Skiddins

Good idea, get your excuses in early for not turning up at 360v2 and showing everyone how great your cars are!

Skiddins

Battery C ratings are marketing BS.
Early on (when RC lipo's first came in) the C ratings were probably closer to being accurate, but ever since it's been an 'arms race' by resellers to persuade the punters that their lipo's are more powerful.

If a lipo puffs up just because you happened to leave it fully charged overnight, it's a crap lipo, there's no excuse for it.
If your cell phone puffed up everytime you left it charging overnight you'd be less than pleased.

I have 2s lipo's that have gone to cutoff before but the case are still dead flat.
The only exception for me is that I have yet to find a 2s shorty that never wants to puff during normal use (and only in an F1)
Thunder Power 5400 I'd accidentally left fully charged for 3 years, I'd changed to a different connector system and somehow that lipo was forgotten about.
It was still in a perfectly shaped case, although it's resistance had gone up far too high to use.

ModeratedUser30082018

iTrader: (-1)

I've seen this parroted on many occasions. Do you have any evidence to support your claim? Or is that factoid made up just like manufacturers C ratings?

gigaplex

iTrader: (2)

My packs are 90C 7500mAh. That's 675 amps. That's insane, the wires would fuse well below that level. It's pretty obvious that they can't sustain that rate.

bertrandsv87

iTrader: (2)

There was a guy on youtube testing batteries with a professional ESR meter, and he was getting lots of high C rated packs only showing about 18C to 25C with the pro tester.

JeffofSpace

bertrandsv87

iTrader: (2)

It may be from cell mismatch, overdischarge and leaving your packs too long at full voltage instead of storage voltage(3.85v/cell)....I puffed my maxxamps cells because I stored them at full voltage, but I never puffed my other cells since using the storage voltage mode in my TP charger...
I also limit my charge rate somewhere between 8A and 23A...

Skiddins

Which bit?
Early lipo's had lower C ratings and lower capacities than we have currently, but their performance was definitely worse as well.
Later generations had better performance and slightly higher C ratings, then all of a sudden we had 60C, 90C 100C etc with seemingly no better peformance.
Every (ill-informed) driver always wants the highest C rating they can buy, yet ask them why and they will tell you because it delivers more power.

If you're asking if C ratings are bollocks, then speak to SMC. I've also had conversations with a guy who works closely with Hobbywing with their development etc.

LJH

iTrader: (2)

There has been a lot of testing in the RC E-Flight world on "true" C ratings. A lot of the hot rod planes (F5B, F3D) are pulling 200+ amps for "extended" lengths of time. From what I have read it is hard to do over 30C for any length of time even with the best cells. In planes we have the option of using more cells to get to get the power necessary but that is not an option in cars that race.

As for puffing, it has been my experience that there are three major factors that cause it:
-Over Discharge
-Stored fully charged
-Asking the cells to deliver more then they are capable of- This was more of a problem in the early days of LiPo's. I puffed plenty of the old Thunder Power 1320 cells (10-12C) in my 150+ MPH SP400 Pylon planes. After a 2-3 minute flight the cells would come out so hot it was not comfortable to hold them.

Cheers,
Jim

silden

iTrader: (12)

Skiddins

I can't think of any class where after one run the voltage would drop as low as 3.6V per cell apart from /12 open Mod perhaps, and even then it's rarely

JeffofSpace

silden

iTrader: (12)

We only dumped with new packs while running 1/12 6.5 during the IIC in 2016.
It took as to long to find the right gearing, but still we ended up with 3.3 Volt after 8 minutes.
Keep an eye on the Battery temps to prevent puffing. Some additives start to Degas at about 60 degree C or 140 F.

I_NeedBigDrink

iTrader: (4)

The extremely high C rate claims are probably the pulse rate, only achieved for milliseconds. Im not sure about offroad vs onroad, but I calculated the average discharge rate on my battery based on a long practice session to be about 5-10C. If you eliminate the downtime from crashes or pauses maybe I could see it being 15C or more. But to have a continuous discharge rate close to 30 is insane, more fantasy than reality, at least for surface vehicles. It wouldn't even be desirable, because batteries would hit their LVC in minutes, and heat would be an issue. Plus you would want beefier ESCs to take advantage of the high current, but the cars have little space already.

Batteries can be kept in good condition for multiple seasons if you simply treat them right

• NEVER overcharge, even if your charger is set to the battery's maximum, it still might overcharge due to charger inaccuracy.
• Set a comfortable LVC.
• Don't store full or at LVC voltage, (I charge my LiHV packs to 4.1V/cell for storage) and store away from direct sunlight.
• Don't charge at a rate that will cause your batteries to overheat. I charge my 5Ah battery at 15A, well under the 5C manufacturer limit but still fast enough for me.
• Measure battery temps after runs, or at least when you make changes.

As mentioned above, get batteries with enough capacity to comfortably last more than one race. You'll avoid LVC situations and give some room for gradual degradation.

071crazy

iTrader: (8)

It's unlikely that you are anywhere near an average discharge rate of 10c, unless you are running 4x4 or e buggy. That would mean that you are dumping a pack completely in 6 minutes or less.