Cut-off Voltages of Mods

[KenD]

The voltage you measure after pulling your batteries from the mod can easily be 0.4V above the actual cutoff voltage. The voltage sag during discharge disappears as soon as the discharge stops as the voltage rises back up to the battery's resting voltage.

The resting voltage determines what the battery was actually discharged down to though.

@Mooch, am I correct in assuming that the resting charge is what counts when it comes to the lowest safe discharge voltage (I seem to remember that you've said something like that)? So, as mentioned in my previous post, the smok Alien discharges the batteries down to 2.8-2.9v. Under load this could be as low as 2.4v, which would damage the batteries if they were actually drained that low, but the resting voltage of 2.8-2.9 is ok.

Oh, and that of course applies to calculating the amp draw at the mod's lowest voltage. That should be calculated at the resting voltage, right?

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[Mooch]

@Mooch, am I correct in assuming that the resting charge is what counts when it comes to the lowest safe discharge voltage (I seem to remember that you've said something like that)? So, as mentioned in my previous post, the Smok Alien discharges the batteries down to 2.8-2.9v. Under load this could be as low as 2.4v, which would damage the batteries if they were actually drained that low, but the resting voltage of 2.8-2.9 is ok.

Oh, and that of course applies to calculating the amp draw at the mod's lowest voltage. That should be calculated at the resting voltage, right?

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Calculate at the voltage under load to get the accurate current level.
Calculate at the resting voltage to get a bit of a safety margin.

You're saying the Smok Alien has a cutoff voltage of about 2.4V? Otherwise the batteries can't reach that low because the cutoff voltage is higher, at the 2.8V-2.9V you mentioned. The mod doesn't know what the voltage sag of the battery is. It just reacts to the voltage at its input.

 

[Mooch]

Thank you Mooch,

but what you wrote was very well known to me before, being an MSEE+MSCS with some technical knowledge.

Good answers to my question didn't come so far, however.

If what I wrote was well known to you before then why are you asking others to post the resting voltages of their batteries? Surely, being a MSEE+MSCS, you knew that the resting voltage fundamentally depends on both the cutoff voltage and the discharge rate?

Asking others what their restings voltages are is useless unless you also know how hard the battery was being discharged at the time. For example, take two of the same batteries and discharge both down to 2.5V. Discharge one at 30A and the other at 0.3A. After the discharges are done the first battery might be at, let's say, 3.2V. The other battery will probably be at 2.6V or less.

Both batteries were discharged down to the same cutoff voltage but their resting voltages are completely different because of the different discharge rates causing different degrees of voltage sag and affecting how long it takes before the 2.5V cutoff is reached. Just asking for others to post their resting voltages will give you meaningless data, even for someone with a MSEE+MSCS.

 

[KenD]

Calculate at the voltage under load to get the accurate current level.
Calculate at the resting voltage to get a bit of a safety margin.

You're saying the Smok Alien has a cutoff voltage of about 2.4V? Otherwise the batteries can't reach that low because the cutoff voltage is higher, at the 2.8V-2.9V you mentioned. The mod doesn't know what the voltage sag of the battery is. It just reacts to the voltage at its input.

In the Djlsb vapes review Daniel has the batteries discharge to 2.8-2.9v. I can only assume that that's what the batteries are at when he measures them after taking them out of the mod. Not sure how far after taking them out, but it wouldn't be when they're under load. Measuring my batteries when taking them out of my rx200 and Pico they're at around 3.2v (having let them sit a while). I'm calling that the "resting voltage" (if that's correct).

The current draw would be calculated higher if under load, wouldn't it? If they're measured at 2.8v when taken from the mod the current draw at 100w would be around 20 amps per battery. If the current should be calculated under load (2.4v) instead the draw would be 23 amps per battery. Something I'm misunderstanding here?

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[Mooch]

In the Djlsb vapes review Daniel has the batteries discharge to 2.8-2.9v. I can only assume that that's what the batteries are at when he measures them after taking them out of the mod. Not sure how far after taking them out, but it wouldn't be when they're under load. Measuring my batteries when taking them out of my rx200 and Pico they're at around 3.2v (having let them sit a while). I'm calling that the "resting voltage" (if that's correct).

