you. BUt with 6 cells I am not really sure there is going to be much if any runtime difference using the MJ1 and a VTC6. Maybe a few hours. But since your goal is 2 or 3 days a couple hours may not make much of a difference or it could mean all the difference

I would look at big al's Ipwm board it lets you set a memory voltage and maintain a steady voltage across the discharge so you do not have to adjust a potentiometer. This is the board I plan to use on my first build for that very reason. because 85-45 watts is a big range for some people
 

Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
The reason why Mooch doesn't discharge cells at .2A is because he comes from a place where time is money. :) He focuses on being able to compare how different batteries perform differently and the safety, and does so by going where no man has gone before. (No woman has gone there before either BTW.) As for how regulated mods work... they constantly keep monitoring Vin and just work from there. They have to because of the safety. They don't know what batteries you put in them so they have no way of knowing what's nominal. So Vin and the resistance of the atomizer/coil is how, based on their design of course, they work out what has to be done to give you the output power signal you want. I'm not delving into specifics about the various design principles, but usually they switch between different levels and smooth out the result to arrive at Vout. Keep in mind that by doing the switching the amp load on the batteries is constantly jumping about, and that also causes Vin to react, but a battery with a smaller voltage sag is going to give you a Vin the shaky patterns in which are going to be less aggressive and overall easier to deal with from an electronics design standpoint. That's part of why a lot of regulated mods if you're vaping them more or less close to 20A per battery with a 20A battery like, for example, the LG HG2, near the second half of the discharge cycle the vape performance starts taking a hit that could have been largely improved simply by choosing the higher CDR and harder hitting VTC5A instead. (Or the VTC5D, which is even more better for that because of the bit of extra capacity it has, and that I like also on the mech.)
 

bestkeptsecret

Bronze Contributor
Member For 3 Years
well you seem to know more than 90% of the vapers out there. Love the star trek reference extra points for that
Thanks for the vote of confidence.:)

mooch's tests are more centered towards pushing batteries to their max potential, because its about what is safe usually. He doesn't focus on the minimums
In the main that's true. It niggles me a little when he starts criticising the labelling of a battery and than assigning his own capacity ratings but he hasn't actually tested it in line with what those ratings actually stand for.

I appreciate its only a very small part of what he does and establishing how hard you can really work a battery is invaluable stuff. Bearing in mind how long it will be taking him to discharge a battery with all the different loads on them, and the number of batteries he tests he is putting a lot of time into doing it so you have to admire the effort as well as the intent behind it.

I think Mooch cuts off at 2.9ish V on his charts because I BELIEVE and I may be wrong he has stated running them down to 2.5 puts more strain on the battery and shortens their life. But I do get what you are saying about why the charts should go that low. PLUS MOST mods that have low battery cutoff stop at 3.0ish volts per cell. I think this is done to limit amp draw on the battery in a VW device
For Li-ion batteries they are fine to 2.5V. If you take them below 2.4 you start to damage them and definitely shorten their life. There really isn't a lot of merit taking a cell much below 3V in practice so like you say, It kinda makes sense to call it quits just under that. Personally I would like to see him test all cells at 0.2 X its Acont rating down to 2.5 and then do his 5, 10, 15 tests and I'd like him to plot V against Time, but hey, I'm not paying the guy for spending his time doing all this work. If you think about it the VW point isn't really valid because you can't change I=V/R and P=IV. As the batteries voltage is dropping as it is discharging I is going to go down and V is going down.So, your W is going to go down whatever you do to your W setting.

Mooch is more interested in safety then what a cell can do or was designed to do. He approaches it as what will vapers do with this battery and people will push the limits of safety and do stupid stuff. So I think he presents his data is a way to show you what's the most or worst you should do to a battery and still be safe-ish since most things concerning safety on a cell revolve around amp draw and temperature
For sure, though he pushes cells to limits I wouldn't dare to as part of doing that. I'd be very interested to see how his rig is set up. A battery sled attached to some nice thick high amp cable so he can keep them behind some decent shielding, well away from his gear - and himself! just in case they go bang I would hope.


When you say PWM...i understand that most mods are pulsing regardless of how they are designed. However in the vaping world PWM is a specific style of mod used MAINLy but not always with a potentiometer. there is no wattage adjustment. I get that VW mods are still pulsing but PWM mods and VW are different animals in the vaping world and the calculations I was taught to determine amp draw on the battery is different P=IV vs W/V/Efficiency.
Ahh OK. When I've been saying PWM, that includes VW, VJ, VV and even most low powered fixed W devices, because they are all doing that in reality. Whether its via you adjusting a pot, Moving a W/V setting on a display or have no control over settings, they all basically do the same thing. I didn't realise there was a special class of mods which attract the PWM moniker. To be fair that sounds like another typical misnomer that doesn't help anyone. Its a bit like everyone calls the little thing they plug into the wall to charge their phone a phone charger. It isn't at all, its a power supply is all. The 'chargers ' or more accurately charging circuits are actually built into the phones.


