LiPo Help!
 

Hi guys,

This is my first post so go easy!

I've just recently gotten back into RC with my RC18MT. Now I've just done a brushless conversion on it and in doing so have changed to LIiPo power! :nod:

I have the Trackstar 6100kv Brushless power system from hobbyking, and the Turnigy 2200mah 2S 20C battery (i actually have 2 of these).

Upon receiving the batteries, i balance charged the first using an Imax B6 charger, charged at 2A.

I then ran the battery in the car for between 5-15 mins (till my lunch break was over!) then switched the car off and put it away. I then had another little go (approx only 5 mins as TX started bleeping low battery) once i got home, i then switched it off and put it away. (did leave the battery plugged in though) Overall i was VERY impressed with the performance, having never seen a brushless/LiPo set up before! :D

Got the car out yesterday (2 days later) put some fresh batteries in the TX and tried to switch it on and nothing really happened, So I am now running a balance charge on my pack, but it is showing one cell as 4.2V and the other is at 1.3V (30 minutes later its at 1.86V)

The pack has also "Puffed" on one side.

So I'm thinking I've probably goosed the pack by leaving it stored at an incorrect voltage?

I'd really appreciate any advice before i use my other pack so i don't destroy that one too!

You do not want to leave the batteries plugged into the ESC when not using the truck. The switch for the ESC only turns the receiver (BEC) off and it will drain the battery. That battery is no good anymore.

Unfortunately this is the case, there are a dozen good ways to ruin a good lipo. A little list of tips:

1 - always balance your lipo (the "charge" feature on your charger is not the same, do not use it)
2 - storage charge when you plan to put it away, too much or too little charge on an idle battery can do damage.
3 - avoid extreme temperatures, especially heat. If you have the car at work with you bring the lipo in so it is not in your hot car this summer.
4 - do not run it down too low, this is not a problem on most ESCs as they have a low voltage cut off, make sure that is set for the battery you use (2s / 3s / 4s / etc.) In cases with no LVC you can get an external "tester" that will beep with an alarm if a cell is at LVC, not as good as using one built into the ESC, but it works.

a battery beeper can be better than using the low voltage cutoff on escs
they will monitor the voltage on each cell and beep when any cell goes too low
the esc watches the whole pack, if 1 cell is high, and the other is low, it wont turn off til both cells read low, or 1 is low enough for it to assume both are low

Thanks for the help guys.

Good job i got a second battery!

My ESC cuts off @ 6V is this ok or should i get an alarm as suggested??

True, but it is also another potential item to get loose in the car during high speed antics. :D

Here are a couple links with a lot of very useful information.
Reading through this will help you learn probably more than you really need to know about the use and care of LiPo's and LiFe's

The info in these links helped me a lot when I got into RC Heli's last year.
I was clueless, except that I knew I didn't want to burn my house down or destroy any of the 6S 5800mAH 65C packs I had to buy for my hell at nearly $200.00 each.

Anyway have a look:

Link to battery forums on helifreak.com http://www.helifreak.com/forumdisplay.php?f=10

And a link to some useful info on the care and feeding of LiPo's with burning your house down...https://sites.google.com/site/tjingu...arging-how-tos

Opinions differ, but I'd suggest a slightly higher setting if it's available, in the 6.4 to 6.8V volt range for a 2S (3.2-3.4V/cell). Lipos drop off in voltage fairly quickly at the end of a run, a slight change will generally cause very little reduction of run time, and it is easier on the cells. Also provides some allowance for cells being out of balance, one being lower.

Even then, stop as soon as the power drops off. I rarely hit LVC and along with reasonably diligent storage practices my packs hold up great for a long time. Much better than they used to.

What I've learned from fly my Heli packs; which are 3-4 times the cost of some of the car packs is this.

If you consistently take more than 80% out of a LiPo pack you'll be buying a new pack sooner rather than later.

Granted large RC heli's are much harder on batteries than our cars are (in general) but you'll have your packs longer and keep some money longer if you follow the 80%. Plus of course charge and store your packs properly.

It's weird to me that the amount of info on our batteries in the RC car world is so sparse. In the Heli hobby how to use and care for your batteries is a big topic.

Maybe it's the size, cost and relative potential danger of the packs Heli use VS the packs we use in cars.

Another thing I've noticed is the parallel charging multiple packs isn't the norm on the car side. I can't tell you how many people at the track come up and ask either what the board I have my batteries plugged into is, or, where I got the charger that can charger that can charge 6 batteries at once.

Yeah it's junk. It will never be the same. Being a new battery, I assume one cell dropped faster than the other, ending up way low. I always cycle my batteries 3 times before I treat them as brokein.

Not to start a flame war, but all the reading I have done, indicates that the chemical has to create optimal crystal size in the cells chemical for optimal life and performance. And that once a cell goes down too far, the crystals grow too large and can puncture the cell membrane/ wrapping. A bad day/ lipo fire.

As a side note, some guys claim to be able to "shatter" the crystals, saving the battery by surging them with varying amounts of voltage, BUT frankly, to me that is playing with fire, literally. I highly frown on that endeavour.

Just toss it, approved disposal, make sure to break the new one in, and always disconnect when done.

Parallel charging is less than ideal for most car uses. Leaving packs sitting fully charged degrades performance. Better to charge each as needed.

The 80% guideline is certainly useful, but needs adjusting as packs age and due to different real vs. claimed capacity of various packs. Going by voltage is probably more reliable, keeping the resting voltage above 3.7V per cell is a good target to shoot for.

Everything mentioned has been discussed here in countless threads.