glennhl

iTrader: (16)

I have two ULCG batteries. They are different brands, but otherwise are identical. I also have 2 LCG batteries. I am getting ready to run 3 cars at our local States race, so I had to get out the LCG batteries and use one of them in the third car. So I checked both of their internal resistance. Battery temps were room temp (68F) and one had 1.9 milliohms/1.8milliohms and the other was 1.9/1.9. So basically the same. I then checked my ULCG batteries and they were 2.5/4.3 and 2.9/4.5. The ULCG are actually the newer batteries (3 months old). Has anyone else noticed that the ULCG batteries have a higher internal resistance?

EDIT: I am checking IR using my 406Duo charger. And so you don't think it could be manufacturers, the two LCG and one of the ULCG are all made by the same company.

glennhl

iTrader: (16)

I talked to an expert. The ULCG batteries have a higher IR because they are a smaller battery.

billdelong

iTrader: (33)

IR also increases over time as well, there are many variables which affect the IR.... if you want to get the best possible IR reading, then you should cycle the batteries with a regenerative discharge bank at high current to boost the cells for optimal performance.

trilerian

iTrader: (51)

Or warm them with a lipo sack that has a heater in it. Warm them to approximately 95F. This is much better for the cells than doing 40amp discharges.

billdelong

iTrader: (33)

Will you please give an example?

I have seen a case where I had a battery that averaged around 3mΩ/cell and was able to get the IR down to roughly 1.5mΩ/cell after cycling the pack @40A

Are you suggesting that placing the pack inside a heater will reduce the IR even farther than a 40A cycle?
I have tire warmers and am willing to experiment, but would be nice to know if someone has already done the homework

trilerian

iTrader: (51)

The reason discharging works to lower the IR is because it heats the battery. You can skip the abusive discharging and just use a lipo sack with warmer, and it has the added benefit of keeping the battery warm right up till the point you put it in the car. Now, a 40amp discharge probably heats the battery to a higher temp the 95*F, and then a 40amp charge heats it pretty well too. But in order to use the high charge, high discharge your timing has to be spot on, because as the battery sits and cools the IR goes up. Also you subject your batteries to abuse while doing this, and they will not last as long. Warming them to 95*F will lower the IR of the battery and will have no negative effects.

glennhl
Your newer ULCG batteries are a bit out of balance with each other, the IRs are too different between the cells. Personally, I would not use them to race with, just practice. As to decent IR on a new ULCG battery, my new EAM 5800 ULCG charged at 15amps reads 2.1/2.1 on my icharger, no heat. My EAM 5300 ULCG when I first got it, read 1.7/1.7 charged at 15 amps, after 100+ cycles it reads 2.4/2.5, and my Sunpadow 5300 reads 1.6/1.7 charged at 15 amps.
When I say IR charged at 15 amps, what I am meaning is that I look at the IR, while charging, at the end of the charge, at the current point in time, with no heat. I do plan on buying a heated lipo safe this week. If I do an independent IR test on the batteries, it is generally lower.

Edit: to compare to a regular size battery, I have a TSR8200 that reads 1.8/1.8 and my 1c TSR batteries read 1.6. I have a Motiv 2s 6000 shorty that read 2.3/2.4 brand new.

billdelong

iTrader: (33)

It doesn't sound like you have any specific examples comparing IR between a pack cycled at 40A vs Warming, so I will be happy to experiment this weekend at the track using my tire warmers.


While I agree that timing is critical for cycling, I would argue that you want to minimize the amount of time that heat is applied where heat does impact the longevity of our packs:
https://batteryuniversity.com/learn/...ased_batteries



I don't have enough experience with testing high rate cycling to say that it is more/less harmful (compared to heating alone), but heating a pack will most definitely have a negative effect on its lifespan.

It would stand to reason that a pack that was cycled just before a race (effectively heated for a very short duration of time) will probably last longer than a pack that is always kept at 95°F... assuming that the pack was designed for high C charge rates.

Regardless, what's more important to me is which method provides the lowest IR

racer1812

iTrader: (31)

I get the curiosity of wanting to know the IR difference but external lipo heating is the biggest "no-no" that I know of, at any track.

trilerian

iTrader: (51)

I would much rather pit next to someone who charges at 2-3c and heats their batteries to a safe temp, than pit next to the guy who has slightly puffed batteries and charges at 40 amps. Then those guys leave their batteries in their cars while charging and walk away on top of it.

billdelong
No, I do not have any experiential knowledge on charging at 40 amps vs heating the battery. I would take a guess though that a 40 amp cycle will produce a lower IR, since it will heat up more than 95*. As to capacity loss because of heat, pretty negligible when you do the math. Take a 100 charges where you apply heat, multiplied by 30 minutes for a charge and use yeilds 3000 minutes, or roughly 2 days. At 40*C (104*F) according to your chart a battery stored with full charge would lose 35% capacity in a year. If you divide the 35% capacity by 365 then multiply by 2 you get approximately a 0.2% capacity loss. Over a 100 cycles the capacity loss due to heating the battery is pretty much nil. You will lose substantially more capacity due to the battery breaking down.

