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Wrong temp sensing on Thinkvape Box 75


maverick83
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Hi all,

As I mentioned in the title, I have a serious problem with the tc feature of a ThinkVape Box 75 device.
The mod was first used 4 days ago, and was working fine for 2 days. Then after a battery change and an atomizer fill the temp was way off. Altough it was set for 210 Celsius, and was working like a charm in the first two days, now the temp did not go even close to the set value.
After a lot of troubleshooting trys we discovered that although the mod measures and work accurately, the "temp sensing" looks like to start form the ambient minimum.
Ohm measurement, volts and watts are accurate, the mod works flawlesly in vw mod, but because of this wrong tc, it is useless as a tc mod.
I tryed everything I can think of, threads were cleaned, atomizer cleaned and rebuilt. I have rebooted the device, restored factoy default, even tryed an earlier fw version, but none of these worked.
I attach three pics. On the first you can see the setup, room and board temp, and that the temp is not going close to the set 195 celsius.
On the second you can see the setup, and the dotts show when I pulse-fired the device. It show -27 celsius, that is why I guess it starts the temp from the ambient minimum (shown on pic 3) and not from room temp.
As I was saying at the beginning, I noticed this after a battery change and tank refill. I did inserted the battery correctly and I did not flood the tank (expromizer 2.0) nor poored juice on the mod. Since that it is doing with all my attys, no matter what resistance wire they have.
I seriously need help please, I have no idea how this bug came to be after 2 days of use. dna01.png  dna02.png  dna03.png

dna03.png

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Personally I will not open word docs posted in forums and suggest you post the pictures directly, just use the button with a tree on it.  A few things you didn't say was what the tank and build were, if you locked ohms and which version of firmware you are running (it shows in the bottom left of device monitor).

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I am sorry, I removed the doc, and inserted the pics.
My setup in my 3 different attys are quite similar (expromizer 2.0, Taifun GT II, Kayfun V3-clone), they are done with 316SS wire, single coint, and around 1 ohm. No matter which atty I try the result is the same.
The fw version is 2016-06-05 (I also tried other one, but the results were the same).

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The first issue is your coils are above the max resistance for full power, this 0.5 of non temp sensing and approximately 0.4 for ss, 0.25 for Ti and 0.22 for Ni.  It is limited by 6.2 V max output voltage and the temp you like to vape at, as the resistance changes you will max out at the hot resistance which need to stay below 0.5 ohm for full power.

Also it is like the resistance is locked too high, the live ohms are lower than the cold ohms in the 2nd screen which should only happen if you go in to extremely cold environment.  If you are locking resistance don't, let the device get a more accurate reading by tracking the res cooling.

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Hi,

I think you are wrong with those numbers. 04 ohm max resistance on ss wire? Even a vtc mini can do temp control until 1.5 ohms with ss wire.
I just made this screenshot, where it shows, that I am not going over the 6 volts. The setup is without preheat, 20W in tc, and it is still showing the wrong temp.
dna04.png
I also made another pic, what shows my latest discovery on this issue. When I start the device monitor, it shows the set temp, and the actual temp. There is that sudden dropp, I do not know if it is relevant information or not.
dna05.png  I am now running the case analyzer, I shall return with the results in an hour.
However, the analyzer looks like this in progress:
dna06.png 

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maverick83 said:

I am sorry, I removed the doc, and inserted the pics.
My setup in my 3 different attys are quite similar (expromizer 2.0, Taifun GT II, Kayfun V3-clone), they are done with 316SS wire, single coint, and around 1 ohm. No matter which atty I try the result is the same.
The fw version is 2016-06-05 (I also tried other one, but the results were the same).



Your cold resistance is all over the place. Every time you post a graph it is different.

Making a 1.0? coil is pretty uncommon. What gauge, wraps and diameter?
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maverick83 said:

Hi,

I think you are wrong with those numbers. 04 ohm max resistance on ss wire? Even a vtc mini can do temp control until 1.5 ohms with ss wire.
I just made this screenshot, where it shows, that I am not going over the 6 volts. The setup is without preheat, 20W in tc, and it is still showing the wrong temp.
dna04.png
I also made another pic, what shows my latest discovery on this issue. When I start the device monitor, it shows the set temp, and the actual temp. There is that sudden dropp, I do not know if it is relevant information or not.
dna05.png  I am now running the case analyzer, I shall return with the results in an hour.
However, the analyzer looks like this in progress:
dna06.png 


It is not temp limiting as your power is too low to get up to the temp limit.

You only set the power to 20 W so the max limit will not get triggered, for 20 W you should be able to go up to 1.65 ohm with no preheat, but you need more power ot get to 190 C anyway. 

For full power though @ 190 C a SS316 coil which is 0.435 ohm at room temp will be 0.5 ohm, I allowed for much higher temps to cater for more people.  Rmax = Vmax squared over Pmax = 38.44/75 = 0.5125 so by the numbers and using a TCR approx of 0.00088 the max cold res would be 0.446 for full power at 190 C.  That is full of approximations and is for full power, but below 0.4 for ss is a reasonable guide IMO.
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So, After yesterday's short success, it started acting up again after an atty swap. Today I ran the case analyzer again without success, so as a final atempt, I cleaned the threads. The idea came to take it apart and have a look at the board and the insides of the mod. And there I felt that the two small screws that hold down the 510 base were a very little bit loose. Nor the base, neither any atty was moving on the mod, so I didn't notice it earlier. And after tightening those screws, magically :) everything works again. It was my stupidity that I did not start the whole troubleshooting with that, but it is what it is. Now everything is working after multiple atty swaps, so I think the issue is fixed. If anyone purchases a Thinkvape Box 75 or a similar mod, where the 510 is screwed down with screws on top, tighten those , just to make sure :)

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Yes it is 0, but it works fine with the 0 as well. However, if anyone could tell me or measure what is the resistance of the ThinkVape Box 75, I would be most greatful. I just could not find this information on the web, and I do not have equipment to measure it. Or do you think if I input the numbers what others measured on the VT75, that would be close to the truth?

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