Resistance does not factor regarding amp draw in regulated mods?

[conanthewarrior]

Hi everyone, I hope you are all OK.

I have a question, mainly regarding amp draw on a regulated mod, and whether resistance has a part to play, or not.

I have always been told on other forums, that resistance does play a role, for example at 0.5 Ohms at 50W, with a freshly charged battery, would be drawing 10A from the battery, stepped up to 5V by the board(Or bucked on a dual 18650 mod).

I did once question whether resistance mattered with regulated mods, to be told by upstanding members "Of course it does, Ohm's law does not change because you are using a regulated mod, 50W at 0.5 Ohms is pulling the same amount at 4.2V (battery voltage) whether on a regulated mod or a mech". EDIT(Sorry, I should of put the correct Wattage, of 35.28 watts for the mech-I get confused sometimes due to what happened, and I think where I was talking about 50W in a regulated mod, this lead to my confusion and I stated 50W at 0.5-I understand even the 35.28W would be in perfect conditions, at 4.2V, with no voltage sag, perfect conductivity, and everything working perfectly, I understand in real world cases it would not even be 35.28W)

I understand that on a regulated mod, as battery voltage decreases, amp load increases to maintain the wattage you have set.
I also understand that resistance plays a role if you want more power from your mod, and are a cloud chaser who wants say 150/200W. (I don't fall into that category, most of my vaping is done under 30W).

But, I have seen on here that resistance has no role to play in regards to amp draw on a regulated device.
So, I want to know really, have I been misinformed for the past 14 months, and resistance does not play a part in regulated mods, and calculating amp draw for them is completely different to how I would of calculated for a mech? Apart from if you want more power, and the narrow band of low resistance necessary on some mods to build at to achieve this?

It seems that on here, things get a lot more in depth, which I like, so I will likely finally get an answer to the question that has been bugging me for a long time.

I apologise in advance if this is not written as perfectly as it should be, I find it hard to express what I want too after what happened.

Thanks everyone, and all the best.

 

[Chips177]

It does play a part, but most regulated mods have amperage restrictions to limit them from firing above a set safe amperage as the battery depletes. So that .5Ω at 50w might hit great on a fresh battery, but will get ramped down once the amperage limit hits

 

[conanthewarrior]

It does play a part, but most regulated mods have amperage restrictions to limit them from firing above a set safe amperage as the battery depletes. So that .5Ω at 50w might hit great on a fresh battery, but will get ramped down once the amperage limit hits

Thank you-that was in essence what I understood.

Glad to know I did get the correct information, as I always make sure that I 100% know things, before I pass on information to others.

I understood that the fresh battery will hit great, but as voltage drops, amp load is increased to maintain your set power, but it can not do this if it hits the amp limit of the mod.

Thank you for your answer .

 

[Completely Average]

The answer is yes, it plays a part, but unlike a mech mod the part it plays is indirect rather than direct.

With a regulated mod it's really your voltage that is adjusted and is the main factor in the power you provide to your atomizer. The resistance is only factored in so far as determining what voltage you can apply. This does influence the amps drawn, but it isn't as directly linked like it is in a mech. With a mech you can damage your battery if you draw too many amps, with a regulated mod the mod will automatically step down the voltage if there aren't enough amps to provide the desired setting.

 

[conanthewarrior]

The answer is yes, it plays a part, but unlike a mech mod the part it plays is indirect rather than direct.

With a regulated mod it's really your voltage that is adjusted and is the main factor in the power you provide to your atomizer. The resistance is only factored in so far as determining what voltage you can apply. This does influence the amps drawn, but it isn't as directly linked like it is in a mech. With a mech you can damage your battery if you draw too many amps, with a regulated mod the mod will automatically step down the voltage if there aren't enough amps to provide the desired setting.

Thank you, in essence this is what I understood, as I have done more reading into the subject, I felt here I would get a solid answer though-which I have, thanks to you and @Chips177.

It was something I was pretty sure I understood, but I did not want to pass on any information until I was 100% on the matter, I am now.

The main reason I own many more regulated mods than mechs is for this, amongst other reasons. With the amp limit on a regulated mod, I feel a lot safer with a regulated mod, that offers a multitude of protection-I still always ensure I am careful, I don't think as the mod offers protection, you should ever slide on safety-but it is reassuring to know it is there, just in case.

 

[daviedog]

You may want to look up an older thread here. What about Watts Law. Last Jan i believe. Consider it the best thread of the year so far..

 

[bwh79]

I did once question whether resistance mattered with regulated mods, to be told by upstanding members "Of course it does, Ohm's law does not change because you are using a regulated mod, 50W at 0.5 Ohms is pulling the same amount at 4.2V (battery voltage) whether on a regulated mod or a mech".