I have never charged a lipo at 40 amps, point of fact, the highest I have charged has been 20 amps, and I race stock. I can guarantee you, I don't lose because my battery is not up to the task. I lose because my driving isn't up to the task. With that being said, I would find a way to measure the lipo battery, inside the case, after a 40 amp cycle. If the temp is over 114* F, you are damaging the battery. And I would guess the temp to be higher than that.

billdelong

iTrader: (33)

I am "That Guy" who charges my packs inside my car @ 40A, which is roughly 7C in my case, but that 40A rate is only for a couple of minutes, then it drops to 30A (5C) for a couple min, then 20A (3.5C) for a couple min, then 10A ( 1.7C) before the pack tops off in about 10 min. I would rather have a LiPo fire in a car to make it easier to grab and toss out of the pit room than a stand alone pack that your only hope is to kick out of the way and pray it can be kicked out of the pit room before the room has filled with smoke. Far less residual smoke when the pack was inside a car, also there was no damage to the other guy's car after the fire other than a melted spur gear, ha!

In the cases of LiPo fires I have personally observed in the pit room ( 4 fires over the past 4 years I have been racing stock at Thornhill) were all due to severely swollen packs or were charged in NiMh mode by guys who didn't have a LiHV charger and were trying to boost their voltage and walked away/forgot they were boosting

I have yet to see a single LiPo fire in our pit room due to 40A and proper IR checks, the rule of thumb we go by is to limit 40A for cells below 5mΩ, 3C for cells below 10mΩ and limit to 1C up to 15mΩ before a pack should be retired. I'd be willing to bet the IR on any of those LiPo fires would've been way higher than 15mΩ if they had been checked beforehand.

As a community, we should preach responsibility as this technology evolves, I believe it's possible for everyone to manage it safely, especially with an iCharger that has the ability for real time IR checking during a charge cycle, it's just a no-brainer IMO.

glennhl

iTrader: (16)

All you are doing by charging and discharging at 40 amps is heating up the battery. As the battery gets hot, the IR goes down. You can get the same effect by charging at a more reasonable rate (10 amps) and heating up the battery with a heater just as Trilerian suggests. And I'm guessing the batteries would last longer.

billdelong

iTrader: (33)

While I agree that temperature is a symptom, I don't believe that temperature is the "only" factor in reducing IR, when you cycle a battery under load you are physically activating the chemistry of the pack in addition to increasing the temperature. When you only apply heat from outside the pack, I challenge its effectiveness as opposed to generating the heat internally from the chemistry of the pack. Best analogy I can come up with is cycling a battery is like re-heating your food in a microwave which heats far more quickly (and efficiently) than re-heating your food in an oven which would be the equivalent to using a battery warmer which applies heat externally (less efficient).


Yes the biggest variable here is heat, and I agree that whichever method generates more heat for a longer period of time will cause more damage. It's entirely possible that excessively heating your pack may cause more damage than shorter bursts of 40A cycling which can have significantly less " combined heat stress".


What I am questioning is which method is more effective, doesn't really matter to me which causes more damage because I run Trinity White Carbon packs which are known to handle 40A charge rates for well over a year before IR fades and a slight hint of swelling may eventually occur. In contrast, most budget brands of batteries I have tested can barely last 6 months before performance drops and significant swelling is visible, even some brands that were charged at only 10A.


There is very little information out there which discusses what actually happens internally with the chemistry, but I would like to share a very important story: TheJANG from URC once shared his experience where he charged several brand new packs inside his home at 1C, then placed all his packs in the trunk of his car and drove about an hour to the beach. When he arrived and pulled out his packs, they had all severely swelled up and were all completely damaged beyond use... they were never used a single time. What happened was that the heat in the trunk caused the voltage of the packs to increase which in turn damaged the cells.


Just a guess, but if TheJANG had probably cycled those packs at 40A, then they would've already been at a high temp and might've survived the heat in the trunk. Regardless, the worst thing anyone can do is to apply heat to a battery after it has been charged! You will be over volting the battery which will cause far more damage than charging at 40A... just ask TheJANG


Pretty good video here from Ryan Harris worth a watch, skip to 6:09 in the clip to see him talk about 40A cycling:

gigaplex

iTrader: (2)

I don't have any specific data to provide, but there's a reason that battery lifespans are often quoted as number of cycles. Cycling the battery does wear them out.

billdelong

iTrader: (33)

I don't think it's realistic for us to measure the lifespan in cycles because heat and age tend to cause our packs to wear out far more quickly than they would ever get a chance to hit any manufacturers claimed cycle count limit.

Just for reference, let's say that a typical racer might cycle their packs 6 times on a given race day assuming they are only running 1 pack. If that racer were to run once a week for a year straight that's 52 weeks x 6 cycles = 312 cycles which is very rare for a budget pack to make half this cycle count before swelling and IR fade occurs

I agree that doubling cycles will shorten pack life, so I typically only perform my regenerative cycle once per race day just before the main and try to time it accordingly

trilerian

iTrader: (51)

Heat and cycle count is what wears out lipo batteries. Age isn't as much of an issue if you follow proper storage procedures. I have a TSR 8200 battery that is 3 years old, and it is still quite strong with low IR. I have Reedy batteries that are over 10 years old that have IRs in the 4 milli ohm per cell. Cycle count is based on a full cycle of the battery, most people charge then run and charge again. This is a partial cycle, which takes less of a toll. Heat however is the true killer. Optimal operating range for a lipo battery is 0-45*c, with some studies suggesting a tighter range of 15-35*c. These studies show that anything over 35*c causes an irreversible creation of lithium oxide inside the cell which leads to puffing and lost capacity.

Ultimately, what is boils down to.
Heat can reduce the IR of the battery.
Too much heat can cause the battery to swell and reduce capacity.
The allowable high end of the temperature range for a lipo is between 35-45*c, 95-113*f.
Do whatever you want to get your batteries to that temp.