Cold weather lipo use...
 

I've read about the precautions that airplane guys take with their lipos in the cold so I thought I'd do some testing. For the last two weeks, I've been running packs under a moderate load (10.5-17.5T and only a few hard speed runs) at night way below freezing in 10-20 minute sessions.

These were in 10th trucks that have battery channels, like T4's, XXT's, etc.; with foam blocks at each end, no insulation beneath and none above unless I rolled up a dob of paper towel to take up space under the battery strap.

They were charged at work table temp of 66F at 1.5C and reached almost 70F when finished:

http://www.rctech.net/forum/members/...r-charging.jpg

For this 1st batch of batches, I balance charged in LiLo mode to about 4.10v because I haven't figured out how to adjust the LiPo end voltage (if even possible.) I stopped the runs at the 1st 3.70v alarm instead of bumping it down to leave the packs in storage mode. I feel like the runtime dropped 15-20% with the LiLo charge:

http://www.rctech.net/forum/members/...ilo-charge.jpg

http://www.rctech.net/forum/members/...o-bal-chrg.jpg

That rested to about 4.07v in all cases after a minute or so:
http://www.rctech.net/forum/members/...-post-chrg.jpg
That's so much less push-back than nickel cells that I'm just amazed, but it might be enough to simply fast-charge in LiPo mode and avoid full-charge/cold-temp problems.

I kept them yummy in this insulated lunch bag filled with paper towels:

http://www.rctech.net/forum/members/...-them-warm.jpg

After each run, I'd take the temp if my fingers could stand it or run inside and temp them.

All the following are averages of about 25 runs:

Run time: 14min
Air temp: 27F
Post run temp: 58F
Post run rested IR rise: less than 1.5mil

This last value was hard to nail down and I'm still working on a consistent timing and temperature evaluation that includes well-rested pre-charge, post-charge, rested post-charge and storage measurements.

http://www.rctech.net/forum/members/...run-rested.jpg

These were all average packs (not ProMatch or SMC) and faired pretty well.

If you can think of some more control points, let me know and I'll try to test them.

:) Gene

I've been racing in freezing, or near freezing, conditions for 5 years. 0 problems as long as you don't leave the batteries out....probably no issues there either actually. I've never seen an trouble with lipos in cold weather.

Neato!

same here. I will admit though that I felt I got better performance and runtime when they were kept closer to a comfortable temp. At one track that was indoors in the winter time, so very very cold, I would just keep the packs in my pockets.

Hey that's a great idea. I had kept one in my vest pocket on one outing just to have it handy in case I could stand the cold (just barely!) and it stayed warm but I didn't think to load them up. It would be easy, though, to keep several handy that way, even if I was running in & out of the house or the car.

I've got lots of pockets in this St. John's Bay fleece sport thingy I usually wear under my jacket. I may have to get some RainX for my glasses or start wearing my contacts, again!

I'm near Chicago. Been running when it's below freezing for years. Even when below zero. My fingers usually usually freeze before any issues with vehicle or battery.

HappyGene, why all the testing? There's virtually zero issue with running Lipos in cold weather. Keep them fairly warm (in your pocket), plug them in and go.

I've heard of people putting LiPo packs in the freezer to try and shrink some of the puffing lol Not surprised that they perform ok in the cold weather. When I go to the track after work, I leave my stuff in the car all day with temperatures sometimes below 0. Never had a problem.

Good deal. I don't hear stories like that around here. Maybe only a few guys drive in the cold like I do sometimes.

But now I know for sure and have some data to boot. I like the details, you know.

Thanks,
:) Gene

Thanks for the info Gene! You Certified it.

:)

If you like testing, and have the means to do so, it would be cool to see the impact of temperature on LiPo performance in terms of Voltage and especially Voltage under (different) load(s).

There was a recent discussion over here on how LiPo temperature does affect pack IR and as a (partial or main?) result its "punch": http://www.rctech.net/forum/electric...l#post14240062.

I also remember reading somewhere that pack Voltage rises slightly with temperature, it was someone claiming his batteries puffed and failed after he had charged them to 4.2V/cell in a cool basement, and then brining them up to higher ambient outside temperature, causing the packs to go beyond 4.2V/cell - at least that's the part that I think I remember, but can't find referenc anymore, so could all just as well be BS existing only in my imagination :D.

I, too, read something similar last month when I was pouring over related posts trying to get a handle on it, but I don't remember where it was, maybe RCGroups.

