Last night I left my 2 Kokam 11.1 V batteries connected in parallel for about 10 hours. They were brand new and were not put under load. To my surprise, they had the same voltage value when checked, (11.55V). When I first checked them their voltages varied by about .02 V.
They had not been charged yet. I wonder if I had harmed my batteries? Or is it normal for them to keep each other at the same level when put in parallel?
It is more than likely that the batteries just settled to the same voltage. Red did some demonstrations regarding parallel packs and didn't seem to think that the small differences in voltage would affect the packs.
When you connect two batteries in parallel, they have a common output. That output can have only one potential. The battery with the higher voltage before connection will charge the other one so that when they are separated they will have similar states of charge.
Why don't you try this? Discharge a pack to .9 volts per cell. Connect it in parallel with a fully charged pack of similar capacity. Let them set for 24 hours and then discharge both again. Come back and tell us how much one pack charged the other.
Thanks, I believe I understand now. As I said they are Li Poly batteries. I have charged each battery separately, then measured their volatages separately and found they were within about .01 volts of each other.
It's too cold to fly outside now. So my next question is, is it all right to store the two packs connected in parallel? Or should they be stored separated?
After all the discussion on how two batteries in parallel would bring each other to the same voltage, you're quite correct about no disassembly.
Now how about the possibility that fully charged batteries stored for a couple months may be a fire hazard? I don't understand it, but I was told that I should discharge Li Poly batteries to a safe level when stored for any length of time. Discharged to what level? Anything to that? Being lazy and trying to learn all I could, Wan
Well Ive got six LIPO cells in 3 series banks of two paralelled cells all soldered up, and I am expectng them to be fine when the wind drops :-)
Since everybody else does this, there is no evidecne to suppose its a Bad Thing. You should store them somewhat charged. And in a cooler rather than warmer place. Don't fast charge or discharge at very low tempertures either. LIPOs seem to like being beween 10 and 30 C
There is no safe level to discharge a LIPO to that does not ruin it.
If you short a pack, it WILL puff up, pop and possibly catch fire very aggressively. So don't let it short.
If you juts leave teh cells cahrged up, there is no problem. A zillion people do that all the time and carry them around in their pockets in cellphones. The dangers is OVER charging or OVER discharging, Anything that causes the pack to heat up generates gas, and because unlike metal cased LI-ION cells they are deliberately desiged to POP not go BANG thy do pop BUT that carries a couple ofattendant problems in that they may short internally when they do, or, if the heating istelf is severe enough, get hot enough to spontanously combust.
If they do, they are small incendiary devices.
Used properly, there is a very small cahnce that they will do this., but the risk is that if they do, they will start a serious fire. At least one car has been burn out from a damaged pack tossed in it after a crash, and a model and charger has gone up due to some kind of overcharge resulting in a fire.
So, the current 'best practice' i snot to discharge them - thatruins them - but to put them somewhere that is cool, that is fireproof, and where they cannot short. For a small pack lie you have its not so critical. ut teh gys using multiple big packs take the sort of care with them that you might well take with a can of gasoline. NOT in the house, NOT in the back of the car...put them in a shed. And just as you take care with flames when messing with gas, take extreme care to get charge rates and cell counts right on the charger, and be ultra careful about shorting them. A second is all right. Ten seconds is an incendiary device OK?
Look, I am a bad boy. I toss them in the drawer alongside my NiCd packs, and I always charge em up to at least halfway before doing so. I OUGHT to get a fireproof safe - that is what people are doing, I ought to stop smoking and get more exercise too. These are all Good Things and I am a Bad Boy.
Those are the risks. its up to you how you deal with em. IF you are concerned, put them in the fridge :-) That way only teh fridge catches fire. :-) :-) If you are really concerned, get a fireproof box and ock em away. I may ultimately make something out of fireproof board and metal myself.
In the meantime, keep getting opinions. And fly the pants off those cells. They make a HUGE difference to any electric plane.
Why would they suddenly short out? You have wiring all over your house, which, if it shorts out, will catch fire.
In fact it is one of the most common cases of house fires.
However I would personally say that its probably better prtactice to take the packs out and store them somewhere safer.
Its also better practice to drain teh oil from your car, and the petrol, and put it up on bricks to save the tyres, when storing it over the winter...
Better than yer house!
Lithoim has been around a fair time. Its juist that techncal issues in manufacturing and safety have held it back.
I saw my forst Nicad cells in the 60's. Remember DEACS? Only when the power tool and mobile phone market took off did we get decent ones.
Now, its the mobile phone and lapop that has driven LIPOS, but, funnily enough, model planes have become a decent market - decent enough so that at least one maker of experimental electric cars was inspired by seeing a plane to investigate LIPOS.
The project finally used a bank of cells designed for mobile phones. This was hugely cheaper than any price quoted fo special large cells..
Expect production LIPO cars in 5-7 years. THEN we will have cheap high power cells...!
Do you mean production of full size passenger cars? Hmm...If so, I wonder how we would charge those batteries, an electrical outlet at every "gas" electric station? Not meaning to disparage your comment, just curious.
On the other hand, we modelers would benefit greatly if cheap high powered Li Po batteries become available. For now they are still rather expensive compared to NiCds or NiMH batteries. 5 to 7 years is too long to wait. Would you venture another guess as to how soon again?