Rapid/Fast charge rates are terrible for cycle life though and create a lot of heat. 
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1C is plenty 
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Also very excited to see @Battery_Mooch here. Fantastic to have somebody around with excellent first hand knowledge of all of our favourite boom sticks .
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Holy fire 
works thatās some heat
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So @Battery_Mooch if I base myself on your chart, Iām way over specs on my secondary pack?
12s3p p42a
12s/8a charger (peaks at 9.6a)
Itās the only 12s charger I have on hand. Use it for my 12s6p 30q
Look at the chart and do the math. Iām just not able to do that for everyone. If youāre not sure how much current is flowing into each cell then STOP! Itās critical that you do as it impacts your safety as well as the health of the pack.
I recommend staying under 4.2A for decent cycle life but you can certainly go up to the P42Aās 8A rating if you want and cycle life is less of a concern. Keeping the pack cool when charging can help.
How much current did you calculate was going into each cell when charging?
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Peaks at 9.6a so Iād imagine if my circuitry building was decent, it should be sending an equal 3.2a per cell
Exactly.
Where were you thinking you were going way over spec?
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There lies the real question 
My brain saw 8.4 and forgot to multiply
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Letās keep the basics questions at a minimum for mooch. His data is easily google found and his time is split between dozens of sites.
@Battery_Mooch I know that electric vehicles are a pretty big departure from the vape world. But weād love to hear your thoughts on battery tech for this Industry.
The overwhelming majority of folks are on 10S or 12S voltage with P counts ranging from 2-10p depending on the build and range goals.
P42A, 40T, 20700b, 50E and 30q cells are routine findings here. These packs range from 50-150 amp output
In general, most never discharge cells below 3.0V Most of us use a BMS only wired for discharge (no over discharge protection)
-Iād love to hear your thoughts on something Iām working on, parallel charging. currently testing successfully with two separate chargers (in this case 2A and 3A 10S chargers with a total 5A input). Lots of people have smaller chargers getting no use. That and some of these 6+ amp chargers are not only exponentially more expensive, but clunkier to travel with.
-Any experiences with thermal performance on the bench vs in the center of a 60 cell pack.
- Iād love an explanation on how to test current flow from a CC CV charger. None of my voltmeters will complete the circuit properly when I try to test a chargers output- light stays green. Iāve seen several chargers that performed well under 70% of advertised amperage
- charger brand recommendations for this voltage US based or aliexpress
- lastly, conductor current limits. We use a variety of 0.15-0.3 nickel strip and 20-10awg wire in sections typically under 12 inches at max. We have some charts displaying estimated amperage ratings but itās derived data nothing experimental.
Thanks again for your contribution
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āDonāt ask question in a place made to ask questionsā 
My question, though wrongly based, was something Google would have answered generically. Why look for a possible response elsewhere if heās gifted his presence here to discuss things pertaining specifically to p42a in this thread
Thank you for that application info, it helps.
I was working with cells for about 25 years before doing testing for the vaping community so Iām definitely not limited to just vaping-related cell stuff.
A bit of background info on meā¦
Since 1992 I have been working full time for my clients designing power electronics (chargers, power supplies, auxiliary power units, electronic loads, BMSā, energy harvesters, etc.), optimizing power electronics designs, doing thermal analysis, and cell testing.
- When you say āparallel chargingā youāre talking about paralleling the chargers, not the packs? Thatās a verrrrrrry bad idea for many chargers and I strongly advise against it. But, having said that, there might be ways to do it universally with some additional components on the charger outputs.
So much depends on the particular charger and its circuit though.
Which chargers did you successfully do it with? How were you able to verify that it went well and that the chargers werenāt overstressed?
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Iāve done a huge amount of work involving thermal management but specifically for a 60-cell 18650 pack? No. The physical configuration of the pack and its provisions for cooling are critical as it can be a little as a 5Ā°C difference from center to outer edge all the way up to a 50Ā°C difference or even more for high power packs with no provisions for cooling the center cells. Conduction cooling is tough, radiative cooling is useless here, and convection cooling means getting air flowing through the pack. Unless you are using some great phase-change compounds to fill the pack and huge heat sinks to get the heat out there are limited options for a sealed pack.
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A clamp ammeter could work well for monitoring a chargerās output or you could buy a few 1% or 0.1% tolerance power resistors and wire as many together in parallel as needed to be able to handle the heat. Then use a multimeter to read the voltage drop across the resistors and Ohmās Law to calculate the current. Perhaps ten 0.1 ohm resistors in parallel so that 10mOhm final resistance doesnāt affect what the charger needs to do. Donāt let the resistors work at over 1/2 their power rating. Even at 1/4 their rating they will get damn hot. Another option is a precision current shunt, typically available with 20A, 50A, 100A, and 200A ratings. Never use beyond 1/2 of the rating and cool it with a fan!
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Sorry, I donāt have any charger recommendations yet. Everyone has such different preferences and priorities thereās no way for me to pick some out. I do like the iCharger series for packs though. I use two 106B+, two 406 DUO, and two 410 DUO.
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Conductor current limits have to take the insulation temp rating into account along with whatās acceptable for power losses. You can run a wire right up to its fusing current level and it will still work. But operating a wire at just below the melting point of copper is typically not a great thing to do.
This all means that 18AWG wire could be rated at 2A for voltage-drop sensitive applications all the way up to 20A or even higher for pulsed applications where power losses arenāt an issue and silicone or Teflon insulation is used. Letās talkā¦maybe thereās some testing I can do with a bunch of 12ā lengths of different wire and some nickel strip.
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a lot of people in the electric unicycle community does this. Just a straight parallel wire splitter into their wheel
Seems to work just fine for them
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Since you worked on chargers, what can you say about non CC/CV chargers small form factor ones?
In my opinion we leave huge gains in charge time by using CC/CV, just look at any EV on the market, even those without active cooling can charge way faster by using some kind of stepped charge curve and still have great cycle life
Thereās got to be at least a current limiter function for anything charging li-ion cells otherwise the power supply would just think it was being short-circuited and āhiccupā (turn off/on until the short was removed) or shut down.
A CC/CV power supply or basic charger is going to be a different approach than a stepped charge algorithm (using a CC/CV supply). Any CC/CV supply or charger will āautomaticallyā have its current level taper down as the cell fills because of the shrinking voltage difference between the cells and the supply. No need to step the current down or anything. Just a ādumbā CC/CV power supply can work great for charging if you disconnect the pack when the current has dropped to, typically, 1/10th the bulk charge rate.
Stepped charging algorithms often use very high charge rates up to a certain SOC point or voltage and then reduce the charge current level to try to minimize cell damage. Itās still done with CC/CV supplies but thereās additional control over the current levels. Done properly this stepped charging can significantly shrink charge times without doing too much damage to the cells. There will always be some additional damage vs low current charging though.
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Using any two different chargers or the same model of a specific charger?
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yes, usually two random chargers. Whatever they have ālaying around at homeā. better than purchasing a singular āfastā charger for $150+
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Thanks.
I have had rather spectacular failures occur when parallel testing some commercial chargers as some circuit types will allow current to back flow into one charger (frying it) if it turns off before the other one does.
Youāve piqued my interest, Iām going to look into this, thanks again!
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