MaxAmps.com's Official Stance on pack heating and bumping....
 

Lipo Battery Warming Devices/”Bumping” Lipo Packs: Do not under any circumstances attempt to “heat up” your batteries or increase the voltage of a pack above 4.2V per cell using these devices or techniques. Some insidious lithium polymer retailers/distributors have suggested using these devices and techniques to increase the performance of your lithium polymer packs. THIS IS NOT SAFE AND IS LITERALLY PLAYING WITH FIRE!

Devices on the market that heat up lithium polymer batteries can increase the risk of a fire. Lithium polymer cell manufacturers suggest that 140 degrees is NOT a safe temperature for a lithium polymer cell. At 140 degrees, the pack can become unstable and very dangerous. The small increase in performance is not worth the risk of a fire. PLEASE STAY SMART AND SAFE BY NOT USING THESE PRODUCTS!

Some retailers/distributors of other brands of lithium polymer batteries have suggested that their customers and racers “bump” the voltage of their packs using settings other than the lithium polymer setting on their charger. The manufacturers of lithium polymer cells suggest a voltage range of 3V-4.2V. Increasing voltage above 4.2V per cell is not safe. You should never attempt to charge your packs beyond the voltage set for lithium polymer packs on your lithium polymer charger. Using other battery settings to “bump” the voltage beyond 4.2V per cell can cause fire and injury. The small increase in performance is not worth the risk of fire. PLEASE DO NOT USE THESE METHODS!

Best regards,

The MaxAmps.com Team

Thank you Jason.

Would you please send this to the ROAR technical director?

I know I'm technically a competitior, but I'd like to (almost) 100% agree with you.

I know Jason's been directly involved with lipo for many years as well, but I was flying Lithium Ion cells even before Lipo came to the flight industry (2001ish?). I've flown/driven only Lipo ever since (8 years now - man I'm old!).

If you start at room temp (75degF), there is actually a discharge performance increase (lower IR, higher average voltage) at 85degF, 95degF, up to around 110degF. BUT - that's about where the tangible benefits end - at 110degF. Battery IR, voltage under load, cycle life - basically everything good about a lipo is irreversably damaged at any temp above 140degF (although my good friend Linger dissagrees about the exact temp that damage starts sometimes).

Pre-heating (heaven help me for saying this publicly) actually can extend the cycle life of a pack IF and ONLY if it's being used at near full discharge capacity. Aircraft use near full capacity quite often and pre-heating has been used since it was discovered to help cold weather flyers since like 2003ish. However, 10th cars and trucks almost NEVER do.

My experienced stance is anything up to 110F is OK, but anything more absolutely does nothing to increase performance, and that 140F mark is danger danger danger!

As far as increasing the resting voltage - I totally agree with NOT doing it for the same reasons as above - it is detrimental to IR, voltage under load and cycle life. If you do it, you're cheating yourself out of hundreds of good cycles from your pack.

Where I disagree with Jason, is that there are actually ZERO real benefits! When two packs start at 8.4v and lets say 8.5v, it only takes about a millionth of a second for the discharge curves (voltage under load) to become identical. If you're racing where having .2v more for a millionth of a second really matters - then by all means turn your 400 cycle lipo into a 50 cycle fire hazard, but not at my local track please! (Adrenaline Raceway and Farmers Hobby & Raceway in Tampa if you're interested :))

Readers please ignore my signature - I'm here as an informative presence, not a competitive one.

<** WITH MY ROAR HAT ON NOW **>

ROAR has already implemented strict rules and consequences (including DQ) against overcharging.

We in the Executive Committee are currently in preliminary discussions about a temp rule with equal enforcement/consequences.

I agree with the fact that battery over-charging is a serious issue.

However, I have found light battery heating to be a very effective way to make my cars run better. I only heat to about 100*F, but when you are starting at a 50*F ambient temperature, it can make a nice change in battery performance. I would never attempt to heat the pack over 110*F however.

My LiPo packs have been giving me great performance and runtime...

At 5*F outside :D

Actually, they've done colder, but it was hella windy outside so I didn't stay.

Unless you're doing anything absolutely hardcore that needs every single erg of energy... It's simpler just to run them as is :nod:

Not true. As Li-Po's get colder they loose capacity. What happens when you loose capacity?? Your available normal amp draw that the pack can handle drops as well. So you now are running a pack that can't handle the amp draw of the vehicle. You risk wrecking the pack. I Fly planes in the winter and run a few of may cars in the snow. I always make sure the packs are at room temp when I start. I then cut back the run times. In most cases by half or more. You can warm packs with a heating pad but I would never go over 100 degrees max. I actually have a heating pad that if set on medium will do 95 to 100 tops. I race 1/8th scale 4WD buggy in a large horse arena up here in the winter and it's usually pretty cold even inside. What I do is put my charged packs in the buggy with the wheels off is set it flat on the Heating pad. I they lay the wheels around the car and cover the whole works with a towel to keep the heat in.This keeps the plastic pliable, keeps the diff and shcok fluids loose, and keeps the packs at a good usable but safe temp. It works like a charm. We felt it necessary after seeing the the 140 degree deal that something needed to be said. That type of temp on a Li-Po is just plain stupid and dangerous and from what we are getting for responses to this it seems that 99.9% of you feel the same way. It's great to know that in most cases everyone is being safe and we at MaxAmps.com commend all of you for that.

Best regards,

Jason

hmm, never gave this any thought. mainly b/c the same batt stays in the car all day.

R

Yep, capacity goes down with cold temps... That's why you get overkill on battery power :D :lol:

Currently running 4800mAh 25C packs.

The runs always start at room temp...
Though, I haven't done a lot of LiPo running in winter yet, but with nimh batteries, they stayed warm just from being used...

The pain of living in the north! R/C is hard outside! :lol:

I know my nimh's had no issues at -40... Not taking my LiPo's out at that temp, though!

You guys have me worried! At a race meeting last December our track temp (measured with laser) reached over 60C (>140F). Ambient temp was +- 45C (113F). We were not using Lipos (only legal here this year). Would it be safe to use Lipos in these conditions?

If your seeing hot air temp above 100 F yes you need to take that into account as well. Maybe add a cooling fan to blow air across your packs.

Jason

Mr. Roper worried
 

Oh geez, now I am worried too. I keep my batteries in a box that keeps my LiPo and NiMH cells organized, nice and neat. However, the box is in the basement. I know it can get cool down there, but is that ok? I mean it is not outside temperature cold, but it can be cool. Is that ok? Or do I need to keep the LiPo batteries in my room?

Dont see it bieng a hassle unless you leave your car standing static on the hot surface for a long time.
The track temp can be 60 deg/c but wont lend to the pack being teh same temp.
As for ambient temp that is static as well when the car is running there is air flowing around the pack.
I have run lipo since June last year and we are fortunate we dont have teh cold temps to wrry about like or cold climate counterparts.
NO need for battery warmers, heating pads etc... since we have a fairly moderate to warm climate.

So dont worry you wont have any issues with it unless you negligent with your charging and discharging.

Storing packs in cool temps is different from using them in cool temps. Sitting in the basement in a cool room isn't going to cause any problems just bring them up and let them get to room temp before you use them.

Jason

Shawn, the voltage rule should be changed (for a 2 cell pack) to 8.40 volts max, not the 8.40 +/- .04 volts. Now you have everyone charging to 8.44 volts. Let's stop the nonsense and make it 8.40 volts max.

Any pack heating should be banned! Otherwise it becomes an enforcment nightmare.

And where did you get a ROAR hat??? :sneaky: