Discharging to fast?

[FishMBMC]

Hey all,

Question. My target mod seems to be over discharging my batteries. I insert a fresh battery and it only sends to be lasting me between 4 and 6 hours max. ( I run it at about 44.0 watts) At that point the screen goes all funky and the mood gets a bit hot. Is there any way i can check the mod or is it just about toast?

 

[untar]

What are those batteries? (manufacturer, model, age)

 

[Zaryk]

What voltage is the battery at when things start going sideways?

4-6 hours can be normal amount of life for a single battery mod, depending on the battery, build, and the amount of use it sees during those 4-6 hours.

 

[Asbestos4004]

Scariest thread title ever.....

 

[Baditude]

Scariest thread title ever.....

I know, right?

Great thread title. Almost as good as "My mod is licking".

 

[Ionori]

44W is 13.75A at 3.2V (most mods will consider the battery fully discharged when it reaches 3-3.2V), which is a fairly spicy amount of current for most 18650 batteries, I'm not surprised the mod is getting warm when the battery is nearly discharged. Batteries also age and lose capacity and safe CDR over time, particularly when warm. If the mod malfunctions with a fresh battery with a high CDR, it may be time to replace it if repair is not an option.

 

[Topwater Elvis]

We need to know which cell you're using to give any helpful advice.

44w with any single cell power device isn't going to have what folks would consider long run time.

 

[jfcooley]

Premature discharge can be remedied.
Nothing to worry about.








(Great title)

 

[Baditude]

At that point the screen goes all funky and the mood gets a bit hot.

Explain "screen goes all funky".
How hot is "a bit hot"? Warm to touch? Too hot to touch for 10 seconds?

Sounds like the circuit board is disfunctioning. Could also be bad batteries.

What are those batteries? (manufacturer, model, age)

We need to know which cell you're using to give any helpful advice. 44w with any single cell power device isn't going to have what folks would consider long run time.

I agree with the above posts.

What batteries specifically (make and model) are you using?
How old are the batteries?
What condition are the insulating wraps and insulating rings on the batteries?

 

[stols001]

Can't address the question accurately if you don't come back to post. And, I hope you do, as you may have inauthentic batteries or other issues going on that trust me, you really want resolved. It's possible it's your build and wattage, but it's also possibly other stuff like the wrong TYPE of batteries, battery rewraps many things.

Please provide more details

Anna

 

[bwh79]

13.75A [...] is a fairly spicy amount of current for most 18650 batteries

What are you considering "most" batteries? Around here, we usually recommend good 20A or higher-rated cells. Last I checked, 13.75 is less than 20.

 

[Ionori]

What are you considering "most" batteries? Around here, we usually recommend good 20A or higher-rated cells. Last I checked, 13.75 is less than 20.

Never said it was over 20, I said it was "fairly spicy", which 2/3 of CDR is. Moreover, what is recommended around here is not necessarily what somebody is going to walk out of a store with.

 

[untar]

Plus we don't know yet what batteries we're even talking about. If it's some 5A CDR fizzlesticks then 13.75A is too much. (though I doubt you'd run 40W on those for long)

 

[bwh79]

I said it was "fairly spicy", which 2/3 of CDR is.

Someone doesn't understand what "CDR" means. Now, I will admit that that "someone" might very well be me, but clearly one of us has got it wrong. See, I was under the impression that CDR meant (bolding mine, for emphasis):

CDR is not a safety or performance limit. It is a statement about how hard you can discharge the battery every single cycle, from 4.2V down to 2.5V, without losing more than a certain amount of capacity, or gaining a certain amount of internal resistance, after a certain number of cycles. It is the "every day" level you can operate at and still get good performance and good overall battery life. The CDR has almost nothing to do with safety except that because it is chosen to ensure decent cycle life it ends up setting a discharge current level that results in a huge safety margin.

What's your definition?

 

[Coastal Cowboy]

Constantly pushing a battery at more than half of its CDR from 4.2v all the way to the mod's cutoff wears it out. Batteries subjected to that kind of use start making the device cut off well above the 3.2v threshold, and it only gets worse.

A factory new 20A battery in a mod set to 35 Watts (or higher) is pushing 10-ish Amps.

I'm guilty of that myself.

 

[untar]

Coincidentally that's from the same guy that has this quote at the top of his blog

Never exceed the battery's continuous discharge rating (CDR) or charge rating.

Note that "almost nothing" doesn't mean "nothing". Mooch selects his CDR so that the battery stays in a safe temperature zone no matter how you vape (if you build below the CDR obviously). That way you avoid potentially damaging the battery and all problems that can come from that.

 

[bwh79]

Constantly pushing a battery at more than half of its CDR from 4.2v all the way to the mod's cutoff wears it out.

I'll admit, I don't know what figures @Mooch had in mind when he defined a "certain amount" of capacity or resistance change, or "certain number" of cycles, and phrases like "good performance" and "good overall battery life" are, of course, subjective.

Coincidentally that's from the same guy that has this quote at the top of his blog

I know what he says. He says "don't go over the CDR." There are lots of other people here saying "don't even go near the CDR." That's not quite the same thing, now is it?

 

[bwh79]

Note that "almost nothing" doesn't mean "nothing".

Right. That's why the full quote is "The CDR has almost nothing to do with safety, except that because it is chosen to ensure decent cycle life it ends up setting a discharge current level that results in a huge safety margin."

 

[untar]

If you read his tests you'll see that temperature is often a factor in selecting the CDR. Higher temperature makes batteries age quicker (which is where the cycle life you mention comes into play) and potentially damage them internally (that's is where unnecessary risk comes into play).

Your provided quote is also quite old, he has since changed his approach for community recommendations (eg dropped "MVA" rating completely).

 

[Coastal Cowboy]

I'll admit, I don't know what figures @Mooch had in mind when he defined a "certain amount" of capacity or resistance change, or "certain number" of cycles, and phrases like "good performance" and "good overall battery life" are, of course, subjective.

Yes, they are. But we can relate some experience. There are measurable data showing that discharging at a rate greater than half of the CDR reduces battery life and capacity over time. There are also data showing that rapid charging (over 1.0 Amp) also reduces battery life. And that charging all the way to 4.2 and discharging all the way to 3.2 (or lower) reduces life and capacity over time.

It's accepted that rapid discharge, rapid recharge and use of the full charge is bad for the battery. We're trading power for life when we do the above.

I know what he says. He says "don't go over the CDR." There are lots of other people here saying "don't even go near the CDR." That's not quite the same thing, now is it?

"Spicy" is just a descriptive term to what's happening, but it's true that routinely discharging a cell at >50% of CDR is not good for the battery over time. In our application of li-ion technology, the ideal situation is always stopping discharge at 3.4v, always stopping recharge at 4.0v, never charging faster than 0.5a and never discharging faster than 50% CDR.

But we're never gonna do that because good 18650's are cheap now.