F1fletch

iTrader: (10)

Sooooo

I have been hearing for years how cycling lipos with high amperage can help with lowering IR’s and give stock class racers more punch. I also know that doing 40/40 charge and discharge can greatly shorten the life of the pack. Totally understandable.

I have several questions about on road spec class racing and specifically how/when and at what amperage for charging and discharging should occur.

Is 40/40 the best rate even for 25.5 and 21.5 Classes or would 25/25 for instance have any positive effect?
What voltage do you use to discharge (LiVH) cells down to?
What voltage do you use to discharge regular LiPo cells down to?
is there a key with timing and temperature to do right before a race only (10 min before for example)?
Do you always charge/discharge lipos in storage mode right after a race?

Lastly, I am hearing the 7.4 LiPo batteries may be better for stock class racing where it is not allowed to charge to 4.35 per cell. Any feedback on this is appreciated. Pursuing USGT, F1 and 17.5 TC this year. I realize opinions may vary and #trythisatyourownrisk, no flaming please. Looking for experience with those who use high amp charge discharge and also those who found a happy medium.

thanks all

gigaplex

iTrader: (2)

Are ROAR rules enforced where you race? 40A charge rates aren't legal under those rules.

riceball777

iTrader: (36)

roar rules state a 1c max charge rate. I can guarantee you almost no one charges at 1c even at roar races. Most people that don’t do the 40amp discharge /charge cycle still charge at 10-20 amps.

ebohon

I tested the theory last year with a bd2000 discharger at 30amp 10 and 15 amp down to 3.3v. I didn’t want to take anecdotal comments. I used my notebook for results. The difference in irr was due to the diff load on the packs. Then I discharged at the same 30 amp and irr remained or dropped on second or third cycle. I also used a resistor bank at 40amp with my 406dou icharger ... no difference in irr after the couple of cycles. and I’ve also tried it on the track and found no difference. I ended up settling at 20charge to cut back on charging time at track and 10disc to prolong battery life. I don’t even use my bd2000 discharger as much. I usually just disc via my icharger at end of day to put batts in storage. Maybe there is a diff but nothing I could find either with electronics or on the track. The biggest diff I found was in the c ratings of packs. Higher c ratings maintained a higher age volt during first 1500-2000 mah disch which is the sweet spot for usgt and f1 for me. The higher amp charge impacts temp so that may be restricted at your track for safety reasons.

Bry195

I really like the way you made observations and provided the information. At some point above you said you noticed IR dropped and it stayed that way. Could you describe that better?

I hate to use the excuse that results may vary base on the battery you use but it might. i can take a cell that is over the 3m down to 1.4 after a couple cycles. Nothing beyond that. Its hard to tell if that is happening from the 30 amp discharge or the 30 amp charge but it does happen and is retained but not overnight. I use LIHV batteries and cycle at HV but I race at 7.4 rates. 9 months no puffing and IRS are now starting to climb into the 3’s on some cells.

I always store charge the batteries. The only difference I see in running a LIHV at LIPO charges is in capacity. At LIPO at 6000mah will have something around 5300 ish.

Also on the batteries that are starting to show their age they have permanently lost about 3-500mah.

F1fletch

iTrader: (10)

Great info guys, thank you! this is exactly the kind of info I was looking for. I am experimenting with 25/25 lately but need to capture the IR’s at the same point each time to get fair measurements. So far two packs seem to like it and IR went down while the other two seemed to rise......

thecaptain

iTrader: (177)

Technically speaking this is illegal in a variety of ways according to ROAR rules... Not that anyone takes them seriously. But a heated lipo safe is a better alternative to discharging. Less cycles on the packs, better IR/Dischsfge curve(fade), batteries do not explode/catch fire from warming them (as opppsed to hard cycling), its already in a Lipo safe/sack.... , you get 2 channels to charge packs, etc.

Zerodefect

Roar rules? Whut.

Actual track rules everywhere I go:
-Anything goes if using a lipo bag
-voltage limit at tech inspection by drivers stand. Usually 4.22v.
-temp gun at tech. Often around 15 over ambient is ok.

30/30 seems to be a fair compromise. Performance vs life.

trilerian

iTrader: (51)

I don't use super high charge rates. Generally I charge around 15-16 amps, which is about 3c. Also, when I discharge my batteries, 90% of the time I only discharge to 3.8v per cell for storage. Every once in awhile I will discharge to 3.2v per cell, but this is to determine battery capacity left. Now, what I have noticed on the track. The first run of the day with a pack is generally a little flatter than the next few runs with the same pack. This correlates to the IR on the pack during charging. I normally notice a .2-.3 milliohm drop per cell on the second charge vs the first, but the third and forth charge are generally the same as the second. While racing, all I do is charge the pack back up, no discharging between heats. I will say that I haven't tried a heated lipo bag/safe yet. This is on my list to try.

ebohon

the batteries def made a diff. The better packs retained a lower irr or dropped just a fraction. For example I would have irr go from 1.23 to 1.24. Imho that was measurable but prob irrelevant. I also had some of my cheaper packs actually go up in irr. That’s why t I just scratched the idea of using high charge rates to reduce IRR. I also tested his discharge rates at 30 and 40 for raising the batt temp deliberately to se if it was the temp that made the difference instead of the current itself creating some type of chem reaction. Same results... all about the same. Higher industrial level equipment might provide better results but it still showed no diff to me at the track. Here is the chart of the batteries I tested . This proved to be much more helpful than reading fractions of irr. Please excuse typos and abbreviations I’m on iPad.

Bry195

Ive never cycled batteries the day of a race and the affects seem to go away overnight.

i did look at a study done on NIMH, NICD, and LIPO batteries in phone applications that showed IR curves and how they are effected by charge and discharge. By looking at the curves the discharge didnt make much of a difference to IR. It also didnt appear that there was a significant change in IR while pushing a heavy charge at the battery in the first 80ish percent of the process. It looked like IR moved when current was high during a charge near 80% capacity.

It makes me think that maybe a lower current charge up to 80% with a bump in the current at 80% would prolong the life of the batter and still be able to move IRS around.

I agree with the 30/30. I always used my sky rc discharger and an x6 charger which both max at 30. After the first one or two cycles it pretty much stabilized. I did this for 9 months or so and watched IR slowly tick up over that time. One cell was getting to about 3.4 so i hit it with 40 amps and it instantly dropped to 1.4. The next day i checked it and it was like 8. I think you can nurse batteries along at 30/30 or maybe less but im not doing 40 again unless I dont care about the battery.

robk

iTrader: (22)

The only thing that makes a difference is the temperature. How you get there, via charge rate, discharge rate, or heating device, really doesn't matter much outside of cell longevity. A heating device is probably the best route, not just for longevity, but also due to less stress on the cell than a cycle. Cycling too close to the race can actually reduce overall performance. A friend is an rc racer and an electrical engineer working on full size electric cars, and most of what I put here is based on his advice and research.

Scott_T

iTrader: (5)

Makes sense to me. The European RC boat guys have been warming packs for many years with good results. I used to do it as well, just up to about 30 Celcius in the colder months. Never bothered in summer.

nexxus

iTrader: (315)

My understanding was that the use of lipo warmers was not allowed over here? (Not sure if it was a roar rule or an rcra/aarcmcc rule or something)

bertrandsv87

iTrader: (2)

I started using 22/22 eventhough my equipment can take 30/30...I did feel a good punch difference in my packs versus just charging at 18amps, but timing the cycling to make all the qualifiers on time was the biggest challenge to me....