Thing is, you don't get 50W from a mech at 4.2V on a .5-ohm load. You only get about 35 watts from that. Watts = Volts^2 / Ohms, so you're looking at 4.2^2 / .5 = 35.28 watts, and never anything else (until the volts and/or ohms are changed, and then the watts will change as well.) That's the thing about mech mods. You can always turn the power up on a regulated device; on a mech, you're stuck with what you get.

The key thing to realize here is that power, or wattage, is the conserved quantity. "Power in equals power out," as they say. So if the device is delivering 50 watts to the atomizer, for example, then it is also, by definition, pulling 50 watts from the battery (plus a few % to power the device itself, but we can ignore that for the moment.) One formula to determine amp draw is:

Amps = Watts / Volts

No matter what the output power of your device is set to, the battery only outputs a single voltage (roughly 4.2 at full charge, less as the battery depletes.) So if your battery is sitting at, for example 4.0 volts, and the device is set for 50 watts, then the amp draw on the battery is 50/4 = 12.5 amps.

Note that I didn't mention the ohms value at all. Note also that I came up with a perfectly valid amp reading, without even knowing what the ohms were! That's because for a wattage-regulated device, amp draw is determined only by the watts setting, and the battery's charge state (and the device's own efficiency, we'll get to that later), and not at all by the resistance value of the attached load. Or to put it another way, ohms don't matter on a wattage-regulated device! All you need to know to determine your amp draw, are what watts the device is set to, how many volts are the battery charged to, and how efficient is the device itself.

Ohms are in there, somewhere, but they're hidden. Watts are equal to Volts*Amps, but, because those "Amps" are themselves equal to "Volts/Ohms," then Watts are also equal to Volts*Volts/Ohms. So when you set the device for 50 watts, it has to read the ohms, multiply it with the watts you set, and then take the square root of that value, to find the appropriate number of volts to provide, so that the actual amount of watts delivered, will be the same as what you've chosen. So when we say that ohms don't matter, we mean they don't matter to you, the user, in determining how hard it will stress your battery. But they do matter very much indeed, to the device itself. You just don't need to concern yourself with them, again, for the purposes of determining amp draw. It will of course make a difference in the overall experience.

About that "device efficiency." When your device pulls 50 watts from the battery, it can't deliver them all to the atomizer. It needs to keep a little bit of that power for itself. So in order to deliver 50 watts, it has to draw a little more than that. To determine the actual amp draw, you take the one calculated earlier, and divide by the device's efficiency (or just use 90% if you aren't sure.) So then we would have a final amp draw of 12.5 / .9 = 13.888... amps, at 50 watts (on any resistance.)

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Now let's look at mech mods for a minute. If watts and volts are all that matter on a regulated, why aren't they all that matter on a mech? And they are, sort of. Again, let's say you're using a mech mod, you're getting 50 watts from it, and your battery is at 4.0 volts. Again, then, you're pulling 50/4 = 12.5 amps from the battery. HOWEVER, all of this is only possible if you have a very specific resistance. Specifically, 0.32 ohms. If it were anything else, then it wouldn't equal 50 watts, and for this example we have already defined it as being 50 watts. And, after you take a hit or two, and the battery drains down from 4.0v to 3.99v, then it won't be 50 anymore, either. But for a very brief moment, it all comes together. See, in a mechanical mod there is no regulation; battery voltage is delivered to the atomizer directly. So if Watts are equal to Volts*Volts/Ohms, and you change the ohms, then you change the watts. If you change the volts, then you change the watts. If you change any one thing, then one or both of the other values have to change as well, to keep everything balanced. But unlike with a regulated device, where you just "set" the watts and let it do the dirty work, with a mechanical mod, the only way to even know the watts in the first place, is to calculate them using the resistance value and battery voltage. Then, since what we're really after is the amps value, you don't even need to check the watts since the volts and ohms are all you need. Of course, you can still figure out the watts if you want to, it just isn't necessary.

To get the amp draw on a mechanical mod, divide battery voltage by resistance. You need to know the resistance, or you can't make this calculation. You could also calculate the watts if you like, but it won't tell you anything about battery safety.
To get the amp draw on a wattage-regulated mod, divide watts setting by battery voltage, and then by device efficiency. You do not need to know the resistance, because the device knows it already, and knowing the reistance wouldn't help anyway, since all you're looking at is watts over volts. Also keep in mind this is battery output voltage, not the same as voltage applied to the atomizer. If those were the same, it wouldn't be a regulated mod. That's the point of regulation, that's what it does. That's what it means.

