li poly batts

[Tbird Man]

Hey, about how big are the Li Poly batts, I am thinking they would be ideal for my chassis. are they like AAA size, or smaller?

[Tbird Man]

never mind, found what i was looking for

[3series takumi]

be careful with those things. this is a pic of a guy that took a nap while his cell was charging

that WAS a rs4 micro

[3series takumi]

another pic

there is also a story of a guy that had a fresh charged cell and left them in his room temp car. any ways the car, some lexus truck, burned to the ground because of the lith poly cell... they werent even being charged if i saw it correctly, they were just sitting there. i think he said that there was possibly a short within the cell that caused it

[Tbird Man]

Yes, I understand, any time you deal with Lithium you have to be careful. highly reactive.

[Hooters Driver]

I believe that guy was using Lithium-Ions, not Lithioum-Polys. Li-Polys are less dangerous because they have a soft shell. With the soft shell when overcharged Li-Polys just bloat and start leaking instead of exploding as the metal case batteries do.

If you have a good quality charger designed for Lithium batteries and you don't abuse them (overcharge or undercharge them) then they are no more dangerous than NiMH batts. All batteries can explode and catch fire if they are abused or overcharged so you should never leave any type unattended when quick charging them.

[3series takumi]

as for the lexus driver i think he was using lith ions but for the rs4 and that chair, they were polys. they can bloat as you said but they have been know to vent fire more often than they leak. i am not saying that i am al knowing on this matter, i just want to make sure that these people know that this stuff happens. the fire in the pix the guy says he did everything that he was told, he didnt use to high an amp rating, he used the right charger for the batts and it still happened. i have been to some airplane forums and they suggest either recharging them in a fireproof lock box or rig a bag of san above the batteries so if they catch fire it will melt the bag and smother the fire. just a couple of ideas

[Hooters Driver]

I have been using both Li-Ions and Li-Polys for several months. About 1 month ago I ruined a Li-Ion pack. From that experience I think I figured out what is happening to cause Lithium batteries to blow up while being charged. Here is what happened in my situation:

After running my car I put it away and forgot to unplug the battery pack. When I noticed the pack was still plugged in two days later I checked the voltage and it showed to be less than 1 volt (this was a 2 cell 7.2 volt pack).

Since I know Lithium batteries are not supposed to be discharged below 3 volts I figured the pack was ruined but I decided to see if it would take a charge anyway. I plugged it into my charger and monitored the voltage of each cell closely. One cell came back up above 3 volts without any problems. The other cell, however, would not take a charge and began heating up almost immediately. I unplugged the charger, disassembled the battery pack and then tried charging each cell individually. The first cell took a full charge without any problems. Once again the second cell would not take a charge. No matter what amperage setting I used the battery would almost immediately begin heating up. I threw that cell away and wrote it off as a lesson learned.

What I think happens to other people is they drain their batteries below 3 volts then plug them into a charger and walk away without monitoring what the cells are doing.

Many people don't realize the damage they cause to the batteries when they allow the voltage to drop below 3 volts. Then when something blows up while the batteries are charging they blame it the charger or on the batteries being defective.

[3series takumi]

i get it! that sound like what most people are doing. how do you know if the cell has dropped down too far or the better question is how can you prevent it. cause as long as you havent burned anything i do see why i shouldnt give it a go

[Hooters Driver]

When the voltage in Lithium batteries starts dropping there is a significant loss of performance which should be easily noticeable. From my experience really the only way to drain Lithiums below 3 volts is to run them until the car dies or gets very slow.

If you do decide to buy Lithiums I would suggest that you just be cautious with them for several packs and check the voltage with a volt meter often until you get a "feel" for when the pack is getting low. I would also suggest checking the voltage of your pack every time before you put it on your charger. If you do ever drop a cell below 3 volts monitor it very closely when its on the charger to make sure you haven't just started the ticker on a time bomb.

If you're looking for Lithium batteries you can often find Lithium cell phone batteries very cheaply on ebay. As an added benefit these batteries have a 3 volt shut-off circuit built in but many hobbiest remove that circuit to save weight.

One more note about the safety of Lithium batteries. As I just stated many cell phones use them. If they were inherently dangerous the cell phone companies couldn't afford the insurance it would take to continue selling them.

[3series takumi]

i have heard of import cells catching fire with those poly's hehe

[dgilpin]

You can get a monitor like this one - <http://www.eflightdesigns.com/docs/L...tructions.html>

I got one for an airplane, but might use it in the mini-x too.

[3series takumi]

thx for all your help and i meant cell phones in the last post not batteries, my bad

but thanx a mill