Questions about battery and software

[yoshiking]

Regarding lithium ion battery set up

1. Operating minmum voltage of evolv board: Spec sheet says 3.0v. Does this mean board shuts off if battery resting voltage is 3.0v or display check battery message?

2. Weak battery: Spec sheet says it will display this message when battery needs to be charged or requires you to use higher amp rated batteries. Is this determined by measuring voltage sag of the battery? Using some form of thermister to monitor battery temperature? I would like to know actual process in triggering this message

3. Check Battery: Pretty much same question as #2. Spec sheet says it will display this message if battery is deeply discharged, needs to be charged or if it is damaged. How does evolv board determine this? By monitoring voltage sag? Temperature? Etc.

4. Soft cell cut off: what is the minimum that you can set? For example if I set to 0.1v will evolv board let me fire the device until it hits that mark? Or is there some automatic protection/prevention trigger system? Yes I know that voltage is not possible, I’m just making a big exaggeration to make my question more clear.

5. Relationship between voltage, amp, and sag: Not really a question for evolv but just curious if anybody can answer. There were two identical batteries, and I am trying to push x amount of watts on both of them. Which of below set up would result in lower voltage sag? 

One with higher resistance, thus requiring higher voltage and less amperage

or one with lower resistance, thus requiring lower voltage but high amperage

It will be best if someone can summarize relationship of voltage sag to discharge voltage and amperage

[VapingBad]

Understanding sag will help you understand the week and check battery warnings, basically the more power you pull from the battery the lower the instantaneous voltage, the voltage at the battery terminals.  All cells have an internal resistance and the lower this is the lower the sag will be, you can work it out with Ohm's Law, but just vaping at different power levels while watching the cell values in device monitor will make it far easier to understand.  The battery voltage raise again quickly when you stop drawing power, so you are vaping at high power with a low battery count the cells could be 3.5 V or higher at rest, but not have enough grunt left to vape at full power as they would sag to the cut off.

The soft cell cut off is the min voltage the board will allow the battery to go before backing off the power, I think all the DNAs have 2.75 V minimum on this which is fine for decent 18650s, but for LiPos 3.09 V (the default) is advisable.   The boards don't show the battery warnings if you just briefly hit the cut off during preheat, once the age cause this to get hit during normal puff conditions the weak battery message will show, the check battery also takes into account how much capacity you have used and how many Watts it judges your batter can supply.

As these are variable wattage devices the coil resistance doesn't affect this, think watts from the battery and watts from the coils, if you are using 50 W at the coil you are pulling just a bit more from the battery (depends on the efficiency rating of the board).  The board converts both voltage and current at the same time so the figure you get for coil current does not apply to the battery.  Now because the battery sags when you draw power causing it voltage to drop the current the board draws raises, EG a cell at 4 V drawing 40 W you would expect current to be 40 W/4 V = 10 A, but if that 10 A draw causes a battery sag of 0.5 V it becomes 40W/3.5 V = 11.4 A.

Have a look at this in device monitor, a picture is worth a 1000 words.

[Wayneo]

50 minutes ago, VapingBad said:

I think all the DNAs have 2.75 V minimum on this which is fine for decent 18650s

Hey @VapingBad, I noticed while testing out v2 SP9 Intl on my regular 75, I had entered a 1v for CSC, and after saying OK to the warning, it changed the value to 2.0V loaded to the device. No other boards tested.

In my old tired mind, the spec on the VTC6 had a fully discharged value of 2.0v or 2.3v value in their datasheet (but we all know there's not much energy down there).

[yoshiking]

Thanks for the quick response Vapong Bad

I understand what voltage sag is... my questions are not troubleshoot questions. They are questions to understand how evolv board function. On device monitor, I can see that the difference between a brand new battery and an year old battery regarding voltage drop. Also, I don’t think minimum soft cell cut off is 2.75v for lithium batteries as you mentioned, because I currently have the setting at 2.5v and can see the board giving me check battery warning at 2.5v under load (on device monitor).

You have answered to question #5 -> all different builds(coil resistance) have same amount of voltage drop if they have the same watt setting on device. 

Could you answer questions #1~4?

[VapingBad]

I'll ave a go

1) min voltage per cell on the 200 specs, it changed after folks on this forum asked for 18650 and especially 2 cell operation, well they asked for 1 cell operation bit not enough voltage to run the chip with a step down only converter like the 200 & 250.  For the 20, 25, 30, 40, 75 & 75C which can boost the voltage I don't think the chip min voltage is a concern and it is more a guide to choose a battery.

2)  based on hitting low cut off, it was simple with the 200 as with 3 cells this was normally when they were very low, but with the 75 on high power you can get a lot of sag (battery contact quality affect this significantly as well with cylindrical cells like 18650s) they put in allowances for it just hitting the low cut off during preheat, but after preheat it's the same: if you hit the cut off you will get the warning.

3) all of 2 (and now I am relying on a bit of memory, guesswork etc) I think it uses the capacity tracking (Wh and csv you can enter for the battery) and IIRC the absolute limit is if your battery cannot sustain 5 W draw.

4) I've never seen them go below 2.75 V for more than an instant and am pretty sure that is the hard limit set on the board, but Escribe lets you set other values that will be ignored if below that as far I know, device monitor will show this very clearly.

[yoshiking]

Thank you Vaping Bad! I am satisfied now! Thanks for spending time to answer the questions.