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Vaportron

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Posts: 45
Reply with quote  #31 
Nicely done
VapingBad

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Reply with quote  #32 
Quote:
Originally Posted by blackcrx
Quote:
Originally Posted by VapingBad
Personally I would not bother with SS, but never had a problem that I can solve with Ni200.  SS can work, obviously not as well as Ni or even Ti, but you need to have the mod res set correctly, an atty with good connections ant the right materials profile.
[TS_wire_comp] 


I do not agree with this chart. You are basing your calculations on resistance instead of wire length.

In order to build a 1ohm coil in Ni200 you would need 56 wraps around a 2.5mm ID.

If you used the same amount of wraps or wire length, it actually shows that SS316L is more accurate.

To keep things consistent, I will also use steam engine for calculations.

Example using 28 gauge in both materials

8 wraps of SS316L on a 2.5mm ID is 0.78ohm at 20c, at 200c the resistance will be 0.8372ohm, a change of 0.0572ohm

8 wraps of Ni200 on a 2.5mm ID is 0.10ohm at 20c, at 200c the resistance will be 0.131032ohm, a change of 0.031032ohm

Also using the formula that was over on ECF for calculating the change in resistance based on TCR and cold ohms. For every 0.01ohm change on a 0.78ohm SS316L coil it will result in 14.25c. For every 0.01ohm change on a 0.10ohm Ni200 coil it will result in 16.67c. 

I was all about the Ni200 wire until I did these calculations which converted me straight to SS316L. Higher over all resistance (less amp draw), greater accuracy, and most importantly it was not flimsy and soft like the Ni200 wire



I think you are reading too much into the table, it just shows the relative TCRs.  Yes there are pros to having higher res coils especially minimising the component introduced by mod and atty resistances, but the proportion of change is important.  But other factors including the length wire and mass of the coil & contact area are also very important for how the heat builds and transfers. 

I think your figures should be:

8 wraps of SS316L on a 2.5mm ID is 0.78ohm at 20c, at 200c the resistance will be 0.911ohm, a change of 0.125ohm.

8 wraps of Ni200 on a 2.5mm ID is 0.10ohm at 20c, at 200c the resistance will be 0.208ohm (TCR) or 0.1923ohm (curve), a change of 0.108ohm (TCR) or 0.0923ohm (curve).


A big question is the accuracy of the electronics, I doubt it is set value in milliohms or a set percentage, somewhere between the 2 probably.  But most measurement equipment is rated by percentage accuracy so I would suspect this is more important, also I get the impression more people struggle with temp limiting using ss the Ni.

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Margucci

Senior Member
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Posts: 117
Reply with quote  #33 
the thing which people dont take into account is the starting resistance. if you build your SS coils with high initial resistance they are more than accurate enough. i find that an initial resistance in the 0.4-0.5 ohm range gives great results. 
blackcrx

Junior Member
Registered:
Posts: 3
Reply with quote  #34 
Quote:
Originally Posted by VapingBad
Quote:
Originally Posted by blackcrx
Quote:
Originally Posted by VapingBad
Personally I would not bother with SS, but never had a problem that I can solve with Ni200.  SS can work, obviously not as well as Ni or even Ti, but you need to have the mod res set correctly, an atty with good connections ant the right materials profile.
[TS_wire_comp] 


I do not agree with this chart. You are basing your calculations on resistance instead of wire length.

In order to build a 1ohm coil in Ni200 you would need 56 wraps around a 2.5mm ID.

If you used the same amount of wraps or wire length, it actually shows that SS316L is more accurate.

To keep things consistent, I will also use steam engine for calculations.

Example using 28 gauge in both materials

8 wraps of SS316L on a 2.5mm ID is 0.78ohm at 20c, at 200c the resistance will be 0.8372ohm, a change of 0.0572ohm

8 wraps of Ni200 on a 2.5mm ID is 0.10ohm at 20c, at 200c the resistance will be 0.131032ohm, a change of 0.031032ohm

Also using the formula that was over on ECF for calculating the change in resistance based on TCR and cold ohms. For every 0.01ohm change on a 0.78ohm SS316L coil it will result in 14.25c. For every 0.01ohm change on a 0.10ohm Ni200 coil it will result in 16.67c. 

I was all about the Ni200 wire until I did these calculations which converted me straight to SS316L. Higher over all resistance (less amp draw), greater accuracy, and most importantly it was not flimsy and soft like the Ni200 wire



I think you are reading too much into the table, it just shows the relative TCRs.  Yes there are pros to having higher res coils especially minimising the component introduced by mod and atty resistances, but the proportion of change is important.  But other factors including the length wire and mass of the coil & contact area are also very important for how the heat builds and transfers. 

I think your figures should be:

8 wraps of SS316L on a 2.5mm ID is 0.78ohm at 20c, at 200c the resistance will be 0.911ohm, a change of 0.125ohm.

8 wraps of Ni200 on a 2.5mm ID is 0.10ohm at 20c, at 200c the resistance will be 0.208ohm (TCR) or 0.1923ohm (curve), a change of 0.108ohm (TCR) or 0.0923ohm (curve).


A big question is the accuracy of the electronics, I doubt it is set value in milliohms or a set percentage, somewhere between the 2 probably.  But most measurement equipment is rated by percentage accuracy so I would suspect this is more important, also I get the impression more people struggle with temp limiting using ss the Ni.


My mistake, I was calculating for 200f and not 200c. Your calculations are correct.
blackcrx

Junior Member
Registered:
Posts: 3
Reply with quote  #35 
Quote:
Originally Posted by Margucci
the thing which people dont take into account is the starting resistance. if you build your SS coils with high initial resistance they are more than accurate enough. i find that an initial resistance in the 0.4-0.5 ohm range gives great results. 


Agreed, I would say minimum cold ohms should be 0.50ohm for SS wire. But this can be hard to achieve for ppl using anything lower than 26 gauge or dual coils. As of right now I am using 28 gauge single coil around 0.80-0.85ohm and it has been working great
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