The current draw would be calculated higher if under load, wouldn't it? If they're measured at 2.8v when taken from the mod the current draw at 100w would be around 20 amps per battery. If the current should be calculated under load (2.4v) instead the draw would be 23 amps per battery. Something I'm misunderstanding here?

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No, you understand perfectly. Perhaps I don't.

I agree. If Daniel measured the battery voltages after removing them from the mod the voltages had already risen up some from their lowest voltage (assuming a moderate to high wattage setting) on their way up to their resting voltages (which takes about 2 hours but comes close in a few minutes).

Daniel uses a scope for a lot of measurements though, directly at the battery or at the atty posts. He might have measured the lowest voltage under load while the batteries were still in the mod. That seems the more likely scenario as I think that these companies would know that going below 2.8V-3.0V gives you almost no additional vaping time and just heats up or damages the pack unnecessarily.

 

[KenD]

No, you understand perfectly. Perhaps I don't.

I agree. If Daniel measured the battery voltages after removing them from the mod the voltages had already risen up some from their lowest voltage (assuming a moderate to high wattage setting) on their way up to their resting voltages (which takes about 2 hours but comes close in a few minutes).

Daniel uses a scope for a lot of measurements though, directly at the battery or at the atty posts. He might have measured the lowest voltage under load while the batteries were still in the mod. That seems the more likely scenario as I think that these companies would know that going below 2.8V-3.0V gives you almost no additional vaping time and just heats up or damages the pack unnecessarily.

Ok. Thank you very much! That would mean that the Alien discharges the batteries pretty much as low as my Joyetech/Wismec/Eleaf mods do (I measure them when putting them on the charger). Seems plenty of the mod manufacturers don't really know what they're doing though

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[Mooch]

Ok. Thank you very much! That would mean that the Alien discharges the batteries pretty much as low as my Joyetech/Wismec/Eleaf mods do (I measure them when putting them on the charger). Seems plenty of the mod manufacturers don't really know what they're doing though

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LOL...damn good point!

 

[KenD]

Daniel uses a scope for a lot of measurements though, directly at the battery or at the atty posts. He might have measured the lowest voltage under load while the batteries were still in the mod. That seems the more likely scenario as I think that these companies would know that going below 2.8V-3.0V gives you almost no additional vaping time and just heats up or damages the pack unnecessarily.

But, a thought. Should the current draw be measured under load voltages or at the resting voltages? I've used 3.2v in my calculations but should I use something as low as 2.8v, for safety?

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[Mooch]

But, a thought. Should the current draw be measured under load voltages or at the resting voltages? I've used 3.2v in my calculations but should I use something as low as 2.8v, for safety?

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In a regulated mod, calculate at the mod's low voltage cutoff. That's where the current will be at the highest.
The actual battery voltage doesn't have to be considered.

 

[KenD]

In a regulated mod, calculate at the mod's low voltage cutoff. That's where the current will be at the highest.
The actual battery voltage doesn't have to be considered.

That puts my mind at ease

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[DaveP]

Without doing a test with a recording meter that measures lowest discharge point of a battery we'll never know the "real" cutoff point of our mods. My batteries are 3.0v, 3.2v, 3.4v in different mods by the time one cuts off and displays the battery low indicator and I get it into the charger and look at its current voltage. I have found that there's no set standard. It's whatever the manufacturer's ROM has programmed into it at the factory (not to mention the accuracy of a mod's voltage measuring circuitry).

SAG recovery voltage probably varies with the brand and type of the battery, as well as its MAH and amperage capacity.

 

[mongo74]

^^^that's my biggest gripe about regulated mods. There's no cut-off standard. One mod cuts off at 3v and another at 3.4v. I just calculate everything at 3~3.2v

 

[Gramdogg]

I don't think he is trying to be disrespectful but for an unknown reason (obviously not to determine Amps) OP wants to know your mod and tank combo and what it cuts off at with that combo. Useless information but that is what he wanted to know lol.
Evic VTC mini with EVOD @ 7w cut off 3.1v
With Tron,RDA,Bellus,Haze around 21.5w cut off around 3.3-3.4v rested. Thats with some old Samsung 25R's... hope that useless info helps