I'll read all that link (it looks pretty interesting and a couple heavy racers are in it) when I'm done with some stuff here at work this week and next. That's a good idea to find at least some ball-park figures about it. I've got a couple packs I could sacrifice.

I'll do some back to back charging to get a baseline and then repeat at significantly varied temps. I don't think it's your imagination because I found some really varying IR's in the same packs depending on charge state & temp and that would affect performance a lot.

Sounds like fun...

Waayyll...I only ran 6 cycles with a couple packs testing the effects of heating them up and I don't even need to finish the process. By letting them "soak" in a bed buddy and reach 95-100F the average IR drop was between 1.5 and 2 mils per cell. That's beyond significant and if you use connectors, it'll feel like you hardwired. For guys already hardwiring, you'll notice the extra still yet. I don't think you can do that anymore at real racing events, though.

Now, these were average packs and the difference will be smaller with already "good" packs, but that certain 20% reduction in IR will be gained. Next I need to measure temp & IR in the middle of a run, then again with re-heating the pack before finishing. Post-run IR's climbed all the way back up and we'd want to find a way to keep them down for the whole run. Now, use of the pack nearing depletion will generate heat, for sure; but my gut feeling about that is the IR is climbing already for some other reason(s.)

My tests were averaged in a 22F ambient, 15F windchill atmosphere and the the pre-heated packs came off the runs at about 58F, which is about 10F higher than the non-heated charge over ambient and the same absolute temp. This is good unless it's a hot day, because if that's consistent and linear, then you'd see 110-115F final temps on a spring or fall day. In the summer, probably don't need to do that unless they got cold after charging or you can afford lots of packs. Really I'm not sure about that last part, because one thing my testing misses, for now, is long term effect.

Of course, the 110F ideal temp has been known for a long time, so really the only advantage would be in cold weather or if your racing that day was not taxing your battery. As a segue into the next paragraph, a smaller battery than you need would stay warmer longer. Hmmm.....

Generally speaking, voltage goes up when IR goes down. So, the pre-heat laps can also help performance if they're hard laps that will heat up the pack and it seems everybody already knows that. Just need to find a balance between pack heating and using up the tippy top of the freshly charged pack. So, unless weight is the greatest factor for the way you drive, we might be back to bigger 'n' better for batteries. I guess that'll never change ;)

I'll have to mull over the cool charge, heat-to-use method. I haven't read what the truly absolute max voltage is and whether it's a "range" of values, or not. When I balance to 4.2v, the packs usually "rest" down to 4.17-4.18v within 2 minutes, so it might be safe. Plus, charging at the bottom of a cell's rated temperature range usually isn't as efficient and in nickel cells can increase granularity and striation of the paste. I did, once by accident, overcharge a cell to 4.6v while trying to bring up a dead cell and it was ok, performing well as a single cell; but I don't recommend that.

I'll toss a couple in my dutch oven and cycle them cold to hot and see what happens.

As for the loading at different temps, I'll need to see if one of my old T30's will allow itself to discharge a "strange" voltaged cell. If so, I'll set up some high & low depletions with heated & cooled bed buddies.

:) Gene

The problem with "cold" and lipos is when you start using the cells when they're cold (below 60'F) and then discharge them at high amps to where they heat up fast, they will almost always puff when this happens. You will almost never see this running cars because your amp draw is too low to really heat the batteries quickly enough to a temp where they are going to puff. I have been running and testing LiPo's for well over 10 years in boats where our amp draw is significantly higher than cars. I can typically take anywhere between 5000-7000mah's out of my packs in a minute and a half race, depending on the boat and setup' and my cells can go from ambient, 75-80' to 140+ in this time. And on the other hand I ran my 1/10 4wd Mod car the other night for over 12 minutes and the pack was 105' when I was done. I also race 1/10th and 1/8th everything (onroad, offroad, 2wd, 4wd, mod stock etc...) and have rarely ever seen a pack get over 110 degrees in almost any racing situation. I have run many packs from colder ambient temps in my boats like in the 40's and 50's and almost always have puffed those packs. You can get the puff out buy cooling them in the freezer like said earlier but the pouch that the cell is in is stretched and will puff back when the packs get hot again. I have a lot of experience with this stuff, also a puffed battery is not a "bad" battery as long as the pack charges and balances out and the IR of one cell is not completely out of whack with the other cells the pack is fine.