Mod Resistance

[alee132]

I am not sure if this is the correct sub forum for this but I was wondering how one figures out what a certain mods resistance is. Like is something that case analyzer or battery analyzer figures out for you or is it something you can measure yourself?  I built my own mod and I have run both battery analyzer and case analyzer and it's still at 0.  I am guessing this is for the resistance each certain mod has as each has different wiring, material and 510, etc, so how would I figure this out or is it the best to just leave it alone? 

[Vape_Like_A_Boss]

alee132 said:

I am not sure if this is the correct sub forum for this but I was wondering how one figures out what a certain mods resistance is. Like is something that case analyzer or battery analyzer figures out for you or is it something you can measure yourself?  I built my own mod and I have run both battery analyzer and case analyzer and it's still at 0.  I am guessing this is for the resistance each certain mod has as each has different wiring, material and 510, etc, so how would I figure this out or is it the best to just leave it alone? 

Others will chime in with much better information, but I can tell you what I've learned about the two features you mentioned. The battery analyzer test runs and discharges the battery from 100% fully charged to find out exactly what the battery's watt/hr rating is (which is how capacity is measured as opposed to just going by the mah to compare lipos and 18650's) and it's discharge curve and I believe cell balance throughout the entire discharge curve. The battery analyzer likely will give data on the battery's internal resistance, but I'm not familiar with how to equate it with the the rest of the connections etc.

The case analyzer is used to determine how the board mounting and the case being used dissipates heat from the board. 

You probably already know those things above and that's the easy part, below I'm just speculating  below and looking forward to John's answer, as his engineer mind and IQ combine to make my intelligence look like I'm from peopleofwalmart.com and my elevator doesn't go all the way to the top.

I know what you're looking for when you talk about the mod's internal resistance, you're meaning something similar to how a battery has a slight bit of internal resistance, but in all the joints and connections and electronics, and I think you're looking to see where it shows up in the mod like voltage drop in a mech mod kind of, to find if there's an abnormal bottleneck.

The board is reading resistance at the 510 connection itself and if wiring is adequate, I'm thinking this internal resistance should be irrelevant as long as power settings are within spec, because the board is going to compensate to get the delivery/readings at the 510 correct.

John or the other evolv guy that are on the electronic engineering side (sorry Brandon, you're probably good for a few things too lol) will probably have such a good answer, I'll edit whatever turns out to be incorrect.

[VapingBad]

I just tried Analysis Atomiser with a Velocity clone with 2.5 sq mm solid copper in place of the coil, the closest thing I could rig to a short, but the atty will have a few milliohm.  I got 10 milliohm for my 1590A mod with a VariTube with stretched spring using 14 AWG wire and 13 milliohm for the Evolv mod, I suspect that the common earth rather than the 510 is why it is higher.  But I don't think the resistance is that high I need a better method like a brass bolt to fit the 510.  27/7/15 fw

     

[alee132]

So basically by shorting it in that way you are trying to get a internal resistance reading?  I am wondering if this is what this setting is for and is this the best way to figure it out.  I just want my mod to be tuned perfectly if possible. Not saying anything is off at all but if there is a way to easily read and adjust for any internal resistance than I am all for it. But I figured maybe I was missing something here as my setting doesn't change on its own I either assume it's not changed any way but manually or my mod was not off enough to need adjustment. If it's changed manually how would one best read for it.

[VapingBad]

I am sure that is what the setting on the Mod tab - Electrical - Mod Resistance and not battery IR, I'm sure John will correct this if I am wrong.  But as I said I am not sure I measured it perfectly or how useful it is.

[dwaindablane]

VapingBad said:

I just tried Analysis Atomiser with a Velocity clone with 2.5 sq mm solid copper in place of the coil, the closest thing I could rig to a short, but the atty will have a few milliohm.  I got 10 milliohm for my 1590A mod with a VariTube with stretched spring using 14 AWG wire and 13 milliohm for the Evolv mod, I suspect that the common earth rather than the 510 is why it is higher.  But I don't think the resistance is that high I need a better method like a brass bolt to fit the 510.  27/7/15 fw

     

I have an internal resistance of around 0.018ohms, I thought that was why Mod-Mod Resistance was there to account for mods internal resistance in the software.

When I don't have any value set in the Mod Resistance field I can not get the correct shorted screen up when shorting the 510, I do when I apply 0.018ohm in the field.

If When I enter my mods resistance I seem to get a weak vape, when I default back nothing in this field the vape goes back to normal, am I going bonkers?

[VapingBad]

I am getting a weaker vape with a 0.05 ohm genesis build at 420 F on my Hammond 1590A box, but I am not happy with the coil build as it is 0.3 mm (about 29 AWG IIRC) Ni200 it is a bit stiffer and doesn't sit snug enough with the steel wicks.  Putting a build with twisted 34 AWG 0.16 mm 0.1 ohm on it is a great vape at 380F I get more vapour than the other at 420 F,  the twisted build is my ADV and I am happy that the 200 with the resistance correction is accurate. A quick test the 0.3 single strand build needs 480 F to get the vapour, just the effect of the wire being a bit too loose on the steel wicks or is it the resistance offset is too high, probably both.

[John]

Okay... Mod resistance...

First, let's look at the power controlled case only. Then we'll extend that to temperature protection. 

From the output of the board, there are several resistances in series that make up the load. First you have the wires running to the connector. Then you have the connector body itself. Then you have the interface between the connector and the atomizer. Then you have the atomizer body, then the connection between the atomizer and the coil. Then and only then do you actually get to the coil. 

All these elements have some resistance, and resistances in series add up. So, you might have

Output wires: .002 ohm
Connector body: .001 ohm
Connector contact resistance: .002 ohm
Atomizer body: .003 ohm
Atomizer contact resistance: .002 ohm
Coil: .10 ohm

So the total resistance would be .108

However, we really only care about the heating power coming out of the coil, not the power being wasted in the wires or the connector. 

So to get 100 watts out of the coil, we need I^2*.10 ohm = 100 watts. So we need 31.6 amps of current to get a true 100 watts out of the coil. 

However, to get that 100 watts at the coil, we need to have the board put out more power, to account for the losses through all the stuff that isn't coils. We know we need 31.6 amps, so the total power we have to put out in this case is 31.6^2*.108, or 108 watts. 

So in this case, power controlled only, we need to put out an extra 8 watts to get our 100 out. If your mod resistance is correct, the DNA will handle this automatically. And yes, this means that in certain circumstances the board will be putting out significantly more than 200 watts. 

That's all good from a power standpoint (except that we have to make a board capable of more like 250 watts total output) but in temperature mode, it is a bit more nuanced. 

With temperature protection, we're looking for a rise in resistance relative to the known cold resistance. With mod resistance, we assume that the mod resistance isn't heated meaningfully.

With nickel 200, a doubling of resistance corresponds to about 412 degrees. So if we have a mod resistance  of .008 and a cold coil resistance of .10, for a total resistance of .108, the following happens:

If we have a 0.0 mod resistance setting, it will assume the entire cold resistance is the coil. So for a temperature setting of 412 degrees, it will have a limit resistance of .216 ohms. 

However, we know in this case that .008 of that isn't the coil. We'll further assume that everything is well constructed and massive enough to not heat up much in operation. That means that our limit resistance's .216 ohms is really .208 ohms at the coil and still .008 ohms in the non-coil stuff. So for a setting of 412F, you are really getting a coil temperature of 430F. 

With a proper mod resistance setting, it will only be looking for a rise in resistance of the actual coil. So a setting of 412 will actually be 412. 

So, the temperature you are getting is closer to the temperature you have set with the mod resistance on. Unfortunately, it is more accurate in a "weaker, cooler vape" direction. To get the same experience as one would have had with a 412 degree setting without mod resistance, you would have to turn the temperature limit up to what you were actually getting before, in this specific case 430 degrees. 

Hope that makes sense. 

[VapingBad]

Thanks John, that makes sense to me anyway (I think) so setting the mod res to 0.01 with a 0.06 coil as measured by the DNA would make the mod take 0.118 ohm as double the temp instead of 0.130 ohm with out the setting, the higher ohm being the warmer vape.  So if we felt that at low res the temperature was a bit high then this is where this setting helps the most.

[Brandon]

John or the other evolv guy that are on the electronic engineering side (sorry Brandon, you're probably good for a few things too lol) will probably have such a good answer, I'll edit whatever turns out to be incorrect.

John, can you reach that knife in my back?  It's in there deep.  

[James]

Two points about Mod Resistance:

(1) If you are experimenting with Mod Resistance, I'd strongly recommend giving the 7/29/2015 (or newer) Early Firmware I posted a try. Mod Resistance directly affects the DNA's resistance reading, so in certain corner cases there's a bit of 'here be dragons'. I've added some extra protections so you can't get the DNA in too bad of a spot.

(2) Always make sure the Mod Resistance you have is conservative -- keep the value you enter at or lower than the real Mod Resistance. If the value you enter is higher than the real Mod Resistance of the device, it can negatively affect the stability of the temperature protection system. It's best to measure it if you can, honestly. And then use, say, 80% of that value to give yourself some margin.

Having a fairly accurate Mod Resistance will deliver a more accurate power and temperature.
The compensation is really only notable in extremely low Ohm coils where the 510's resistance is significant though.

[scoopy]

This all confuses me lol.....sorry Can someone (John preferably) tell me step by step how to do this test to get my mod resistance (what wire gauge or whatever to put in the atty and what shape) I really want to get my mod resistance to be more accurate but just don't understand all this and how to do it.....sorry if this sounds dumb and newbieish

[John]

Take your RDA, short across the terminals with the shortest, fattest piece of copper wire you can fit in the terminals, then fire up atomizer analyzer and read the reaistance. Put that value into the field for mod resistance. Upload settings. Done. To get the same feel as before you applied the mod resistance, expect to have to turn the power down and the temperature up.

