Weak Battery warning on a fresh 18650

[Pathian]

So I know the board is fairly new and it's unlikely that a lot of people have done much testing, but I figured I'd ask.

I built a single 18650 DNA75 last night and I'm running into some strange behavior when running in temp mode and occasionally in wattage mode.

I've tried running on a fresh LGHG2 and a Samsung 25R, and in wattage mode at 70w with a .13 ohm Nifethal70 build, everything seems to run smoothly, but when running in Nifethal Temp control mode at 60w-70w and 410F, I hit a weak battery warning >50% of the time.

I can post some dev monitor graphs when I get home, but can anyone think of what might be going on?

[dsidab81]

Sure you're not just hitting amperage limits on these batteries?  18650's sag considerably more under load than lipo.
25r's are basically a 20amp battery right, and doesn't the 75 pull about 26amps under max load?

[turbocad6]

battery contacts are a big part of this, even if your contacts are optimal a single cell is going to struggle at 70 amps at anything less than a full charge but combine this with less than optimal contacts and I'd pretty much expect to see what you are seeing. either hard wire the cell ( I know you don't want to do that) or improve the contacts for best results at those kinds of drain. 

[mikepetro]

Nifethal is not one of the "materials" that ships loaded in the DNA75, so you are largely charting unknown territory.

What would be most helpful is if you post a screen cap of Device Monitor while you are taking a hit and getting the low battery message.  Otherwise we are only guessing as to whats going on.

[Spector NS5 RD]

the coil material shouldn't be the culprit of the weak batt message. i run nife48 wire myself and haven't noticed that specific wire cause any problems for me. my guess is we're going to see a lot people posting about weak battery messages in days and months to come. 18650's will have considerably more sag than lipos. 26650's will have even more. that's why i plan to make a lipo'd 75 mod, or at least a dual 18650 one.  we're asking a lot now from a single battery. maybe ditch the high mah batts and try the LG HB6, HB4, or HB2 - those batts have lower mah but a higher CDR (30 amps).

[mikepetro]

You are quite right about voltage sag, look at these two (albeit mediocre choices) of 18650, then look at the lipo sag on the last screen cap.

[awsum140]

You just convinced me to drop the 18650 idea and try my hand at soldering LiPOs to make a pack, Mike.

[mikepetro]

Love my Lipo 75, gotta say......

[mikepetro]

ChunkyButt200 said:

the coil material shouldn't be the culprit of the weak batt message. i run nife48 wire myself and haven't noticed that specific wire cause any problems for me. my guess is we're going to see a lot people posting about weak battery messages in days and months to come. 18650's will have considerably more sag than lipos. 26650's will have even more. that's why i plan to make a lipo'd 75 mod, or at least a dual 18650 one.  we're asking a lot now from a single battery. maybe ditch the high mah batts and try the LG HB6, HB4, or HB2 - those batts have lower mah but a higher CDR (30 amps).

The HB6/HB4/HB2 all have nice current capability, and will certainly perform well, but with only 1500mAh it certainly wont last long. Lipo is still the choice for me. A 3000 1S Lipo can still be made into a reasonably small mod.

[Spector NS5 RD]

mikepetro said:

The HB6/HB4/HB2 all have nice current capability, and will certainly perform well, but with only 1500mAh it certainly wont last long. Lipo is still the choice for me. A 3000 1S Lipo can still be made into a reasonably small mod.

ya their capacity sucks but that's the trade off. an in between battery would be the VTC4 or the LG HD2C both are 25 amps CDR and 2100 mah with the LG being slightly better out of the two. i'm all for the lipo for the 75. in fact i have plans for the one i should be receiving friday from a place where i was sworn to secrecy . that board shall dine on lipo power. no weak batt message for me. i hope, lol. 

[VapingBad]

Personally I have been doing fine with 25R, running them until they are about 3.25 V and just get a bit of a drop off on preheat toward the end, but I do max the preheat.  "Weak battery" is just the board warning you that your battery sagged to 2.5 V under load and not the your battery needs changing warning "check battery".   Poor battery contacts also play a part in this as well, I replaced the standard Keystone contacts for something more solid and only get the warning when the battery is getting low now.  You can also reduce your preheat watts because in temp mode it is probably only sagging that badly for a fraction of a second during preheat.

[Spector NS5 RD]

VapingBad said:

Personally I have been doing fine with 25R, running them until they are about 3.25 V and just get a bit of a drop off on preheat toward the end, but I do max the preheat.  "Weak battery" is just the board warning you that your battery sagged to 2.5 V under load and not the your battery needs changing warning "check battery".   Poor battery contacts also play a part in this as well, I replaced the standard Keystone contacts for something more solid and only get the warning when the battery is getting low now.  You can also reduce your preheat watts because in temp mode it is probably only sagging that badly for a fraction of a second during preheat.

i wonder if people will mod their DNA 75 mods with heavier battery contact springs and contacts.....

[dwcraig1]

Just my opinion/thoughts. So you take a 900 mah 3s lipo and re-wire it parallel, now it's a 2700 mah lipo. Sounds good, right? Well it's still just 10 watt hours. Given those numbers I see no advantage to building a DNA75 using a lipo, I would just spend a few bucks more and use the 200 board. I do see a market for the 75 with interchangeable 18650/26650 though as most folks vape at way less than 75 watts. Again just my way of looking at it.