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With a mech you can damage your battery if you draw too many amps, with a regulated mod the mod will automatically step down the voltage if there aren't enough amps to provide the desired setting.

And how, pray tell, does the device know whether you have a 5A or a 25A battery installed? Maybe it has an amp limit of 17.5 amps, perfectly safe to put a 20A battery in there and push it as hard as the mod will allow. Try that with a 5A battery in there and you're going to have a problem. Whether or not it's a mech is not the issue here, you can still "draw too many amps" and damage the battery, the device, or yourself, if you expect it to do all of the thinking for you...

 

[Completely Average]

And how, pray tell, does the device know whether you have a 5A or a 25A battery installed? Maybe it has an amp limit of 17.5 amps, perfectly safe to put a 20A battery in there and push it as hard as the mod will allow. Try that with a 5A battery in there and you're going to have a problem. Whether or not it's a mech is not the issue here, you can still "draw too many amps" and damage the battery, the device, or yourself, if you expect it to do all of the thinking for you...

Two words.

Voltage Sag

If your batteries can't supply the necessary amps then the voltage drops through the floor, triggering the low voltage protection. Most mods will simply not fire, some of the newer ones will throttle the voltage back.

This is why people who subohm at high wattage settings with regulated mods may see a quarter or more charge left in their battery indicator, but the mod doesn't fire and the batteries indicator instantly shows the batteries fully depleted when the fire button is pressed. The required amp draw is more than the batteries can provide, so the voltage sags below the minimum limit of the mod. If you put a fully charged 5A battery into a 75W mod and try to fire it at 75W it will instantly go into low voltage protection because the amp drain causes a massive amount of voltage sag.

 

[speedy_r6]

At any fixed wattage number, the resistance doesn't really play any role in the amp draw from the battery on a regulated mod. If you are drawing 37 watts from a single battery holding a steady 3.7 volts, you are drawing 10 amps from the battery. It doesn't matter if the coil is a 0.2 ohm coil or a 2 ohm coil. 37 watts at 3.7 volts will always be drawing 10 amps. The mod will either step the voltage up or down to the voltage required(assuming the mod can step it up to the voltage needed to run the watts you are trying for) to fire the coil at the wattage you specify.

For ease of explanation, we are just going to assume the battery is holding a steady 3.7v in all instances for this explanation. We are also going to assume the mod is perfectly efficient, even though that won't happen in the real world. In the real world, the amp draw will be slightly higher because of the inefficiency of the mod.

In the case of the 0.2 ohm coil, it will draw 3.7v from the battery at 10 amps to get the 37 watts needed, and then the chip will buck down the voltage and send 2.72v at 13.6 amps to the coil.

In the case of the 2 ohm coil, it will again draw 3.7v from the battery at 10 amps to get the 37 watts needed. From there, the chip will step up the voltage and send 8.6 volts at 4.3 amps to the coil.

In both cases, the amp draw on the battery is 10 amps.

 

[Ryedan]

I have a question, mainly regarding amp draw on a regulated mod, and whether resistance has a part to play, or not.

There are two kinds of regulated mods, variable resistance and variable wattage. Most of our mods today are VW, but there are still a few VV mods on the market and I suspect there are still a whole bunch of older ones in use.

With a VW mod you set the watts and the mod does its best to output that. Resistance theoretically (mostly) doesn't matter. If you set 50 watts, the mod will put 50 watts into the atty. It will draw about 5-10% more than that from the battery(s) to compensate for efficiency loss from the electronics, but that's pretty minor.

Looking at battery amp draw, you have to take battery voltage into consideration though. I like to use the Steam Engine battery drain calculator for that. The lower the battery voltage is, the higher the battery amp draw is for a given wattage. For one battery mods I use 3V (under load) to calculate max amp battery draw. Play around with the calculator and you'll get a feel for how things work.

With VV mods resistance is as important as in mechanical mods, but you have the voltage regulator to limit the amp draw if you get things wrong. Change the Steam Engine page to VV and play around with it. I input battery voltage as 4.2V 3V also in that scenario as battery amp draw is highest in this case with VV. It's the opposite with mech mods.

ETA: Corrected battery voltage for calculating battery max amp draw for VV mods.

 

[Jim_ MDP]

I input battery voltage as 4.2V in that scenario as battery amp draw is highest in this case with VV, as it is with mech mods.

This is the only part I disagree with and it's just a feeling.

It's not bypass or mech mode.
If it's still regulated with a boost circuit the mod will draw what it needs, within its limits, and that means a higher draw as the cell depletes.

Yes?

If I'm in VV mode set at 4.1v... I can't see it being easier on the cell when it hits 3.4v.

