Understanding Ohm's Law better?

[Rarebird]

OK, I watched a video on Ohm's Law, and I'm still a little confused. I'm taking it that the 3000 mah figure on my LG HG2's is not the same as the amperage rating? And if I'm using two, does this mean I can vape at double the safe wattage for one?

Also, if one is using TC, how does one know what wattage one is using, and how can you be sure one is in the safe range?

Thanks for any help!

 

[APathos]

Your LG HG2’s have 3000 mAh capacity. Their max continuous discharge rate is 20A (Mooch rated at 18A). So if you want to know Amp drain at a specific Wattage (I assume you’re on a regulated mod since you mention TC), use the equation I=P/V. Voltage is the actual state of your battery(ies) with sag taken into account. If your 2 batteries are in series you are doubling the Voltage with the capacity of a single. In parallel you can double the continuous discharge rate with a combined capacity. For an example, let’s say @70 Watts on a 3.0 Voltage (What I consider the very low end with battery sag - ~3.4 Volts resting?):

Single 70W/3.0V = 23.3A (LG HG2? Probably not. Even 3.6 Volts is 19.4 Amp drain.)
Double series 70W/6.0V = 11.6A (Under 18 Amps. Sure)
Double parallel 70W/3.0V = 23.3A (Under 36 Amps. Sure)

In TC on my dna’s, I have the screen set to display the Wattage they are using to maintain the temperature. Think most show the Wattage they are using? Hopefully yours does, or just lets you set the max Wattage to stay under the max discharge rate for your batteries.

 

[bwh79]

Also, if one is using TC, how does one know what wattage one is using, and how can you be sure one is in the safe range?

TC will adjust the wattage automatically. Depending on your device, it will either have you select a max watts which it will not go over, or else sometimes the max wattage is not adjustable in TC mode and the device will simply use all available power up to its maximum setting (60W, 100W, or however high the device can go in wattage mode.) I've not seen a device that will output more watts in TC mode than it can be set to in wattage mode.

 

[sonicbomb]

@Rarebird

mAh
In short how long the battery will last.
More specifically one milliamp hour is 1000th of an amp hour, so divide by 1000 and get amp hours.
So a 3000mAh hour battery will provide 1 amp for 3 hours, 3 amps for one hour, 6 amps for half an hour etc. down to the usable cutoff of an 18650 which is about 3.3 volts.

CDR
This is the maximum safe amp limit of the battery, as in the maximum you can safely continuously draw from it. Many battery suppliers will exaggerate this figure or use a 'pulse' value to dupe unwitting buyers into thinking it is a superior product. Venturing out of the CDR green zone into higher red zone amp draws will shorten the lifespan of the cell, and in the extreme cause them to malfunction with potentially catastrophic results. Read Mooch's blog to find out all you need to know about choosing a good battery with a known tested CDR.

Ohms Law
On a regulated mod amp draw will increase as the battery voltage drops, peaking when the battery is discharged. You need to calculate this and make sure the CDR of your cell matches or exceeds this value. Have a read of this article if you want to see how to calculate this. The rule of thumb is a 20 amp CDR battery is good for 60 watts, so two is good for 120 watts etc.

TC
An analogy would be a cars cruise control. You set the maximum speed (temp) and then the amount of throttle (wattage) to get to that speed. When you reach the desired temperature the mod will back off the wattage to maintain that temperature. So in essence the only value that matters is the maximum temperature assuming there is enough wattage to reach it. The temp you set needs to hot enough to provide the vapor quantity and heat to make you happy. If you do some searching her on ECF you will find lots of information on the specifics of tuning a TC build.

 

[cigatron]

With regulated devices you need to use batteries rated for the CDR recommended by the mod manufacturer. That ensures that your batts won't overheat when you reach the mod's max output current. Once you have the correct batts in your mod you need not be concerned about your build res or power settings as the mod will current limit itself.

 

[KenD]

With regulated devices you need to use batteries rated for the CDR recommended by the mod manufacturer. That ensures that your batts won't overheat when you reach the mod's max output current. Once you have the correct batts in your mod you need not be concerned about your build res or power settings as the mod will current limit itself.

Worth noting: with the current two-battery 200+ Watt mods there are no batteries that can handle the maximum power within their cdr. These devices are simply overpowered.

Sent from my K6000 Pro using Tapatalk

 

[cigatron]

Worth noting: with the current two-battery 200+ Watt mods there are no batteries that can handle the maximum power within their cdr. These devices are simply overpowered.

