Maximum Resistance for TC

[nystyletaco]

Is there a maximum resistance needed for the DNA to view a coil as being a valid material for TC?  I've been playing around with SS 316L and when I use a Triton coil (.4ohm) or a dual coil setup with 26ga (.36 ohm) it works great but I build a 1ohm single coil in a tank and its not registering with temp control, even with the profile setup with the proper TCR values.

Is there any way to "force" a profile to always use TC regardless of resistance?

[Mad Scientist]

According to the data sheet, stay at 0.2 Ohm or less for full 200 Watt capability and 0.4 Ohm or less for 100 Watt. I'm not positive but based on my own experiences, these are cold resistance values.

[nystyletaco]

Not really what I was asking.  It seems like there is some sort of condition that triggers the DNA to realize that it can perform TC vs materials that it cannot (like Kanthal).  What I'm trying to figure out is what that condition is.  I rebuilt my coil again with 5 wraps of 26ga SS 316L.  Resistance of approx .6ohm but again it doesn't sense that it can perform temp control with this material despite having the TCR values for SS 316L added to this profile.

Edit: Now I'm even more confused.  I unscrewed my atomizer multiple times on my original profile and never got it to register TC.  I created a new profile, locked the ohms and uploaded the TCR values to that.  After switching to that profile, now it registers TC on both my new profile and the original profile I was trying before 

[blueridgedog]

Curious as well.  I put a dual coil, dual 28g nickel twisted coil in my tugboat this weekend and it came to .35 and would only run in non tc mode.  I did not have time to trouble shoot it.

[Daz 7401]

I'm using a 0.4 single TI coil in a Sub Tank Plus RBA at 50w TC and it is working ok. But a SS coil at 1.0 in TC with 317L profile did not work just burnt taste, I plan to try thicker wire to bring the resistance down and try again.

[Mad Scientist]

nystyletaco said:

Not really what I was asking.  It seems like there is some sort of condition that triggers the DNA to realize that it can perform TC vs materials that it cannot (like Kanthal).  What I'm trying to figure out is what that condition is.  I rebuilt my coil again with 5 wraps of 26ga SS 316L.  Resistance of approx .6ohm but again it doesn't sense that it can perform temp control with this material despite having the TCR values for SS 316L added to this profile.

Edit: Now I'm even more confused.  I unscrewed my atomizer multiple times on my original profile and never got it to register TC.  I created a new profile, locked the ohms and uploaded the TCR values to that.  After switching to that profile, now it registers TC on both my new profile and the original profile I was trying before 

I think it uses the cold resistance times a calculated TCR for the temp from the TCR curve for the temp delta desired and then knows how much resistance "should" increase to reach set temp. When you fire it applies power and expects to see the resistance increase proportionally within those calculations. If it doesn't, it thinks you have a wire type with too low TCR so drops out of temp mode.

The higher the cold resistance, the more it is a factor in the calculation as indicated. Same with higher TCR. The opposite for lower values of each. Low cold resistance coupled with low TCR of the wire makes for less temperature dependent resistance increase when adding power to heat the coil. There must be limits -- you may have found what they are. Possibly the locking resistance thing was enough to have the measured cold resistance come up just high enough for it to work.

I would try a SS coil of higher cold resistance -- maybe get extreme and go for 0.2 Ohms cold (with the appropriate TCR curve entered in the profile) to see what it does. The higher cold resistance, despite the low TCR of SS, "should" be enough total temp dependent change in coil resistance for TC to work. I don't know what the limits are -- would take a lot of experimentation to find it exactly for any particular manufacturer's board, but there is a number representing cold resistance times TCR of the wire, below which TC won't work reliably so knows enough not to try. It will drop out of TC mode below that limit.

[Brandon]

+1 Mad Scientist.  It looks for a rise in resistance equivalent to 150F in the first second.  If it doesn't see it then it drops out of temp control.  If you set your wattage too low on a freshly connected temp coil (remember no preheat on the first fire after a disconnect) it may not see enough resistance rise and drop out of temp control.  Or if you place a hot coil on it may not see enough of a rise to continue to temp control.

[nystyletaco]

Thanks Brandon, that is exactly what I was looking for and actually makes a lot of sense in my case because I usually keep the wattage low on a newly built coil so I don't inhale flaming cotton, but I'll usually crank it right up when I put on a pre-built coil. 

[Seigfried]

Had a .51 316L that worked great at 26w and 390f  with 100w preheat and punch of 1.