[James]

Use 80% or 90% of what you measure, btw. You really do want some stability margin.
And the 7/29/2015 (or newer) firmware from https://forum.evolvapor.com/topic/66731-topic/

[VapingBad]

Already running it James and it all seems good

[scoopy]

Thank you John and James.....u say this makes the mod pretty much exactly accurate then right

[Vape_Like_A_Boss]

Brandon said:

John or the other evolv guy that are on the electronic engineering side (sorry Brandon, you're probably good for a few things too lol) will probably have such a good answer, I'll edit whatever turns out to be incorrect.

John, can you reach that knife in my back?  It's in there deep.  

Lol sorry Brandon, I had to poke a little fun John doesn't get to deal with us much, so we have to take a few swings for him.

On a serious note, both of you have truly been inspiring motivation in this industry and honestly made one of the biggest impacts on what we know today as vaping. Neither of you takes the credit you deserve, but there's a lot of us that appreciate the hell out of Evolv as a company, including you two and all of your staff. Brandon you had a vision, and did so much to make it happen. Big thanks to both of you.

While I'm being all sweet, I'm really impressed with the level of customer service and communication that's gone on with the early adoption part of this testing phase. I know several of the non staff had a part in it too here on the forums, but you guys together nailed it. The innovation of the product but also the customer interaction and service you've provided even when we screw up, deserves some big appreciation and respect.

Thanks guys, and sorry OP for the derailment.

[Justin]

If anyone knows the mod resistance for the Opus 200, that would be extremely useful. I realize it can vary a bit from each device, but a roundabout would be great. Unfortunately I don't have any solid copper or a temp gun around.

[ndb]

Hey, this is extremely interesting, as fighting static resistances has been my main hobby since when I completely moved to TC last year, so forgive me if I'm nitpicking, but I want to be sure I understand, so here are my 3 Qs related to the quotes below:

John said:

.
.
All these elements have some resistance, and resistances in series add up. So, you might have

Output wires: .002 ohm
Connector body: .001 ohm
Connector contact resistance: .002 ohm
Atomizer body: .003 ohm
Atomizer contact resistance: .002 ohm
Coil: .10 ohm

So the total resistance would be .108
.
.

QUESTION 1)
Why .108? Wouldn't all the contributors above sum up to .002 + .001 + .002 + .003 + .002 + .10 = .11?
Is it just a typo or is there some reasoning by which not all the contributes have to be considered?

And this brings me straight to

QUESTION 2)
Regardless it being .108 or .11, would it be correct to say that for the _mod_ resistance (i.e. excluding atomizer + coil) I only have to consider

• output wires
• connector body
• connector contact resistance

For a _mod_ resistance of .002 + .001 + .002 = .005?
Maybe this is the reason you suggest to "trim" off the measured shorted-atomizer resistance to about its 80% value?
IOW: we have to shelve off a bit of what we measure short-circuiting the atomizer so that we effectively take only the _pure_ mod static resistance into account?

And now the final question, strictly related to ni200 TCR: 

John said:

.
.
With nickel 200, a doubling of resistance corresponds to about 412 degrees. 
.
.

QUESTION 3)

If I'm not mistaken, (using the linear approx of the TCR, i.e. dR/R = TCR * dT), given that 412F = 211,11C, this would imply that TCR = 1/211,11 = 0,00473.
But I've always heard something along the lines of "ni200 increases its resistance by about 62% every 100C", which makes it for the TCR = 0,0062 that is usually (at least by me) associated with ni200.
Is this discrepancy due to the fact that you account for the non-linearity (and hence the simple formula above doesn't hold) or has using 0,0062 always been a mistake?

[VapingBad]

I think John just meant 70 F to 412 F rather than doubles every 400 F, but I would have expected around 68 to 350 F doubles r with TCR of 0.00641.

[Havensal]

Is the board supposed to tick when analyzing the atomizer?  Is it polling once per second?  I just updated the firmware to 7/29 and this is the first time I noticed it.  I have it the atty shorted to check the mod resistance.

[Brandon]

Yes, it is polling once per second but I haven't noticed the ticking.  If you drop back to 7/16 firmware are you still getting the ticking in refinement?

[John]

With a short, a tick isn't that surprising. That's a lot of di/dt

[Tomr1088]

Noticed something scary that was my mistake. Don't ever accidentally set mod resistance to something high. I accidentally set it to .2 ohm instead of .02. Once I uploaded settings and opened atomizer analyzer it constantly kept pulse firing my ni200 build. Due to sampling the coil for resistance readings it was using way more power. Scary lol

[John]

Oh. Yeah. Don't do that. You can make it put out 250 watts, easy, from a fully charged battery. It won't hurt the board as such, but you'll basically be pin-balling between various protective features, so the vape won't be any good.