Sent from my K6000 Pro using Tapatalk

Continuous no, pulse yes. I still think it's a bad idea that they do it though.
In addition, mod manufacturers claiming to have 30A regulators and specifying requirements for 30A or higher 18650 batteries should have their products removed from stores worldwide. Just my thoughts.

 

[Rarebird]

Thanks for all your thoughtful replies.

I am trying to calculate what the top safe wattage is for the resistance of the coils I'm using. Should I be using Ohm's Law at all? A big problem I'm having is that in the calculators, when I set the resistance, power, and current where I want it, when I enter a value for the wattage, one of the other values changes. And is the wattage it shows the top wattage I should use for the resistance? Also, it is my undertanding that the volts change as the battery is depleted, further complicating matters.

I hate to sound thick in the head, but the purpose of Ohm's Law is a little confusing to me. I have heard it is very important to understand if you're using a device such as mine, so I want to understand it better. My math skills are a bit weak, so using the calculator is a must.

Thanks for any help!

 

[sonicbomb]

Use steam-engine. Job done.
Steam Engine | free vaping calculators

 

[Joergl100]

Rudiments...

Ohm's law | Steam Engine | free vaping calculators

But NOTHING will make You understand that....except yourself!

Go for it. It is essential. And funny. And more...find out!

 

[Eskie]

Thanks for all your thoughtful replies.

I am trying to calculate what the top safe wattage is for the resistance of the coils I'm using. Should I be using Ohm's Law at all? A big problem I'm having is that in the calculators, when I set the resistance, power, and current where I want it, when I enter a value for the wattage, one of the other values changes. And is the wattage it shows the top wattage I should use for the resistance? Also, it is my undertanding that the volts change as the battery is depleted, further complicating matters.

I hate to sound thick in the head, but the purpose of Ohm's Law is a little confusing to me. I have heard it is very important to understand if you're using a device such as mine, so I want to understand it better. My math skills are a bit weak, so using the calculator is a must.

Thanks for any help!

Remember, Ohms law is useful for mech/unregulated mods. Watts law is appropriate for regulated mods. The resistance of your coil is of no matter on a regulated mod as the current comes from the DC/DC converter in the mod, not directly from the battery.

 

[fido5150]

The main thing to commit to memory is that Ohm's Law is:

Volts x Amps = Watts

So if you have a 4.2 volt battery, and a coil rated at 2 amps, your wattage output would be 8.4 watts. Easy peasy.

If you can remember the main formula, you can then use basic algebra (when needed) to change the Ohm's Law equation into:

Amps / Watts = Volts

and

Watts / Volts = Amps

When you choose an ohm rating for your coil, the gauge and windings set the amperage via Ohms. The trick is finding the proper amount of mass in your coils to control the heat generated from the wattage (you're not gonna run 30ga at 60 watts, unless you're a masochist.) And it all performs differently. Lots of trial and error.

When it comes to batteries, if you know your battery has a rating of 20 amps, then the maximum wattage setting would be 84 watts in TC mode (4.2 x 20 = 84). That is however the battery's max rating, so I would shoot for a bit lower on the settings to be on the safe side.

Remembering the Ohm's Law formula is very helpful in all walks of life, and I actually picked it up back when I was in the car audio scene in the late 80s/early 90s. Of course we used it a bit differently (estimating wattage to speakers), but we also used it to laugh at the cheap 1200 watt (!) Chinese amps that had a single 20A fuse (14.4v x 20A = 288 watts, not 1200, lol) or 300w EQ/Boosters with a 5A fuse.

Ah the good'ol days.

 

[Joergl100]

...the cheap 1200 watt (!) Chinese amps that had a single 20A fuse (14.4v x 20A = 288 watts, not 1200, lol) or 300w EQ/Boosters with a 5A fuse.

Ah the good'ol days.

1200 watts PMPO...„Præ Mortem Power Output“

 

[Rarebird]

The main thing to commit to memory is that Ohm's Law is:

Volts x Amps = Watts

So if you have a 4.2 volt battery, and a coil rated at 2 amps, your wattage output would be 8.4 watts. Easy peasy.

Thanks so much for your thoughtful reply. The reason I was trying to use the calculator on Steam Engine was to figure out the max wattage for my coils based on resistance. Is this misled? Also, I've never heard of amp ratings for coils. The calculator allows you to fix one variable for when you alter another, ie. fix volts when you are changing wattage. It doesn't seem to work properly, because when I fix the voltage and change the wattage, the voltage still changes. I fix the voltage because I'm not using a variable voltage device, and the batteries when fully charge have 4.2 volts according to Mooch and according to my multimeter. But the big question is how can I find out the max wattage rating for a coil I twist up so I can set the wattage somewhere below that to be on the safe side?

When you choose an ohm rating for your coil, the gauge and windings set the amperage via Ohms. The trick is finding the proper amount of mass in your coils to control the heat generated from the wattage (you're not gonna run 30ga at 60 watts, unless you're a masochist.) And it all performs differently. Lots of trial and error.

I can assume we don't want the coil to be too hot if simply because we don't want to burn our cotton. However, stock coils come with a recommended minimum and maximum wattage rating. Yet, since I am building my own coils, I'd like to use Ohm's Law to tell me the maximum wattage rating for the resistance I am using based on the amps and voltage my batteries put out. Is this a useless exercise with a regulated mod?

When it comes to batteries, if you know your battery has a rating of 20 amps, then the maximum wattage setting would be 84 watts in TC mode (4.2 x 20 = 84). That is however the battery's max rating, so I would shoot for a bit lower on the settings to be on the safe side.

I guess the question in this case is, is this all Ohm's Law is for is to determine the maximum safe wattage for the batteries I am using? I've got good batteries, just got a couple of Samsung 25r's to use, but if the max wattage for my batteries is 164 watts for a dual battery device, I can't even go that high on my 120 watt device. However, I don't want to set my coils on fire either, rofl. Is there a separate calculator for determining the max wattage you should use for a given awg wire and resistance?

Thanks in advance for any help!

 

[Rarebird]

Your LG HG2’s have 3000 mAh capacity. Their max continuous discharge rate is 20A (Mooch rated at 18A). So if you want to know Amp drain at a specific Wattage (I assume you’re on a regulated mod since you mention TC), use the equation I=P/V. Voltage is the actual state of your battery(ies) with sag taken into account. If your 2 batteries are in series you are doubling the Voltage with the capacity of a single. In parallel you can double the continuous discharge rate with a combined capacity. For an example, let’s say @70 Watts on a 3.0 Voltage (What I consider the very low end with battery sag - ~3.4 Volts resting?):

Single 70W/3.0V = 23.3A (LG HG2? Probably not. Even 3.6 Volts is 19.4 Amp drain.)
Double series 70W/6.0V = 11.6A (Under 18 Amps. Sure)
Double parallel 70W/3.0V = 23.3A (Under 36 Amps. Sure)

In TC on my dna’s, I have the screen set to display the Wattage they are using to maintain the temperature. Think most show the Wattage they are using? Hopefully yours does, or just lets you set the max Wattage to stay under the max discharge rate for your batteries.

When I first read this it seemed entirely like Greek to me, but I had an "aha" moment just now.

I am using the Eleaf Istick TC100w mod, however with the firmware upgrade it can go to 120 watts. So, is this device serial or parallel? Anyway I can find out? I'm thinking it's parallel based on the way the device is built. And yes, I can control the max wattage on it now, was having problems with that in TC mode. I am, however, at the moment using wattage mode with Kanthal A1 coils. I am fixing to put titanium in it with my next build. I have had good results with titanium except that over a few days they start to produce a lot less vape.

 

[Rarebird]

OK, looking at the Steam Engine Ohm's Law calculator right now. I set the resistance at 4.2 ohms, which is the resistance my dual coil tank is reading at. I tell the calculator, when adjusting current, keep power constant. Yet when I change the amps BOTH the voltage and the wattage change. I don't want it to change the wattage, I have the wattage set at 60 on my device.

However, with the wattage set on 60 and the resistance set on 4.2, it is showing 15.87 volts and 3.78 amps, more than the combined voltage of my batteries.

What I'd like to do is set the resistance, and then play with the wattage to see how high I can go without exceeding the voltage of my batteries. Right?

*edit* Oops, it's .42 ohms not 4.2. Looking at this thing again. Okay, setting it at .42 ohms, and the wattage at 60. Now it says 5.02 volts and 11.95 amps, well within the safe range for the batteries, IF the batteries are in series. Still don't know how to see the wattage rating of the coil though.

 

[fido5150]

I may have confused you a bit when I started talking about amp ratings, but that was mainly to tie everything back into Ohm's Law.

When we pick how many ohms we want our coils to be, what we're actually doing is setting the amperage rating of the coils which determines the amount of current to let through. Steam engine uses a resistance formula to reverse-calculate the watts based on the current rating we choose for our coils.

So, it sounds like you mainly need some help figuring out Steam Engine. For starters, I highly recommend you play around with the Wire Wizard, and plug in some different values so you can see the relationships between the gauge, windings, heat capacity, heat flux and current per volt. This is the hardest part to figure out, and four years later I still have a lot of trial and error when I build coils.

Just select your inner coil diameter and amount of wraps (8 is default, but 6.5 is a good number). Then select single wire and Kanthal A1 30g should be the default. The display area on the left will show you the attributes of your selection, and this is what you want to pay attention to as you play around. As you change the number of windings, gauge, inner diameter, etc, these numbers will all change.

I've found, through my trials and tribulations, that I prefer a heat flux in the 10mW/mm2, and a heat capacity in the 35mJ/K range. The heat flux determines how hot the vape is, and your heat capacity determines the ramp-up time. Basically it's a warm vape with a medium-quick ramp up period. However this is all personal preference and your preferred vape will probably be different.

Of course I also build for a mechanical squonker (a Reo Grand) so I'm completely at the mercy of Ohm's Law, while you have some adjustability.

Your max wattage will be determined by your batteries' max amperage. Two 20A batteries in parallel can handle 40A max, which would be 168 watts (4.2 x 40 = 168) riding the ragged edge.

I'm not sure if steam engine has a reverse calculator, however it does give you a "current per volt" rating on the Wire Wizard page. So if you want to figure it out yourself, the formula would be:

Voltage x (voltage x current per volt) = max watts.

For instance you have a 26ga coil with 7.5 wraps and a 2.5mm ID, giving a current per volt of 1.12A. That would look like:

4.2 x (4.2 x 1.12) = 4.2 x (4.7) = 19.76 watts @ 4.7 amps

Hope that helps clear up some of the confusion and gets you a bit further along.

 

[KenD]

Your max wattage will be determined by your batteries' max amperage. Two 20A batteries in parallel can handle 40A max, which would be 168 watts (4.2 x 40 = 168) riding the ragged edge.

On a regulated mod the amp draw is the highest at the cutoff voltage (3.2v seems to be the most common cutoff voltage). Also, the device efficiency should be taken into account (I use 90% in my calculations):

3.2 x 20 = 64 amps
64 * .9 = 57.6 amps per 20 amp battery

A two-battery mod with a 3.2v battery cutoff will be good up to about 115-120w when using two 20-amp batteries, whether parallel or series.

Sent from my K6000 Pro using Tapatalk

 

[Rarebird]

I appreciate all your informative replies, and have learned a lot about Ohm's Law. However, I put this thread in the "wick and wire" forum because that's what my question is and was really about. I was unclear in my original post. When I asked about the "safe range" I meant the safe range for the coil, not the battery, though I understand that the rating of the battery is very important.

Let's say I'm using nickel in TC mode (I don't use nickel but for purposes of the discussion). Nickel has a low melting point. If I get anywhere even close to what the batteries are rated at in terms of how I set my wattage, the coils will heat up too quickly and melt. I was informed in another thread that TC mods often get 100 degrees Farenheit above the temperature the mod is set at.

I will mess with the Wire Wizard on Steam Engine, but I took a look at it to see if I could calculate the max wattage for a given coil, and didn't find my answer. Of course if my coil heats up to that high a temperature, I will immediately taste burned cotton and know it. But better to know beforehand if a given wattage is too high.

That's what I thought the purpose of Ohm's Law is. Ohm's Law might still bear on this, or I could be entirely misconstrued. I mess with titanium a lot, and don't want to take any chances with the wattage.

So, if not Ohm's Law, how does one calculate the max wattage for a coil of this resistance, this awg, and made of this material? Is there a resource I can use?

Thanks again for your replies. I generally vape about 60 watts on Kanthal A1, so I'm not really concerned about maxing out my batteries, however, it's been an education, and good to know the margins of safety.

*edit* I looked at the Wire Wizard again and noticed the heat capacity. However, it's listed as millijoules per Kelvin. I can't find a converter to F. on Google, and who besides scientists use Kelvin anyway? So still stuck.

 

[puffon]

Nickle melting point: 2651F
tempertature nickle melts - Google Search