RcFlyer06

My Feedback: (4)

Hey all!
I'm new to li-po batteries. I'm working with an Apex 2200mAh 11.1V battery and a 2000mAh "Common Sense Rc" 11.1V battery. I've succesfuly charged (with a triton charger) and ran (in a t-rex with stock speed control and brushless motor) the batteries a few times. I don't want to wait so long for my batteries to charge, I've been read that you should NEVER charge over 1C. But I've talked to some people who regularly safely charge at as much as a 2C rating. Is it possible to safely charge a lipo over 1C safely? I've pushed the 2200mAh pack to a charge rate of 2.5 amps and it's doing alright, will it continue to be safe???
And just wondering, can lipos spontaneously combust or will it swell or leak first????
Thanks for the help!

guver

My Feedback: (325)

Lots of the time is the slow ramp-up of the triton and the slow ramp-down. I charge my SC 2000 at the max of 2.5 amps on triton.

jdetray

Many of the serious problems (fires, etc.) that have occurred with lipos have happened when they were being charged improperly, so charging at a greater rate than the manufacturer recommends would not be my choice.

Charging at high rates decreases the lifespan of lipos. Many people charge lipos at about 0.7C, which has been shown to increase the lifespan, compared to charging at even 1C. I haven't done the math, but it could be that over the long run, owning more packs and charging them slower might work out to be just as economical as owning fewer packs and charging them faster.

- Jeff

Chocks_Away

I always charge mine up at half a C simply because I heard or read somewhere that it may increase the lifespan if you charge them at a slower rate than the maximum of 1 C

Some manufactures say theirs can be charged at higher rates, but I wouldn't bother anyway.
After all whats the rush ? Just to get it done in half an hour or so less.
Not worth it in my opinion if it's going to end up reducing the life of it anyway.
Besides, the price that lipos are, you don't wan't to be throwing money away for the sake of it.

I'd stick to no more than a 1C rate if you value your cells.

jdetray

There are some lipo systems specifically designed for charging at greater than 1C. For example, FMA has their 3C [link=http://www.fmadirect.com/products.htm?cat=38&nid=4]BalancePro HD system[/link]. I think there are others.

- Jeff

Chocks_Away

I wouldn't like to try charging one at 3C !
You know how hot nicads get by charging them at 2C in 30 minutes yet alone at 3C in 20 mins ! [X(]

Lipos certainly don't like getting hot, and excess heat damages them no end, and I reckon that a 3C charge will generate a fair amount of heat in a lipo as well whether they say they can take a 3C charge or not ?

jdetray

I have not used the FMA system, but my understanding is that the cells are specifically designed to withstand the 3C charge rate and not suffer damage. Further, I believe that you must use the FMA charging system with their cells to charge at the 3C rate.

Perhaps someone with actual experience with this system will let us know how well it works.

- Jeff

Chocks_Away

that would probably be best.

RcFlyer06

My Feedback: (4)

Thanks everyone for the input!!! One last question though. I've been watching my common sense RC battery (the 8C 2000mAh pack) and it's making me nervous. I don't know if it's my brain of it's acutally happening but it looks mildly swollen. It flys fine and seems to charge fine. Using an align 25amp speed control and an align 420lf outrunner motor. Could be overdrawing the battery??? The battery is pretty warm after flights (so far only consisting of regular forward rights-side-up flight). It's warm but not necessarily hot. It's been through about....I'll say 8-10 cycles so far. Suggestions???

jdetray

RcFlyer06-

Your 8C 2000 mAh pack can provide a maximum of 16A. Does your power system draw more than that? If it does, you are asking too much of the battery and may have damaged it.

Suggestions? Measure the current draw of your power system!

- Jeff

RcFlyer06

My Feedback: (4)

A perfect idea!!! How exactly DO I check current draw??? I am (was) a nitro guy so kinda new to electric.
How do I tell if the pack was damaged??? When I connect to my triton charger it never reads below 9.9V (usually at 10.14 or something close to that) And it peaks just dandy. Is a balancer worth it for small 3-cell packs like these?

As a note for previous posters if your looking, I'm taking your suggestions to heart and have turned down charge rates!

