Lipo question
 

Hi,
is there any tips/tricks on how to get the best performance out of the race packs? I remember reading something about it on car action but I can't find that article again.

You can't really extract more performance from your lipos with any "tricks". Some chargers have a competition mode that will charge them to the legal max voltage instead of the standard cut-off (i.e. 8.44 instead of 8.40) but otherwise, a charge is a charge on lipos and their performance is related to their manufactured specs, not anything you can do with them.

What you can do is ruin your lipos. So, the tips/tricks you read were probably related to never ever leave them plugged into your car overnight, store them with a storage charge if you won't be using them for more than few weeks, balance charge at least every 10 or so cycles, etc.

There has been some alleged voodoo floated around, but what MarkA said is spot on. Take care of them properly. Don't overcharge, use warmers, dip them in pickle juice or dance around them on a moonless night.

Having an old gypsy woman place the curse of eternal diarrhea on your competition is a good idea, though.

Never let them sit fully charged for any longer than necessary. Sitting fully charged raises internal resistance (and can cause puffing). Don’t charge them the night before, don’t charge them before going to the track, etc. Temperature changes at full charge can make it worse. Charge them as you need them. Compromise: Charge one to 70-75% before heading out, then it only needs a quick top off while you’re getting unpacked and ready.

If running mod consider charging only to 90-95%. Saves a lot of time too by avoiding the slowest portion of the charge routine.

New packs need a few cycles to wake up. Similarly packs sitting for a while get a little stale. Run race packs in practice.

Don't allow them to get hot, don't leave them in sunlight, etc. Store in a cool place, my dry basement, 65~70 F, seems to work well.

Don't charge or use them when cold. This really drops performance.

Opinions/experiences seem to vary on deep discharges. Generally I try to avoid deep discharges, but an occasional one doesn't seem to hurt and may actually help. I'd like to hear other's experiences.

Store around half capacity. Most recommendations are in the 3.7 to 3.85V/cell range, and at least for me seem to work equally well.

Get a good charger, one that has IR measurement, to keep track of performance. Perhaps one that allows charge to a controlled percentage, I find that very useful.

By following these guidelines I've had great results, packs last and maintain low internal resistance and good punch, much better than before I learned them.


Note on rules, the ROAR rule book needs updating. While it says 4.22V/cell is the max charge voltage, there is an amendment that states 4.20V is the max. It is checked and enforced at national events, perhaps others that use ROAR rules.

^All great tips^

Are they checking at 4.20 now? Any race that's done a voltage check that I've heard of has done it at 4.22/cell all the way through this summer.

Since the voltage tends to come up with heat, on a hot day at an outdoor race, you'd have to cut the charge at say 8.35 for 2s pack then to ensure legality so I though the .22 was the allowance for that if charged to .20 and then naturally, people had to push their luck by charging to the .22.

I know it's nitpicking, but it really sucks that people actually argued enough that the redundant '0" had to be added. 4.2 is 4.20, but some argued that they could go to 4.22 and it's still not over, because if you round down it's 4.2. Ugh. Anything to win, huh?

That was the deal at the 2010 off road Nationals at Leisure Hours. They checked voltages as part of tech before each qualifier and main, 8.40V max for a 2S. They made the official meter available during practice so you could check your stuff. Also they checked pack temp, had to be within 5 degrees of ambient if I remember correctly, but I’m not as sure on that.

It was fairly warm, but we were pitting outside under a canopy. Tech was the same, so we didn’t have any temp issues. Hit 8.40V every time. :sweat: :cool:

Believe I’ve seen the same limit discussed in Nats and ROAR threads since, including some lively chat about the elimination of the “tolerance” that was allowed for a while and the lack of rule book updates. But I tried to find the rules update and struck out?

If it has changed since hopefully someone will chime in. If not I know guys who have went to all the Nats, I’ll ask around when I see them and follow up if I find out different.

Thanks for the props on my comments.