***Lipo Heating = Performance ***

[Chris_The_Battery_Man]

I had a guy ask to see a graph comparing a room temp lipo to a heated one. Temp dramatically effects your performance. Mainly when super cold. This is why I have gotten my local club into the habit of keeping their packs in their pockets during the colder months. Makes a noticeable difference. Below is a graph showing a cell at room temp(68-70 degrees) and the same one heated to 120 degrees.


I do not advise heating this high unless you know your pack can take the heat. We are professionals and do this for a living. Do not pre-heat pass 100 degrees to be safe.


As you can see, the Black curve is the heated test. This is higher because temp will effect the IR. Higher temp = lower IR(Internal Resistance) the lower the temp, the higher the IR. More IR = less performance.

Disregard the yellow curve. That is a 20C test Mike forgot to take off.

[binaryterror]

Originally Posted by Chris_The_Battery_Man

This is why I have gotten my local club into the habit of keeping their packs in their pockets during the colder months.

Been doing this since Midwest Champs in 2009 @ Iowa. Lots of the on-road racers told me about heating them...so I figured keep them as warm as I can.

[boosted4lyf]

this may be a dumbass question but what are the figures on the graph pertaining to. i have learned alot reading your posts, thanks

[EddieO]

Danny from SMC posted a ton of stuff on this a couple of years ago......mainly to just disprove the "they are all the same" and "there is no voodoo" theories the brushless/lipo fanatics were preaching to everyone so they would convert....

Danny found that heating gave higher avg voltage and lower IR.....at a certain point though, it effects cell life.....

ROAR fairly quickly banned the heating of packs right after trinity came out with a pack heater....

Chris is spot on with keeping them around 100 degrees.....you will get better performance and you will not effect cell life really.....

Later EddieO

[Chris_The_Battery_Man]

Originally Posted by boosted4lyf

this may be a dumbass question but what are the figures on the graph pertaining to. i have learned alot reading your posts, thanks

The left vertical side is voltage, and the bottom horizontal line is MAH or runtime, You are looking at how much voltage the cell has throughout the cycle.

[boosted4lyf]

this is good to know ive had a few packs left in my daily driver on 100+* days i was always worried that that was gonna shorten their lifespan

[Chris_The_Battery_Man]

Originally Posted by boosted4lyf

this is good to know ive had a few packs left in my daily driver on 100+* days i was always worried that that was gonna shorten their lifespan

Doing that will make em puff. Trust me, I've had it happen to me

[boosted4lyf]

ya i've made a habit to not forget them in there anymore one was starting to look a little puffy

[JohnRobHolmes]

For sure, pack temp is a big factor on how the cells perform. An indication that the pack is too cold or too high of IR is that the voltage will bounce back during discharge, the blue line almost shows it. This is also part of the thermal runaway, hence why it is dangerous to get a cell near 140f. A more extreme example, the lowest lines are the point where IR of the pack begins to heat the pack under load, thus raising the temp and lowering the IR.






One problem with crawling during the winter is that the cells are not pushed hard enough to keep them warm during long outings. I have found that swapping packs often or using very large packs to be the best compromise. Swapping them allows them to warm back up in the pocket. Large packs will have a low enough IR that even when cold they perform well, although performance and runtime still suffers.

[Chris_The_Battery_Man]

Originally Posted by JohnRobHolmes

For sure, pack temp is a big factor on how the cells perform. An indication that the pack is too cold or too high of IR is that the voltage will bounce back during discharge, the blue line almost shows it. This is also part of the thermal runaway, hence why it is dangerous to get a cell near 140f. A more extreme example, the lowest lines are the point where IR of the pack begins to heat the pack under load, thus raising the temp and lowering the IR.



One problem with crawling during the winter is that the cells are not pushed hard enough to keep them warm during long outings. I have found that swapping packs often or using very large packs to be the best compromise. Swapping them allows them to warm back up in the pocket. Large packs will have a low enough IR that even when cold they perform well, although performance and runtime still suffers.

Yeah, I forgot to mention the dips in the curves. Very true there.

I got the locals pulling the pack when they are done with their course, and keep it in their pocket until the next one. We don't put enough load on them to keep them warm. So if you're free-crawling in the cold, you may notice some performance loss at the end as the cells cool

[JohnRobHolmes]

Heck yeah, free crawling in the cold is where I get most of my issues. Under 5 minute course times it isn't nearly as bad if you can yank the pack out.


I got in a habit of keeping a hand warmer in the lipo pocket as well. Maybe overkill, but for competitions it isn't a bad idea if it isn't too hot.

[Chris_The_Battery_Man]

Alot of my locals to that too

[JohnRobHolmes]

Bonus, it keeps the jewels warm too!

[Rubbaneck]

I think last year at Snowbirds a few racers had little ovens in the pits to heat packs up . A few overcooked...

[toyofast]

Originally Posted by Chris_The_Battery_Man

So if you're free-crawling in the cold, you may notice some performance loss at the end as the cells cool

I noticed very poor performance when out in the snow the other day... Time to stock up on hand warmers I guess

[EddieO]

If guys were doing that at the birds, they are lucky they did not get caught.....was against the rules.

Later EddieO

[Chris_The_Battery_Man]

Originally Posted by toyofast

I noticed very poor performance when out in the snow the other day... Time to stock up on hand warmers I guess

Get yourself like a small niporine camera bag, and a couple handwarmers. Put them in the bag with the lipo and run it that way with the end sinched up. Should be golden. When the Amigo is finished, and we go scalin, I can give you some little pointers if you want

[Gula]

You know what I always noticed my packs (NIMH) had way more punch while deployed that while at home (130 degree deployed ambient temp) and only 90+ at home. Huh makes sense

[losikid]

I've heard stories of people putting lipos in their pockets and having keys and change and other stuff causing them to short circuit in their pants., ever since then i haven't had anything in my pocket except a lipo., i like the hand warmer idea, maybey run it next to your batt on the crawler to keep everything nice and warm and keep snow from packing up in your chassis.

[Shadow Fox]

I noticed that as well...I was in Florida for 2 weeks with my Slash...and hell I got slightly longer run times then I would get back home in Canada...pretty neat.