 

[conanthewarrior]

There are two kinds of regulated mods, variable resistance and variable wattage. Most of our mods today are VW, but there are still a few VV mods on the market and I suspect there are still a whole bunch of older ones in use.

With a VW mod you set the watts and the mod does its best to output that. Resistance theoretically (mostly) doesn't matter. If you set 50 watts, the mod will put 50 watts into the atty. It will draw about 5-10% more than that from the battery(s) to compensate for efficiency loss from the electronics, but that's pretty minor.

Looking at battery amp draw, you have to take battery voltage into consideration though. I like to use the Steam Engine battery drain calculator for that. The lower the battery voltage is, the higher the battery amp draw is for a given wattage. For one battery mods I use 3V (under load) to calculate max amp battery draw. Play around with the calculator and you'll get a feel for how things work.

With VV mods resistance is as important as in mechanical mods, but you have the voltage regulator to limit the amp draw if you get things wrong. Change the Steam Engine page to VV and play around with it. I input battery voltage as 4.2V in that scenario as battery amp draw is highest in this case with VV, as it is with mech mods.

Thank you .

I used 50W as an example, I realise this is not what you would get at 4.2V at 0.5 on a mech. It should read 35.28W, and that would be in a perfect case scenario without any voltage sag, perfect conductivity, and a dead on 0.50 build.
I think where I was talking about a regulated mod stepping up/down voltage to 5V lead to my confusion.

I apologise here, I have a bit of damage up top after something that happened in 2014(it is not severe), so sometimes I do not get my point across in the best way possible, or may get confused- I type just what I am thinking when I am discussing my own questions, I apologise for that, my thinking patterns are no longer the same as they once were-an example that makes sense to me for my own questions will often be phrased wrong, or asked about in a long fashion. Sorry.

I had used the steam engine battery drain calculator before, plus the mod range calculator, at first I was not sure if you entered actual battery voltage, or voltage after the board on screen-I realised it was actual battery voltage soon enough though.

I am really glad my thoughts on what I read was true,And have 100% clarification on the matter, so I can also help others-I do in other areas, but I do not like passing information on I know could be untrue.

All of the mods I own are either Vw, or Mechanical (More VW though).
I understood efficiency had a role to play in this too, but like you say it is relatively minor.

I also understood that the lower the actual Voltage of the battery/batteries, the more amps are drawn to compensate to provide the same wattage for as long as possible, until max amp draw is hit, and then power will be reduced-or not fire at all.

Even after all this time, I still double check all my calculations on steam engine-just in case. Steam engine was my friend from my first mod, to now, a very useful website indeed.

EDIT:I just saw @bwh79 's explanation-thank you so much for your detailed, in depth explanation. So, watts/volts is what I use to get a correct example of amp load-then divided by the devices efficiency, and if I am not sure, use 90% yes? That makes perfect sense, and I finally know after 14 months how to calculate properly for a regulated mod.
I have been using other forums a lot, with many posts, and I have clarified something here in just a few days that I have not over 14 Months at other places. I was calculating using Ohms law still.

Thank you all, and all the best, Conan.

PS:Hi @Jim_ MDP , I did not know you was here as well .

 

[suprtrkr]

Resistance does mater, but not like it does with a mech mod. It's easier to think of a regulated mod as having two circuits; a power circuit where the batteries power the board, and a firing circuit where the board fires the coil. Coil resistance does not matter to the batteries because they are in a different circuit. The way to calculate battery amp loading in a series regulated mod is (set watts) / (battery low voltage x number of batteries) = (maximum amp draw); where set watts is the number you set with the up/dn buttons, battery low voltage is the charge on the batteries when the mod kicks them out as too discharged to work. Thus, a two battery mod set to 50 watts, where the mod stops working at 3.2V per battery would be: 50 / 6.4 = 7.8125A per battery. (For a parallel regulated mod the calculation is different, but there are very few parallel regulated mods.) For best accuracy, you must also account for efficiency losses on the board. These are usually in the range of 5-10%, and are very hard to measure, so a guess is about all you can do. How to do so is to just multiply the answer you get times 1.05 or 1.1, depending on whether you want to allow 5 or 10%, like so: 1.05 ((set watts) / (batt low V)) = Amps.

 

[Ryedan]

This is the only part I disagree with and it's just a feeling.

It's not bypass or mech mode.
If it's still regulated with a boost circuit the mod will draw what it needs, within its limits, and that means a higher draw as the cell depletes.

Yes?

If I'm in VV mode set at 4.1v... I can't see it being easier on the cell when it hits 3.4v.