RcFlyer06

My Feedback: (4)

Just checked Align's "power collocation suggestion" sheet. Says that an 11.1V 1800mAh 12C battery using my motor setup, draws an ABSOLUTE MAX of about 18.5A. With the blades and gearing I have it says that 18.5A is the max at max throttle +/- 9 degrees pitch. Like I said I'm doing mostly hovering and forward flight. Am I safe???
ALso no one answered, do batteries just explode or do they give warnings first???

Chocks_Away

A balancer is a must for all lipos with more than one cell in them, as they will eventually need rebalancing.

To check current draw, you need a flighmeter that connects up between the battery and the speed controller.
Many of these now show current, voltage and watts consumed.

You could do it with a cheap multimeter, but most of these only have the ability to measure upto only 10 amps,
Most flightmeters can measure upto 100 amps !

Although the suggestion sheet says that the motor will only draw a maximum of 18.5 amps, it all depends on what size prop you are using, and what pitch it is.
You could for example be using a 6x4 inch prop which might only draw 9 amps, but a 8x6 prop might draw 20 amps
All set ups vary, so you will only know with a tester.

Remember, the current draw is always governed by the size and pitch of prop used.
The suggestion sheet is probably just saying that the motor will handle a maximum of 18.5 amps before any more current will knacker it.


Lipos don't just explode, they do give warnings:

Firstly, the pack will get warm,
then hot,
then expand to about 4 times it's thickness, before smoking & then self combusting !

The fire from a lipo apparently cannot be extinguished, as it creates it's own oxygen when burning ! [X(]

If you have damaged your pack, then you may not notice any difference other than maybe reduced flight times from some of the lipos lost capacity.
You may be lucky and have not damaged it at all though.

jdetray

The flightmeter is perhaps better known as a wattmeter. Here's one example:



There are many brands, and some are fancier than others. I think a wattmeter is an essential tool if you plan to stay with electronic flight.

- Jeff

RcFlyer06

My Feedback: (4)

very cool guys! I think this battery is ok. I'm actually MEASURING it's dimensions before flight and after flight to check for swelling. Capacity and flight time is normal, definatley gonna invest in a balancer and a flightmeter. Thanks everyone for the help!!!

RcFlyer06

My Feedback: (4)

Just got done flying the battery, I think it delfated about 1/32 of an inch. Also battery temp is approx 110-120 degrees F. Flight time was the normal 13min+. Safe? Unsafe?

Chocks_Away

Temp shouldn't really get any more than warm to the touch to stay within the limits.
Thats how I go by mine anyway.

If it's hot, then it's probably being killed for all it's worth and then you risk damaging it.
If it's too hot to hold, then it's in serious trouble

RcFlyer06

My Feedback: (4)

Well, I could still hold it (I'm personally resilient to heat but meh, I dunno). So I guess it's ok ^^;. Anyone know where I can get balancers and flight meters for good prices?

elevation

The way FMA gets away with charging over 1C is that they do cell balancing during the charge. Charging at up to 3C doesn't seem to cause any heat.

From the information I've gathered Lipoly cells have a shelf life of about 3 years or 300-1000 cycles which ever comes first. I am able to fly 3-4 flights for about 1/2 the weekends a year. The cells will be lethargic after 3 years of flying before they reach their cycle life. So a 10-20% decrease in cycle life if it even does happen does not bother me.

mGerben

Fyi. The chemical process that happens when you charge a Lipo is endothermic.
So forget all you have learned from NiCad and NiMH batteries: The charging process does not generate heat. So the fact that the LiPo stays cool during charging at 3C does not mean it's not being damaged.

Apart from very ultra special Lipos, I would say that the indication is that Lipo chemistry does not allow the battery to be charged at more than 1C without taking damage.
Hence, it won't blow up your battery when you do it, but you are damaging your battery. More specifically you are freeing chemicals in a faster rate than they can be converted back; hence, you are loosing chemicals in your battery (mostly: oxygen gas).
Those chemicals are lost and will not be replaced.

If you charge at lower than 1C, you give the cathode and anode more time to adsorb the chemicals, and far fewer are lost.

If you want to recharge your pack quickly, here's what you can do:
- Use a lipo charger (of course).
- Charge at 1C.
- When the current starts to fall near the end of the charging process, the battery is 85-90% full. Take it off the charger and forget the extra 10% you get by completing the cycle.

Does this not damage the battery? Nope, first of all, there is no memory-effect. Seconcly there are indications that not topping your Lipo to the full 100% might even increase its life (due to the loss of chemicals in the final stage of the charge cycle).