I'll be the first to admit I do not understand exactly what is going on in the chips. I just research and do my best.
Thats all you can do really. I just wish manufacturers of electronic gear put a little more technical information in their information sheets and literature so we were more informed and could make better decisions as a matter of course. The only reason I know my mod has a 1.4A charging circuit for example is because I tested it. If the cells are balanced I know there is no chance I will be doing any damage by charging them using it from a current perspective. when I connect the USB up to a 5V supply it cuts off charging at 4.15V so I know its not going to overcharge my cells when I hook it up to a 5V supply. I only know that because I tested that too though. This sort of info should be readily available in the sodding instruction manual for everyone to know.


In terms of my own setups I use 2x18650s PWM mods in series that at 50% on the potentiometer simulate more like 50 watts on my .8ohm coils
I know the V of the batteries because my charger tells me that when I put them in so I know it's around 3.1 per cell where my PWMs start lacking even if I start turning the potentiometer up
That's interesting. If you are using 2X18650s in series and your charger is telling you they both have 3.1V when you take them out you are taking that battery from 8.4V to 6.1V. The information we don't have is what average voltage is being seen across your coils at full charge and when you call it quits because we don't know what the pot is doing to the PWM i.e when you turn it right up is it it pulling low for 0 time giving you the full V that the battery has, or is it still stepping the V down a touch. Similarly when it is set to "50%" is that as low as it will go or is it actually at 50% of the range that it can be turned. Does the 50% represent 50% time at 0V = Time at Vmax when it comes to pulse width, so at full charge is setting giving you 4.2% across the coils dropping very rapidly towards 3.6V unless you adjust.


Based on what you have said I would suspect you might get the same or better run time on the vtc6 at the 2.4-3.5 amp draw you are proposing
Not likely. Based on those graphs you posted earlier I'd say with some degree of confidence you would be looking at around 3.3Ah on the LG's before it hit 2.8V and then on the MJ1s you should just about hit the 3Ah it is rated at. On the voltage, going by the graphs you might see maybe 100mV or so higher V on the MJ1s reducing to no more than 50mV mid discharge and by 3/4 discharge the LG's would then be starting to show a slightly higher V than the MJ1's.

The MJ1's would be slightly harder hitting initially, but that would fade away and by the time you got to 3/4 discharge the more satisfying vape would be coming from the LG's. The LG's would go on longer and give just around 10% more run time than the MJ1's. So say we all.

Having done a little more digging there is a sneeky little cell out there in the 3500 class that might just be worth taking over the LG. The Sanyo NCR18650GA. Its officially rated as a 3300 cell but bucking the trend, it seems Sanyo may have actually understated its capacity.

Your concept is A Typical I feel. I am still not sure the advantage of carrying around a big ass mod that is 6x 18650s vs a 2x18650 and carrying extra batteries.
Well the advantage of having all 6 in the device rather than running them in pairs is the reduced load on each individual cell. This will reduce Vsag and you will get less of a Vdrop under load. It will mean each cell is working less hard, generating less heat and will increase overall runtime.

The downside is the big ass mod, but then I'm already fixated on modding an original gameboy or similar so going there is going to give me a big ass mod anyway.


But everyone has their own unique situations. SO you should do what works best for you. BUt with 6 cells I am not really sure there is going to be much if any runtime difference using the MJ1 and a VTC6. Maybe a few hours. But since your goal is 2 or 3 days a couple hours may not make much of a difference or it could mean all the difference.
Thats the beauty of building your own kit from scratch I suppose, the ability to make things just the way you want it. (The smart money would say 10% additional run time as above.)

I would look at big al's Ipwm board it lets you set a memory voltage and maintain a steady voltage across the discharge so you do not have to adjust a potentiometer. This is the board I plan to use on my first build for that very reason. because 85-45 watts is a big range for some people
That is a great tip. I will look into that. the idea of actually regulating voltage in that way interests me a lot. My thoughts were to use a buck regulator setup to achieve that sort of thing. I'm fascinated to see how someone else has approached it.
 

Mattp169

Platinum Contributor
Vape Media
Member For 5 Years
PWM mods work this way
Full voltage of the battery to the atty at all times less sag
the potentiometer only controls the speed of the pulse. SO at 100 its almost as if there was no pwm chip but then the closer you go to 0 the slower the pulses so it's like turning down the voltage even though it still applies full voltage per pulse.
 

Carambrda

Platinum Contributor
ECF Refugee
Member For 5 Years
The reason why Mooch plots V against mAh instead of plotting it against time is because when you're doing a constant-current discharge test you're testing for capacity so it's only logical you're going to use the unit for electrical charge. It's what the test equipment does because it makes proper sense that way. As for the reason why he doesn't actually test it in line with what those ratings actually stand for, it's because he prefers to test it in line with what it actually stands for in the vaping world, which means the amount of guesswork that he adds is totally acceptable both in that particular context and in view of the fact he only really ever criticizes 60A 9000mAh 18650s. :p
 

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