You're absolutely right Jim and thanks for catching it

Corrected my post

 

[conanthewarrior]

Thanks everyone for the input on this thread-it has really helped me understand the exact calculations needed to work out amp load on my regulated mods.

I understand that at 0.1 or 1Ohm, at say 50W, pulls the same from the battery.

A quick question about amp limits. I notice a lot of the devices that claim 200W on dual 18650 devices have high amp limits, such as 45A.

Following the calculations given here, at 200W, with a fresh set of batteries at 8.4V (I vape nowhere near this level, mostly around 30W), using 90% efficiency, that gives an amp load of 26.45A. As the batteries fall in voltage, to near cutoff in a series regulated mod, amps drawn are around 34.72A.(Please-if I have made a mistake, let me know).

If this is so, why do dual 18650 mods, that claim 200W, have such high amp limits, like 45A?(With exceptions, such as the cuboid, that I class as a 150W device).

I would never use a dual 18650 device at 200W, it is just not my thing, plus safety concerns as my battery of choice is the 25R or LG HE4. I don't like overstressing my batteries.

Does anyone have an explanation as to why the amp limit on some devices is so high?

Thanks to everyone that helps me out, I do appreciate it.

All the best, Conan.

 

[speedy_r6]

A quick question about amp limits. I notice a lot of the devices that claim 200W on dual 18650 devices have high amp limits, such as 45A.

Following the calculations given here, at 200W, with a fresh set of batteries at 8.4V (I vape nowhere near this level, mostly around 30W), using 90% efficiency, that gives an amp load of 26.45A. As the batteries fall in voltage, to near cutoff in a series regulated mod, amps drawn are around 34.72A.(Please-if I have made a mistake, let me know).

If this is so, why do dual 18650 mods, that claim 200W, have such high amp limits, like 45A?(With exceptions, such as the cuboid, that I class as a 150W device).

I would never use a dual 18650 device at 200W, it is just not my thing, plus safety concerns as my battery of choice is the 25R or LG HE4. I don't like overstressing my batteries.

Does anyone have an explanation as to why the amp limit on some devices is so high?

Biggest reason is that people will buy it. Simple as that.

Now, as for the way they can get to 200 watts, they can either have the batteries charge up an onboard capacitor that can boost the power from the say 30 amps the batteries can feed, they can either pulse the power, they can overstress the batteries, or they can just flat out lie and only be delivering ~160w when they are saying 200w.

If i recall correctly, most just pulse the power.

 

[suprtrkr]

Thanks everyone for the input on this thread-it has really helped me understand the exact calculations needed to work out amp load on my regulated mods.

I understand that at 0.1 or 1Ohm, at say 50W, pulls the same from the battery.

A quick question about amp limits. I notice a lot of the devices that claim 200W on dual 18650 devices have high amp limits, such as 45A.

Following the calculations given here, at 200W, with a fresh set of batteries at 8.4V (I vape nowhere near this level, mostly around 30W), using 90% efficiency, that gives an amp load of 26.45A. As the batteries fall in voltage, to near cutoff in a series regulated mod, amps drawn are around 34.72A.(Please-if I have made a mistake, let me know).

If this is so, why do dual 18650 mods, that claim 200W, have such high amp limits, like 45A?(With exceptions, such as the cuboid, that I class as a 150W device).

I would never use a dual 18650 device at 200W, it is just not my thing, plus safety concerns as my battery of choice is the 25R or LG HE4. I don't like overstressing my batteries.

Does anyone have an explanation as to why the amp limit on some devices is so high?

Thanks to everyone that helps me out, I do appreciate it.

All the best, Conan.

THey don't actually make 200 watts by the RMS method. They do make 200 watts, sort of, in microsecond pulses (PWM) but this changes the loading factor on the batteries. Batteries can tolerate higher loadings with very short durations. This is why they are given Pulse and Continuous ratings. The Pulse rating is always higher.

 

[conanthewarrior]

I understood this to be the case, in general a lot of mods use PWM after 150W don't they?

I realised the pulse rating to be higher, reading the 25R datasheet it is pretty amazing what they can actually go through. (100A for less than 1 second, 45A for 5 seconds, 30A for 6 seconds-according to their official datasheet-then there is the stress tests).

I also found out for myself that mods can lie, around about 7-8 months ago. I had a thing back then that each mod I got, I wanted to max out, just once. I no longer do this-it was just something I did so I had done it the once.(This was with VTC4's)

I had it connected to my phone, and it was outputting around 145W with new batteries, while the device screen showed 160W. The 180W update did allow it to hit 156W, but this was with 180W on the mod screen.

Thanks everyone for your help. I do appreciate it.

All the best, Conan.