LiPo Pack Safety Grades and Performance Table
How I am setting LiPo ratings
I am about to start posting the 1800mAh LiPo pack test results so I wanted to review what the ratings mean in the new 1800mAh LiPo ratings table that will be posted soon.
You can go over any of these ratings while vaping!
The ratings are not limits. They are used for directly comparing the performance of one pack against another, seeing which pack assemblers are bull....ting us, and for setting reasonable safety margins while vaping. Using these ratings can help you decide which pack to use and how hard you want to use it.
I don't care what battery you use or how hard you use it. Just so long as you know its true ratings.
The 1800mAh packs I am testing this time around are the only ones that will be tested for a few months. I have a huge backlog of 18650's to test and then the 2200mAh and 3000mAh LiPo's before I can even consider testing additional 1800mAh packs. Hopefully this round of testing will give everyone an idea of what packs might be good to use in their mods.
There are several concerns when using LiPo packs....
They use the most volatile of the Li-Ion chemistries, going into thermal runaway and bursting with flames at the lowest battery temperature and the most violently. Keeping LiPo packs in perfect physical condition and not short-circuiting them is critical.
They are damaged at much lower temperatures than the round batteries we use. Most LiPo's are badly stressed at about 60°C and permanently damaged by 80°C. The round batteries we use are rated to be run at about 80°C and typically aren't badly damaged until they reach over 110°C.
This means that we need to think differently about judging whether we are running a LiPo pack too hard. Accelerated aging occurs when the outside of a LiPo pack is just a bit warm and the recommended temperature limit is reached by the time a pack is around what most would call very warm.
Puffing up of the silver "pouch" of a LiPo cell indicates that it is being severely stressed. If the puffing goes away when the pack cools then it probably wasn't badly damaged. If the puffing remains after it has cooled then the pack is damaged and should not be used again. Tape up the connections to prevent a short circuit and recycle the pack.
C ratings are useless. Some packs exaggerate them beyond comprehension with some actually rated above the point where 12AWG wire would melt. Melt! Even if we call that a "pulse" rating the wiring would reach several hundred degrees.
If we need to multiply the capacity by the C rating to get the current rating then why not just include the current rating on the wrap and drop the C rating? It is promoted as a way to compare packs but that means it is the first thing that gets manipulated to entice us to buy a pack. Be wary when buying a pack based on its C rating.
Some would argue that just a single C rating on the wrap means it's a pulse rating. But how long a pulse? How much time between pulses do we need to have? What criteria were used to set the rating (run time? temperature? voltage sag?)? Without this information for each pack a "pulse" rating is useless as we can't compare any packs using it.
Here are the ratings I am using for LiPo's...
CDR = Continuous Discharge Rating. The nearest 5A-multiple of constant-current continuous discharge current that brings the inner cell of a 3S pack to a temperature of 60°C. This is what the LiPo assemblers recommend as the max running temperature so it makes sense to use it as the rating. Especially since the inner cell will be hotter internally than this temperature, perhaps considerably.
Testing shows that the temperature of the middle cell in a 3S pack is 7°C-10°C higher than the temperature of the outer cells (but still under the shrink wrap and protection wrap). This means that when I measure a temperature of about 50°C-53°C the inner cell of a pack has reached at least 60°C, its limit. A 2S pack will run a bit cooler and a 4S, or higher, pack will run a bit hotter than this.
Most of the 3S packs I have start puffing (temporarily) at around 60°C or lower so I agree with the pack assemblers that it should be used as the max running temperature for decent cycle life. Going over this temperature will start damaging the pack a lot faster. Note that at an internal temperature of 60°C the outside of a pack is just warm.
The protective and shrink wraps used on these packs are very effective insulators. It takes at least an hour for each pack to cool back down to room temperature internally. These 1800mAh packs are small too. Larger packs would take at least a couple of hours to cool.
MVA = Maximum Vaping Amps rating. To help prevent overheating during chain vaping and for a safety margin in case of mod malfunction, don't exceed the MVA rating. It helps to limit the pack temperature to 60°C or lower.
MaxSafe = Maximum Safety Amps rating. To help prevent the possibility of venting or thermal runaway in case of a mod malfunction or accidental button press never go over the MaxSafe rating. It helps to limit the pack temperature to 80°C or lower. The pack can still be damaged, perhaps permanently, at this temperature though.
The minimum temperature at which a LiPo pack will go into thermal runaway is considerably above 80°C but the temperature of a pack in a mod can be a lot higher than seen during my testing. Older cells (which run hotter), being inside a warm mod, operating near a hot circuit board and/or atomizer, or vaping on a hot day can all bring the temperature of a pack considerably higher.
I want to state again that these ratings are not hard limits. They're just for directly comparing the performance of different packs and for figuring out how hard we want to use them.