[turbocad6]

I agree, I only picked up a few 75's just for the hell of it to play with for maybe a really small mod but honestly I'm much more into the dna200's. to me anything over 50 watts and a small battery will just suck, the 75 may be good as a replacement to the 40 but once you start to use most of it's potential then the 200 just makes more sense I think, especially if the cell size would accommodate the 200 anyway at that point

I find my happy place is the 200 in 2S 133w config. I love my dual 18650's, yeah 6,000 mah in the same space that a lipo would be only half that... even factoring in the excess sag it still far out performs to me, I get 16ml's out of a pair of 18650's but the trick is you must have good battery contacts, this is where a lipo really seems so much better because they usually have much better connections in general, but even with a good 1,000 man 3s lipo I can get through only ~ 12ml of juice. 2 18650's are about the same size as a 1,000 mah 3S, yeah more sag but literally double the mah and the ability to go lower in voltage before swap out more than makes up for it and then some from my experience with it but you need good battery contacts, most 18650 mods fall short there I think

[mikepetro]

Well, if it says anything, when I stocked for my 20 year FDApocolypse plan, I stocked a dozen DNA200 boards, and zero 75s.

[VapingBad]

Been mainly vaping on the 75s, but no doubt will be back DNA 200 soon, but very different price points especially when you factor in the same cost for the screen $38 vs $68 and the swappable battery is a big plus for me.  They are far better than the Evic Mini especially with SS316 IMO, the difference in vape quality with SS316 between the 2 is night and day I let a friend try both at a vape meet and has been using cheap mods for 2 years and he ordered a DNA 200 a few days later.

[Lilpetabread]

I'm getting "weak battery" when my HG2 18650's are at ~3.7 volts. That's at about 50% on-screen battery life. Is that normal, or are my HG2's just getting old? I do have 18650s set up thru Escribe, and I have preheat off, with a 0.38 316L build at 42 watts.

[mikepetro]

Lilpetabread said:

I'm getting "weak battery" when my HG2 18650's are at ~3.7 volts. That's at about 50% on-screen battery life. Is that normal, or are my HG2's just getting old? I do have 18650s set up thru Escribe, and I have preheat off, with a 0.38 316L build at 42 watts.

Yes, pretty normal. Dont worry about it though. It is probably voltage drop during preheat triggering the "weak bat" message. Take a look at it in Device Manager.

[Spector NS5 RD]

Lilpetabread said:

I'm getting "weak battery" when my HG2 18650's are at ~3.7 volts. That's at about 50% on-screen battery life. Is that normal, or are my HG2's just getting old? I do have 18650s set up thru Escribe, and I have preheat off, with a 0.38 316L build at 42 watts.

question, since u have the preheat off and only running 42 watts.........how old are your hg2's and at wattage did you normally run them at before your 42 watt setting now? if you were hard on em before and they're up in age might be time to get a new pair. it all depends on how hard you beat on them and for how long....  might want to look into the LG HD2C 18650 very good high drain batt. slightly better than the vtc4 when vaping at the 75's max wattage. just my two cents. buy what works for you, obviously.

[Lilpetabread]

ChunkyButt200 said:

question, since u have the preheat off and only running 42 watts.........how old are your hg2's and at wattage did you normally run them at before your 42 watt setting now? if you were hard on em before and they're up in age might be time to get a new pair. it all depends on how hard you beat on them and for how long....  might want to look into the LG HD2C 18650 very good high drain batt. slightly better than the vtc4 when vaping at the 75's max wattage. just my two cents. buy what works for you, obviously.

I'd say, on average, maybe 60 watts. Nothing too crazy. They're probably 8 months old now. I'll likely just grab a new pair and recycle these, just in case. Thanks for the heads up and the advice! You guys here are awesome!

[camerajunkie]

Hello all! I apologize for my noobishness, but would a couple of resistors or would mosfets help the situation for safety purposes if someone where to put in a 20A battery into the mod, or is this already built into the chip.

[Spector NS5 RD]

camerajunkie said:

Hello all! I apologize for my noobishness, but would a couple of resistors or would mosfets help the situation for safety purposes if someone where to put in a 20A battery into the mod, or is this already built into the chip.

not needed. in escribe under manufacturers settings you can set the current limit of your particular battery you are using.

[awsum140]

I think the biggest reason for premature "weak battery" warnings, with hand-built mods, is marginal contacts inside the battery holder.  I rebuilt the holders in the DNA75s I built.  I just got  "weak battery" warning, changed the battery out and put it on a charger.  The battery was showing 3.27 volts when it went into charge mode.

[Nils]

Hi. I have a dna 40 26650 hand made mod batteries ijoy and i have the same problem with weak battery warning from the middle of the battery bar. The modder explain to me that is caused beacause of the ohm law. My set up is 40mm wire kanthal a, 0,6-0,7 ohm and i vape at 22-24 watt. With the same setcup i vape normally in other mods but in the dna40 i have the weak battery warning and the strength of battery falls down from the middle of the bar. Thecmoder also told me that i must vape at 16 watt with 0,5 ohm setup to avoid the warning. But i cant satisfy the vaping in these watts. What can i do? Thanx

[giz_60]

There is a really handy ohm's law calculator here...http://www.steam-engine.org/ohm.html...and if I am reading it correctly, with a 3.7v battery, the max watts on a .6? coil is 22.82 & .7? coil is 19.56...but I could be mistaken...